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1. The MUSE Beamline Calorimeter

Author: Lin, W., Rostomyan, T., Gilman, R., Strauch, S., Meier, C., Nestler, C., Ali, M., Atac, H., Bernauer, J. C., Briscoe, W. J., Ndukwe, A. Christopher, Cline, E. W., Deiters, K., Dogra, S., Downie, E. J., Duan, Z., Fernando, I. P., Flannery, A., Ghosal, D., Golossanov, A., Guo, J., Ifat, N. S., Ilieva, Y., Kohl, M., Lavrukhin, I., Li, L., Lorenzon, W., Mohanmurthy, P., Nazeer, S. J., Nicol, M., Patel, T., Prosnyakov, A., Ransome, R. D., Ratvasky, R., Reid, H., Reimer, P. E., Richards, R., Ron, G., Ruimi, O. M., Salamone, K., Sparveris, N., Wuerfel, N., and Yaari, D. A.
Subjects: Physics - Instrumentation and Detectors, Nuclear Experiment
Abstract: The MUon Scattering Experiment (MUSE) was motivated by the proton radius puzzle arising from the discrepancy between muonic hydrogen spectroscopy and electron-proton measurements. The MUSE physics goals also include testing lepton universality, precisely measuring two-photon exchange contribution, and testing radiative corrections. MUSE addresses these physics goals through simultaneous measurement of high precision cross sections for electron-proton and muon-proton scattering using a mixed-species beam. The experiment will run at both positive and negative beam polarities. Measuring precise cross sections requires understanding both the incident beam energy and the radiative corrections. For this purpose, a lead-glass calorimeter was installed at the end of the beam line in the MUSE detector system. In this article we discuss the detector specifications, calibration and performance. We demonstrate that the detector performance is well reproduced by simulation, and meets experimental requirements.
Published: 2024

2. First measurement using elliptically polarized photons of the double-polarization observable $E$ for $\gamma p \to p \pi^0$ and $\gamma p \to n \pi^+$

Author: A2 Collaboration, Afzal, F., Spieker, K., Hurck, P., Abt, S., Achenbach, P., Adlarson, P., Ahmed, Z., Akondi, C. S., Annand, J. R. M., Arends, H. J., Bashkanov, M., Beck, R., Biroth, M., Borisov, N., Braghieri, A., Briscoe, W. J., Cividini, F., Collicott, C., Costanza, S., Denig, A., Dieterle, M., Downie, E. J., Drexler, P., Fegan, S., Gardner, S., Ghosal, D., Glazier, D. I., Gorodnov, I., Gradl, W., Gurevich, D., Heijkenskjöld, L., Hornidge, D., Huber, G. M., Kashevarov, V. L., Kay, S. J. D., Korolija, M., Krusche, B., Lazarev, A., Livingston, K., Lutterer, S., MacGregor, I. J. D., Macrae, R. G., Manley, D. M., Martel, P. P., Miskimen, R., Mocanu, M., Mornacchi, E., Mullen, C., Neganov, A., Neiser, A., Oberle, M., Ostrick, M., Otte, P. B., Paudyal, D., Pedroni, P., Powell, A., Reicherz, G., Rostomyan, T., Sfienti, C., Sokhoyan, V., Steffen, O., Strakovsky, I. I., Strub, T., Supek, I., Thiel, A., Thiel, M., Thomas, A., Usov, Yu. A., Wagner, S., Walford, N. K., Watts, D. P., Werthmüller, D., Wettig, J., Witthauer, L., Wolfes, M., and Zachariou, N.
Subjects: Nuclear Experiment
Abstract: We report the measurement of the helicity asymmetry $E$ for the $p\pi^0$ and $n\pi^+$ final states using, for the first time, an elliptically polarized photon beam in combination with a longitudinally polarized target at the Crystal Ball experiment at MAMI. The results agree very well with data that were taken with a circularly polarized photon beam, showing that it is possible to simultaneously measure polarization observables that require linearly (e.g.~$G$) and circularly polarized photons (e.g.~$E$) and a longitudinally polarized target. The new data cover a photon energy range 270 - 1400 MeV for the $p\pi^0$ final state (230 - 842 MeV for the $n\pi^+$ final state) and the full range of pion polar angles, $\theta$, providing the most precise measurement of the observable $E$. A moment analysis gives a clear observation of the $p\eta$ cusp in the $p\pi^0$ final state.
Published: 2024

3. Evaluation of the E2/M1 ratio in the $N\to \Delta(1232)$ transition from the $ \vec{\gamma} \vec{p} \to p \pi^0 $ reaction

Author: Mornacchi, E., Pedroni, P., Afzal, F., Wunderlich, Y., Abt, S., Achenbach, P., Annand, J. R. M., Arends, H. J., Bashkanov, M., Biroth, M., Beck, R., Borisov, N., Braghieri, A., Briscoe, W. J., Cividini, F., Collicott, C., Denig, A., Dolzhikov, A. S., Downie, E., Fegan, S., Fix, A., Ghosal, D., Gorodnov, I., Gradl, W., Gurevich, D., Heijkenskjoeld, L., Hornidge, D., Huber, G. M., Kashevarov, V. L., Kay, S. J. D., Korolija, M., Lazarev, A., Livingston, K., Lutterer, S., MacGregor, I. J. D., Manley, D. M., Martel, P. P., Miskimen, R., Mocanu, M., Mullen, C., Neganov, A., Neiser, A., Oberle, M., Ostrick, M., Otte, P. B., Paudyal, D., Powell, A., Rostomyan, T., Sokhoyan, V., Spieker, K., Steffen, O., Strakovsky, I. I., Thiel, M., Thomas, A., Usov, Yu. A., Wagner, S., Watts, D. P., Werthmueller, D., Wettig, J., Witthauer, L., Wolfes, M., and Zachariou, N.
Subjects: Nuclear Experiment
Abstract: A new data set for the helicity-dependent differential cross section of the single-meson photoproduction reaction $\gamma p \to p \pi^{0}$ was obtained for the photon energy interval 150-400 MeV. The experiment was performed at the A2 tagged photon facility of the Mainz Microtron MAMI using a circularly polarized photon beam and a longitudinally polarized proton target. The reaction products were detected with the large acceptance Crystal Ball/TAPS calorimeter covering 97\% of the full solid angle. These new results, obtained with a fine energy and polar angle binning, greatly increase both the existing quantity and quality of the data available for this observable. A moment analysis, based on a finite expansion in Legendre polynomials, was applied to these data by using a bootstrap-based fitting method to correctly account for their systematic uncertainties. From the resulting decomposition of the differential cross sections, the $E2/M1$ ratio for the $N\to \Delta(1232)$ transition was determined to be $[-2.38 \pm 0.16{\hbox{ (stat.+sys.)}} \pm 0.10 {\hbox{ (model)}}] \%$. Combining this value with previous results also allowed us to evaluate the most precise available estimate of the $E2/M1$ ratio to be used for all further reference and model comparisons., Comment: 16 pages, 14 figures
Published: 2023

4. Blinding for precision scattering experiments: The MUSE approach as a case study

Author: Bernauer, J. C., Cline, E. W., Atac, H., Briscoe, W. J., Ndukwe, A. Christopher, Downie, E. J., Fernando, I. P., Gautam, T., Gilman, R., Goldin, R., Kohl, M., Lavrukhin, I., Lin, W., Lorenzon, W., Mohanmurthy, P., Nazeer, S. J., Nicol, M., Patel, T., Prosnyakov, A., Ransome, R. D., Ratvasky, R., Reid, H., Reimer, P. E., Ron, G., Rostomyan, T., Ruimi, O. M., Salamone, K., Sparveris, N., Strauch, S., and Yaari, D. A.
Subjects: Physics - Data Analysis, Statistics and Probability, Nuclear Experiment
Abstract: Human bias is capable of changing the analysis of measured data sufficiently to alter the results of an experiment. It is incumbent upon modern experiments, especially those investigating quantities considered contentious in the broader community, to blind their analysis in an effort to minimize bias. The choice of a blinding model is experiment specific, but should also aim to prevent accidental release of results before an analysis is finalized. In this paper, we discuss common threats to an unbiased analysis, as well as common quantities that can be blinded in different types of nuclear physics experiments. We use the Muon Scattering Experiment as an example, and detail the blinding scheme used therein., Comment: 6 pages, 3 figures
Published: 2023

5. Helicity dependent cross sections for the photoproduction of $\pi^0\pi^{\pm}$ pairs from quasi-free nucleons

Author: A2 Collaboration, Ghosal, D., Sokhoyan, V., Fix, A., Lutterer, S., Abt, S., Achenbach, P., Afzal, F., Ahmed, Z., Annand, J. R. M., Bashkanov, M., Beck, R., Biroth, M., Borisov, N., Braghieri, A., Briscoe, W. J., Cividini, F., Collicot, C., Costanza, S., Denig, A., Dieterle, M., Dolzhikov, A. S., Downie, E. J., Drexler, P., Fegan, S., Gardner, S., Glazier, D. I., Gorodnov, I., Gradl, W., Günther, M., Gurevich, D., Heijkenskjöld, L., Hornidge, D., Huber, G. M., Jermann, N., Käser, A., Kashevarov, V. L., Korolija, M., Krusche, B., Lazarev, A., Livingston, K., MacGregor, I. J. D., Manley, D. M., Martel, P. P., Meier, Ch., Miskimen, R., Mocanu, M., Mornacchi, E., Mullen, C., Neganov, A., Neiser, A., Ostrick, M., Otte, P., Paudyal, D., Pedroni, P., Powell, A., Reicherz, G., Rostomyan, T., Spieker, K., Steffen, O., Strakovsky, I. I., Thiel, A., Thiel, M., Thomas, A., Unverzagt, M., Usov, Yu. A., Wagner, S., Walford, N. K., Watts, D. P., Werthmüller, D., Wettig, J., Witthauer, L., Wolfes, M., and Zachariou, N.
Subjects: Nuclear Experiment
Abstract: Photoproduction of $\pi^0\pi^{\pm}$-pairs from quasifree nucleons bound in the deuteron has been investigated to study the helicity dependence of this reaction. Measurements with a liquid deuterium target were used to extract the unpolarized cross sections for reactions on protons and neutrons. A deuterated, longitudinally polarized solid-butanol target, together with a circularly polarized photon beam, determined the double polarization observable $E$. From these results the spin-dependent cross sections $\sigma_{1/2}$ and $\sigma_{3/2}$, corresponding to the anti-parallel and parallel spin configurations of the beam photon and target nucleon, have been derived. The measurements were performed at the Mainz MAMI accelerator with tagged, circularly-polarized photon beams produced via bremsstrahlung from longitudinally polarized electron beams. The reaction products were detected with an almost $4\pi$ solid-angle covering calorimeter composed of the Crystal Ball and TAPS detectors, supplemented by plastic scintillation detectors for charged particle identification. The results are sensitive to sequential decays of nucleon resonances via intermediate states and also to the decay of nucleon resonances by emission of charged $\rho$ mesons, and are compared to recent model results., Comment: 9 pages, 6 figures
Published: 2023
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6. Instrumental uncertainties in radiative corrections for the MUSE experiment

Author: Li, L., Strauch, S., Bernauer, J. C., Briscoe, W. J., Ndukwe, A. Christopher, Cline, E., Cohen, D., Deiters, K., Downie, E. J., Fernando, I. P., Flannery, A., Gilman, R., Ilieva, Y., Kohl, M., Lavrukhin, I., Lin, W., Lorenzon, W., Lunkenheimer, S., Mohanmurthy, P., Nazeer, J., Nicol, M., Patel, T., Prosnyakov, A., Reid, H., Reimer, P. E., Ron, G., Rostomyan, T., Ruimi, O. M., Sparveris, N., and Yaari, D.
Subjects: High Energy Physics - Experiment, Nuclear Experiment
Abstract: The MUSE experiment at the Paul Scherrer Institute is measuring elastic lepton-proton scattering cross sections in a four-momentum transfer range from $Q^2$ of approximately 0.002 to 0.08 GeV$^2$ using positively and negatively charged electrons and muons. The extraction of the Born cross sections from the experimental data requires radiative corrections. Estimates of the instrumental uncertainties in those corrections have been made using the ESEPP event generator. The results depend in particular on the minimum lepton momentum that contributes to the experimental cross section and the fraction of events with hard initial-state radiation that is detected in the MUSE calorimeter and is excluded from the data. These results show that the angular-dependent instrumental uncertainties in radiative corrections to the electron cross section are better than 0.4 % and are negligible for the muon cross section., Comment: Accepted version of the manuscript submitted to the EPJ A Topical Collection on radiative corrections
Published: 2023
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7. The Present and Future of QCD

Author: Achenbach, P., Adhikari, D., Afanasev, A., Afzal, F., Aidala, C. A., Al-bataineh, A., Almaalol, D. K., Amaryan, M., Androić, D., Armstrong, W. R., Arratia, M., Arrington, J., Asaturyan, A., Aschenauer, E. C., Atac, H., Avakian, H., Averett, T., Gayoso, C. Ayerbe, Bai, X., Barish, K. N., Barnea, N., Basar, G., Battaglieri, M., Baty, A. A., Bautista, I., Bazilevsky, A., Beattie, C., Behera, S. C., Bellini, V., Bellwied, R., Benesch, J. F., Benmokhtar, F., Bernardes, C. A., Bernauer, J. C., Bhatt, H., Bhatta, S., Boer, M., Boettcher, T. J., Bogacz, S. A., Bossi, H. J., Brandenburg, J. D., Brash, E. J., Briceño, R. A., Briscoe, W. J., Brodsky, S. J., Brown, D. A., Burkert, V. D., Caines, H., Cali, I. A., Camsonne, A., Carman, D. S., Caylor, J., Cerci, S., Llatas, M. Chamizo, Chatterjee, S., Chen, J. P., Chen, Y., Chen, Y. -C., Chien, Y. -T., Chou, P. -C., Chu, X., Chudakov, E., Cline, E., Cloët, I. C., Cole, P. L., Connors, M. E., Constantinou, M., Cosyn, W., Dusa, S. Covrig, Cruz-Torres, R., D'Alesio, U., da Silva, C., Davoudi, Z., Dean, C. T., Dean, D. J., Demarteau, M., Deshpande, A., Detmold, W., Deur, A., Devkota, B. R., Dhital, S., Diefenthaler, M., Dobbs, S., Döring, M., Dong, X., Dotel, R., Dow, K. A., Downie, E. J., Drachenberg, J. L., Dumitru, A., Dunlop, J. C., Dupre, R., Durham, J. M., Dutta, D., Edwards, R. G., Ehlers, R. J., Fassi, L. El, Elaasar, M., Elouadrhiri, L., Engelhardt, M., Ent, R., Esumi, S., Evdokimov, O., Eyser, O., Fanelli, C., Fatemi, R., Fernando, I. P., Flor, F. A., Fomin, N., Frawley, A. D., Frederico, T., Fries, R. J., Gal, C., Gamage, B. R., Gamberg, L., Gao, H., Gaskell, D., Geurts, F., Ghandilyan, Y., Ghimire, N., Gilman, R., Gleason, C., Gnanvo, K., Gothe, R. W., Greene, S. V., Grießhammer, H. W., Grossberndt, S. K., Grube, B., Hackett, D. C., Hague, T. J., Hakobyan, H., Hansen, J. -O., Hatta, Y., Hattawy, M., Havener, L. B., Hen, O., Henry, W., Higinbotham, D. W., Hobbs, T. J., Hodges, A. M., Holmstrom, T., Hong, B., Horn, T., Howell, C. R., Huang, H. Z., Huang, M., Huang, S., Huber, G. M., Hyde, C. E., Isupov, E. L., Jacobs, P. M., Jalilian-Marian, J., Jentsch, A., Jheng, H., Ji, C. -R., Ji, X., Jia, J., Jones, D. C., Jones, M. K., Kalantarians, N., Kalicy, G., Kang, Z. B., Karthein, J. M., Keller, D., Keppel, C., Khachatryan, V., Kharzeev, D. E., Kim, H., Kim, M., Kim, Y., King, P. M., Kinney, E., Klein, S. R., Ko, H. S., Koch, V., Kohl, M., Kovchegov, Y. V., Krintiras, G. K., Kubarovsky, V., Kuhn, S. E., Kumar, K. S., Kutz, T., Lajoie, J. G., Lauret, J., Lavrukhin, I., Lawrence, D., Lee, J. H., Lee, K., Lee, S., Lee, Y. -J., Li, S., Li, W., Li, Xiaqing, Li, Xuan, Liao, J., Lin, H. -W., Lisa, M. A., Liu, K. -F., Liu, M. X., Liu, T., Liuti, S., Liyanage, N., Llope, W. J., Loizides, C., Longo, R., Lorenzon, W., Lunkenheimer, S., Luo, X., Ma, R., McKinnon, B., Meekins, D. G., Mehtar-Tani, Y., Melnitchouk, W., Metz, A., Meyer, C. A., Meziani, Z. -E., Michaels, R., Michel, J. K. L., Milner, R. G., Mkrtchyan, H., Mohanmurthy, P., Mohanty, B., Mokeev, V. I., Moon, D. H., Mooney, I. A., Morningstar, C., Morrison, D. P., Müller, B., Mukherjee, S., Mulligan, J., Camacho, C. Munoz, Quijada, J. A. Murillo, Murray, M. J., Nadeeshani, S. A., Nadel-Turonski, P., Nam, J. D., Nattrass, C. E., Nijs, G., Noronha, J., Noronha-Hostler, J., Novitzky, N., Nycz, M., Olness, F. I., Osborn, J. D., Pak, R., Pandey, B., Paolone, M., Papandreou, Z., Paquet, J. -F., Park, S., Paschke, K. D., Pasquini, B., Pasyuk, E., Patel, T., Patton, A., Paudel, C., Peng, C., Peng, J. C., Da Costa, H. Pereira, Perepelitsa, D. V., Peters, M. J., Petreczky, P., Pisarski, R. D., Pitonyak, D., Ploskon, M. A., Posik, M., Poudel, J., Pradhan, R., Prokudin, A., Pruneau, C. A., Puckett, A. J. R., Pujahari, P., Putschke, J., Pybus, J. R., Qiu, J. -W., Rajagopal, K., Ratti, C., Read, K. F., Reed, R., Richards, D. G., Riedl, C., Ringer, F., Rinn, T., West, J. Rittenhouse, Roche, J., Rodas, A., Roland, G., Romero-López, F., Rossi, P., Rostomyan, T., Ruan, L., Ruimi, O. M., Saha, N. R., Sahoo, N. R., Sakaguchi, T., Salazar, F., Salgado, C. W., Salmè, G., Salur, S., Santiesteban, S. N., Sargsian, M. M., Sarsour, M., Sato, N., Satogata, T., Sawada, S., Schäfer, T., Scheihing-Hitschfeld, B., Schenke, B., Schindler, S. T., Schmidt, A., Seidl, R., Shabestari, M. H., Shanahan, P. E., Shen, C., Sheng, T. -A., Shepherd, M. R., Sickles, A. M., Sievert, M. D., Smith, K. L., Song, Y., Sorensen, A., Souder, P. A., Sparveris, N., Srednyak, S., Leiton, A. G. Stahl, Stasto, A. M., Steinberg, P., Stepanyan, S., Stephanov, M., Stevens, J. R., Stewart, D. J., Stewart, I. W., Stojanovic, M., Strakovsky, I., Strauch, S., Strickland, M., Cerci, D. Sunar, Suresh, M., Surrow, B., Syritsyn, S., Szczepaniak, A. P., Tadepalli, A. S., Tang, A. H., Takaki, J. D. Tapia, Tarnowsky, T. J., Tawfik, A. N., Taylor, M. I., Tennant, C., Thiel, A., Thomas, D., Tian, Y., Timmins, A. R., Tribedy, P., Tu, Z., Tuo, S., Ullrich, T., Umaka, E., Upton, D. W., Vary, J. P., Velkovska, J., Venugopalan, R., Vijayakumar, A., Vitev, I., Vogelsang, W., Vogt, R., Vossen, A., Voutier, E., Vovchenko, V., Walker-Loud, A., Wang, F., Wang, J., Wang, X., Wang, X. -N., Weinstein, L. B., Wenaus, T. J., Weyhmiller, S., Wissink, S. W., Wojtsekhowski, B., Wong, C. P., Wood, M. H., Wunderlich, Y., Wyslouch, B., Xiao, B. W., Xie, W., Xiong, W., Xu, N., Xu, Q. H., Xu, Z., Yaari, D., Yao, X., Ye, Z., Ye, Z. H., Yero, C., Yuan, F., Zajc, W. A., Zhang, C., Zhang, J., Zhao, F., Zhao, Y., Zhao, Z. W., Zheng, X., Zhou, J., and Zurek, M.
Subjects: High Energy Physics - Phenomenology, High Energy Physics - Experiment, Nuclear Experiment, Nuclear Theory
Abstract: This White Paper presents the community inputs and scientific conclusions from the Hot and Cold QCD Town Meeting that took place September 23-25, 2022 at MIT, as part of the Nuclear Science Advisory Committee (NSAC) 2023 Long Range Planning process. A total of 424 physicists registered for the meeting. The meeting highlighted progress in Quantum Chromodynamics (QCD) nuclear physics since the 2015 LRP (LRP15) and identified key questions and plausible paths to obtaining answers to those questions, defining priorities for our research over the coming decade. In defining the priority of outstanding physics opportunities for the future, both prospects for the short (~ 5 years) and longer term (5-10 years and beyond) are identified together with the facilities, personnel and other resources needed to maximize the discovery potential and maintain United States leadership in QCD physics worldwide. This White Paper is organized as follows: In the Executive Summary, we detail the Recommendations and Initiatives that were presented and discussed at the Town Meeting, and their supporting rationales. Section 2 highlights major progress and accomplishments of the past seven years. It is followed, in Section 3, by an overview of the physics opportunities for the immediate future, and in relation with the next QCD frontier: the EIC. Section 4 provides an overview of the physics motivations and goals associated with the EIC. Section 5 is devoted to the workforce development and support of diversity, equity and inclusion. This is followed by a dedicated section on computing in Section 6. Section 7 describes the national need for nuclear data science and the relevance to QCD research., Comment: QCD Town Meeting White Paper, as submitted to 2023 NSAC LRP committee on Feb. 28, 2023
Published: 2023
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8. Neutron polarisation transfer, $C_{x'}^n$, in $\pi^+$ photoproduction off the proton

