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1. 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 (hep-ex), FOS: Physical sciences, Nuclear Experiment (nucl-ex), Nuclear Experiment, High Energy Physics - 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: Article to be submitted to the EPJ A Topical Collection on radiative corrections. 9 pages, 5 figures, 2 tables
Published: 2023
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2. Measurement of Compton Scattering at MAMI for the Extraction of the Electric and Magnetic Polarizabilities of the Proton

Author: 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., Zachariou, N., and Publica
Subjects: Electromagnetic transitions, Nuclear structure & decays, Photonuclear reactions, General Physics and Astronomy, Nuclear reactions
Abstract: A precise measurement of the differential cross sections \ud d\ud σ\ud /\ud d\ud Ω\ud and the linearly polarized photon beam asymmetry \ud Σ\ud 3\ud for Compton scattering on the proton below pion threshold has been performed with a tagged photon beam and almost \ud 4\ud π\ud 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 setup. 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-\ud t\ud dispersion relation model, constraining the fits with the Baldin sum rule, we have obtained the proton electric and magnetic polarizabilities with unprecedented precision: \ud α\ud E\ud 1\ud =\ud 10.99\ud ±\ud 0.16\ud ±\ud 0.47\ud ±\ud 0.17\ud ±\ud 0.34\ud , \ud β\ud M\ud 1\ud =\ud 3.14\ud ±\ud 0.21\ud ±\ud 0.24\ud ±\ud 0.20\ud ±\ud 0.35\ud ; in units of \ud 10\ud −\ud 4\ud \ud \ud fm\ud 3\ud where the errors are statistical, systematic, spin polarizability dependent, and model dependent.
Published: 2022

3. Neutron polarisation transfer, $C_{x'}^n$, in $π^+$ 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: FOS: Physical sciences, Nuclear Experiment (nucl-ex)
Abstract: We report a first measurement of the double-polarisation observable, $C_{x'}$, in $π^+$ 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
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4. Target and beam-target asymmetries for the $γp \to π^0 π^0 p$ 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 (hep-ex), FOS: Physical sciences
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 $γp \to π^0 π^0 p$. 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., 16 pages, 12 figures, 5 tables
Published: 2022
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5. 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 Theory (nucl-th), Nuclear Theory, FOS: Physical sciences, High Energy Physics::Experiment, Nuclear Experiment (nucl-ex), Nuclear Experiment
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
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6. Observation of a structure in the M$_{p��}$ invariant mass distribution near 1700 MeV/$c^2$ in the $\mathbf{��p \rightarrow p ��^0 ��} $ 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., Gr��ner, 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., Mitlas��czky, B., M��ller, J., M��llers, 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., Werthm��ller, D., Wiedner, U., Wilson, A., Winnebeck, A., Witthauer, L., and Wunderlich, Y.
Subjects: Nuclear Theory (nucl-th), Nuclear Theory, Physics::Accelerator Physics, FOS: Physical sciences, Nuclear Experiment (nucl-ex), Nuclear Experiment
Abstract: The reaction $��p \rightarrow p ��^0 ��$ 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$_{N��}$ 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$_��$ = 1400 - 1500 MeV and the cut M$_{p��^0} \le 1190 $ MeV/$c^2$ a statistically significant structure in the M$_{p��}$ invariant mass distribution near 1700 MeV/$c^2$ is observed with a width of $��\approx 35$ MeV/$c^2$ while the mass resolution is $��_{res}$ = 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$_�� \approx$ 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$_{p��}$ invariant mass distribution. The most likely interpretation is that it is due to a triangular singularity in the $��p \rightarrow p a_0 \rightarrow p ��^0 ��$ reaction, 16 pages, 18 figure
Published: 2021
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7. Single $��^0$ 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 Theory (nucl-th), High Energy Physics - Experiment (hep-ex), High Energy Physics - Phenomenology (hep-ph), Nuclear Theory, FOS: Physical sciences, Nuclear Experiment (nucl-ex), Nuclear Experiment
Abstract: The quasifree $\overrightarrow�� d\to��^0n(p)$ photon beam asymmetry, $��$, has been measured at photon energies, $E_��$, 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 $��(1232)$ and $N(1440)$ resonances. The extracted values of $��$ 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 $��$ measurements, has also been performed. In addition, isospin symmetry is examined as a way to predict $��^0n$ photoproduction observables, based on fits to published data in the channels $��^0p$, $��^+n$, and $��^-p$., 11 pages, 9 figures, 5 tables; fixed 2 glitches
Published: 2021
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8. Helicity-dependent cross sections for the photoproduction of $��^0$ 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{��, M., Nther, Gurevich, D., Heijkenskj{��, L., Hornidge, D., Huber, G. M., K{��, 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., Werthm��ller, D., Wettig, J., Wolfes, M., and Zana, L. A.
Subjects: Nuclear Theory, FOS: Physical sciences, Nuclear Experiment (nucl-ex), Nuclear Experiment
Abstract: The double-polarization observable $E$ and helicity-dependent cross sections $��_{1/2}$, $��_{3/2}$ have been measured for the photoproduction of $��^0$ 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 $4��$ covering calorimeter. The results reveal for the first time the helicity- and isospin-dependent structure of the $��N\rightarrow N��^0��^0$ 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., Submitted to Phys. Rev. Lett
Published: 2020
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9. Measurement of the beam-helicity asymmetry in photoproduction of $��^{0}��$ pairs on carbon, aluminum, and lead

Author: Sokhoyan, V., Prakhov, S., Fix, A., Abt, S., Achenbach, P., Adlarson, P., Afzal, F., Aguar-Bartolom��, 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., G��nther, M., Gurevich, G. M., Heijkenskj��ld, L., Hornidge, D., Huber, G. M., K��ser, 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., Werthm��ller, D., Wettig, J., Witthauer, L., Wolfes, M., and Zachariou, N.
Subjects: Nuclear Theory, FOS: Physical sciences, High Energy Physics::Experiment, Nuclear Experiment (nucl-ex), Nuclear Experiment
Abstract: The beam-helicity asymmetry was measured, for the first time, in photoproduction of $��^{0}��$ 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 $��^{0}��$ pairs on nuclei is similar to photoproduction on a free nucleon. This process is dominated by the $D_{33}$ partial wave with the $��(1232)$ intermediate state., Accepted for publication in Physics Letters B (2020)
Published: 2019
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10. 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: FOS: Physical sciences, High Energy Physics::Experiment, Nuclear Experiment (nucl-ex), 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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11. Measurement of the Helicity Asymmetry $E$ for the reaction $ ��p\to ��^0 p$

Author: TAPS Collaboration, 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., Gr��ner, 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., M��ller, J., M��llers, 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., Werthm��ller, D., Wiedner, U., Wilson, A., Winnebeck, A., Witthauer, L., and Wunderlich, Y.
Subjects: Nuclear Theory, Physics::Accelerator Physics, FOS: Physical sciences, Nuclear Experiment (nucl-ex), Nuclear Experiment
Abstract: A measurement of the double-polarization observable $E$ for the reaction $��p\to ��^0 p$ 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 $E_��=600$~MeV to $E_��=2310$~MeV and nearly the complete angular range. The results are compared to and have been included in recent partial wave analyses., 21 pages
Published: 2019
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12. New data on $\vec�� \vec{p}\rightarrow ��p$ with polarized photons and protons and their implications for $N^* \to N��$ decays