Author: Bashkanov, M., Watts, D. P., Kay, S. J. D., Abt, S., Achenbach, P., Adlarson, P., Afzal, F., Ahmed, Z., Akondi, C. S., Annand, J. R. M., Beck, R., Biroth, M., Borisov, N., Braghieri, A., Briscoe, W. J., Cividini, F., Collicott, C., Costanza, S., Denig, A., Downie, E. J., Drexler, P., Fegan, S., Fix, A., Gardner, S., Ghosal, D., Glazier, D. I., Gorodnov, I., Gradl, W., Gurevich, D., Heijkenskjöld, L., Hornidge, D., Huber, G. M., Kashevarov, V. L., Korolija, M., Krusche, B., Lazarev, A., Livingston, K., Lutterer, S., MacGregor, I. J. D., Manley, D. M., Martel, P. P., Miskimen, R., Mornacchi, E., Mullen, C., Neganov, A., Neiser, A., Ostrick, M., Otte, P. B., Paudyal, D., Pedroni, P., Rostomyan, T., Sokhoyan, V., Spieker, K., Steffen, O., Strakovsky, I. I., Strub, T., Supek, I., Thiel, A., Thiel, M., Thomas, A., Usov, Yu. A., Wagner, S., Walford, N. K., Wettig, J., Wolfes, M., and Zachariou, N.
Subjects: Nuclear Experiment
Abstract: We report a first measurement of the double-polarisation observable, $C_{x'}$, in $\pi^+$ photoproduction off the proton. The $C_{x'}$ double-polarisation observable represents the transfer of polarisation from a circularly polarised photon beam to the recoiling neutron. The MAMI circularly polarised photon beam impinged on a liquid deuterium target cell, with reaction products detected in the Crystal Ball calorimeter. Ancillary apparatus surrounding the target provided tracking, particle identification and determination of recoil nucleon polarisation. The $C_{x'}$ observable is determined for photon energies 800-1400 MeV, providing new constraints on models aiming to elucidate the spectrum and properties of nucleon resonances. This is the first determination of any polarisation observable from the beam-recoil group of observables for this reaction, providing a valuable constraint and systematic check of the current solutions of partial wave analysis based theoretical models.
Published: 2022

9. Target and beam-target asymmetries for the $\gamma p \to \pi^0 \pi^0 p$ reaction

Author: Garni, S., Kashevarov, V. L., Fix, A., Abt, S., Afzal, F., Bartolome, P. Aguar, Ahmed, Z., Ahrens, J., Annand, J. R. M., Arends, H. J., Bashkanov, M., Beck, R., Biroth, M., Borisov, N., Braghieri, A., Briscoe, W. J., Cherepnya, S., Cividini, F., Collicott, C., Costanza, S., Denig, A., Downie, E. J., Dolzhikov, A. S., Drexler, P., Filkov, L. V., Glazier, D. I., Gorodnov, I., Gradl, W., Günther, M., Gurevich, G., Heijkenskjöld, L., Hornidge, D., Huber, G. M., Käser, A., Kay, S., Keshelashvili, I., Kondratiev, R., Korolija, M., Krusche, B., Lazarev, A., Lisin, V., Livingston, K., Lutterer, S., MacGregor, I. J. D., Maghrbi, Y., Manley, D. M., Martel, P. P., McGeorge, J. C., Middleton, D. G., Miskimen, R., Mornacchi, E., Mushkarenkov, A., Neganov, A., Neiser, A., Oberle, M., Ostrick, M., Otte, P. B., Oussena, B., Paudyal, D., Pedroni, P., Pheron, F., Polonski, A., Prakhov, S. N., Ron, G., Rostomyan, T., Sarty, A., Sfienti, C., Sokhoyan, V., Spieker, K., Steffen, O., Strakovsky, I. I., Supek, I., Thiel, A., Thiel, M., Thomas, A., Unverzagt, M., Usov, Yu. A., Wagner, S., Walford, N. K., Watts, D. P., Wettig, J., Wolfes, M., Zana, L. A., and Zehr, F.
Subjects: High Energy Physics - Experiment
Abstract: Background: Photoproduction of pion pairs allows to study sequential decays of nucleon resonances via excited intermediate states. Such decays are important e.g. for states which in the quark model have both oscillators excited and de-excite them in a two-step process. However, analyses of multi-meson final states is difficult and requires more than unpolarized cross section measurements. Purpose: Experimental study and model analysis in view of resonant contributions of target and beam-target polarization observables for the reaction $\gamma p \to \pi^0 \pi^0 p$. Methods: Investigated were target (single) and beam-target (double) polarization asymmetries in dependence of several parameters. The experiments were performed at the Mainz Microtron (MAMI) using circularly polarized photon beams and transversally polarized solid-state butanol targets. The reaction products were analyzed with the Crystal Ball and TAPS detectors. Results: Studied were the polarization observables Py (unpolarized beam, target polarized in y direction) and Px (circularly polarized beam, target polarized in x direction), which are similar to T (target asymmetry) and F (beam-target asymmetry) for single pion production. The asymmetries were analyzed with three independent methods, revealing systematic uncertainties., Comment: 16 pages, 12 figures, 5 tables
Published: 2022

10. Polarization observables in double neutral pion photoproduction

Author: Collaboration, CBELSA/TAPS, Seifen, T., Hartmann, J., Afzal, F., Anisovich, A. V., Beck, R., Becker, M., Berlin, A., Bichow, M., Brinkmann, K. -Th., Crede, V., Dieterle, M., Dutz, H., Eberhardt, H., Elsner, D., Fornet-Ponse, K., Friedrich, St., Frommberger, F., Funke, Ch., Gottschall, M., Grüner, M., Görtz, St., Gutz, E., Hammann, Ch., Hannappel, J., Herick, J., Hillert, W., Hoffmeister, Ph., Honisch, Ch., Jahn, O., Jude, T., Käser, A., Kaiser, D., Kalinowsky, H., Kalischewski, F., Klassen, P., Keshelashvili, I., Klein, F., Klempt, E., Koop, K., Krusche, B., Lang, M., Mahlberg, Ph., Makonyi, K., Messi, F., Metag, V., Meyer, W., Müller, J., Müllers, J., Nanova, M., Nikonov, K., Nikonov, V. A., Novotny, R., Reeve, S., Roth, B., Reicherz, G., Rostomyan, T., Runkel, St., Sarantsev, A. V., Schmidt, Ch., Schmieden, H., Schmitz, R., Schultes, J., Sokhoyan, V., Stausberg, N., Thiel, A., Thoma, U., Urban, M., Urff, G., van Pee, H., Walther, D., Wendel, Ch., Wiedner, U., Wilson, A., Witthauer, L., and Wunderlich, Y.
Subjects: Nuclear Experiment
Abstract: Measurements of target asymmetries and double-polarization observables for the reaction $\gamma p\to p\pi^0\pi^0$ are reported. The data were taken with the CBELSA/TAPS experiment at the ELSA facility (Bonn University) using the Bonn frozen-spin butanol (C$_4$H$_9$OH) target, which provided transversely polarized protons. Linearly polarized photons were produced via bremsstrahlung off a diamond crystal. The data cover the photon energy range from $E_{\gamma}$=650 MeV to $E_{\gamma}$=2600 MeV and nearly the complete angular range. The results have been included in the BnGa partial wave analysis. Experimental results and the fit agree very well. Observed systematic differences in the branching ratios for decays of $N^*$ and $\Delta^*$ resonances are attributed to the internal structure of these excited nucleon states. Resonances which can be assigned to SU(6)$\times$O(3) two-oscillator configurations show larger branching ratios to intermediate states with non-zero intrinsic orbital angular momenta than resonances assigned to one-oscillator configurations., Comment: 21 pages, 27 figures
Published: 2022

11. Instrumental uncertainties in radiative corrections for the MUSE experiment

Author: Li, L., Strauch, S., Bernauer, J. C., Briscoe, W. J., Christopher Ndukwe, A., Cline, E., Cohen, D., Deiters, K., Downie, E. J., Fernando, I. P., Flannery, A., Gilman, R., Ilieva, Y., Kohl, M., Lavrukhin, I., Lin, W., Lorenzon, W., Lunkenheimer, S., Mohanmurthy, P., Nazeer, J., Nicol, M., Patel, T., Prosnyakov, A., Reid, H., Reimer, P. E., Ron, G., Rostomyan, T., Ruimi, O. M., Sparveris, N., and Yaari, D.
Published: 2024
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12. Measurement of the helicity dependence for single $\pi^{0}$ photoproduction from the deuteron

Author: The A2 collaboration, Cividini, F., Dieterle, M., Abt, S., Achenbach, P., Adlarson, P., Afzal, F., Ahmed, Z., Annand, J. R. M., Arends, H. J., Bashkanov, M., Beck, R., Biroth, M., Borisov, N., Braghieri, A., Briscoe, W. J., Collicott, C., Costanza, S., Denig, A., Dolzhikov, A. S., Downie, E. J., Drexler, P., Fegan, S., Fix, A., Gardner, S., Ghosal, D., Glazier, D. I., Gorodnov, I., Gradl, W., Günther, M., Gurevich, D., Heijkenskjöld, L., Hornidge, D., Huber, G. M., Käser, A., Kashevarov, V. L., Kay, S. J. D., Korolija, M., Krusche, B., Lazarev, A., Livingston, K., Lutterer, S., MacGregor, I. J. D., Manley, D. M., Martel, P. P., Miskimen, R., Mocanu, M., Mornacchi, E., Mullen, C., Neganov, A., Neiser, A., Ostrick, M., Otte, P. B., Paudyal, D., Pedroni, P., Powell, A., Rostomyan, T., Sokhoyan, V., Spieker, K., Steffen, O., Strakovsky, I., Strub, T., Supek, I., Thiel, A., Thiel, M., Thomas, A., Usov, Yu. A., Wagner, S., Walford, N. K., Watts, D. P., Werthmüller, D., Wettig, J., Witthauer, L., Wolfes, M., and Zachariou, N.
Subjects: Nuclear Experiment
Abstract: The helicity-dependent single $\pi^{0}$ photoproduction cross section on the deuteron and the angular dependence of the double polarisation observable $E$ for the quasi-free single $\pi^0$ production off the proton and the neutron have been measured for the first time from the threshold region up to the photon energy 1.4 GeV. The experiment was performed at the tagged photon facility of the MAMI accelerator and used a circularly polarised photon beam and longitudinally polarised deuteron target. The reaction products were detected using the large acceptance Crystal Ball/TAPS calorimeter, which covered 97% of the full solid angle. Comparing the cross section from the deuteron with the sum of free nucleon cross sections provides a quantitative estimate of the effects of the nuclear medium on pion production. In contrast, comparison of $E$ helicity asymmetry data from quasi-free protons off deuterium with data from a free proton target indicates that nuclear effects do not significantly affect this observable. As a consequence, it is deduced that the helicity asymmetry $E$ on a free neutron can be reliably extracted from measurements on a deuteron in quasi-free kinematics., Comment: 22 pages, 22 figures; version accepted for publication on Eur. Phys. J. A
Published: 2022