Author: M��ller, J., Hartmann, J., Gr��ner, M., Afzal, F., Anisovich, A. V., Bantes, B., Bayadilov, D., Beck, R., Becker, M., Beloglazov, Y., Berlin, M., Bichow, M., B��se, 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., K��ser, 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., M��llers, 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 Theory, FOS: Physical sciences, High Energy Physics::Experiment, Nuclear Experiment (nucl-ex), Nuclear Experiment
Abstract: The polarization observables $T, E, P, H$, and $G$ in photoproduction of $��$ 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��Bo, and BnGa partial-wave analyses. A refit within the BnGa approach including further data yields precise branching ratios for the $N��$ decay of nucleon resonances. A $N��$-branching ratio of $0.33\pm 0.04$ for $N(1650)1/2^-$ is found, which reduces the large and controversially discussed $N��$-branching ratio difference of the two lowest mass $J^P=1/2^-$-resonances significantly., 10 pages, 11 figures
Published: 2019
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13. Cross Section for $��n \to ��^0 n$ 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 Theory (nucl-th), High Energy Physics - Experiment (hep-ex), High Energy Physics - Phenomenology (hep-ph), Nuclear Theory, FOS: Physical sciences, Nuclear Experiment (nucl-ex), Nuclear Experiment
Abstract: The $��n \to ��^0 n$ 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 $��n \to ��^0 n$ 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 $N^* \to ��n$ at the resonance poles are determined for the first time., 16 pages, 12 figures, 3 tables
Published: 2019
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14. 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-Bartolom��, 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., Heijkenskj��ld, L., Hornidge, D., Huber, G. M., K��ser, 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., Werthm��ller, D., Wettig, J., Witthauer, L., Wolfes, M., and Zana, L. A.
Subjects: High Energy Physics - Experiment (hep-ex), FOS: Physical sciences, High Energy Physics::Experiment, Nuclear Experiment (nucl-ex), 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., 11 pages, 6 figures, 1 table
Published: 2018
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15. Experimental study of the $��p\rightarrow K^0��^+$, $��n\rightarrow K^0��$, and $��n\rightarrow K^0 ��^0$ reactions at the Mainz Microtron

Author: Akondi, C. S., Bantawa, K., Manley, D. M., Abt, S., Achenbach, P., Afzal, F., Aguar-Bartolom��, 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., G��nther, M., Gurevich, D., Kay, S., Heijkenskj��ld, L., Hornidge, D., Huber, G. M., K��ser, 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., Werthm��ller, D., Wettig, J., Witthauer, L., and Wolfes, M.
Subjects: FOS: Physical sciences, Nuclear Experiment (nucl-ex), Nuclear Experiment
Abstract: This work measured $d��/d��$ for neutral kaon photoproduction reactions from threshold up to a c.m.\ energy of 1855MeV, focussing specifically on the $��p\rightarrow K^0��^+$, $��n\rightarrow K^0��$, and $��n\rightarrow K^0 ��^0$ reactions. Our results for $��n\rightarrow K^0 ��^0$ 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 $��N$ 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., 16 pages, 13 figures, 7 tables
Published: 2018
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16. Photoproduction of {\boldmath{$��^{0}$}} Mesons off Protons and Neutrons in the Second and Third Nucleon Resonance Region

Author: Dieterle, M., Werthm��ller, 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., G��nther, M., Gurevich, D., Heijkenskj��ld, L., Hornidge, D., Huber, G. M., K��ser, 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 Theory, FOS: Physical sciences, Nuclear Experiment (nucl-ex), 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 $��^0$ 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 $4��$ 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 $��n\rightarrow n��^{0}$, 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., excepted for publication in Phys. Rev. C
Published: 2018
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17. Study of the $��p\to ��^0��p$ reaction with the A2 setup at MAMI

Author: Sokhoyan, V., Prakhov, S., Fix, A., Abt, S., Achenbach, P., Adlarson, P., Afzal, F., Aguar-Bartolom��, 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., G��nther, M., Gurevich, G. M., Hamill, C. B., Heijkenskj��ld, L., Hornidge, D., Huber, G. M., Jude, T. C., K��ser, 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., Werthm��ller, D., Wettig, J., Witthauer, L., Wolfes, M., and Zana, L. A.
Subjects: FOS: Physical sciences, Nuclear Experiment (nucl-ex), Nuclear Experiment
Abstract: The data available from the A2 Collaboration at MAMI were analyzed to select the $��p\to ��^0��p$ 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 $E_��=1.45$ 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., 15 pages, 18 figures
Published: 2018
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18. Threshold π 0 photoproduction on transverse polarised protons at MAMI

Author: Schumann, S., Otte, P.B., Akondi, C.S., Annand, J.R.M., Arends, H.-J., Beck, R., Bernstein, A.M., Borisov, N., Braghieri, A., Briscoe, W.J., Cherepnya, S., Collicott, C., Costanza, S., Downie, E.J., Dieterle, M., Fernández-Ramírez, C., Fix, A., Fil'kov, L.V., Garni, S., Glazier, D.I., Gradl, W., Gurevich, G., Hall-Barrientos, P., Hamilton, D., Hornidge, D., Howdle, D., Huber, G.M., Kashevarov, V.L., Keshelashvili, I., Kondratiev, R., Korolija, M., Krusche, B., Lazarev, A., Lisin, V., Livingston, K., MacGregor, I.J.D., Mancel, J., Manley, D.M., Martel, P.P., McNicoll, E.F., Meyer, W., Middleton, D., Miskimen, R., Mushkarenkov, A., Nefkens, B.M.K., Neganov, A., Nikolaev, A., Oberle, M., Ostrick, M., Ortega, H., Ott, P., Oussena, B., Paudyal, D., Pedroni, P., Polonski, A., Polyanski, V.V., Prakhov, S., Reicherz, G., Rostomyan, T., Sarty, A., Sikora, M.H., Sokhoyan, V., Steffen, O., Strakovsky, I.I., Strub, Th., Supek, I., Tiator, L., Thomas, A., Unverzagt, M., Usov, Yu.A., Watts, D.P., Werthmüller, D., Witthauer, L., and Wolfes, M.
Subjects: Nuclear and High Energy Physics
Published: 2015
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19. The polarization observables T, P, and H and their impact on γp→pπ0 multipoles

Author: Hartmann, J., Dutz, H., Anisovich, A.V., Bayadilov, D., Beck, R., Becker, M., Beloglazov, Y., Berlin, A., Bichow, M., Böse, S., Brinkmann, K.-Th., Crede, V., Dieterle, M., Eberhardt, H., Elsner, D., Fornet-Ponse, K., Friedrich, St., Frommberger, F., Funke, Ch., Gottschall, M., Gridnev, A., Grüner, M., Goertz, St., Gutz, E., Hammann, Ch., Hannappel, J., Hannen, V., 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., Kube, M., Lang, M., Lopatin, I., Makonyi, K., Messi, F., Metag, V., Meyer, W., Müller, J., Nanova, M., Nikonov, V., Novinski, D., Novotny, R., Piontek, D., Reeve, S., Rosenbaum, Ch., Roth, B., Reicherz, G., Rostomyan, T., Runkel, St., Sarantsev, A., Schmidt, Ch., Schmieden, H., Schmitz, R., Seifen, T., Sokhoyan, V., Thämer, Ph., Thiel, A., Thoma, U., Urban, M., van Pee, H., Walther, D., Wendel, Ch., Wiedner, U., Wilson, A., Winnebeck, A., and Witthauer, L.
Subjects: Nuclear and High Energy Physics
Published: 2015
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20. Measurement of the ω→π0e+e− and η→e+e−γ Dalitz decays with the A2 setup at the Mainz Microtron

Author: Adlarson, P., Afzal, F., Aguar-Bartolome, P., Ahmed, Z., Annand, J. R. M., Arends, H. J., Bantawa, K., Beck, R., Berghaeuser, 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., Kaeser, 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., Werthmueller, D., Wettig, J., Witthauer, L., Wolfes, M., and Zana, L. A.
Abstract: The Dalitz decays η→e+e−γ and ω→π0e+e− have been measured in the γp→ηp and γp→ωp reactions, respectively, with the A2 tagged-photon facility at the Mainz Microtron. The value obtained for the slope parameter of the electromagnetic transition form factor of η, Λ−2η=(1.97±0.11tot)GeV−2, is in good agreement with previous measurements of the η→e+e−γ and η→μ+μ−γ decays. The uncertainty obtained in the value of Λ−2η is lower than in previous results based on the η→e+e−γ decay. The value obtained for the ω slope parameter, Λ−2ωπ0=(1.99±0.21tot)GeV−2, is somewhat lower than previous measurements based on ω→π0μ+μ−, but the results for the ω transition form factor are in better agreement with theoretical calculations, compared to earlier experiments.
Published: 2017
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21. Insight into the narrow structure in {\boldmath{$��$}}-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., G��nther, M., Gurevich, G. M., Hamilton, D., Hornidge, D., Huber, G. M., K��ser, 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., Werthm��ller, D., Wettig, J., Wolfes, M., and Zana, L.
Subjects: Nuclear Theory, FOS: Physical sciences, Nuclear Experiment (nucl-ex), Nuclear Experiment
Abstract: The double polarization observable $E$ and the helicity dependent cross sections $��_{1/2}$ and $��_{3/2}$ were measured for $��$ 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 $4��$ detector setup of the Crystal Ball and TAPS is ideally suited to detect the recoil nucleons and the decay photons from $��\rightarrow 2��$ and $��\rightarrow 3��^0$. The results show that the narrow structure previously observed in $��$ photoproduction from the neutron is only apparent in $��_{1/2}$ and hence, most likely related to a spin-1/2 amplitude. Nucleon resonances that contribute to this partial wave in $��$ production are only $N1/2^-$ ($S_{11}$) and $N1/2^+$ ($P_{11}$). Furthermore, the extracted Legendre coefficients of the angular distributions for $��_{1/2}$ 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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22. Study of η and η' 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., Ferretti Bondy, M.I., 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., Käser, 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., Reicherz, G., 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., Werthmüller, D., Wettig, J., Witthauer, L., Wolfes, M., Workman, R.L., and Zana, L.
Subjects: ddc:550
Abstract: The reactions γp → ηp and γp → η0\ud p are measured from their thresholds up to the center-of-mass\ud energy W ¼ 1.96 GeV with the tagged-photon facilities at the Mainz Microtron, MAMI. Differential cross\ud sections are obtained with unprecedented statistical accuracy, providing fine energy binning and full\ud production-angle coverage. A strong cusp is observed in the total cross section for η photoproduction at the\ud energies in the vicinity of the η0 threshold, W ¼ 1896 MeV (Eγ ¼ 1447 MeV). Within the framework of a\ud revised ηMAID isobar model, the cusp, in connection with a steep rise of the η0 total cross section from its\ud threshold, can only be explained by a strong coupling of the poorly known Nð1895Þ1=2− state to both ηp\ud and η0\ud p. Including the new high-accuracy results in the ηMAID fit to available η and η0 photoproduction\ud data allows the determination of the Nð1895Þ1=2− properties.
Published: 2017
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23. Technical Design Report for the Paul Scherrer Institute Experiment R-12-01.1: Studying the Proton 'Radius' Puzzle with ��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: FOS: Physical sciences, Instrumentation and Detectors (physics.ins-det), Nuclear Experiment (nucl-ex)
Abstract: The difference in proton radii measured with $��p$ atoms and with $ep$ atoms and scattering remains an unexplained puzzle. The PSI MUSE proposal is to measure $��p$ 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 $��p$ 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 $��p$ 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$5$��$ significance, similar to that already established between the regular and muonic hydrogen Lamb shift.
Published: 2017
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24. Measurement of the decay $��^{\prime}\to��^{0}��^{0}��$ 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., K��ser, 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., Werthm��ller, D., Wettig, J., Witthauer, L., Wolfes, M., Workman, R. L., and Zana, L. A.
Subjects: High Energy Physics - Experiment (hep-ex), FOS: Physical sciences, Nuclear Experiment
Abstract: An experimental study of the $��'\to ��^0��^0��\to 6��$ decay has been conducted with the best up-to-date statistical accuracy, by measuring $��'$ mesons produced in the $��p \to ��' p$ reaction with the A2 tagged-photon facility at the Mainz Microtron, MAMI. The results obtained for the standard parametrization of the $��'\to ��^0��^0��$ matrix element are consistent with the most recent results for $��'\to��$ decays, but have smaller uncertainties. The available statistics and experimental resolution allowed, for the first time, an observation of a structure below the $��^+��^-$ 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 $��$ scattering length combination, $a_0-a_2$, extracted from $K \to 3��$ decays., 15 pages, 8 figures, 2 tables, accepted for publication in Phys. Rev. D
Published: 2017
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25. 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: FOS: Physical sciences, Nuclear Experiment (nucl-ex), 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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26. K+Λ and K+Σ0 photoproduction with fine center-of-mass energy resolution

Author: Jude, T.C., Glazier, D.I., Watts, D.P., Aguar-Bartolomé, P., Akasoy, L.K., Annand, J.R.M., Arends, H.J., Bantawa, K., Beck, R., Bekrenev, V.S., Berghäuser, H., Braghieri, A., Branford, D., Briscoe, W.J., Brudvik, J., Cherepnya, S., Demissie, B.T., Dieterle, M., Downie, E.J., Fil'kov, L.V., Gregor, R., Heid, E., Hornidge, D., Jaegle, I., Jahn, O., Kashevarov, V.L., Keshelashvili, I., Kondratiev, R., Korolija, M., Koulbardis, A.A., Kruglov, S.P., Krusche, B., Lisin, V., Livingston, K., MacGregor, I.J.D., Maghrbi, Y., Manley, D.M., Marinides, Z., Mart, T., Martinez, M., McGeorge, J.C., McNicoll, E.F., Middleton, D.G., Mushkarenkov, A., Nefkens, B.M.K., Nikolaev, A., Nikonov, V.A., Oberle, M., Ostrick, M., Otte, P.B., Oussena, B., Pedroni, P., Pheron, F., Polonski, A., Prakhov, S., Robinson, J., Rosner, G., Rostomyan, T., Sarantsev, A.V., Schumann, S., Sikora, M.H., Sober, D.I., Starostin, A., Strakovsky, I., Suarez, I.M., Supek, I., Thiel, M., Thomas, A., Unverzagt, M., Werthmüller, D., Witthauer, L., and Zehr, F.
Subjects: Nuclear and High Energy Physics
Published: 2014
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27. First measurement of the helicity dependence of 3He photoreactions in the Δ(1232) resonance region