13. The present and future of QCD

Author: Achenbach, P., Adhikari, D., Afanasev, A., Afzal, F., Aidala, C.A., Al-bataineh, A., Almaalol, D.K., Amaryan, M., Androić, D., Armstrong, W.R., Arratia, M., Arrington, J., Asaturyan, A., Aschenauer, E.C., Atac, H., Avakian, H., Averett, T., Ayerbe Gayoso, C., Bai, X., Barish, K.N., Barnea, N., Basar, G., Battaglieri, M., Baty, A.A., Bautista, I., Bazilevsky, A., Beattie, C., Behera, S.C., Bellini, V., Bellwied, R., Benesch, J.F., Benmokhtar, F., Bernardes, C.A., Bernauer, J.C., Bhatt, H., Bhatta, S., Boer, M., Boettcher, T.J., Bogacz, S.A., Bossi, H.J., Brandenburg, J.D., Brash, E.J., Briceño, R.A., Briscoe, W.J., Brodsky, S.J., Brown, D.A., Burkert, V.D., Caines, H., Cali, I.A., Camsonne, A., Carman, D.S., Caylor, J., Cerci, D.S., Cerci, S., Chamizo Llatas, M., Chatterjee, S., Chen, J.P., Chen, Y., Chen, Y.-C., Chien, Y.-T., Chou, P.-C., Chu, X., Chudakov, E., Cline, E., Cloët, I.C., Cole, P.L., Connors, M.E., Constantinou, M., Cosyn, W., Covrig Dusa, S., Cruz-Torres, R., D'Alesio, U., da Silva, C., Davoudi, Z., Dean, C.T., Dean, D.J., Demarteau, M., Deshpande, A., Detmold, W., Deur, A., Devkota, B.R., Dhital, S., Diefenthaler, M., Dobbs, S., Döring, M., Dong, X., Dotel, R., Dow, K.A., Downie, E.J., Drachenberg, J.L., Dumitru, A., Dunlop, J.C., Dupre, R., Durham, J.M., Dutta, D., Edwards, R.G., Ehlers, R.J., El Fassi, L., Elaasar, M., Elouadrhiri, L., Engelhardt, M., Ent, R., Esumi, S., Evdokimov, O., Eyser, O., Fanelli, C., Fatemi, R., Fernando, I.P., Flor, F.A., Fomin, N., Frawley, A.D., Frederico, T., Fries, R.J., Gal, C., Gamage, B.R., Gamberg, L., Gao, H., Gaskell, D., Geurts, F., Ghandilyan, Y., Ghimire, N., Gilman, R., Gleason, C., Gnanvo, K., Gothe, R.W., Greene, S.V., Grießhammer, H.W., Grossberndt, S.K., Grube, B., Hackett, D.C., Hague, T.J., Hakobyan, H., Hansen, J.-O., Hatta, Y., Hattawy, M., Havener, L.B., Hen, O., Henry, W., Higinbotham, D.W., Hobbs, T.J., Hodges, A.M., Holmstrom, T., Hong, B., Horn, T., Howell, C.R., Huang, H.Z., Huang, M., Huang, S., Huber, G.M., Hyde, C.E., Isupov, E.L., Jacobs, P.M., Jalilian-Marian, J., Jentsch, A., Jheng, H., Ji, C.-R., Ji, X., Jia, J., Jones, D.C., Jones, M.K., Joosten, S., Kalantarians, N., Kalicy, G., Kang, Z.B., Karthein, J.M., Keller, D., Keppel, C., Khachatryan, V., Kharzeev, D.E., Kim, H., Kim, M., Kim, Y., King, P.M., Kinney, E., Klein, S.R., Ko, H.S., Koch, V., Kohl, M., Kovchegov, Y.V., Krintiras, G.K., Kubarovsky, V., Kuhn, S.E., Kumar, K.S., Kutz, T., Lajoie, J.G., Lauret, J., Lavrukhin, I., Lawrence, D., Lee, J.H., Lee, K., Lee, S., Lee, Y.-J., Li, S., Li, W., Li, Xiaqing, Li, Xuan, Liao, J., Lin, H.-W., Lisa, M.A., Liu, K.-F., Liu, M.X., Liu, T., Liuti, S., Liyanage, N., Llope, W.J., Loizides, C., Longo, R., Lorenzon, W., Lunkenheimer, S., Luo, X., Ma, R., McKinnon, B., Meekins, D.G., Mehtar-Tani, Y., Melnitchouk, W., Metz, A., Meyer, C.A., Meziani, Z.-E., Michaels, R., Michel, J.K.L., Milner, R.G., Mkrtchyan, H., Mohanmurthy, P., Mohanty, B., Mokeev, V.I., Moon, D.H., Mooney, I.A., Morningstar, C., Morrison, D.P., Müller, B., Mukherjee, S., Mulligan, J., Munoz Camacho, C., Murillo Quijada, J.A., Murray, M.J., Nadeeshani, S.A., Nadel-Turonski, P., Nam, J.D., Nattrass, C.E., Nijs, G., Noronha, J., Noronha-Hostler, J., Novitzky, N., Nycz, M., Olness, F.I., Osborn, J.D., Pak, R., Pandey, B., Paolone, M., Papandreou, Z., Paquet, J.-F., Park, S., Paschke, K.D., Pasquini, B., Pasyuk, E., Patel, T., Patton, A., Paudel, C., Peng, C., Peng, J.C., Pereira Da Costa, H., Perepelitsa, D.V., Peters, M.J., Petreczky, P., Pisarski, R.D., Pitonyak, D., Ploskon, M.A., Posik, M., Poudel, J., Pradhan, R., Prokudin, A., Pruneau, C.A., Puckett, A.J.R., Pujahari, P., Putschke, J., Pybus, J.R., Qiu, J.-W., Rajagopal, K., Ratti, C., Read, K.F., Reed, R., Richards, D.G., Riedl, C., Ringer, F., Rinn, T., Rittenhouse West, J., Roche, J., Rodas, A., Roland, G., Romero-López, F., Rossi, P., Rostomyan, T., Ruan, L., Ruimi, O.M., Saha, N.R., Sahoo, N.R., Sakaguchi, T., Salazar, F., Salgado, C.W., Salmè, G., Salur, S., Santiesteban, S.N., Sargsian, M.M., Sarsour, M., Sato, N., Satogata, T., Sawada, S., Schäfer, T., Scheihing-Hitschfeld, B., Schenke, B., Schindler, S.T., Schmidt, A., Seidl, R., Shabestari, M.H., Shanahan, P.E., Shen, C., Sheng, T.-A., Shepherd, M.R., Sickles, A.M., Sievert, M.D., Smith, K.L., Song, Y., Sorensen, A., Souder, P.A., Sparveris, N., Srednyak, S., Stahl Leiton, A.G., Stasto, A.M., Steinberg, P., Stepanyan, S., Stephanov, M., Stevens, J.R., Stewart, D.J., Stewart, I.W., Stojanovic, M., Strakovsky, I., Strauch, S., Strickland, M., Sunar Cerci, D., Suresh, M., Surrow, B., Syritsyn, S., Szczepaniak, A.P., Tadepalli, A.S., Tang, A.H., Tapia Takaki, J.D., Tarnowsky, T.J., Tawfik, A.N., Taylor, M.I., Tennant, C., Thiel, A., Thomas, D., Tian, Y., Timmins, A.R., Tribedy, P., Tu, Z., Tuo, S., Ullrich, T., Umaka, E., Upton, D.W., Vary, J.P., Velkovska, J., Venugopalan, R., Vijayakumar, A., Vitev, I., Vogelsang, W., Vogt, R., Vossen, A., Voutier, E., Vovchenko, V., Walker-Loud, A., Wang, F., Wang, J., Wang, X., Wang, X.-N., Weinstein, L.B., Wenaus, T.J., Weyhmiller, S., Wissink, S.W., Wojtsekhowski, B., Wong, C.P., Wood, M.H., Wunderlich, Y., Wyslouch, B., Xiao, B.W., Xie, W., Xiong, W., Xu, N., Xu, Q.H., Xu, Z., Yaari, D., Yao, X., Ye, Z., Ye, Z.H., Yero, C., Yuan, F., Zajc, W.A., Zhang, C., Zhang, J., Zhao, F., Zhao, Y., Zhao, Z.W., Zheng, X., Zhou, J., and Zurek, M.
Published: 2024
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14. Measurement of Compton scattering at MAMI for the extraction of the electric and magnetic polarizabilities of the proton

Author: A2 Collaboration, Mornacchi, E., Martel, P. P., Abt, S., Achenbach, P., Adlarson, P., Afzal, F., Ahmed, Z., Annand, J. R. M., Arends, H. J., Bashkanov, M., Beck, R., Biroth, M., Borisov, N., Braghieri, A., Briscoe, W. J., Cividini, F., Collicott, C., Costanza, S., Denig, A., Dolzhikov, A. S., Downie, E. J., Drexler, P., Fegan, S., Gardner, S., Ghosal, D., Glazier, D. I., Gorodnov, I., Gradl, W., Günther, M., Gurevich, D., Heijkenskjöld, L., Hornidge, D., Huber, G. M., Käser, A., Kashevarov, V. L., Kay, S. J. D., Korolija, M., Krusche, B., Lazarev, A., Livingston, K., Lutterer, S., MacGregor, I. J. D., Manley, D. M., Miskimen, R., Mocanu, M., Mullen, C., Neganov, A., Neiser, A., Ostrick, M., Paudyal, D., Pedroni, P., Powell, A., Rostomyan, T., Sokhoyan, V., Spieker, K., Steffen, O., Strakovsky, I., Strub, T., Thiel, M., Thomas, A., Usov, Yu. A., Wagner, S., Watts, D. P., Werthmüller, D., Wettig, J., Wolfes, M., and Zachariou, N.
Subjects: Nuclear Experiment, Nuclear Theory
Abstract: A precise measurement of the differential cross-sections $d\sigma/d\Omega$ and the linearly polarized photon beam asymmetry $\Sigma_3$ for Compton scattering on the proton below pion threshold has been performed with a tagged photon beam and almost $4\pi$ detector at the Mainz Microtron. The incident photons were produced by the recently upgraded Glasgow-Mainz photon tagging facility and impinged on a cryogenic liquid hydrogen target, with the scattered photons detected in the Crystal Ball/TAPS set-up. Using the highest statistics Compton scattering data ever measured on the proton along with two effective field theories (both covariant baryon and heavy-baryon) and one fixed-$t$ dispersion relation model, constraining the fits with the Baldin sum rule, we have obtained the proton electric and magnetic polarizabilities with unprecedented precision: \begin{align*} &{}\alpha_{E1} = 10.99 \pm 0.16 \pm 0.47 \pm 0.17 \pm 0.34 &{}\beta_{M1} = 3.14 \pm 0.21 \pm 0.24 \pm 0.20 \pm 0.35 \end{align*} in units of $10^{-4}$\,fm$^3$ where the errors are statistical, systematic, spin polarizability dependent and model dependent.
Published: 2021

15. Observation of a structure in the M$_{p\eta}$ invariant mass distribution near 1700 MeV/$c^2$ in the $\mathbf{\gamma p \rightarrow p \pi^0 \eta} $ reaction

Author: Metag, V., Nanova, M., Hartmann, J., Mahlberg, P., Afzal, F., Bartels, C., Bayadilov, D., Beck, R., Becker, M., Blanke, E., Brinkmann, K. -T., Ciupka, S., Crede, V., Dieterle, M., Dutz, H., Elsner, D., Frommberger, F., Gridnev, A., Gottschall, M., Grüner, M., Hammann, Ch., Hannappel, J., Hillert, W., Hoff, J., Hoffmeister, Ph., Honisch, Ch., Jude, T., Kalinowsky, H., Kalischewski, F., Keshelashvili, I., Ketzer, B., Klassen, P., Klein, F., Koop, K., Kroenert, P., Krusche, B., Lang, M., Lopatin, I., Messi, F., Meyer, W., Mitlasóczky, B., Müller, J., Müllers, J., Nikonov, V., Novinsky, V., Novotny, R., Piontek, D., Reicherz, G., Richter, L., Rostomyan, T., Runkel, S., Salisbury, B., Sarantsev, A., Schaab, D., Schmidt, Ch., Schmieden, H., Schultes, J., Seifen, T., Sokhoyan, V., Sowa, C., Spieker, K., Stausberg, N., Thiel, A., Thoma, U., Triffterer, T., Urban, M., Urff, G., van Pee, H., Wagner, M., Walther, D., Wendel, Ch., Werthmüller, D., Wiedner, U., Wilson, A., Winnebeck, A., Witthauer, L., and Wunderlich, Y.
Subjects: Nuclear Experiment, Nuclear Theory
Abstract: The reaction $\gamma p \rightarrow p \pi^0 \eta$ has been studied with the CBELSA/TAPS detector at the electron stretcher accelerator ELSA in Bonn for incident photon energies from threshold up to 3.1 GeV. This paper has been motivated by the recently claimed observation of a narrow structure in the M$_{N\eta}$ invariant mass distribution at a mass of 1678 MeV/$c^2$. The existence of this structure cannot be confirmed in the present work. Instead, for E$_{\gamma}$ = 1400 - 1500 MeV and the cut M$_{p\pi^0} \le 1190 $ MeV/$c^2$ a statistically significant structure in the M$_{p\eta}$ invariant mass distribution near 1700 MeV/$c^2$ is observed with a width of $\Gamma\approx 35$ MeV/$c^2$ while the mass resolution is $\sigma_{res}$ = 5 MeV/$c^2$. Increasing the incident photon energy from 1420 to 1540 MeV this structure shifts in mass from $\approx$ 1700MeV/c$^2$ to $\approx$ 1725 MeV/$c^2$; the width increases to about 50 MeV/$c^2$ and decreases thereafter. The cross section associated with this structure reaches a maximum of $\approx$ 100 nb around E$_{\gamma} \approx$ 1490 MeV (W $\approx $ 1920 MeV), which coincides with the $p a_0$ threshold. Three scenarios are discussed which might be the origin of this structure in the M$_{p\eta}$ invariant mass distribution. The most likely interpretation is that it is due to a triangular singularity in the $\gamma p \rightarrow p a_0 \rightarrow p \pi^0 \eta$ reaction, Comment: 16 pages, 18 figure
Published: 2021
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16. Commissioning and initial experimental program of the BGO-OD experiment at ELSA

Author: Alef S., Bauer P., Bayadilov D., Beck R., Becker M., Bella A., Bielefeldt P., Böse S., Braghieri A., Brinkmann K., Cole P., Di Salvo R., Dutz H., Elsner D., Fantini A., Freyermuth O., Friedrich S., Frommberger F., Ganenko V., Geffers D., Gervino G., Ghio F., Görtz S., Gridnev A., Gutz E., Hammann D., Hannappel J., Hillert W., Ignatov A., Jahn R., Joosten R., Jude T.C., Klein F., Knaust J., Kohl K., Koop K., Krusche B., Lapik A., Levi Sandri P., Lopatin I.V., Mandaglio G., Messi F., Messi R., Metag V., Moricciani D., Mushkarenkov A., Nanova M., Nedorezov V., Novinskiy D., Pedroni P., Reitz B., Romaniuk M., Rostomyan T., Rudnev N., Schaerf C., Scheluchin G., Schmieden H., Stugelev A., Sumachev V., Tarakanov V., Vegna V., Walther D., Watts D., Zaunick H., and Zimmermann T.
Subjects: Physics, QC1-999
Abstract: BGO-OD is a new meson photoproduction experiment at the ELSA facility of Bonn University. It aims at the investigation of non strange and strange baryon excitations, and is especially designed to be able to detect weekly bound meson-baryon type structures. The setup for the BGO-OD experiment is presented, the characteristics of the photon beam and the detector performances are shown and the initial experimental program is discussed.
Published: 2016
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17. Characterization of Muon and Electron Beams in the Paul Scherrer Institute PiM1 Channel for the MUSE Experiment

Author: Cline, E., Lin, W., Roy, P., Reimer, P. E., Mesick, K. E., Akmal, A., Alie, A., Atac, H., Atencio, A., Gayoso, C. Ayerbe, Benmouna, N., Benmokhtar, F., Bernauer, J. C., Briscoe, W. J., Campbell, J., Cohen, D., Cohen, E. O., Collicott, C., Deiters, K., Dogra, S., Downie, E., Fernando, I. P., Flannery, A., Gautam, T., Ghosal, D., Gilman, R., Golossanov, A., Halter, B. F., Hirschman, J., Ilieva, Y., Kim, M., Kohl, M., Krusche, B., Lavrukhin, I., Li, L., Liang-Gilman, B., Liyanage, A., Lorenzon, W., Mohanmurthy, P., Mokal, R., Moran, P., Nazeer, S. J., Or, P., Patel, T., Piasetzky, E., Rauber, T., Raymond, R. S., Reggiani, D., Reid, H., Ron, G., Rooney, E., Rostomyan, T., Schwarz, M., Sneath, A., Solazzo, P. G., Sparveris, N., Steinberg, N., Strauch, S., Sulkosky, V., and Wuerfel, N.
Subjects: Physics - Instrumentation and Detectors, Nuclear Experiment
Abstract: The MUon Scattering Experiment, MUSE, at the Paul Scherrer Institute, Switzerland, investigates the proton charge radius puzzle, lepton universality, and two-photon exchange, via simultaneous measurements of elastic muon-proton and electron-proton scattering. The experiment uses the PiM1 secondary beam channel, which was designed for high precision pion scattering measurements. We review the properties of the beam line established for pions. We discuss the production processes that generate the electron and muon beams, and the simulations of these processes. Simulations of the $\pi$/$\mu$/$e$ beams through the channel using TURTLE and G4beamline are compared. The G4beamline simulation is then compared to several experimental measurements of the channel, including the momentum dispersion at the IFP and target, the shape of the beam spot at the target, and timing measurements that allow the beam momenta to be determined. We conclude that the PiM1 channel can be used for high precision $\pi$, $\mu$, and $e$ scattering., Comment: 20 pages, 18 figures
Published: 2021
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18. Single $\pi^0$ Production Off Neutrons Bound in Deuteron with Linearly Polarized Photons

Author: Mullen, C., Gardner, S., Glazier, D. I., Kay, S. J. D., Livingston, K., Strakovsky, I. I., Workman, R. L., Abt, S., Achenbach, P., Afzal, F., Ahmed, Z., Akondi, C. S., Annand, J. R. M., Bashkanov, M., Beck, R., Biroth, M., Borisov, N. S., Braghieri, A., Briscoe, W. J., Cividini, F., Collicott, C., Costanza, S., Denig, A., Dieterle, M., Downie, E. J., Drexler, P., Fegan, S., Ferretti-Bondy, M. I., Ghosal, D., Gorodnov, I., Gradl, W., Gunther, M., Gurevic, G., Heijkenskjold, L., Hornidge, D., Huber, G. M., Jermann, N., Kaeser, A., Korolija, M., Kashevarov, V. L, Krusche, B., Kulikov, V. V., Lazarev, A., Lutterer, S., MacGregor, I. J. D., Manley, D. M., Martel, P. P., Martemianov, M. A., Meier, C., Miskimen, R., Mocanu, M., Mornacchi, E., Neganov, A., Oberle, M., Ostrick, M., Otte, P., Paudyal, D., Pedroni, P., Powell, A., Prakhov, S. N., Reicherz, G., Ron, G., Rostomyan, T., Sfienti, C., Sokhoyan, V., Spieker, K., Steffen, O., Strub, Th., Supek, I., Thie, A., Thiel, M., Thomas, A., Unverzagt, M., Usov, Yu. A., Wagner, S., Walford, N. K., Watts, D. P., Werthmuller, D., Wettig, J., Witthauer, L., Wolfes, M., and Zachariou, N.
Subjects: Nuclear Experiment, High Energy Physics - Experiment, High Energy Physics - Phenomenology, Nuclear Theory
Abstract: The quasifree $\overrightarrow{\gamma} d\to\pi^0n(p)$ photon beam asymmetry, $\Sigma$, has been measured at photon energies, $E_\gamma$, from 390 to 610 MeV, corresponding to center of mass energy from 1.271 to 1.424 GeV, for the first time. The data were collected in the A2 hall of the MAMI electron beam facility with the Crystal Ball and TAPS calorimeters covering pion center-of-mass angles from 49 to 148$^\circ$. In this kinematic region, polarization observables are sensitive to contributions from the $\Delta (1232)$ and $N(1440)$ resonances. The extracted values of $\Sigma$ have been compared to predictions based on partial-wave analyses (PWAs) of the existing pion photoproduction database. Our comparison includes the SAID, MAID, and Bonn-Gatchina analyses; while a revised SAID fit, including the new $\Sigma$ measurements, has also been performed. In addition, isospin symmetry is examined as a way to predict $\pi^0n$ photoproduction observables, based on fits to published data in the channels $\pi^0p$, $\pi^+n$, and $\pi^-p$., Comment: 11 pages, 9 figures, 5 tables; fixed 2 glitches
Published: 2021
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19. Helicity-dependent cross sections for the photoproduction of $\pi^0$ pairs from nucleons