Author: Aguar Bartolomé, P., Mushkarenkov, A., Ahrens, J., Annand, J.R.M., Arends, H.-J., Beck, R., Bekrenev, V., Berghäuser, H., Braghieri, A., Briscoe, W.J., Cherepnya, S.N., Costanza, S., Drexler, P., Filʼkov, L.V., Fix, A., Giardina, G., Glazier, D.I., Hamilton, D., Heid, E., Heil, W., Hornidge, D., Howdle, D., Jaegle, I., Jahn, O., Jude, T., Kashevarov, V.L., Keshelashvili, I., Kondratiev, R., Korolija, M., Krimmer, J., Krusche, B., Kruglov, S., Kulbardis, A., Lisin, V., Livingston, K., Mancell, J., Middleton, D.G., MacGregor, I.J.D., Manley, D.M., McGeorge, J.C., Metag, V., Nefkens, B.M.K., Nikolaev, A., Oberle, M., Ostrick, M., Ortega, H., Otte, P.B., Oussena, B., Pedroni, P., Pheron, F., Prakhov, S., Polonski, A., Rigamonti, F., Romaniuk, M., Rosner, G., Rostomyan, T., Schumann, S., Sober, D., Starostin, A., Supek, I., Thiel, M., Thomas, A., Unverzagt, M., Watts, D., and Werthmüller, D.
Subjects: Nuclear and High Energy Physics
Published: 2013
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28. Insight into the Narrow Structure in η Photoproduction on the Neutron from Helicity-Dependent Cross Sections

Author: Witthauer, L., Dieterle, M., Biroth, M., Borisov, N. S., Braghieri, A., Briscoe, W. J., Cividini, F., Costanza, S., Collicott, C., Denig, A., Downie, E. J., Drexler, P., Abt, S., Ferretti-Bondy, M. I., Gardner, S., Garni, S., Glazier, D. I., Glowa, D., Gradl, W., Günther, M., Gurevich, G. M., Hamilton, D., Hornidge, D., Achenbach, P., Huber, G. M., Käser, A., Kashevarov, V. L., Kay, S., Keshelashvili, I., Kondratiev, R., Korolija, M., Krusche, B., Lazarev, A. B., Linturi, J. M., Afzal, F., Lisin, V., Livingston, K., Lutterer, S., MacGregor, I. J. D., Mancell, J., Manley, D. M., Martel, P. P., Metag, V., Meyer, W., Miskimen, R., Ahmed, Z., Mornacchi, E., Mushkarenkov, A., Neganov, A. B., Neiser, A., Oberle, M., Ostrick, M., Otte, P. B., Paudyal, D., Pedroni, P., Polonski, A., Annand, J. R. M., Prakhov, S. N., Rajabi, A., Reicherz, G., Ron, G., Rostomyan, T., Sarty, A., Sfienti, C., Sikora, M. H., Sokhoyan, V., Spieker, K., Arends, H. J., Steffen, O., Strakovski, I. I., Strub, Th., Supek, I., Thiel, A., Thiel, M., Thomas, A., Unverzagt, M., Usov, Yu. A., Wagner, S., Bashkanov, M., Walford, N. K., Watts, D. P., Werthmüller, D., Wettig, J., Wolfes, M., Zana, L., and Beck, R.
Subjects: Nuclear Theory, ddc:550, Nuclear Experiment
Abstract: The double polarization observable E and the helicity dependent cross sections σ_{1/2} and σ_{3/2} were measured for η photoproduction from quasifree 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 4π detector setup of the Crystal Ball and TAPS is ideally suited to detect the recoil nucleons and the decay photons from η→2γ and η→3π^{0}. The results show that the narrow structure previously observed in η photoproduction from the neutron is only apparent in σ_{1/2} and hence, most likely related to a spin-1/2 amplitude. Nucleon resonances that contribute to this partial wave in η production are only N 1/2^{-} (S_{11}) and N 1/2^{+} (P_{11}). Furthermore, the extracted Legendre coefficients of the angular distributions for σ_{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: 2016

29. Insight into the Narrow Structure in eta Photoproduction on the Neutron from Helicity-Dependent Cross Sections

Author: Witthauer, L., Dieterle, M., Achenbach, S., 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., Gunther, M., Gurevich, G. M., Hamilton, D., Hornidge, D., Huber, G. M., Kaser, 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., Strakovski, 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., Werthmuller, D., Wettig, J., Wolfes, M., Zana, L., and Abt, P.
Subjects: Nuclear Theory, Nuclear Experiment
Abstract: The double polarization observable E and the helicity dependent cross sections σ1/2 and σ3/2 were measured for η photoproduction from quasifree 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 4π detector setup of the Crystal Ball and TAPS is ideally suited to detect the recoil nucleons and the decay photons from η→2γ and η→3π0. The results show that the narrow structure previously observed in η photoproduction from the neutron is only apparent in σ1/2 and hence, most likely related to a spin-1/2 amplitude. Nucleon resonances that contribute to this partial wave in η production are only N1/2− (S11) and N 1/2+ (P11). Furthermore, the extracted Legendre coefficients of the angular distributions for σ1/2 are in good agreement with recent reaction model predictions assuming a narrow resonance in the P11 wave as the origin of this structure.
Published: 2016
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30. Determination of the real part of the ��'-Nb optical potential

Author: Nanova, M., Friedrich, S., Metag, V., Paryev, E. Ya., Afzal, F. N., Bayadilov, D., Beck, R., Becker, M., B��se, 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., M��ller, J., M��llers, 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., Werthm��ller, D., Wiedner, U., Wilson, A., Witthauer, L., Wunderlich, Y., and Zaunick, H. -G.
Subjects: Nuclear Theory, FOS: Physical sciences, High Energy Physics::Experiment, Nuclear Experiment (nucl-ex), Nuclear Experiment
Abstract: The excitation function and momentum distribution of ��' 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 ��'-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 ��'-nucleus potential will make the search for ��'-nucleus bound states more difficult., 9 pages, 6 figures
Published: 2016
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31. Determination of the scalar polarizabilities of the proton using beam asymmetry $��_{3}$ 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., K��ser, 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., Werthm��ller, D., Wolfes, M., and Zana, L.
Subjects: Nuclear Theory, Physics::Accelerator Physics, FOS: Physical sciences, Physics::Atomic Physics, Nuclear Experiment (nucl-ex), Nuclear Experiment
Abstract: The scalar dipole polarizabilities, $��_{E1}$ and $��_{M1}$, 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 $��_{3}$ 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., 6 pages, 5 figures
Published: 2016
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32. Photon asymmetry measurements of $\overrightarrow�� \mathrm{p} \rightarrow ��^{0} \mathrm{p}$ for E$_��$=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., G��nther, M., Gurevich, G. M., Hamilton, D., Heid, E., Hornidge, D., Huber, G. M., Jahn, O., Jude, T. C., K��ser, 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., Werthm��ller, D., Wettig, J., Wolfes, M., Witthauer, L., and Zana, L.
Subjects: FOS: Physical sciences, Nuclear Experiment (nucl-ex), Nuclear Experiment
Abstract: High statistics measurements of the photon asymmetry $\mathrm��$ for the $\overrightarrow��$p$\rightarrow��^{0}$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, $\check{\mathrm��}$ (= $��_{0}\mathrm��$), 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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33. Momentum dependence of the imaginary part of the $��$- and $��^\prime$-nucleus optical potential

Author: Friedrich, S., Nanova, M., Metag, V., Afzal, F. N., Bayadilov, D., Bantes, B., Beck, R., Becker, M., B��se, S., Brinkmann, K. -T., Crede, V., Drexler, P., Eberhardt, H., Elsner, D., Frommberger, F., Funke, Ch., Gottschall, M., Gr��ner, 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., M��ller, J., M��llers, 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., Werthm��ller, D., Wiedner, U., Wilson, A., Witthauer, L., Wunderlich, Y., and Zaunick, H. -G.
Subjects: High Energy Physics::Phenomenology, Nuclear Theory, FOS: Physical sciences, High Energy Physics::Experiment, Nuclear Experiment (nucl-ex), Nuclear Experiment
Abstract: The photoproduction of $��$ and $��^\prime$ 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 $��\rightarrow ��^0 ��\rightarrow 3 ��$ and $��^\prime\rightarrow ��^0 ��^0��\rightarrow 6 ��$ 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 $��$ and $��^\prime$ 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 $��$ width and $��^\prime$-N absorption cross sections. The energy dependence of the imaginary part of the $��$- and $��^\prime$-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 $��^\prime$ nucleus potential is found to be about three times smaller than recently determined values of the real part of the $��^\prime$-nucleus potential, which makes the $��^\prime$ meson a suitable candidate for the search for meson-nucleus bound states. For the $��$ 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 $��$ mesic states very difficult experimentally., 10 pages, 8 figures
Published: 2016
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34. Measurement of the pi^0 -> e^+e^-gamma Dalitz decay at the Mainz Microtron

Author: Adlarson, P., Afzal, F., Aguar-Bartolom��, P., Ahmed, Z., Akondi, C. S., Annand, J. R. M., Arends, H. J., Bantawa, K., Beck, R., Bergh��user, 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., K��ser, 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., Werthm��ller, D., Wettig, J., Witthauer, L., Wolfes, M., and Zana, L. A.
Subjects: High Energy Physics - Experiment (hep-ex), FOS: Physical sciences, Nuclear Experiment (nucl-ex)
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., 11 pages, 7 figures, 1 table
Published: 2016
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35. 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-Bartolom��, P., Ahmed, Z., Annand, J. R. M., Arends, H. J., Bantawa, K., Beck, R., Bergh��user, 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., K��ser, 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., Werthm��ller, D., Wettig, J., Witthauer, L., Wolfes, M., and Zana, L. A.
Subjects: High Energy Physics - Experiment (hep-ex), FOS: Physical sciences, High Energy Physics::Experiment, Nuclear Experiment (nucl-ex), 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., 19 figures, 2 tables
Published: 2016
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36. The isospin structure of photoproduction of pi-eta pairs from the nucleon in the threshold region

Author: Käser, A., 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., Dieterle, M., Downie, E. J., Drexler, P., Fil'kov, L. V., Fix, A., Glazier, D. I., Hamilton, D., Heid, E., Hornidge, D., Howdle, D., Huber, G. M., Jahn, O., Jaegle, I., Jude, T. C., Kashevarov, V. L., Keshelashvili, I., Kondratiev, R., Korolija, M., Kruglov, S. P., 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. N., Robinson, J., Rosner, G., Rostomyan, T., Schumann, S., Sikora, M. H., Sober, D. I., Starostin, A., Supek, I., Thiel, M., Thomas, A., Unverzagt, M., Watts, D. P., Werthmüller, D., and Witthauer, L.
Subjects: High Energy Physics::Phenomenology, Nuclear Theory, FOS: Physical sciences, High Energy Physics::Experiment, Nuclear Experiment (nucl-ex), Nuclear Experiment
Abstract: Photoproduction of $\pi\eta$-pairs from nucleons has been investigated from threshold up to incident photon energies of $\approx$~1.4~GeV. The quasi-free reactions $\gamma p\rightarrow p\pi^0\eta$, $\gamma n\rightarrow n\pi^0\eta$, $\gamma p\rightarrow n\pi^+\eta$, and $\gamma n\rightarrow p\pi^-\eta$ were for the first time measured from nucleons bound in the deuteron. The corresponding reactions from a free-proton target were also studied to investigate final-state interaction effects (for neutral pions the free-proton results could be compared to previous measurements; the $\gamma p\rightarrow n\pi^+\eta$ reaction was measured for the first time). For the $\pi^0\eta$ final state coherent production via the $\gamma d\rightarrow d\pi^0\eta$ reaction was also investigated. The experiments were performed at the tagged photon beam of the Mainz MAMI accelerator using an almost $4\pi$ coverage electromagnetic calorimeter composed of the Crystal Ball and TAPS detectors. The total cross sections for the four different final states obey the relation $\sigma(p\pi^0\eta)$ $\approx$ $\sigma(n\pi^0\eta)$ $\approx$ $2\sigma(p\pi^-\eta)$ $\approx$ $2\sigma(n\pi^+\eta)$ as expected for a dominant contribution from a $\Delta^{\star}\rightarrow\eta\Delta(1232)\rightarrow\pi\eta N$ reaction chain, which is also supported by the shapes of the invariant-mass distributions of nucleon-meson and $\pi$-$\eta$ pairs. The experimental results are compared to the predictions from an isobar reaction model., Comment: accepted for publication in Phys. Lett. B
Published: 2015
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37. The polarization observables T, P, and H and their impact on $��p \to p��^0$ multipoles