Author: Dieterle, M., Witthauer, L., Fix, A., Abt, S., Achenbach, P., Adlarson, P., Afzal, F., Bartolome, P. Aguar, Ahmed, Z., Annand, J. R. M., Arends, H. J., Bashkanov, M., Beck, R., Biroth, M., Borisov, N., Braghieri, A., Briscoe, W. J., Cividini, F., Collicott, C., Costanza, S., Denig, A., Dolzhikov, A. S., Downie, E. J., Drexler, P., Gardner, S., Ghosal, D., Glazier, D. I., Gorodnov, I., Gradl, W., G{ü, M., nther, Gurevich, D., Heijkenskj{ö, L., ld, Hornidge, D., Huber, G. M., K{ä, A., ser, Kashevarov, V. L., Kay, S., Keshelashvili, I., Kondratiev, R., Korolija, M., Krusche, B., Lazarev, A., Lisin, V., Livingston, K., Lutterer, S., MacGregor, I. J. D., Manley, D. M., Martel, P. P., Metag, V., Meyer, W., Middleton, D. G., Miskimen, R., Mornacchi, E., Mullen, C., Mushkarenkov, A., Neganov, A., Neiser, A., Oberle, M., Ostrick, M., Otte, P. B., Paudyal, D., Pedroni, P., Polonski, A., Powell, A., Prakhov, S. N., Reicherz, G., Ron, G., Rostomyan, T., Sarty, A., Sfienti, C., Sokhoyan, V., Spieker, K., Steffen, O., Strakovsky, I. I., Strub, T., Supek, I., Thiel, A., Thiel, M., Thomas, A., Unverzagt, M., Usov, Yu. A., Wagner, S., Walford, N. K., Watts, D. P., Werthmüller, D., Wettig, J., Wolfes, M., and Zana, L. A.
Subjects: Nuclear Experiment
Abstract: The double-polarization observable $E$ and helicity-dependent cross sections $\sigma_{1/2}$, $\sigma_{3/2}$ have been measured for the photoproduction of $\pi^0$ pairs off quasi-free protons and neutrons at the Mainz MAMI accelerator with the Crystal Ball/TAPS setup. A circularly polarized photon beam was produced by bremsstrahlung from longitudinally polarized electrons and impinged on a longitudinally polarized deuterated butanol target. The reaction products were detected with an almost $4\pi$ covering calorimeter. The results reveal for the first time the helicity- and isospin-dependent structure of the $\gamma N\rightarrow N\pi^0\pi^0$ reaction. They are compared to predictions from reaction models in view of nucleon resonance contributions and also to a refit of one model that predicted results for the proton and for the neutron target. The comparison of the prediction and the refit demonstrate the large impact of the new data., Comment: Submitted to Phys. Rev. Lett
Published: 2020
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20. The BGOOD experimental setup at ELSA

Author: Alef, S., Bauer, P., Bayadilov, D., Beck, R., Becker, M., Bella, A., Bieling, J., Boese, S., Braghieri, A., Brinkmann, K. -Th., Cole, P., Di Salvo, R., Elsner, D., Fantini, A., Freyermuth, O., Frommberger, F., Gervino, G., Ghio, F., Goertz, S., Gridnev, A., Gutz, E., Hammann, D., Hannappel, J., Hillert, W., Jahn, O., Jahn, R., Johnstone, J. R., Joosten, R., Jude, T. C., Kleber, V., Klein, F., Kohl, K., Koop, K., Kozlenko, N., Krusche, B., Lapik, A., Sandri, P. Levi, Lisin, V., Lopatin, I., Mandaglio, G., Manganaro, M., Messi, F., Messi, R., Moricciani, D., Mushkarenkov, A., Nedorezov, V., Novinskiy, D., Pedroni, P., Polonskiy, A., Reitz, B. -E., Romaniuk, M., Rostomyan, T., Scheluchin, G., Schmieden, H., Stugelev, A., Sumachev, V., Tarakanov, V., Vegna, V., Walther, D., Zaunick, H. -G., and Zimmermann, T.
Subjects: Physics - Instrumentation and Detectors, Nuclear Experiment
Abstract: The BGOOD experiment at the ELSA facility in Bonn has been commissioned within the framework of an international collaboration. The experiment pursues a systematic investigation of non-strange and strange meson photoproduction, in particular $t$-channel processes at low momentum transfer. The setup uniquely combines a central almost $4\pi$ acceptance BGO crystal calorimeter with a large aperture forward magnetic spectrometer providing excellent detection of both neutral and charged particles, complementary to other setups such as Crystal Barrel, Crystal Ball, LEPS and CLAS., Comment: 26 pages, 37 figures
Published: 2019
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21. New data on $\vec{\gamma} \vec{p}\rightarrow \eta p$ with polarized photons and protons and their implications for $N^* \to N\eta$ decays

Author: Müller, J., Hartmann, J., Grüner, M., Afzal, F., Anisovich, A. V., Bantes, B., Bayadilov, D., Beck, R., Becker, M., Beloglazov, Y., Berlin, M., Bichow, M., Böse, S., Brinkmann, K. -T., Challand, T., Crede, V., Dietz, F., Dieterle, M., Drexler, P., Dutz, H., Eberhardt, H., Elsner, D., Ewald, R., Fornet-Ponse, K., Friedrich, S., Frommberger, F., Funke, C., Gottschall, M., Gridnev, A., Goertz, S., Gutz, E., Hammann, C., Hannen, V., Hannappel, J., Herick, J., Hillert, W., Hoffmeister, P., Honisch, C., Jahn, O., Jude, T., Jaegle, I., Käser, A., Kaiser, D., Kalinowsky, H., Kalischewski, F., Kammer, S., Keshelashvili, I., Klassen, P., Kleber, V., Klein, F., Klempt, E., Koop, K., Krusche, B., Kube, M., Lang, M., Lopatin, I., Maghrbi, Y., Mahlberg, P., Makonyi, K., Messi, F., Metag, V., Meyer, W., Müllers, J., Nanova, M., Nikonov, V., Novinski, D., Novotny, R., Piontek, D., Reicherz, G., Rosenbaum, C., Rostomyan, T., Roth, B., Sarantsev, A., Schmidt, C., Schmieden, H., Schmitz, R., Seifen, T., Sokhoyan, V., Thiel, A., Thoma, U., Urban, M., van Pee, H., Walther, D., Wendel, C., Wiedner, U., Wilson, A., Winnebeck, A., Witthauer, L., and Collaboration, CBELSA/TAPS
Subjects: Nuclear Experiment
Abstract: The polarization observables $T, E, P, H$, and $G$ in photoproduction of $\eta$ mesons off protons are measured for photon energies from threshold to $W=2400\,$MeV ($T$), 2280 MeV ($E$), 1620 MeV ($P, H$), or 1820 MeV ($G$), covering nearly the full solid angle. The data are compared to predictions from the SAID, MAID, J\"uBo, and BnGa partial-wave analyses. A refit within the BnGa approach including further data yields precise branching ratios for the $N\eta$ decay of nucleon resonances. A $N\eta$-branching ratio of $0.33\pm 0.04$ for $N(1650)1/2^-$ is found, which reduces the large and controversially discussed $N\eta$-branching ratio difference of the two lowest mass $J^P=1/2^-$-resonances significantly., Comment: 10 pages, 11 figures
Published: 2019
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22. Spin polarizabilities of the proton by measurement of Compton double-polarization observables

Author: Paudyal, D., Martel, P. P., Huber, G. M., Hornidge, D., Abt, S., Achenbach, P., Adlarson, P., Afzal, F., Ahmed, Z., Akondi, C. S., Annand, J. R. M., Arends, H. J., Bashkanov, M., Beck, R., Biroth, M., Borisov, N. S., Braghieri, A., Briscoe, W. J., Cividini, F., Costanza, S., Collicott, C., Denig, A., Dieterle, M., Downie, E. J., Drexler, P., Ferretti-Bondy, M. I., Gardner, S., Garni, S., Glazier, D. I., Glowa, D., Gorodnov, I., Gradl, W., Günther, S., Gurevich, G. M., Hamilton, D., Heijkenskjöld, L., Käser, A., Kashevarov, V. L., Kay, S., Keshelashvili, I., Kondratiev, R., Korolija, M., Krusche, B., Lazarev, A. B., Linturi, J. M., Lisin, V., Livingston, K., Lutterer, S., MacGregor, I. J. D., Macrae, R., Mancell, J., Manley, D. M., Metag, V., Meyer, W., Miskimen, R., Mornacchi, E., Mullen, C., Mushkarenkov, A., Neganov, A. B., Neiser, A., Oberle, M., Ostrick, M., Otte, P. B., Pedroni, P., Polonski, A., Powell, A., Prakhov, S. N., Rajabi, A., Reicherz, G., Ron, G., Rostomyan, T., Sarty, A., Sfienti, C., Sikora, M. H., Sokhoyan, V., Spieker, K., Steffen, O., Strakovsky, I. I., Strub, Th., Supek, I., Thiel, A., Thiel, M., Thomas, A., Unverzagt, M., Usov, Yu. A., Wagner, S., Walford, N. K., Watts, D. P., Werthmüller, D., Wettig, J., Witthauer, L., Wolfes, M., and Zana, L.
Subjects: Nuclear Experiment
Abstract: The Compton double-polarization observable $\Sigma_{2z}$ has been measured for the first time in the $\Delta(1232)$ resonance region using a circularly polarized photon beam incident on a longitudinally polarized target at the Mainz Microtron. This paper reports these results, together with the model-dependent extraction of four proton spin polarizabilities from fits to additional asymmetry data using dispersion relation and chiral perturbation theory calculations, with the former resulting in: $\gamma_{E1E1} = -3.18 \pm 0.52$, $\gamma_{M1M1} = 2.98 \pm 0.43$, $\gamma_{E1M2} = -0.44 \pm 0.67$ and $\gamma_{M1E2} = 1.58 \pm 0.43$, in units of $10^{-4}~\mathrm{fm}^{4}$., Comment: 7 pages, 5 figures, 2 tables, accepted for publication in PRC
Published: 2019
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23. Cross Section for $\gamma n \to \pi^0 n$ measured at Mainz/A2

Author: Briscoe, W. J., Hadzimehmedovi, M., Kudryavtsev, A. E., Kulikov, V. V., Martemianov, M. A., Strakovsky, I. I., Svarc, A., Tarasov, V. E., Workman, R. L., Abt, S., Achenbach, P., Akondi, C. S., Afzal, F., Aguar-Bartolome, P., Ahmed, Z., Annand, J. R. M., Arends, H. J., Bantawa, K., Bashkanov, M., Beck, R., Biroth, M., Borisov, N., Braghieri, A., Bulychjov, S. A., Cividini, F., Collicott, C., Costanza, S., Denig, A., Downie, E. J., Drexler, P., Fegan, S., Bondy, M. I. Ferretti, Gardner, S., Ghosal, D., Glazier, D. I., Gorodnov, I., Gradl, W., Gunther, M., Gurevich, D., Heijkenskjold, L., Hornidge, D., Huber, G. M., Kaeser, M., Kashevarov, V. L., Kay, S., Korolija, M., Krusche, B., Lazarev, A., Livingston, K., Lutterer, S., MacGregor, I. J. D., Macrae, R., Manley, D. M., Martel, P. P., McGeorge, J. C., Middleton, D. G., Miskimen, R., Mornacchi, E., Mushkarenkov, A., Mullen, C., Neganov, A., Neiser, A., Ostrick, M., Otte, P. B., Osmanovic, H., Oussena, R. Omerovic B., Paudyal, D., Pedroni, P., Powell, A., Prakhov, S. N., Ron, G., Rostomyan, T., Sarty, A., Senti, C., Sokhoyan, V., Spieker, K., Stahov, J., Steffen, O., Supek, I., Thiel, A., Thiel, M., Thomas, A., Tiator, L., Unverzagt, M., Usov, Yu. A., Walford, N. K., Watts, D. P., Wagner, S., Werthmueller, D., Wettig, J., Wolfes, M., and Zachariou, N.
Subjects: Nuclear Experiment, High Energy Physics - Experiment, High Energy Physics - Phenomenology, Nuclear Theory
Abstract: The $\gamma n \to \pi^0 n$ differential cross section evaluated for 27 energy bins span the photon-energy range 290-813 MeV (W = 1.195-1.553 GeV) and the pion c.m. polar production angles, ranging from 18 deg to 162 deg, making use of model-dependent nuclear corrections to extract pi0 production data on the neutron from measurements on the deuteron target. Additionally, the total photoabsorption cross section was measured. The tagged photon beam produced by the 883-MeV electron beam of the Mainz Microtron MAMI was used for the 0-meson production. Our accumulation of 3.6 x 10^6 $\gamma n \to \pi^0 n$ events allowed a detailed study of the reaction dynamics. Our data are in reasonable agreement with previous A2 measurements and extend them to lower energies. The data are compared to predictions of previous SAID, MAID, and BnGa partial-wave analyses and to the latest SAID fit MA19 that included our data. Selected photon decay amplitudes $N^* \to \gamma n$ at the resonance poles are determined for the first time., Comment: 16 pages, 12 figures, 3 tables
Published: 2019
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24. A Liquid Hydrogen Target for the MUSE Experiment at PSI

Author: Roy, P., Corsetti, S., Dimond, M., Kim, M., Pottier, L. Le, Lorenzon, W., Raymond, R., Reid, H., Steinberg, N., Wuerfel, N., Deiters, K., Briscoe, W. J., Golossanov, A., and Rostomyan, T.
Subjects: Physics - Instrumentation and Detectors
Abstract: A 280 ml liquid hydrogen target has been constructed and tested for the MUSE experiment at PSI to investigate the proton charge radius via simultaneous measurement of elastic muon-proton and elastic electron-proton scattering. To control systematic uncertainties at a sub-percent level, strong constraints were put on the amount of material surrounding the target and on its temperature stability. The target cell wall is made of $120\,\mu$m-thick Kapton, while the beam entrance and exit windows are made of $125\,\mu$m-thick aluminized Kapton. The side exit windows are made of Mylar laminated on aramid fabric with an areal density of $368\,$g/m$^2$. The target system was successfully operated during a commissioning run at PSI at the end of 2018. The target temperature was stable at the 0.01 K level. This suggests a density stability at the $0.02\,$% level, which is about a factor of ten better than required., Comment: 7 pages, 10 figures
Published: 2019
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25. Measurement of the beam-helicity asymmetry in photoproduction of $\pi^{0}\eta$ pairs on carbon, aluminum, and lead

Author: Sokhoyan, V., Prakhov, S., Fix, A., Abt, S., Achenbach, P., Adlarson, P., Afzal, F., Aguar-Bartolomé, P., Ahmed, Z., Altangerel, K., Annand, J. R. M., Arends, H. J., Bantawa, K., Bashkanov, M., Beck, R., Biroth, M., Borisov, N. S., Braghieri, A., Briscoe, W. J., Cherepnya, S., Cividini, F., Collicott, C., Costanza, S., Denig, A., Dieterle, M., Downie, E. J., Drexler, P., Bondy, M. I. Ferretti, Fil'kov, L. V., Gardner, S., Garni, S., Glazier, D. I., Gorodnov, I., Gradl, W., Günther, M., Gurevich, G. M., Heijkenskjöld, L., Hornidge, D., Huber, G. M., Käser, A., Kashevarov, V. L., Kay, S., Keshelashvili, I., Kondratiev, R., Korolija, M., Krusche, B., Lazarev, A., Livingston, K., Lutterer, S., MacGregor, I. J. D., Macrae, R., Manley, D. M., Martel, P. P., McGeorge, J. C., Middleton, D. G., Miskimen, R., Mornacchi, E., Mullen, C., Mushkarenkov, A., Neganov, A., Neiser, A., Oberle, M., Ostrick, M., Otte, P. B., Paudyal, D., Pedroni, P., Powell, A., Rickert, E., Ron, G., Rostomyan, T., Sarty, A., Sfienti, C., Spieker, K., Steffen, O., Strakovsky, I. I., Strandberg, B., Strub, Th., Supek, I., Thiel, A., Thiel, M., Thomas, A., Unverzagt, M., Usov, Yu. A., Wagner, S., Walford, N. K., Watts, D. P., Werthmüller, D., Wettig, J., Witthauer, L., Wolfes, M., and Zachariou, N.
Subjects: Nuclear Experiment
Abstract: The beam-helicity asymmetry was measured, for the first time, in photoproduction of $\pi^{0}\eta$ pairs on carbon, aluminum, and lead, with the A2 experimental setup at MAMI. The results are compared to an earlier measurement on a free proton and to the corresponding theoretical calculations. The Mainz model is used to predict the beam-helicity asymmetry for the nuclear targets. The present results indicate that the photoproduction mechanism for $\pi^{0}\eta$ pairs on nuclei is similar to photoproduction on a free nucleon. This process is dominated by the $D_{33}$ partial wave with the $\eta\Delta(1232)$ intermediate state., Comment: Accepted for publication in Physics Letters B (2020)
Published: 2019
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26. Measurement of the Helicity Asymmetry $E$ for the reaction $ \gamma p\to \pi^0 p$

Author: collaboration, CBELSA/TAPS, Gottschall, M., Afzal, F., Anisovich, A. V., Bayadilov, D., Beck, R., Bichow, M., Brinkmann, K. -Th., Crede, V., Dieterle, M., Dietz, F., Dutz, H., Eberhardt, H., Elsner, D., Ewald, R., Fornet-Ponse, K., Friedrich, St., Frommberger, F., Gridnev, A., Grüner, M., Gutz, E., Hammann, Ch., Hannappel, J., Hartmann, J., Hillert, W., Hoffmeister, Ph., Honisch, Ch., Jude, T., Kammer, S., Kalinowsky, H., Keshelashvili, I., Klassen, P., Klein, F., Klempt, E., Koop, K., Krusche, B., Kube, M., Lang, M., Lopatin, I., Mahlberg, P., Makonyi, K., Metag, V., Meyer, W., Müller, J., Müllers, J., Nanova, M., Nikonov, V., Novotny, R., Piontek, D., Reicherz, G., Rostomyan, T., Sarantsev, A., Schmidt, Ch., Schmieden, H., Seifen, T., Sokhoyan, V., Spieker, K., Thiel, A., Thoma, U., Urban, M., van Pee, H., Walther, D., Wendel, Ch., Werthmüller, D., Wiedner, U., Wilson, A., Winnebeck, A., Witthauer, L., and Wunderlich, Y.
Subjects: Nuclear Experiment
Abstract: A measurement of the double-polarization observable $E$ for the reaction $\gamma p\to \pi^0 p$ is reported. The data were taken with the CBELSA/TAPS experiment at the ELSA facility in Bonn using the Bonn frozen-spin butanol (C$_4$H$_9$OH) target, which provided longitudinally-polarized protons. Circularly-polarized photons were produced via bremsstrahlung of longitudinally-polarized electrons. The data cover the photon energy range from $E_\gamma =600$~MeV to $E_\gamma =2310$~MeV and nearly the complete angular range. The results are compared to and have been included in recent partial wave analyses., Comment: 21 pages
Published: 2019