Author: Hartmann, J., Dutz, H., Anisovich, A. V., Bayadilov, D., Beck, R., Becker, M., Beloglazov, Y., Berlin, A., Bichow, M., B��se, S., Brinkmann, K. -Th., Crede, V., Dieterle, M., Eberhardt, H., Elsner, D., Fornet-Ponse, K., Friedrich, St., Frommberger, F., Funke, Ch., Gottschall, M., Gridnev, A., Gr��ner, M., G��rtz, St., Gutz, E., Hammann, Ch., Hannappel, J., Hannen, V., Herick, J., Hillert, W., Hoffmeister, Ph., Honisch, Ch., Jahn, O., Jude, T., K��ser, A., Kaiser, D., Kalinowsky, H., Kalischewski, F., Klassen, P., Keshelashvili, I., Klein, F., Klempt, E., Koop, K., Krusche, B., Kube, M., Lang, M., Lopatin, I., Makonyi, K., Messi, F., Metag, V., Meyer, W., M��ller, J., Nanova, M., Nikonov, V., Novinski, D., Novotny, R., Piontek, D., Reeve, S., Rosenbaum, Ch., Roth, B., Reicherz, G., Rostomyan, T., Runkel, St., Sarantsev, A., Schmidt, Ch., Schmieden, H., Schmitz, R., Seifen, T., Sokhoyan, V., Th��mer, Ph., Thiel, A., Thoma, U., Urban, M., van Pee, H., Walther, D., Wendel, Ch., Wiedner, U., Wilson, A., Winnebeck, A., and Witthauer, L.
Subjects: Nuclear Theory, FOS: Physical sciences, Nuclear Experiment (nucl-ex), Nuclear Experiment
Abstract: Data on the polarization observables T, P, and H for the reaction $��p\to p��^0$ are reported. Compared to earlier data from other experiments, our data are more precise and extend the covered range in energy and angle substantially. The results were extracted from azimuthal asymmetries measured using a transversely polarized target and linearly polarized photons. The data were taken at the Bonn electron stretcher accelerator ELSA with the CBELSA/TAPS detector. Within the Bonn-Gatchina partial wave analysis, the new polarization data lead to a significant narrowing of the error band for the multipoles for neutral-pion photoproduction.
Published: 2015
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38. Measurement of double polarisation asymmetries in $��$-photoproduction

Author: Eberhardt, H., Jude, T. C., Schmieden, H., Anisovich, A. V., Bantes, B., Bayadilov, D., Beck, R., Beloglazov, Yu., Bichow, M., Boese, S., Brinkmann, K. -Th., Challand, Th., Crede, V., Diez, F., Drexler, P., Dutz, H., Elsner, D., Ewald, R., Fornet-Ponse, K., Friedrich, St., Frommberger, F., Funke, Ch., Gottschall, M., Gridnev, A., Gruener, M., Gutz, E., Hammann, Ch., Hannappel, J., Hartmann, J., Hillert, W., Hoffmeister, Ph., Honisch, Ch., Jaegle, I., Kaiser, D., Kalinowsky, H., Kalischewski, F., Kammer, S., Keshelashvili, I., Kleber, V., Klein, F., Klempt, E., Koop, K., Krusche, B., Kube, M., Lang, M., Lopatin, I., Maghrbi, Y., Makonyi, K., Metag, V., Meyer, W., Mueller, J., Nanova, M., Nikonov, V., Novotny, R., Piontek, D., Reeve, S., Reicherz, G., Rostomyan, T., Runkel, S., Sarantsev, A., Schaepe, St., Schmidt, Ch., Schmitz, R., Seifen, T., Sokhoyan, V., Sumachev, V., Thiel, A., Thoma, U., Urban, M., van Pee, H., Walther, D., Wendel, Ch., Wiedner, U., Wilson, A., and Winnebeck, A.
Subjects: FOS: Physical sciences, Nuclear Experiment (nucl-ex), Nuclear Experiment
Abstract: The first measurements of the beam-target-helicity-asymmetries $E$ and $G$ in the photoproduction of $��$-mesons off protons at the CBELSA/TAPS experiment are reported. $E$ ($G$) was measured using circularly (linearly) polarised photons and a longitudinally polarised target. $E$ was measured over the photon energy range from close to threshold ($E_��= 1108$~MeV) to $E_��= 2300$~MeV and $G$ at a single energy interval of $1108 < E_��, 6 pages, 6 figures
Published: 2015
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39. First measurement of target and beam-target asymmetries in the $��p\to ��^0��p$ reaction

Author: Annand, J. R. M., Arends, H. J., Beck, R., Borisov, N., Braghieri, A., Briscoe, W. J., Cherepnya, S., Collicott, C., Costanza, S., Downie, E. J., Dieterle, M., Fix, A., Fil'kov, L. V., Garni, S., Glazier, D. I., Gradl, W., Gurevich, G., Barrientos, P. H., Hamilton, D., Hornidge, D., Howdle, D., Huber, G. M., Kashevarov, V. L., Keshelashvili, I., Kondratiev, R., Korolija, M., Krusche, B., Lazarev, A., Lisin, V., Livingston, K., MacGregor, I. J. D., Mancel, J., Manley, D. M., Martel, P., McNicoll, E. F., Meyer, W., Middleton, D., Miskimen, R., Mushkarenkov, A., Neganov, A., Nikolaev, A., Oberle, M., Ortega, H., Ostrick, M., Ott, P., Otte, P. B., Oussena, B., Pedroni, P., Polonski, A., Polyanski, V. V., Prakhov, S., Reicherz, G., Rostomyan, T., Sarty, A., Schumann, S., Steffen, O., Strakovsky, I. I., Strub, T., Supek, I., Tiator, L., Thomas, A., Unverzagt, M., Usov, Y. A., Watts, D. P., Werthm��ller, D., Witthauer, L., and Wolfes, M.
Subjects: Nuclear Theory (nucl-th), High Energy Physics - Experiment (hep-ex), Physics::Accelerator Physics, FOS: Physical sciences, Nuclear Experiment (nucl-ex), Nuclear Experiment
Abstract: The first data on target and beam-target asymmetries for the $��p\to��^0��p$ reaction at photon energies from 1050 up to 1450 MeV are presented. The measurements were performed using the Crystal Ball and TAPS detector setup at the Glasgow tagged photon facility of the Mainz Microtron MAMI. The general assumption that the reaction is dominated by the $��3/2^-$ amplitude is confirmed. The data are in particular sensitive to small contributions from other partial waves., 9 pages, 9 figures
Published: 2015
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40. Photoproduction of $��^0$-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., Bergh��user, 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., K��ser, 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., Werthm��ller, D., and Witthauer, L.
Subjects: Nuclear Theory, Physics::Accelerator Physics, FOS: Physical sciences, Nuclear Experiment (nucl-ex), Nuclear Experiment
Abstract: Total cross sections, angular distributions, and invariant-mass distributions have been measured for the photoproduction of $��^0��^0$ 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 $N(1520)3/2^-\rightarrow ��(1232)3/2^+��$ 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 $N^{\star}\rightarrow N��$ decay for the proton, while the reaction is dominated by a sequential decay via a $��$ intermediate state for the neutron. The data are compared to predictions from the Two-Pion-MAID model and the Bonn-Gatchina coupled channel analysis., accepted for publication in Eur. Phys. J. A
Published: 2015
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41. <math altimg='si1.gif' xmlns='http://www.w3.org/1998/Math/MathML'><msup><mrow><mi>K</mi></mrow><mrow><mo>+</mo></mrow></msup><mi>Λ</mi></math> and <math altimg='si2.gif' xmlns='http://www.w3.org/1998/Math/MathML'><msup><mrow><mi>K</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>Σ</mi></mrow><mrow><mn>0</mn></mrow></msup></math> photoproduction with fine center-of-mass energy resolution