27. Experimental study of the $\gamma p\rightarrow K^0\Sigma^+$, $\gamma n\rightarrow K^0\Lambda$, and $\gamma n\rightarrow K^0 \Sigma^0$ reactions at the Mainz Microtron

Author: Akondi, C. S., Bantawa, K., Manley, D. M., Abt, S., Achenbach, P., Afzal, F., Aguar-Bartolomé, P., Ahmed, Z., Annand, J. R. M., Arends, H. J., Bashkanov, M., Beck, R., Biroth, M., Borisov, N., Braghieri, A., Briscoe, W. J., Cividini, F., Collicott, C., Costanza, S., Denig, A., Dieterle, M., Downie, E. J., Drexler, P., Bondy, M. I. Ferretti, Gardner, S., Glazier, D. I., Gorodnov, I., Gradl, W., Günther, M., Gurevich, D., Kay, S., Heijkenskjöld, L., Hornidge, D., Huber, G. M., Käser, M., Kashevarov, V. L., Korolija, M., Krusche, B., Lazarev, A., Livingston, K., Lutterer, S., McGeorge, J. C., MacGregor, I. J. D., Martel, P. P., Middleton, D. G., Miskimen, R., Mornacchi, E., Mushkarenkov, A., Mullen, C., Neganov, A., Neiser, A., Oberle, M., Ostrick, M., Otte, P. B., Oussena, B., Paudyal, D., Pedroni, P., Powell, A., Prakhov, S. N., Ron, G., Rostomyan, T., Sarty, A., Sfienti, C., Sokhoyan, V., Spieker, K., Steffen, O., Strakovsky, I. I., Strub, Th., Supek, I., Thiel, A., Thiel, M., Thomas, A., Unverzagt, M., Usov, Yu. A., Walford, N. K., Watts, D. P., Wagner, S., Werthmüller, D., Wettig, J., Witthauer, L., and Wolfes, M.
Subjects: Nuclear Experiment
Abstract: This work measured $d\sigma/d\Omega$ for neutral kaon photoproduction reactions from threshold up to a c.m.\ energy of 1855MeV, focussing specifically on the $\gamma p\rightarrow K^0\Sigma^+$, $\gamma n\rightarrow K^0\Lambda$, and $\gamma n\rightarrow K^0 \Sigma^0$ reactions. Our results for $\gamma n\rightarrow K^0 \Sigma^0$ are the first-ever measurements for that reaction. These data will provide insight into the properties of $N^*$ resonances and, in particular, will lead to an improved knowledge about those states that couple only weakly to the $\pi N$ channel. Integrated cross sections were extracted by fitting the differential cross sections for each reaction as a series of Legendre polynomials and our results are compared with prior experimental results and theoretical predictions., Comment: 16 pages, 13 figures, 7 tables
Published: 2018
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28. First measurement of helicity-dependent cross sections in pi0-eta photoproduction from quasi-free nucleons

Author: Käser, A., Dieterle, M., Witthauer, L., Abt, S., Achenbach, P., Adlarson, P., Afzal, F., Ahmed, Z., Ahrens, J., Annand, J. R. M., Arends, H. J., Bashkanov, M., Beck, R., Biroth, M., Borisov, N. S., Braghieri, A., Briscoe, W. J., Cividini, F., Collicott, C., Costanza, S., Denig, A., Downie, E. J., Drexler, P., Fix, A., Garni, S., Glazier, D. I., Gorodnov, I., Gradl, W., Günther, M., Gurevich, G. M., Heijkenskjöld, L., Hornidge, D., Huber, G. M., Kashevarov, V. L., Kay, S., Keshelashvili, I., Kondratiev, R., Korolija, M., Krusche, B., Lazarev, A. B., Lisin, V., Livingston, K., Lutterer, S., MacGregor, I. J. D., Manley, D. M., Martel, P. P., Metag, V., Meyer, W., Miskimen, R., Mornacchi, E., Mushkarenkov, A., Neganov, A. B., Neiser, A., Oberle, M., Ostrick, M., Otte, P. B., Paudyal, D., Pedroni, P., Polonski, A., Prakhov, S. N., Reicherz, G., Ron, G., Rostomyan, T., Sarty, A., Sfienti, C., Sokhoyan, V., Spieker, K., Steffen, O., Strakovsky, I. I., Strub, Th., Supek, I., Thiel, A., Thiel, M., Thomas, A., Unverzagt, M., Usov, Yu. A., Wagner, S., Walford, N. K., Watts, D. P., Werthmüller, D., Wettig, J., Wolfes, M., and Zana, L.
Subjects: Nuclear Experiment
Abstract: The helicity-dependent cross sections for the photoproduction of $\pi^0\eta$ pairs have been measured for the first time. The experiment was performed at the tagged photon facility of the Mainz MAMI accelerator with the combined Crystal Ball - TAPS calorimeter. The experiment used a polarized deuterated butanol target and a circularly polarized photon beam. This arrangement allowed the $\sigma_{1/2}$ (photon and target spin antiparallel) and $\sigma_{3/2}$ (parallel spins) components to be measured for quasi-free production of $\pi^0\eta$ pairs off protons and neutrons. The main finding is that the two helicity components contribute identically, within uncertainties, for both participant protons and neutrons. The absolute couplings for protons and neutrons are also identical. This means that nucleon resonances contributing to this reaction in the investigated energy range have almost equal electromagnetic helicity couplings, $A_{1/2}^{n,p}$ and $A_{3/2}^{n,p}$. Identical couplings for protons and neutrons are typical for $\Delta$ resonances and identical $A_{1/2}$ and $A_{3/2}$ components are only possible for $J\geq 3/2$ states, which constrains possible contributions of nucleon resonances., Comment: accepted for publication in Phys. Lett. B
Published: 2018
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29. The {\eta}'-carbon potential at low meson momenta

Author: Nanova, M., Friedrich, S., Metag, V., Paryev, E. Ya., Afzal, F. N., Bayadilov, D., Bantes, B., Beck, R., Becker, M., Böse, S., Brinkmann, K. -T., Crede, V., Drexler, P., Eberhardt, H., Elsner, D., Frommberger, F., Funke, Ch., Gottschall, M., Grüner, M., Gutz, E., Hammann, Ch., Hannappel, J., Hartmann, J., Hillert, W., Hoffmeister, Ph., Honisch, Ch., Jude, T., Kaiser, D., Kalischewski, F., Keshelashvili, I., Klein, F., Koop, K., Krusche, B., Lang, M., Makonyi, K., Messi, F., Müller, J., Müllers, J., Piontek, D., Rostomyan, T., Schaab, D., Schmidt, Ch., Schmieden, H., Schmitz, R., Seifen, T., Sokhoyan, V., Sowa, C., Spieker, K., Thiel, A., Thoma, U., Triffterer, T., Urban, M., van Pee, H., Walther, D., Wendel, Ch., Werthmüller, D., Wiedner, U., Wilson, A., Witthauer, L., Wunderlich, Y., and Zaunick, H. -G.
Subjects: Nuclear Experiment
Abstract: The production of $\eta^\prime$ mesons in coincidence with forward-going protons has been studied in photon-induced reactions on $^{12}$C and on a liquid hydrogen (LH$_2$) target for incoming photon energies of 1.3-2.6 GeV at the electron accelerator ELSA. The $\eta^\prime$ mesons have been identified via the $\eta^\prime\rightarrow \pi^0 \pi^0\eta \rightarrow 6 \gamma$ decay registered with the CBELSA/TAPS detector system. Coincident protons have been identified in the MiniTAPS BaF$_2$ array at polar angles of $2^{\circ} \le \theta _{p} \le 11^{\circ}$. Under these kinematic constraints the $\eta^\prime$ mesons are produced with relatively low kinetic energy ($\approx$ 150 MeV) since the coincident protons take over most of the momentum of the incident-photon beam. For the C-target this allows the determination of the real part of the $\eta^\prime$-carbon potential at low meson momenta by comparing with collision model calculations of the $\eta^\prime$ kinetic energy distribution and excitation function. Fitting the latter data for $\eta^\prime$ mesons going backwards in the center-of-mass system yields a potential depth of V = $-$(44 $\pm$ 16(stat)$\pm$15(syst)) MeV, consistent with earlier determinations of the potential depth in inclusive measurements for average $\eta^\prime$ momenta of $\approx$ 1.1 GeV/$c$. Within the experimental uncertainties, there is no indication of a momentum dependence of the $\eta^\prime$-carbon potential. The LH$_2$ data, taken as a reference to check the data analysis and the model calculations, provide differential and integral cross sections in good agreement with previous results for $\eta^\prime$ photoproduction off the free proton., Comment: 9 pages, 13 figures. arXiv admin note: text overlap with arXiv:1608.06074
Published: 2018
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30. Deuteron photodisintegration by polarized photons in the region of the $d^*(2380)$

Author: Bashkanov, M., Kay, S., Watts, D. P., Mullen, C., Abt, S., Achenbach, P., Adlarson, P., Afzal, F., Ahmed, Z., Akondi, C. S., Annand, J. R. M., Arends, H. J., Beck, R., Biroth, M., Borisov, N., Braghieri, A., Briscoe, W. J., Cividini, F., Collicott, C., Costanza, S., Denig, A., Downie, E. J., Drexler, P., Garni, S., Glazier, D. I., Gorodnov, I., Gradl, W., Günther, M., Gurevich, D., Heijkenskjöld, L., Hornidge, D., Huber, G. M., Käser, A., Kashevarov, V. L., Korolija, M., Krusche, B., Lazarev, A., Livingston, K., Lutterer, S., MacGregor, I. J. D., Macrae, R., Manley, D. M., Martel, P. P., Miskimen, R., Mornacchi, E., Neganov, A., Neiser, A., Ostrick, M., Otte, P. B., Paudyal, D., Pedroni, P., Powell, A., Prakhov, S. N., Ron, G., Rostomyan, T., Sarty, A., Sfienti, C., Sokhoyan, V., Spieker, K., Steffen, O., Strakovsky, I. I., Strub, T., Supek, I., Thiel, A., Thiel, M., Thomas, A., Usov, Yu. A., Wagner, S., Walford, N. K., Werthmüller, D., Wettig, J., Wolfes, M., and Zana, L. A.
Subjects: Nuclear Experiment
Abstract: We report the first large-acceptance measurement of the beam-spin asymmetry for deuteron photodisintegration ($\vec{\gamma} d\to pn$) in the photon energy range $400
Published: 2018
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31. Photoproduction of {\boldmath{$\pi^{0}$}} Mesons off Protons and Neutrons in the Second and Third Nucleon Resonance Region

Author: Dieterle, M., Werthmüller, D., Abt, S., Afzal, F., Bartolome, P. Aguar, Ahmed, Z., Ahrens, J., Annand, J. R. M., Arends, H. J., Bashkanov, M., Beck, R., Biroth, M., Borisov, N., Braghieri, A., Briscoe, W. J., Cherepnya, S., Cividini, F., Collicott, C., Costanza, S., Denig, A., Downie, E. J., Drexler, P., Fil'kov, L. V., Garni, S., Glazier, D. I., Gorodnov, I., Gradl, W., Günther, M., Gurevich, D., Heijkenskjöld, L., Hornidge, D., Huber, G. M., Käser, A., Kashevarov, V. L., Kay, S., Keshelashvili, I., Kondratiev, R., Korolija, M., Krusche, B., Lazarev, A., Lisin, V., Livingston, K., Lutterer, S., MacGregor, I. J. D., Manley, D. M., Martel, P. P., McGeorge, J. C., Metag, V., Middleton, D. G., Miskimen, R., Mornacchi, E., Mushkarenkov, A., Neganov, A., Neiser, A., Oberle, M., Ostrick, M., Otte, P. B., Oussena, B., Paudyal, D., Pedroni, P., Polonski, A., Prakhov, S. N., Ron, G., Rostomyan, T., Sarty, A., Sfienti, C., Sokhoyan, V., Spieker, K., Steffen, O., Strakovsky, I. I., Strub, T., Supek, I., Thiel, A., Thiel, M., Thomas, A., Unverzagt, M., Usov, Yu. A., Wagner, S., Walford, N. K., Watts, D. P., Wettig, J., Witthauer, L., Wolfes, M., and Zana, L. A.
Subjects: Nuclear Experiment
Abstract: Photoproduction of mesons off quasi-free nucleons bound in the deuteron allows to study the electromagnetic excitation spectrum of the neutron and the isospin structure of the excitation of nucleon resonances. The database for such reactions is much more sparse than for free proton targets. Single $\pi^0$ photoproduction off quasi-free nucleons from the deuteron was experimentally studied. Nuclear effects were investigated by a comparison of the results for free protons and quasi-free protons and used as a correction for the quasi-free neutron data. The experiment was performed at the tagged photon beam of the Mainz MAMI accelerator for photon energies between 0.45~GeV and 1.4~GeV, using an almost $4\pi$ electromagnetic calorimeter composed of the Crystal Ball and TAPS detectors. A complete kinematic reconstruction of the final state removed the effects of Fermi motion. Reaction model predictions and PWA for $\gamma n\rightarrow n\pi^{0}$, based on fits to data for the other isospin channels, disagreed between themselves and no model provided a good description of the new data. The results demonstrate clearly the importance of a measurement of the fully neutral final state for the isospin decomposition of the cross section. Model refits, for example from the Bonn-Gatchina analysis, show that the new and the previous data for the other three isospin channels can be simultaneously described when the contributions of several partial waves are modified. The results are also relevant for the suppression of the higher resonance bumps in total photoabsorption on nuclei, which are not well understood., Comment: excepted for publication in Phys. Rev. C
Published: 2018
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32. High-statistics measurement of the eta->3pi^0 decay at the Mainz Microtron

Author: Prakhov, S., Abt, S., Achenbach, P., Adlarson, P., Afzal, F., Aguar-Bartolomé, P., Ahmed, Z., Ahrens, J., Annand, J. R. M., Arends, H. J., Bantawa, K., Bashkanov, M., Beck, R., Biroth, M., Borisov, N. S., Braghieri, A., Briscoe, W. J., Cherepnya, S., Cividini, F., Collicott, C., Costanza, S., Denig, A., Dieterle, M., Downie, E. J., Drexler, P., Bondy, M. I. Ferretti, Fil'kov, L. V., Fix, A., Gardner, S., Garni, S., Glazier, D. I., Gorodnov, I., Gradl, W., Gurevich, G. M., Hamill, C. B., Heijkenskjöld, L., Hornidge, D., Huber, G. M., Käser, A., Kashevarov, V. L., Kay, S., Keshelashvili, I., Kondratiev, R., Korolija, M., Krusche, B., Lazarev, A., Lisin, V., Livingston, K., Lutterer, S., MacGregor, I. J. D., Manley, D. M., Martel, P. P., McGeorge, J. C., Middleton, D. G., Miskimen, R., Mornacchi, E., Mushkarenkov, A., Neganov, A., Neiser, A., Oberle, M., Ostrick, M., Otte, P. B., Paudyal, D., Pedroni, P., Polonski, A., Ron, G., Rostomyan, T., Sfienti, C., Sokhoyan, V., Spieker, K., Steffen, O., Strakovsky, I. I., Strandberg, B., Strub, Th., Supek, I., Thiel, A., Thiel, M., Thomas, A., Unverzagt, M., Usov, Yu. A., Wagner, S., Walford, N. K., Watts, D. P., Werthmüller, D., Wettig, J., Witthauer, L., Wolfes, M., and Zana, L. A.
Subjects: High Energy Physics - Experiment, Nuclear Experiment
Abstract: The largest, at the moment, statistics of 7x10^6 eta->3pi^0 decays, based on 6.2x10^7 eta mesons produced in the gamma p -> eta p reaction, has been accumulated by the A2 Collaboration at the Mainz Microtron, MAMI. It allowed a detailed study of the eta->3pi^0 dynamics beyond its conventional parametrization with just the quadratic slope parameter alpha and enabled, for the first time, a measurement of the second-order term and a better understanding of the cusp structure in the neutral decay. The present data are also compared to recent theoretical calculations that predict a nonlinear dependence along the quadratic distance from the Dalitz-plot center., Comment: 11 pages, 6 figures, 1 table
Published: 2018
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33. Study of the $\gamma p\to \pi^0\eta p$ reaction with the A2 setup at MAMI

Author: Sokhoyan, V., Prakhov, S., Fix, A., Abt, S., Achenbach, P., Adlarson, P., Afzal, F., Aguar-Bartolomé, P., Ahmed, Z., Ahrens, J., Annand, J. R. M., Arends, H. J., Bantawa, K., Bashkanov, M., Beck, R., Biroth, M., Borisov, N. S., Braghieri, A., Briscoe, W. J., Cherepnya, S., Cividini, F., Collicott, C., Costanza, S., Denig, A., Dieterle, M., Downie, E. J., Drexler, P., Bondy, M. I. Ferretti, Fil'kov, L. V., Gardner, S., Garni, S., Glazier, D. I., Glowa, D., Gorodnov, I., Gradl, W., Günther, M., Gurevich, G. M., Hamill, C. B., Heijkenskjöld, L., Hornidge, D., Huber, G. M., Jude, T. C., Käser, A., Kashevarov, V. L., Kay, S., Keshelashvili, I., Kondratiev, R., Korolija, M., Krusche, B., Lazarev, A., Linturi, J., Lisin, V., Livingston, K., Lutterer, S., MacGregor, I. J. D., Macrae, R., Manley, D. M., Martel, P. P., McGeorge, J. C., McNicoll, E. F., Middleton, D. G., Miskimen, R., Mornacchi, E., Mullen, C., Mushkarenkov, A., Neganov, A., Neiser, A., Nikolaev, A., Oberle, M., Ostrick, M., Ott, P., Otte, P. B., Paudyal, D., Pedroni, P., Polonski, A., Rajabi, A., Robinson, J., Ron, G., Rosner, G., Rostomyan, T., Sarty, A., Sfienti, C., Sikora, M. H., Spieker, K., Steffen, O., Strakovsky, I. I., Strandberg, B., Strub, Th., Supek, I., Thiel, A., Thiel, M., Thomas, A., Unverzagt, M., Usov, Yu. A., Wagner, S., Walford, N. K., Watts, D. P., Werthmüller, D., Wettig, J., Witthauer, L., Wolfes, M., and Zana, L. A.
Subjects: Nuclear Experiment
Abstract: The data available from the A2 Collaboration at MAMI were analyzed to select the $\gamma p\to \pi^0\eta p$ reaction on an event-by-event basis, which allows for partial-wave analyses of three-body final states to obtain more reliable results, compared to fits to measured distributions. These data provide the world's best statistical accuracy in the energy range from threshold to $E_{\gamma}=1.45$ GeV, allowing a finer energy binning in the measurement of all observables needed for understanding the reaction dynamics. The results obtained for the measured observables are compared to existing models, and the impact from the new data is checked by the fit with the revised Mainz model., Comment: 15 pages, 18 figures
Published: 2018
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34. Technical Design Report for the Paul Scherrer Institute Experiment R-12-01.1: Studying the Proton 'Radius' Puzzle with {\mu}p Elastic Scattering