Author: Jude, T.C.(School of Physics, University of Edinburgh, Edinburgh, EH9 3JZ, UK), Glazier, D.I.(School of Physics, University of Edinburgh, Edinburgh, EH9 3JZ, UK), Watts, D.P.(School of Physics, University of Edinburgh, Edinburgh, EH9 3JZ, UK), Aguar-Bartolomé, P.(Institut für Kernphysik, University of Mainz, Mainz, D-55099, Germany), Akasoy, L.K.(Institut für Kernphysik, University of Mainz, Mainz, D-55099, Germany), Annand, J.R.M.(Department of Physics and Astronomy, University of Glasgow, Glasgow, G12 8QQ, UK), Arends, H.J.(Institut für Kernphysik, University of Mainz, Mainz, D-55099, Germany), Bantawa, K.(Kent State University, Kent, OH, 44242, USA), Beck, R.(Helmholtz-Institut für Strahlen- und Kernphysik, University of Bonn, Bonn, D-53115, Germany), Bekrenev, V.S.(Petersburg Nuclear Physics Institute, Gatchina, 188300, Russia), Berghäuser, H.(Physikalisches Institut, University of Giessen, Giessen, D-35392, Germany), Braghieri, A.(INFN Sezione di Pavia, Pavia, I-27100, Italy), Branford, D.(School of Physics, University of Edinburgh, Edinburgh, EH9 3JZ, UK), Briscoe, W.J.(The George Washington University, Washington, DC, 20052, USA), Brudvik, J.(The George Washington University, Washington, DC, 20052, USA), Cherepnya, S.(Lebedev Physical Institute, Moscow, 119991, Russia), Demissie, B.T.(The George Washington University, Washington, DC, 20052, USA), Dieterle, M.(Institut für Physik, University of Basel, Basel, CH-4056, Switzerland), Downie, E.J.(Institut für Kernphysik, University of Mainz, Mainz, D-55099, Germany), Fil'kov, L.V.(Lebedev Physical Institute, Moscow, 119991, Russia), Gregor, R.(Physikalisches Institut, University of Giessen, Giessen, D-35392, Germany), Heid, E.(Institut für Kernphysik, University of Mainz, Mainz, D-55099, Germany), Hornidge, D.(Mount Allison University, Sackville, New Brunswick, E4L3B5, Canada), Jaegle, I.(Institut für Physik, University of Basel, Basel, CH-4056, Switzerland), Jahn, O.(Institut für Kernphysik, University of Mainz, Mainz, D-55099, Germany), Kashevarov, V.L.(Institut für Kernphysik, University of Mainz, Mainz, D-55099, Germany), Keshelashvili, I.(Institut für Physik, University of Basel, Basel, CH-4056, Switzerland), Kondratiev, R.(Institute for Nuclear Research, Moscow, 125047, Russia), Korolija, M.(Rudjer Boskovic Institute, Zagreb, HR-10000, Croatia), Koulbardis, A.A.(Petersburg Nuclear Physics Institute, Gatchina, 188300, Russia), Kruglov, S.P.(Petersburg Nuclear Physics Institute, Gatchina, 188300, Russia), Krusche, B.(Institut für Physik, University of Basel, Basel, CH-4056, Switzerland), Lisin, V.(Institute for Nuclear Research, Moscow, 125047, Russia), Livingston, K.(Department of Physics and Astronomy, University of Glasgow, Glasgow, G12 8QQ, UK), MacGregor, I.J.D.(Department of Physics and Astronomy, University of Glasgow, Glasgow, G12 8QQ, UK), Maghrbi, Y.(Institut für Physik, University of Basel, Basel, CH-4056, Switzerland), Manley, D.M.(Kent State University, Kent, OH, 44242, USA), Marinides, Z.(The George Washington University, Washington, DC, 20052, USA), Mart, T.(Departemen Fisika, FMIPA, Universitas Indonesia, Depok, 16424, Indonesia), Martinez, M.(Institut für Kernphysik, University of Mainz, Mainz, D-55099, Germany), McGeorge, J.C.(Department of Physics and Astronomy, University of Glasgow, Glasgow, G12 8QQ, UK), McNicoll, E.F.(Department of Physics and Astronomy, University of Glasgow, Glasgow, G12 8QQ, UK), Middleton, D.G.(Mount Allison University, Sackville, New Brunswick, E4L3B5, Canada), Mushkarenkov, A.(INFN Sezione di Pavia, Pavia, I-27100, Italy), Nefkens, B.M.K.(The George Washington University, Washington, DC, 20052, USA), Nikolaev, A.(Helmholtz-Institut für Strahlen- und Kernphysik, University of Bonn, Bonn, D-53115, Germany), Nikonov, V.A.(Petersburg Nuclear Physics Institute, Gatchina, 188300, Russia), Oberle, M.(Institut für Physik, University of Basel, Basel, CH-4056, Switzerland), Ostrick, M.(Institut für Kernphysik, University of Mainz, Mainz, D-55099, Germany), Otte, P.B.(Institut für Kernphysik, University of Mainz, Mainz, D-55099, Germany), Oussena, B.(Institut für Kernphysik, University of Mainz, Mainz, D-55099, Germany), Pedroni, P.(INFN Sezione di Pavia, Pavia, I-27100, Italy), Pheron, F.(Institut für Physik, University of Basel, Basel, CH-4056, Switzerland), Polonski, A.(Institute for Nuclear Research, Moscow, 125047, Russia), Prakhov, S.(The George Washington University, Washington, DC, 20052, USA), Robinson, J.(Department of Physics and Astronomy, University of Glasgow, Glasgow, G12 8QQ, UK), Rosner, G.(Department of Physics and Astronomy, University of Glasgow, Glasgow, G12 8QQ, UK), Rostomyan, T.(INFN Sezione di Pavia, Pavia, I-27100, Italy), Sarantsev, A.V.(Helmholtz-Institut für Strahlen- und Kernphysik, University of Bonn, Bonn, D-53115, Germany), Schumann, S.(Institut für Kernphysik, University of Mainz, Mainz, D-55099, Germany), Sikora, M.H.(School of Physics, University of Edinburgh, Edinburgh, EH9 3JZ, UK), Sober, D.I.(The Catholic University of America, Washington, DC, 20064, USA), Starostin, A.(The George Washington University, Washington, DC, 20052, USA), Strakovsky, I.(The George Washington University, Washington, DC, 20052, USA), Suarez, I.M.(The George Washington University, Washington, DC, 20052, USA), Supek, I.(Rudjer Boskovic Institute, Zagreb, HR-10000, Croatia), Thiel, M.(Physikalisches Institut, University of Giessen, Giessen, D-35392, Germany), Thomas, A.(Helmholtz-Institut für Strahlen- und Kernphysik, University of Bonn, Bonn, D-53115, Germany), Unverzagt, M.(Institut für Kernphysik, University of Mainz, Mainz, D-55099, Germany), Werthmüller, D.(Institut für Physik, University of Basel, Basel, CH-4056, Switzerland), Witthauer, L.(Institut für Physik, University of Basel, Basel, CH-4056, Switzerland), and Zehr, F.(Institut für Physik, University of Basel, Basel, CH-4056, Switzerland)
Abstract: Measurements of γp→K+Λ and γp→K+Σ0 cross-sections have been obtained with the photon tagging facility and the Crystal Ball calorimeter at MAMI-C. The measurement uses a novel K+ meson identification technique in which the weak decay products are characterized using the energy and timing characteristics of the energy deposit in the calorimeter, a method that has the potential to be applied at many other facilities. The fine center-of-mass energy ( W ) resolution and statistical accuracy of the new data results in a significant impact on partial wave analyses aiming to better establish the excitation spectrum of the nucleon. The new analyses disfavor a strong role for quark–diquark dynamics in the nucleon.
Published: 2014