Author: Gilman, R., Downie, E. J., Ron, G., Strauch, S., Afanasev, A., Akmal, A., Arrington, J., Atac, H., Ayerbe-Gayoso, C., Benmokhtar, F., Benmouna, N., Bernauer, J., Blomberg, A., Briscoe, W. J., Cioffi, D., Cline, E., Cohen, D., Cohen, E. O., Collicott, C., Deiters, K., Diefenbach, J., Dongwi, B., Ghosal, D., Golossanov, A., Gothe, R., Higinbotham, D., Hornidge, D., Ilieva, Y., Kalantarians, N., Kohl, M., Krusche, B., Kumbartzki, G., Lavrukhin, I., Li, L., Lichtenstadt, J., Lin, W., Liyanage, A., Lorenzon, W., Mesick, K. E., Meziani, Z. -E., Mohanmurthy, P., Moran, P., Nazeer, J., Piasetzsky, E., Ransome, R., Raymond, R., Reggiani, D., Reimer, P. E., Richter, A., Rostomyan, T., Roy, P., Sarty, A., Shamai, Y., Sparveris, N., Steinberg, N., Strakovsky, I., Sulkosky, V., Tadepalli, A. S., and Taragin, M.
Subjects: Physics - Instrumentation and Detectors, Nuclear Experiment
Abstract: The difference in proton radii measured with $\mu p$ atoms and with $ep$ atoms and scattering remains an unexplained puzzle. The PSI MUSE proposal is to measure $\mu p$ and $e p$ scattering in the same experiment at the same time. The experiment will determine cross sections, two-photon effects, form factors, and radii independently for the two reactions, and will allow $\mu p$ and $ep$ results to be compared with reduced systematic uncertainties. These data should provide the best test of lepton universality in a scattering experiment to date, about an order of magnitude improvement over previous tests. Measuring scattering with both particle polarities will allow a test of two-photon exchange at the sub-percent level, about a factor of four improvement on uncertainties and over an order of magnitude more data points than previous low momentum transfer determinations, and similar to the current generation of higher momentum transfer electron experiments. The experiment has the potential to demonstrate whether the $\mu p$ and $ep$ interactions are consistent or different, and whether any difference results from novel physics or two-photon exchange. The uncertainties are such that if the discrepancy is real it should be confirmed with $\approx$5$\sigma$ significance, similar to that already established between the regular and muonic hydrogen Lamb shift.
Published: 2017

35. Measurement of the decay $\eta^{\prime}\to\pi^{0}\pi^{0}\eta$ at MAMI

Author: Adlarson, P., Afzal, F., Akondi, C. S., Annand, J. R. M., Arends, H. J., Beck, R., Borisov, N., Braghieri, A., Briscoe, W. J., Cividini, F., Collicott, C., Costanza, S., Denig, A., Downie, E. J., Dieterle, M., Bondy, M. I. Ferretti, Gardner, S., Garni, S., Glazier, D. I., Glowa, D., Gradl, W., Gurevich, G., Hamilton, D. J., Hornidge, D., Huber, G. M., Käser, A., Kashevarov, V. L., Kay, S., Keshelashvili, I., Kondratiev, R., Korolija, M., Krusche, B., Lazarev, A., Linturi, J., Livingston, K., MacGregor, I. J. D., Manley, D. M., Martel, P. P., McGeorge, J. C., Middleton, D. G., Miskimen, R., Mushkarenkov, A., Neganov, A., Neiser, A., Oberle, M., Ostrick, M., Ott, P., Otte, P. B., Oussena, B., Paudyal, D., Pedroni, P., Polonski, A., Prakhov, S., Rajabi, A., Ron, G., Rostomyan, T., Sarty, A., Sfienti, C., Sokhoyan, V., Spieker, K., Steffen, O., Strakovsky, I. I., Strub, T., Supek, I., Thiel, A., Thiel, M., Tiator, L., Thomas, A., Unverzagt, M., Usov, Y. A., Wagner, S., Watts, D. P., Werthmüller, D., Wettig, J., Witthauer, L., Wolfes, M., Workman, R. L., and Zana, L. A.
Subjects: High Energy Physics - Experiment
Abstract: An experimental study of the $\eta'\to \pi^0\pi^0\eta \to 6\gamma$ decay has been conducted with the best up-to-date statistical accuracy, by measuring $\eta'$ mesons produced in the $\gamma p \to \eta' p$ reaction with the A2 tagged-photon facility at the Mainz Microtron, MAMI. The results obtained for the standard parametrization of the $\eta'\to \pi^0\pi^0\eta$ matrix element are consistent with the most recent results for $\eta'\to\pi\pi\eta$ decays, but have smaller uncertainties. The available statistics and experimental resolution allowed, for the first time, an observation of a structure below the $\pi^+\pi^-$ mass threshold, the magnitude and sign of which, checked within the framework of the nonrelativistic effective-field theory, demonstrated good agreement with the cusp that was predicted based on the $\pi\pi$ scattering length combination, $a_0-a_2$, extracted from $K \to 3\pi$ decays., Comment: 15 pages, 8 figures, 2 tables, accepted for publication in Phys. Rev. D
Published: 2017
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36. First measurement of the polarization observable $E$ and helicity-dependent cross sections in single $\pi^{0}$ photoproduction from quasi-free nucleons

Author: Dieterle, M., Witthauer, L., Cividini, F., Abt, S., Achenbach, P., Adlarson, P., Afzal, F., Ahmed, Z., Akondi, C. S., Annand, J. R. M., Arends, H. J., Bashkanov, M., Beck, R., Biroth, M., Borisov, N. S., Braghieri, A., Briscoe, W. J., Costanza, S., Collicott, C., Denig, A., Downie, E. J., Drexler, P., Ferretti-Bondy, M. I., Gardner, S., Garni, S., Glazier, D. I., Glowa, D., Gradl, W., Günther, M., Gurevich, G. M., Hamilton, D., Hornidge, D., Huber, G. M., Käser, A., Kashevarov, V. L., Kay, S., Keshelashvili, I., Kondratiev, R., Korolija, M., Krusche, B., Lazarev, A. B., Linturi, J. M., Lisin, V., Livingston, K., Lutterer, S., MacGregor, I. J. D., Mancell, J., Manley, D. M., Martel, P. P., Metag, V., Meyer, W., Miskimen, R., Mornacchi, E., Mushkarenkov, A., Neganov, A. B., Neiser, A., Oberle, M., Ostrick, M., Otte, P. B., Paudyal, D., Pedroni, P., Polonski, A., Prakhov, S. N., Rajabi, A., Reicherz, G., Ron, G., Rostomyan, T., Sarty, A., Sfienti, C., Sikora, M. H., Sokhoyan, V., Spieker, K., Steffen, O., Strakovsky, I. I., Strub, Th., Supek, I., Thiel, A., Thiel, M., Thomas, A., Unverzagt, M., Usov, Yu. A., Wagner, S., Watts, N. K. Walford D. P., Werthmüller, D., Wettig, J., Wolfes, M., and Zana, L.
Subjects: Nuclear Experiment
Abstract: The double-polarization observable $E$ and the helicity-dependent cross sections $\sigma_{1/2}$ and $\sigma_{3/2}$ have been measured for the first time for single $\pi^{0}$ photoproduction from protons and neutrons bound in the deuteron at the electron accelerator facility MAMI in Mainz, Germany. The experiment used a circularly polarized photon beam and a longitudinally polarized deuterated butanol target. The reaction products, recoil nucleons and decay photons from the $\pi^0$ meson were detected with the Crystal Ball and TAPS electromagnetic calorimeters. Effects from nuclear Fermi motion were removed by a kinematic reconstruction of the $\pi^{0}N$ final state. A comparison to data measured with a free proton target showed that the absolute scale of the cross sections is significantly modified by nuclear final-state interaction (FSI) effects. However, there is no significant effect on the asymmetry $E$ since the $\sigma_{1/2}$ and $\sigma_{3/2}$ components appear to be influenced in a similar way. Thus, the best approximation of the two helicity-dependent cross sections for the free neutron is obtained by combining the asymmetry $E$ measured with quasi-free neutrons and the unpolarized cross section corrected for FSI effects under the assumption that the FSI effects are similar for neutrons and protons., Comment: accepted for publication in Phys. Lett. B
Published: 2017
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37. Helicity-dependent cross sections and double-polarization observable E in eta photoproduction from quasi-free protons and neutrons

Author: Witthauer, L., Dieterle, M., Abt, S., Achenbach, P., Afzal, F., Ahmed, Z., Akondi, C. S., Annand, J. R. M., Arends, H. J., Bashkanov, M., Beck, R., Biroth, M., Borisov, N. S., Braghieri, A., Briscoe, W. J., Cividini, F., Costanza, S., Collicott, C., Denig, A., Downie, E. J., Drexler, P., Ferretti-Bondy, M. I., Gardner, S., Garni, S., Glazier, D. I., Glowa, D., Gradl, W., Günther, M., Gurevich, G. M., Hamilton, D., Hornidge, D., Huber, G. M., Käser, A., Kashevarov, V. L., Kay, S., Keshelashvili, I., Kondratiev, R., Korolija, M., Krusche, B., Lazarev, A. B., Linturi, J. M., Lisin, V., Livingston, K., Lutterer, S., MacGregor, I. J. D., Mancell, J., Manley, D. M., Martel, P. P., Metag, V., Meyer, W., Miskimen, R., Mornacchi, E., Mushkarenkov, A., Neganov, A. B., Neiser, A., Oberle, M., Ostrick, M., Otte, P. B., Paudyal, D., Pedroni, P., Polonski, A., Prakhov, S. N., Rajabi, A., Reicherz, G., Ron, G., Rostomyan, T., Sarty, A., Sfienti, C., Sikora, M. H., Sokhoyan, V., Spieker, K., Steffen, O., Strakovsky, I. I., Strub, Th., Supek, I., Thiel, A., Thiel, M., Thomas, A., Unverzagt, M., Usov, Yu. A., Wagner, S., Walford, N. K., Watts, D. P., Werthmüller, D., Wettig, J., Wolfes, M., and Zana, L.
Subjects: Nuclear Experiment
Abstract: Precise helicity-dependent cross sections and the double-polarization observable $E$ were measured for $\eta$ photoproduction from quasi-free protons and neutrons bound in the deuteron. The $\eta\rightarrow 2\gamma$ and $\eta\rightarrow 3\pi^0\rightarrow 6\gamma$ decay modes were used to optimize the statistical quality of the data and to estimate systematic uncertainties. The measurement used the A2 detector setup at the tagged photon beam of the electron accelerator MAMI in Mainz. A longitudinally polarized deuterated butanol target was used in combination with a circularly polarized photon beam from bremsstrahlung of a longitudinally polarized electron beam. The reaction products were detected with the electromagnetic calorimeters Crystal Ball and TAPS, which covered 98\% of the full solid angle. The results show that the narrow structure observed earlier in the unpolarized excitation function of $\eta$ photoproduction off the neutron appears only in reactions with antiparallel photon and nucleon spin ($\sigma_{1/2}$). It is absent for reactions with parallel spin orientation ($\sigma_{3/2}$) and thus very probably related to partial waves with total spin 1/2. The behavior of the angular distributions of the helicity-dependent cross sections was analyzed by fitting them with Legendre polynomials. The results are in good agreement with a model from the Bonn-Gatchina group, which uses an interference of $P_{11}$ and $S_{11}$ partial waves to explain the narrow structure., Comment: accepted for publication in Phys. Rev. C
Published: 2017
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38. Photoproduction of eta mesons from the neutron: cross sections and double polarization observable E

Author: Witthauer, L., Dieterle, M., Afzal, F., Anisovich, A. V., Bantes, B., Bayadilov, D., Beck, R., Bichow, M., Brinkmann, K. -T., Böse, S., Challand, Th., Crede, V., Dutz, H., Eberhardt, H., Elsner, D., Ewald, R., Fornet-Ponse, K., Friedrich, St., Frommberger, F., Funke, Ch., Goertz, St., Gottschall, M., Gridnev, A., Grüner, M., Gutzınst, E., Hammann, D., Hammann, Ch., Hannappel, J., Hartmann, J., Hillert, W., Hoffmeister, Ph., Honisch, Ch., Jude, T., Kaiser, D., Kalinowsky, H., Kalischewski, F., Kammer, S., Käser, A., Keshelashvili, I., Klassen, P., Kleber, V., Klein, F., Koop, K., Krusche, B., Lang, M., Lopatin, I., Mahlberg, Ph., Makonyi, K., Metag, V., Meyer, W., Müller, J., Müllers, J., Nanova, M., Nikonov, V., Piontek, D., Reicherz, G., Rostomyan, T., Sarantsev, A., Schmidt, Ch., Schmieden, H., Seifen, T., Sokhoyan, V., Spieker, K., Thiel, A., Thoma, U., Urban, M., van Pee, H., Walford, N. K., Walther, D., Wendel, Ch., Werthmüller, D., Wilson, A., and Winnebeck, A.
Subjects: Nuclear Experiment
Abstract: Photoproduction of $\eta$ mesons from neutrons} \abstract{Results from measurements of the photoproduction of $\eta$ mesons from quasifree protons and neutrons are summarized. The experiments were performed with the CBELSA/TAPS detector at the electron accelerator ELSA in Bonn using the $\eta\to3\pi^{0}\to6\gamma$ decay. A liquid deuterium target was used for the measurement of total cross sections and angular distributions. The results confirm earlier measurements from Bonn and the MAMI facility in Mainz about the existence of a narrow structure in the excitation function of $\gamma n\rightarrow n\eta$. The current angular distributions show a forward-backward asymmetry, which was previously not seen, but was predicted by model calculations including an additional narrow $P_{11}$ state. Furthermore, data obtained with a longitudinally polarized, deuterated butanol target and a circularly polarized photon beam were analyzed to determine the double polarization observable $E$. Both data sets together were also used to extract the helicity dependent cross sections $\sigma_{1/2}$ and $\sigma_{3/2}$. The narrow structure in the excitation function of $\gamma n\rightarrow n\eta$ appears associated with the helicity-1/2 component of the reaction.
Published: 2017
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39. Insight into the narrow structure in {\boldmath{$\eta$}}-photoproduction on the neutron from helicity dependent cross sections

Author: Witthauer, L., Dieterle, M., Abt, S., Achenbach, P., Afzal, F., Ahmed, Z., Annand, J. R. M., Arends, H. J., Bashkanov, M., Beck, R., Biroth, M., Borisov, N. S., Braghieri, A., Briscoe, W. J., Cividini, F., Costanza, S., Collicott, C., Denig, A., Downie, E. J., Drexler, P., Ferretti-Bondy, M. I., Gardner, S., Garni, S., Glazier, D. I., Glowa, D., Gradl, W., Günther, M., Gurevich, G. M., Hamilton, D., Hornidge, D., Huber, G. M., Käser, A., Kashevarov, V. L., Kay, S., Keshelashvili, I., Kondratiev, R., Korolija, M., Krusche, B., Lazarev, A. B., Linturi, J. M., Lisin, V., Livingston, ., Lutterer, S., MacGregor, I. J. D., Mancell, J., Manley, D. M., Martel, P. P., Metag, V., Meyer, W., Miskimen, R., Mornacchi, E., Mushkarenkov, A., Neganov, A. B., Neiser, A., Oberle, M., Ostrick, M., Otte, P. B., Paudyal, D., Pedroni, P., Polonski, A., Prakhov, S. N., Rajabi, A., Reicherz, G., Ron, G., Rostomyan, T., Sarty, A., Sfienti, C., Sikora, M. H., Sokhoyan, V., Spieker, K., Steffen, O., Strakovsky, I. I., Strub, Th., Supek, I., Thiel, A., Thiel, M., Thomas, A., Unverzagt, M., Usov, Yu. A., Wagner, S., Walford, N. K., Watts, D. P., Werthmüller, D., Wettig, J., Wolfes, M., and Zana, L.
Subjects: Nuclear Experiment
Abstract: The double polarization observable $E$ and the helicity dependent cross sections $\sigma_{1/2}$ and $\sigma_{3/2}$ were measured for $\eta$ photoproduction from quasi-free protons and neutrons. The circularly polarized tagged photon beam of the A2 experiment at the Mainz MAMI accelerator was used in combination with a longitudinally polarized deuterated butanol target. The almost $4\pi$ detector setup of the Crystal Ball and TAPS is ideally suited to detect the recoil nucleons and the decay photons from $\eta\rightarrow 2\gamma$ and $\eta\rightarrow 3\pi^0$. The results show that the narrow structure previously observed in $\eta$ photoproduction from the neutron is only apparent in $\sigma_{1/2}$ and hence, most likely related to a spin-1/2 amplitude. Nucleon resonances that contribute to this partial wave in $\eta$ production are only $N1/2^-$ ($S_{11}$) and $N1/2^+$ ($P_{11}$). Furthermore, the extracted Legendre coefficients of the angular distributions for $\sigma_{1/2}$ are in good agreement with recent reaction model predictions assuming a narrow resonance in the $P_{11}$ wave as the origin of this structure.
Published: 2017
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40. Study of $\eta$ and $\eta'$ photoproduction at MAMI

Author: Kashevarov, V. L., Ott, P., Prakhov, S., Adlarson, P., Afzal, F., Ahmed, Z., Akondi, C. S., Annand, J. R. M., Arends, H. J., Beck, R., Braghieri, A., Briscoe, W. J., Cividini, F., Codling, R., Collicott, C., Costanza, S., Denig, A., Downie, E. J., Dieterle, M., Bondy, M. I. Ferretti, Filkov, L. V., Fix, A., Gardner, S., Garni, S., Glazier, D. I., Glowa, D., Gradl, W., Gurevich, G., Hamilton, D. J., Hornidge, D., Howdle, D., Huber, G. M., Kaeser, A., Kay, S., Keshelashvili, I., Kondratiev, R., Korolija, M., Krusche, B., Linturi, J., Lisin, V., Livingston, K., MacGregor, I. J. D., MacRae, R., Mancell, J., Manley, D. M., Martel, P. P., McGeorge, J. C., McNicol, E., Middleton, D. G., Miskimen, R., Mornacchi, E., Mullen, C., Mushkarenkov, A., Neiser, A., Oberle, M., Ostrick, M., Otte, P. B., Oussena, B., Paudyal, D., Pedroni, P., Polyanski, V. V., Rajabi, A., Robinson, J., Rosner, G., Rostomyan, T., Sarty, A., Schott, D. M., Schumann, S., Sfienti, C., Sokhoyan, V., Spieker, K., Steffen, O., Strandberg, B., Strakovsky, I. I., Strub, Th., Supek, I., Taragin, M. F., Thiel, A., Thiel, M., Tiator, L., Thomas, A., Unverzagt, M., Wagner, S., Watts, D. P., Werthmueller, D., Wettig, J., Witthauer, L., Wolfes, M., Workman, R. L., and Zana, L.
Subjects: Nuclear Experiment, High Energy Physics - Experiment, High Energy Physics - Phenomenology
Abstract: The reactions $\gamma p\to \eta p$ and $\gamma p\to \eta' p$ have been measured from their thresholds up to the center-of-mass energy $W=1.96$GeV with the tagged-photon facilities at the Mainz Microtron, MAMI. Differential cross sections were obtained with unprecedented accuracy, providing fine energy binning and full production-angle coverage. A strong cusp is observed in the total cross section and excitation functions for $\eta$ photoproduction at the energies in vicinity of the $\eta'$ threshold, $W=1896$MeV ($E_\gamma=1447$MeV). This behavior is explained in a revised $\eta$MAID isobar model by a significant branching of the $N(1895)1/2^-$ nucleon resonance to both, $\eta p$ and $\eta' p$, confirming the existence and constraining the properties of this poorly known state.
Published: 2017
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41. Measurement of the pi^0 -> e^+e^-gamma Dalitz decay at the Mainz Microtron

Author: Adlarson, P., Afzal, F., Aguar-Bartolomé, P., Ahmed, Z., Akondi, C. S., Annand, J. R. M., Arends, H. J., Bantawa, K., Beck, R., Berghäuser, H., Biroth, M., Borisov, N. S., Braghieri, A., Briscoe, W. J., Cherepnya, S., Cividini, F., Collicott, C., Costanza, S., Denig, A., Dieterle, M., Downie, E. J., Drexler, P., Bondy, M. I. Ferretti, Fil'kov, L. V., Gardner, S., Garni, S., Glazier, D. I., Glowa, D., Gradl, W., Gurevich, G. M., Hamilton, D. J., Hornidge, D., Huber, G. M., Jude, T. C., Käser, A., Kashevarov, V. L., Kay, S., Keshelashvili, I., Kondratiev, R., Korolija, M., Krusche, B., Kulikov, V. V., Lazarev, A., Linturi, J., Lisin, V., Livingston, K., MacGregor, I. J. D., Macrae, R., Manley, D. M., Martel, P. P., Martemianov, M., McGeorge, J. C., McNicoll, E. F., Metag, V., Middleton, D. G., Miskimen, R., Mornacchi, E., Mullen, C., Mushkarenkov, A., Neganov, A., Neiser, A., Nikolaev, A., Oberle, M., Ostrick, M., Ott, P., Otte, P. B., Paudyal, D., Pedroni, P., Polonski, A., Prakhov, S., Rajabi, A., Robinson, J., Ron, G., Rosner, G., Rostomyan, T., Sfienti, C., Sikora, M. H., Sokhoyan, V., Spieker, K., Steffen, O., Strakovsky, I. I., Strandberg, B., Strub, Th., Supek, I., Thiel, A., Thiel, M., Thomas, A., Unverzagt, M., Usov, Yu. A., Wagner, S., Walford, N., Watts, D. P., Werthmüller, D., Wettig, J., Witthauer, L., Wolfes, M., and Zana, L. A.
Subjects: High Energy Physics - Experiment, Nuclear Experiment
Abstract: The Dalitz decay pi^0 -> e^+e^-gamma has been measured in the gamma p -> pi^0 p reaction with the A2 tagged-photon facility at the Mainz Microtron, MAMI. The value obtained for the slope parameter of the pi^0 electromagnetic transition form factor, a_pi = 0.030+/-0.010_tot, is in agreement with existing measurements of this decay and with recent theoretical calculations. The uncertainty obtained in the value of a_pi is lower than in previous results based on the pi^0 -> e^+e^-gamma decay., Comment: 11 pages, 7 figures, 1 table
Published: 2016
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42. Determination of the scalar polarizabilities of the proton using beam asymmetry $\Sigma_{3}$ in Compton scattering

Author: Sokhoyan, V., Downie, E. J., Mornacchi, E., McGovern, J. A., Krupina, N., Afzal, F., Ahrens, J., Akondi, C. S., Annand, J. R. M., Arends, H. J., Beck, R., Braghieri, A., Briscoe, W. J., Cividini, F., Collicott, C., Costanza, S., Denig, A., Dieterle, M., Ferretti, M., Gardner, S., Garni, S., Glazier, D. I., Glowa, D., Gradl, W., Gurevich, G., Hamilton, D., Hornidge, D., Huber, G. M., Käser, A., Kashevarov, V. L., Keshelashvili, I., Kondratiev, R., Korolija, M., Krusche, B., Lensky, V., Linturi, J., Lisin, V., Livingston, K., MacGregor, I. J. D., Macrae, R., Manley, D. M., Martel, P. P., Middleton, D. G., Miskimen, R., Mushkarenkov, A., Neiser, A., Oberle, M., Spina, H. Ortega, Ostrick, M., Ott, P., Otte, P. B., Oussena, B., Paudyal, D., Pedroni, P., Polonski, A., Polyansky, V., Prakhov, S., Rajabi, A., Rostomyan, T., Sarty, A., Schumann, S., Steffen, O., Strakovsky, I. I., Strandberg, B., Strub, T., Supek, I., Thiel, M., Thomas, A., Unverzagt, M., Wagner, S., Watts, D. P., Wettig, J., Witthauer, L., Werthmüller, D., Wolfes, M., and Zana, L.
Subjects: Nuclear Experiment
Abstract: The scalar dipole polarizabilities, $\alpha_{E1}$ and $\beta_{M1}$, are fundamental properties related to the internal dynamics of the nucleon. The currently accepted values of the proton polarizabilities were determined by fitting to unpolarized proton Compton scattering cross section data. The measurement of the beam asymmetry $\Sigma_{3}$ in a certain kinematical range provides an alternative approach to the extraction of the scalar polarizabilities. At the Mainz Microtron (MAMI) the beam asymmetry was measured for Compton scattering below pion photoproduction threshold for the first time. The results are compared with model calculations and the influence of the experimental data on the extraction of the scalar polarizabilities is determined., Comment: 6 pages, 5 figures
Published: 2016
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43. The Present and Future of QCD: QCD Town Meeting White Paper -- An INput to the 2023 NSAC Long Range Plan

Author: Achenbach, P, primary, Adhikari, D, additional, Afanasev, A, additional, Afzal, F, additional, Aidala, C, additional, Al-bataineh, A, additional, Almaaloi, D, additional, Amaryan, M, additional, Androic, D, additional, Armstrong, W, additional, Arriatia, M, additional, Arrington, J, additional, Asaturyan, A, additional, Aschenauer, E, additional, Atac, H, additional, Avakian, H, additional, Averett, T, additional, Ayerbe Gayoso, C, additional, Bai, X, additional, Barish, K, additional, Barnea, N, additional, Basar, G, additional, Battaglieri, M, additional, Baty, A, additional, Bautista, I, additional, Bazilevsky, A, additional, Beattie, C, additional, Behera, S, additional, Bellini, V, additional, Bellwied, R, additional, Benesch, J, additional, Benmokhtar, F, additional, Bernardes, C, additional, Bernauer, J, additional, Bhatt, H, additional, Bhatta, S, additional, Boer, M, additional, Boettcher, T, additional, Bogacz, S, additional, Bossi, H, additional, Brandenburg, J, additional, Brash, E, additional, Briceno, R, additional, Briscoe, W, additional, Brodsky, S, additional, Brown, D, additional, Burkert, V, additional, Caines, H, additional, Cali, I, additional, Camsonne, A, additional, Carman, D, additional, Caylor, J, additional, Cerci, S, additional, Chamizo Llatas, M, additional, Chen, J, additional, Chen, Y, additional, Chien, Y, additional, Chou, P, additional, Chu, X, additional, Chudakov, E, additional, Cline, E, additional, Cloet, I, additional, Cole, P, additional, Conners, M, additional, Constantinou, M, additional, Cosyn, W, additional, Covrig Dusa, S, additional, Cruz-Torres, R, additional, D'Alesio, U, additional, da Silva, C, additional, Davoudi, Z, additional, Dean, C, additional, Dean, D, additional, Demarteau, M, additional, Deshpande, A, additional, Detmold, W, additional, Deur, A, additional, Devkota, B, additional, Dhital, S, additional, Diefenthaler, M, additional, Dobbs, S, additional, Doring, M, additional, Dong, X, additional, Dotel, R, additional, Dow, K, additional, Downie, E, additional, Drachenberg, J, additional, Dumitru, A, additional, Dunlop, J, additional, Dupre, R, additional, Durham, J, additional, Dutta, D, additional, Edwards, R, additional, Ehlers, R, additional, El Fassi, L, additional, Elaasar, M, additional, Elouadrhiri, L, additional, Engelhardt, M, additional, Ent, R, additional, Esumi, S, additional, Evdokimov, O, additional, Eyser, O, additional, Fanelli, C, additional, Fatemi, R, additional, Fernando, I, additional, Flor, F, additional, Fomin, N, additional, Frawley, A, additional, Federico, T, additional, Fries, R, additional, Gal, C, additional, Gamage, B, additional, Gamberg, L, additional, Gao, H, additional, Gaskell, D, additional, Geurts, F, additional, Ghandilyan, Y, additional, Gilman, R, additional, Gleason, C, additional, Gnanvo, K, additional, Gothe, R, additional, Greene, S, additional, Griesshammer, H, additional, Grossberndt, S, additional, Grube, B, additional, Hackett, D, additional, Hague, T, additional, Hakobyan, H, additional, Hansen, J, additional, Hatta, Y, additional, Hattawy, M, additional, Havener, L, additional, Hen, O, additional, Henry, W, additional, Higinbotham, D, additional, Hobbs, T, additional, Hodges, A, additional, Holmstrom, T, additional, Hong, B, additional, Horn, T, additional, Howell, C, additional, Huang, H, additional, Huang, M, additional, Huang, S, additional, Huber, G, additional, Hyde, C, additional, Isupov, E, additional, Jacobs, P, additional, Jalilian-Marian, J, additional, Jentsch, A, additional, Jheng, H, additional, Ji, C, additional, Ji, X, additional, Jia, J, additional, Jones, D, additional, Jones, M, additional, Kalantarians, N, additional, Kalicy, G, additional, Kang, Z, additional, Karthein, J, additional, Keller, D, additional, Keppel, C, additional, Khachartryan, V, additional, Kharzeev, D, additional, Kim, M, additional, Kim, Y, additional, King, P, additional, Kinney, E, additional, Klein, S, additional, Ko, H, additional, Koch, V, additional, Kohl, M, additional, Kovchegov, Y, additional, Krintiras, G, additional, Kubarovsky, V, additional, Kuhn, S, additional, Kumar, K, additional, Kutz, T, additional, Lajoie, J, additional, Lauret, J, additional, Lavrukhin, I, additional, Lawrence, D, additional, Lee, J, additional, Lee, K, additional, Lee, S, additional, Lee, Y, additional, Li, S, additional, Li, W, additional, Li, X, additional, Liao, J, additional, Lin, H, additional, Lisa, M, additional, Liu, K, additional, Liu, M, additional, Liu, T, additional, Liuti, S, additional, Liyanage, N, additional, Llope, W, additional, Loizides, C, additional, Longo, R, additional, Lorenzon, W, additional, Luo, X, additional, Ma, R, additional, McKinnon, B, additional, Meekins, D, additional, Mehtar-Tani, Y, additional, Melnitchouk, W, additional, Metz, A, additional, Meyer, C, additional, Meziani, Z, additional, Michaels, R, additional, Milner, R, additional, Mkrtchyan, H, additional, Mohanmurthy, P, additional, Mohanty, B, additional, Mokeev, V, additional, Mooney, I, additional, Morningstar, C, additional, Morrison, D, additional, Muller, B, additional, Mukherjee, S, additional, Mulligan, J, additional, Munoz Camacho, C, additional, Murillo Quijada, J, additional, Murray, M, additional, Nadeeshani, S, additional, Nadel-Turonski, P, additional, Nam, J, additional, Nattrass, C, additional, Nijs, G, additional, Norohna, J, additional, Noronha-Hostler, J, additional, Novitzky, N, additional, Nycz, M, additional, Olness, F, additional, Osborn, J, additional, Pak, R, additional, Pandey, B, additional, Paolone, M, additional, Papandreou, Z, additional, Paquet, J, additional, Park, S, additional, Paschke, K, additional, Pasquini, B, additional, Pasyuk, E, additional, Patel, T, additional, Patton, A, additional, Paudel, C, additional, Peng, C, additional, Peng, J, additional, Pereira Da Costa, H, additional, Perepelitsa, D, additional, Peters, M, additional, Petreczky, P, additional, Pisarski, R, additional, Pitonyak, D, additional, Ploskon, M, additional, Posik, M, additional, Poudel, J, additional, Pradhan, R, additional, Prokudin, A, additional, Pruneau, C, additional, Putschke, J, additional, Pybus, J, additional, Qiu, J, additional, Rajagopal, K, additional, Ratti, C, additional, Read, K, additional, Reed, R, additional, Richards, D, additional, Riedl, C, additional, Ringer, F, additional, Rinn, T, additional, Rittenhouse West, J, additional, Roche, J, additional, Rodas, A, additional, Roland, G, additional, Romero-Lopez, F, additional, Rossi, P, additional, Rostomyan, T, additional, Ruan, L, additional, Ruimi, O, additional, Saha, N, additional, Sahoo, N, additional, Sakaguchi, T, additional, Salazar, F, additional, Salgado, C, additional, Salme, G, additional, Salur, S, additional, Santiesteban, S, additional, Sargsian, M, additional, Sarsour, M, additional, Sato, N, additional, Satogata, T, additional, Sawada, S, additional, Schafer, T, additional, Scheihing-Hitschfeld, B, additional, Schenke, B, additional, Schindler, S, additional, Schmidt, A, additional, Seidl, R, additional, Sabestari, M, additional, Shanahan, P, additional, Shen, C, additional, Sheng, T, additional, Shepherd, M, additional, M Sickles, A, additional, Sievert, M, additional, Smith, K, additional, Song, Y, additional, Sorensen, A, additional, Souder, P, additional, Spareveris, N, additional, Srednyak, S, additional, Stahl Leiton, A, additional, Stasto, A, additional, Steinberg, P, additional, Stepanyan, S, additional, Stephanov, M, additional, Stevens, J, additional, Stewart, D, additional, Stewart, I, additional, Stojanovic, M, additional, Strakovsky, I, additional, Strauch, S, additional, Strickland, M, additional, Sunar Cerci, D, additional, Suresh, M, additional, Surrow, B, additional, Syritsyn, S, additional, Szczepaniak, A, additional, Tadepalli, A, additional, H Tang, A, additional, Tapia Takaki, J, additional, Tarnowsky, T, additional, Tawfik, A, additional, Taylor, M, additional, Tennant, C, additional, Thiel, A, additional, Thomas, D, additional, Tian, Y, additional, Timmins, A, additional, Tribedy, P, additional, Tu, Z, additional, Tuo, S, additional, Ullrich, T, additional, Umaka, E, additional, Ghimire, N, additional, Vary, J, additional, Velkovska, J, additional, Venugopalan, R, additional, Vijayakumar, A, additional, Vitev, I, additional, Vogelsang, W, additional, Vogt, R, additional, Vossen, A, additional, Voutier, E, additional, Vovchenko, V, additional, Walker-Loud, A, additional, Wang, F, additional, Wang, J, additional, Wang, X, additional, Weinstein, L, additional, Wenaus, T, additional, Weyhmiller, S, additional, Wissink, S, additional, Wojtsekhowski, B, additional, Wong, C, additional, Wood, M, additional, Wunderlich, Y, additional, Wyslouch, B, additional, Xiao, B, additional, Xie, W, additional, Xiong, W, additional, Xu, N, additional, Xu, Q, additional, Xu, Z, additional, Yaari, D, additional, Yao, X, additional, Ye, Z, additional, Yero, C, additional, Yuan, F, additional, Zajc, W, additional, Zhang, C, additional, Zhang, J, additional, Zhao, F, additional, Zhao, Y, additional, Zhao, Z, additional, Zheng, X, additional, and Zhou, J, additional
Published: 2023
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44. Measurement of the omega -> pi^0 e^+e^- and eta -> e^+e^-g Dalitz decays with the A2 setup at MAMI

Author: Adlarson, P., Afzal, F., Aguar-Bartolomé, P., Ahmed, Z., Annand, J. R. M., Arends, H. J., Bantawa, K., Beck, R., Berghäuser, H., Biroth, M., Borisov, N. S., Braghieri, A., Briscoe, W. J., Cherepnya, S., Cividini, F., Collicott, C., Costanza, S., Danilkin, I. V., Denig, A., Dieterle, M., Downie, E. J., Drexler, P., Bondy, M. I. Ferretti, Fil'kov, L. V., Gardner, S., Garni, S., Glazier, D. I., Glowa, D., Gradl, W., Gurevich, G. M., Hamilton, D. J., Hornidge, D., Huber, G. M., Jude, T. C., Käser, A., Kashevarov, V. L., Kay, S., Keshelashvili, I., Kondratiev, R., Korolija, M., Krusche, B., Lazarev, A., Linturi, J., Lisin, V., Livingston, K., MacGregor, I. J. D., Macrae, R., Manley, D. M., Martel, P. P., McGeorge, J. C., McNicoll, E. F., Metag, V., Middleton, D. G., Miskimen, R., Mornacchi, E., Mullen, C., Mushkarenkov, A., Neganov, A., Neiser, A., Nikolaev, A., Oberle, M., Ostrick, M., Ott, P., Otte, P. B., Paudyal, D., Pedroni, P., Polonski, A., Prakhov, S., Rajabi, A., Robinson, J., Ron, G., Rosner, G., Rostomyan, T., Sfienti, C., Sikora, M. H., Sokhoyan, V., Spieker, K., Steffen, O., Strakovsky, I. I., Strandberg, B., Strub, Th., Supek, I., Thiel, A., Thiel, M., Thomas, A., Unverzagt, M., Usov, Yu. A., Wagner, S., Walford, N., Watts, D. P., Werthmüller, D., Wettig, J., Witthauer, L., Wolfes, M., and Zana, L. A.
Subjects: High Energy Physics - Experiment, Nuclear Experiment
Abstract: The Dalitz decays eta -> e^+e^-g and omega -> pi^0 e^+e^- have been measured in the g p -> eta p and g p -> omega p reactions, respectively, with the A2 tagged-photon facility at the Mainz Microtron, MAMI. The value obtained for the slope parameter of the electromagnetic transition form factor of eta, Lambda^{-2}_eta=(1.97+/-0.11_tot) GeV^{-2}, is in good agreement with previous measurements of the eta -> e^+e^-g and eta -> mu^+mu^-g decays. The uncertainty obtained in the value of Lambda^{-2}_eta is lower than in previous results based on the eta -> e^+e^-g decay. The value obtained for the omega slope parameter, Lambda^{-2}_omega_pi^0 = (1.99+/-0.21_tot) GeV^{-2}, is somewhat lower than previous measurements based on omega -> pi^0 mu^+mu^-, but the results for the omega transition form factor are in better agreement with theoretical calculations, compared to earlier experiments., Comment: 19 figures, 2 tables
Published: 2016
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45. Photoproduction ofeta-pi pairs off nucleons and deuterons

Author: Kaeser, A., Mueller, F., Ahrens, J., Annand, J. R. M., Arends, H. J., Bantawa, K., Bartolome, P. A., Beck, R., Braghieri, A., Briscoe, W. J., Cherepnya, S., Costanza, S., Dieterle, M., Downie, E. J., Drexler, P., Fil'kov, L. V., Fix, A., Garni, S., Glazier, D. I., Hamilton, D., Hornidge, D., Howdle, D., Huber, G. M., Jaegle, I., Jude, T. C., Kashevarov, V. L., Keshelashvili, I., Kondratiev, R., Korolija, M., Krusche, B., Lisin, V., Livingston, K., MacGregor, I. J. D., Maghrbi, Y., Mancell, J., Manley, D. M., Marinides, Z., McGeorge, J. C., McNicoll, E., Mekterovic, D., Metag, V., Micanovic, S., Middleton, D. G., Mushkarenkov, A., Nikolaev, A., Novotny, R., Oberle, M., Ostrick, M., Otte, P., Oussena, B., Pedroni, P., Pheron, F., Polonski, A., Prakhov, S., Robinson, J., Rostomyan, T., Schumann, S., Sikora, M. H., Sober, D., Starostin, A., Strub, Th., Supek, I., Thiel, M., Thomas, A., Unverzagt, M., Walford, N. K., Watts, D. P., Werthmueller, D., and Witthauer, L.
Subjects: Nuclear Experiment
Abstract: Quasi-free photoproduction of $\pi\eta$-pairs has been investigated from threshold up to incident photon energies of 1.4 GeV, respectively up to photon-nucleon invariant masses up to 1.9 GeV. Total cross sections, angular distributions, invariant-mass distributions of the $\pi\eta$ and meson-nucleon pairs, and beam-helicity asymmetries have been measured for the reactions $\gamma p\rightarrow p\pi^0\eta$, $\gamma n\rightarrow n\pi^0\eta$, $\gamma p\rightarrow n\pi^+\eta$, and $\gamma n\rightarrow p\pi^-\eta$ from nucleons bound inside the deuteron. For the $\gamma p$ initial state data for free protons have also been analyzed. Finally, the total cross sections for quasi-free production of $\pi^0\eta$ pairs from nucleons bound in $^3$He nuclei have been investigated in view of final state interaction (FSI) effects. The experiments were performed at the tagged photon beam facility of the Mainz MAMI accelerator using an almost $4\pi$ covering electromagnetic calorimeter composed of the Crystal Ball and TAPS detectors. The shapes of all differential cross section data and the asymmetries are very similar for protons and neutrons and agree with the conjecture that the reactions are dominated by the sequential $\Delta^{\star}3/2^-\rightarrow\eta\Delta(1232)\rightarrow\pi\eta N$ decay chain, mainly with $\Delta(1700)3/2^-$ and $\Delta(1940)3/2^-$. The ratios of the magnitude of the total cross sections also agree with this assumption. However, the absolute magnitudes of the cross sections are reduced by FSI effects with respect to free proton data., Comment: accepted for publication in Eur. Phys. J. A
Published: 2016
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46. Momentum dependence of the imaginary part of the $\omega$- and $\eta^\prime$-nucleus optical potential

Author: Friedrich, S., Nanova, M., Metag, V., Afzal, F. N., Bayadilov, D., Bantes, B., Beck, R., Becker, M., Böse, S., Brinkmann, K. -T., Crede, V., Drexler, P., Eberhardt, H., Elsner, D., Frommberger, F., Funke, Ch., Gottschall, M., Grüner, M., Gutz, E., Hammann, Ch., Hannappel, J., Hartmann, J., Hillert, W., Hoffmeister, Ph., Honisch, Ch., Jude, T., Kaiser, D., Kalischewski, F., Keshelashvili, I., Klein, F., Koop, K., Krusche, B., Lang, M., Makonyi, K., Messi, F., Müller, J., Müllers, J., Piontek, D. -M., Rostomyan, T., Schaab, D., Schmidt, Ch., Schmieden, H., Schmitz, R., Seifen, T., Sokhoyan, V., Sowa, C., Spieker, K., Thiel, A., Thoma, U., Triffterer, T., Urban, M., van Pee, H., Walther, D., Wendel, Ch., Werthmüller, D., Wiedner, U., Wilson, A., Witthauer, L., Wunderlich, Y., and Zaunick, H. -G.
Subjects: Nuclear Experiment
Abstract: The photoproduction of $\omega$ and $\eta^\prime$ mesons off carbon and niobium nuclei has been measured as a function of the meson momentum for incident photon energies of 1.2-2.9 GeV at the electron accelerator ELSA. The mesons have been identified via the $\omega \rightarrow \pi^0 \gamma \rightarrow 3 \gamma$ and $\eta^\prime\rightarrow \pi^0 \pi^0\eta \rightarrow 6 \gamma$ decays, respectively, registered with the CBELSA/TAPS detector system. From the measured meson momentum distributions the momentum dependence of the transparency ratio has been determined for both mesons. Within a Glauber analysis the in-medium $\omega$ and $\eta^\prime$ widths and the corresponding absorption cross sections have been deduced as a function of the meson momentum. The results are compared to recent theoretical predictions for the in-medium $\omega$ width and $\eta^\prime$-N absorption cross sections. The energy dependence of the imaginary part of the $\omega$- and $\eta^\prime$-nucleus optical potential has been extracted. The finer binning of the present data compared to the existing data allows a more reliable extrapolation towards the production threshold. The modulus of the imaginary part of the $\eta^\prime$ nucleus potential is found to be about three times smaller than recently determined values of the real part of the $\eta^\prime$-nucleus potential, which makes the $\eta^\prime$ meson a suitable candidate for the search for meson-nucleus bound states. For the $\omega$ meson, the modulus of the imaginary part near threshold is comparable to the modulus of the real part of the potential. As a consequence, only broad structures can be expected which makes the observation of $\omega$ mesic states very difficult experimentally., Comment: 10 pages, 8 figures
Published: 2016
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47. Determination of the real part of the {\eta}'-Nb optical potential

Author: Nanova, M., Friedrich, S., Metag, V., Paryev, E. Ya., Afzal, F. N., Bayadilov, D., Beck, R., Becker, M., Böse, S., Brinkmann, K. -T., Crede, V., Elsner, D., Frommberger, F., Grtuner, M., Gutz, E., Hammann, Ch., Hannappel, J., Hartmann, J., Hillert, W., Hoffmeister, P., Honisch, Ch., Jude, T., Kalischewski, F., Keshelashvili, I., Klein, F., Koop, K., Krusche, B., Lang, M., Makonyi, K., Messi, F., Müller, J., Müllers, J., Piontek, D. M., Rostomyan, T., Schaab, D., Schmidt, C., Schmieden, H., Schmitz, R., Seifen, T., Sowa, C., Spieker, K., Thiel, A., Thoma, U., Tristerer, T., Urban, M., van Pee, H., Walther, D., Wendel, C., Werthmüller, D., Wiedner, U., Wilson, A., Witthauer, L., Wunderlich, Y., and Zaunick, H. -G.
Subjects: Nuclear Experiment
Abstract: The excitation function and momentum distribution of {\eta}' mesons have been measured in photoproduction off 93^Nb in the energy range of 1.2-2.9 GeV. The experiment has been performed with the combined Crystal Barrel and MiniTAPS detector system, using tagged photon beams from the ELSA electron accelerator. Information on the sign and magnitude of the real part of the {\eta}'-Nb potential has been extracted from a comparison of the data with model calculations. An attractive potential of -(41 \pm 10(stat) \pm 15(syst)) MeV depth at normal nuclear matter density is deduced within model uncertainties. This value is consistent with the potential depth of -(37 \pm 10(stat) \pm 10(syst)) MeV obtained in an earlier measurement for a light nucleus (carbon). This relatively shallow {\eta}'-nucleus potential will make the search for {\eta}'-nucleus bound states more difficult., Comment: 9 pages, 6 figures
Published: 2016
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48. Photon asymmetry measurements of $\overrightarrow{\gamma} \mathrm{p} \rightarrow \pi^{0} \mathrm{p}$ for E$_{\gamma}$=320$-$650 MeV

Author: Gardner, S., Howdle, D., Sikora, M. H., Wunderlich, Y., Abt, S., Achenbach, P., Afzal, F., Aguar-Bartolome, P., Ahmed, Z., Annand, J. R. M., Arends, H. J., Bantawa, K., Bashkanov, M., Beck, R., Biroth, M., Borisov, N. S., Braghieri, A., Briscoe, W. J., Cherepnya, S., Cividini, F., Costanza, S., Collicott, C., Demissie, B. T., Denig, A., Dieterle, M., Downie, E. J., Drexler, P., Ferretti-Bondy, M. I., Filkov, L. V., Glazier, D. I., Garni, S., Gradl, W., Günther, M., Gurevich, G. M., Hamilton, D., Heid, E., Hornidge, D., Huber, G. M., Jahn, O., Jude, T. C., Käser, A., Kay, S., Kashevarov, V. L., Keshelashvili, I., Kondratiev, R., Korolija, M., Krusche, B., Linturi, J. M., Lisin, V., Livingston, K., Lutterer, S., MacGregor, I. J. D., Macrae, R., Mancell, J., Manley, D. M., Martel, P. P., McGeorge, J. C., McNicoll, E. F., Middleton, D. G., Miskimen, R., Mullen, C., Mushkarenkov, A., Neganov, A. B., Neiser, A., Nikolaev, A., Oberle, M., Ostrick, M., Owens, R. O., Otte, P. B., Oussena, B., Paudyal, D., Pedroni, P., Polonski, A., Prakhov, S., Rajabi, A., Robinson, J., Rosner, G., Rostomyan, T., Sarty, A., Schumann, S., Sokhoyan, V., Spieker, K., Steffen, O., Sfienti, C., Strakovsky, I. I., Strandberg, B., Strub, Th., Supek, I., Tarbert, C. M., Thiel, A., Thiel, M., Thomas, A., Unverzagt, M., Usov, Yu. A., Watts, D. P., Werthmüller, D., Wettig, J., Wolfes, M., Witthauer, L., and Zana, L.
Subjects: Nuclear Experiment
Abstract: High statistics measurements of the photon asymmetry $\mathrm{\Sigma}$ for the $\overrightarrow{\gamma}$p$\rightarrow\pi^{0}$p reaction have been made in the center of mass energy range W=1214-1450 MeV. The data were measured with the MAMI A2 real photon beam and Crystal Ball/TAPS detector systems in Mainz, Germany. The results significantly improve the existing world data and are shown to be in good agreement with previous measurements, and with the MAID, SAID, and Bonn-Gatchina predictions. We have also combined the photon asymmetry results with recent cross-section measurements from Mainz to calculate the profile functions, $\check{\mathrm{\Sigma}}$ (= $\sigma_{0}\mathrm{\Sigma}$), and perform a moment analysis. Comparison with calculations from the Bonn-Gatchina model shows that the precision of the data is good enough to further constrain the higher partial waves, and there is an indication of interference between the very small $F$-waves and the $N(1520) 3/2^{-}$ and $N(1535) 1/2^{-}$ resonances.
Published: 2016
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49. Photoproduction of $\pi^0$-pairs off protons and off neutrons

Author: Dieterle, M., Oberle, M., Ahrens, J., Annand, J. R. M., Arends, H. J., Bantawa, K., Bartolome, P. A., Beck, R., Bekrenev, V., Berghäuser, H., Braghieri, A., Branford, D., Briscoe, W. J., Brudvik, J., Cherepnya, S., Costanza, S., Demissie, B., Downie, E. J., Drexler, P., Fil'kov, L. V., Fix, A., Garni, S., Glazier, D. I., Hamilton, D., Heid, E., Hornidge, D., Howdle, D., Huber, G. M., Jahn, O., Jude, T. C., Käser, A., Kashevarov, V. L., Keshelashvili, I., Kondratiev, R., Korolija, M., Krusche, B., Lisin, V., Livingston, K., MacGregor, I. J. D., Maghrbi, Y., Mancell, J., Manley, D. M., Marinides, Z., McGeorge, J. C., McNicoll, E., Mekterovic, D., Metag, V., Micanovic, S., Middleton, D. G., Mushkarenkov, A., Nikolaev, A., Novotny, R., Ostrick, M., Otte, P., Oussena, B., Pedroni, P., Pheron, F., Polonski, A., Prakhov, S., Robinson, J., Rostomyan, T., Schumann, S., Sikora, M. H., Sober, D. I., Starostin, A., Strub, Th., Supek, I., Thiel, M., Thomas, A., Unverzagt, M., Walford, N. K., Watts, D. P., Werthmüller, D., and Witthauer, L.
Subjects: Nuclear Experiment
Abstract: Total cross sections, angular distributions, and invariant-mass distributions have been measured for the photoproduction of $\pi^0\pi^0$ pairs off free protons and off nucleons bound in the deuteron. The experiments were performed at the MAMI accelerator facility in Mainz using the Glasgow photon tagging spectrometer and the Crystal Ball/TAPS detector. The accelerator delivered electron beams of 1508 and 1557~MeV, which produced bremsstrahlung in thin radiator foils. The tagged photon beam covered energies up to 1400~MeV. The data from the free proton target are in good agreement with previous measurements and were only used to test the analysis procedures. The results for differential cross sections (angular distributions and invariant-mass distributions) for free and quasi-free protons are almost identical in shape, but differ in absolute magnitude up to 15\%. Thus, moderate final-state interaction effects are present. The data for quasi-free neutrons are similar to the proton data in the second resonance region (final state invariant masses up to $\approx$1550~MeV), where both reactions are dominated by the $N(1520)3/2^-\rightarrow \Delta(1232)3/2^+\pi$ decay. At higher energies, angular and invariant-mass distributions are different. A simple analysis of the shapes of the invariant-mass distributions in the third resonance region is consistent with strong contributions of an $N^{\star}\rightarrow N\sigma$ decay for the proton, while the reaction is dominated by a sequential decay via a $\Delta\pi$ intermediate state for the neutron. The data are compared to predictions from the Two-Pion-MAID model and the Bonn-Gatchina coupled channel analysis., Comment: accepted for publication in Eur. Phys. J. A
Published: 2015

50. Strangeness Photoproduction at the BGO-OD Experiment

Author: Jude, T. C., Alef, S., Bayadilov, D., Beck, R., Becker, M., Bella, A., Bielefeldt, P., Boese, S., Braghieri, A., Brinkmann, K., Cole, P., Curciarello, F., De Leo, V., Di Salvo, R., Dutz, H., Elsner, D., Fantini, A., Freyermuth, O., Friedrich, S., Frommberger, F., Ganenko, V., Gervino, G., Ghio, F., Giardina, G., Goertz, S., Gridnev, A., Gutz, E., Hammann, D., Hannappel, J., Hartmann, P., Hillert, W., Ignatov, A., Jahn, R., Joosten, R., Klein, F., Koop, K., Krusche, B., Lapik, A., Sandri, P. Levi, Lopatin, I. V., Mandaglio, G., Messi, F., Messi, R., Metag, V., Moricciani, D., Mushkarenkov, A., Nanova, M., Nedorezov, V., Novinskiy, D., Pedroni, P., Reitz, B., Romaniuk, M., Rostomyan, T., Rudnev, N., Scheluchin, G., Schmieden, H., Stugelev, A., Sumachev, V., Tarakanov, V., Vegna, V., Walther, D., Watts, D., Zaunick, H., and Zimmermann, T.
Subjects: Nuclear Experiment
Abstract: BGO-OD is a newly commissioned experiment to investigate the internal structure of the nucleon, using an energy tagged bremsstrahlung photon beam at the ELSA electron facility. The setup consists of a highly segmented BGO calorimeter surrounding the target, with a particle tracking magnetic spectrometer at forward angles. BGO-OD is ideal for investigating meson photoproduction. The extensive physics programme for open strangeness photoproduction is introduced, and preliminary analysis presented., Comment: 6 pages, 4 figures. Proceedings for the 10th International Workshop on the Physics of Excited Nucleons (NSTAR2015)
Published: 2015

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