42. Quasifree photoproduction of $��$ mesons off protons and neutrons

Author: A2 Collaboration, Werthm��ller, D., Witthauer, L., Keshelashvili, I., Aguar-Bartolom��, P., Ahrens, J., Annand, J. R. M., Arends, H. J., Bantawa, K., Beck, R., Bekrenev, V., Braghieri, A., Branford, D., Briscoe, W. J., Brudvik, J., Cherepnya, S., Costanza, S., Demissie, B., Dieterle, M., Downie, E. J., Drexler, P., Fil'kov, L. V., Fix, A., Glazier, D. I., Hamilton, D., Heid, E., Hornidge, D., Howdle, D., Huber, G. M., Jaegle, I., Jahn, O., Jude, T. C., K��ser, A., Kashevarov, V. L., Kondratiev, R., Korolija, M., Kruglov, S. P., Krusche, B., Kulbardis, A., Lisin, V., Livingston, K., MacGregor, I. J. D., Maghrbi, Y., Mancell, J., Manley, D. M., Marinides, Z., Martinez, M., McGeorge, J. C., McNicoll, E. F., Metag, V., Middleton, D. G., Mushkarenkov, A., Nefkens, B. M. K., Nikolaev, A., Novotny, R., Oberle, M., Ostrick, M., Otte, P. B., Oussena, B., Pedroni, P., Pheron, F., Polonski, A., Prakhov, S. N., Robinson, J., Rosner, G., Rostomyan, T., Schumann, S., Sikora, M. H., Sober, D., Starostin, A., Supek, I., Thiel, M., Thomas, A., Unverzagt, M., and Watts, D. P.
Subjects: Nuclear Theory (nucl-th), High Energy Physics - Experiment (hep-ex), Nuclear Theory, FOS: Physical sciences, Nuclear Experiment (nucl-ex), Nuclear Experiment
Abstract: Differential and total cross sections for the quasifree reactions $��p\rightarrow��p$ and $��n\rightarrow��n$ have been determined at the MAMI-C electron accelerator using a liquid deuterium target. Photons were produced via bremsstrahlung from the 1.5 GeV incident electron beam and energy-tagged with the Glasgow photon tagger. Decay photons of the neutral decay modes $��\rightarrow 2��$ and $��\rightarrow 3��^0 \rightarrow 6��$ and coincident recoil nucleons were detected in a combined setup of the Crystal Ball and the TAPS calorimeters. The $��$-production cross sections were measured in coincidence with recoil protons, recoil neutrons, and in an inclusive mode without a condition on recoil nucleons, which allowed a check of the internal consistency of the data. The effects from nuclear Fermi motion were removed by a kinematic reconstruction of the final-state invariant mass and possible nuclear effects on the quasifree cross section were investigated by a comparison of free and quasifree proton data. The results, which represent a significant improvement in statistical quality compared to previous measurements, agree with the known neutron-to-proton cross-section ratio in the peak of the $S_{11}(1535)$ resonance and confirm a peak in the neutron cross section, which is absent for the proton, at a center-of-mass energy $W = (1670\pm 5)$ MeV with an intrinsic width of $��\approx 30$ MeV.
Published: 2014
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43. A new measurement of the rare decay eta -> pi^0 gamma gamma with the Crystal Ball/TAPS detectors at the Mainz Microtron

Author: Nefkens, B. M. K., Prakhov, S., Aguar-Bartolom��, P., Annand, J. R. M., Arends, H. J., Bantawa, K., Beck, R., Bekrenev, V., Bergh��user, H., Braghieri, A., Briscoe, W. J., Brudvik, J., Cherepnya, S., Codling, R. F. B., Collicott, C., Costanza, S., Danilkin, I. V., Denig, A., Demissie, B., Dieterle, M., Downie, E. J., Drexler, P., Fil'kov, L. V., Fix, A., Garni, S., Glazier, D. I., Gregor, R., Hamilton, D., Heid, E., Hornidge, D., Howdle, D., Jahn, O., Jude, T. C., Kashevarov, V. L., K��ser, A., Keshelashvili, I., Kondratiev, R., Korolija, M., Kotulla, M., Koulbardis, A., Kruglov, S., Krusche, B., Lisin, V., Livingston, K., MacGregor, I. J. D., Maghrbi, Y., Mancel, J., Manley, D. M., McNicoll, E. F., Mekterovic, D., Metag, V., Mushkarenkov, A., Nikolaev, A., Novotny, R., Oberle, M., Ortega, H., Ostrick, M., Ott, P., Otte, P. B., Oussena, B., Pedroni, P., Polonski, A., Robinson, J., Rosner, G., Rostomyan, T., Schumann, S., Sikora, M. H., Starostin, A., Strakovsky, I. I., Strub, T., Suarez, I. M., Supek, I., Tarbert, C. M., Thiel, M., Thomas, A., Unverzagt, M., Watts, D. P., Werthm��ller, D., and Witthauer., L.
Subjects: High Energy Physics - Experiment (hep-ex), Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, High Energy Physics::Experiment, Nuclear Experiment (nucl-ex), Nuclear Experiment
Abstract: A new measurement of the rare, doubly radiative decay eta->pi^0 gamma gamma was conducted with the Crystal Ball and TAPS multiphoton spectrometers together with the photon tagging facility at the Mainz Microtron MAMI. New data on the dependence of the partial decay width, Gamma(eta->pi^0 gamma gamma), on the two-photon invariant mass squared, m^2(gamma gamma), as well as a new, more precise value for the decay width, Gamma(eta->pi^0 gamma gamma) = (0.33+/-0.03_tot) eV, are based on analysis of 1.2 x 10^3 eta->pi^0 gamma gamma decays from a total of 6 x 10^7 eta mesons produced in the gamma p -> eta p reaction. The present results for dGamma(eta->pi^0 gamma gamma)/dm^2(gamma gamma) are in good agreement with previous measurements and recent theoretical calculations for this dependence., 10 pages, 8 figures, 1 table
Published: 2014
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44. Photoproduction of pi0-mesons off neutrons in the nucleon resonance region

Author: Dieterle, M., Keshelashvili, I., Ahrens, J., Annand, J. R. M., Arends, H. J., Bantawa, K., Bartolome, P. A., Beck, R., Bekrenev, V., Braghieri, A., Branford, D., Briscoe, W. J., Brudvik, J., Cherepnya, S., Demissie, B., Downie, E. J., Drexler, P., Fil'kov, L. V., Fix, A., Glazier, D. I., Hamilton, D., Heid, E., Hornidge, D., Howdle, D., Huber, G. M., Jaegle, I., Jahn, O., Jude, T. C., Kaeser, A., Kashevarov, V. L., Kondratiev, R., Korolija, M., Kruglov, S. P., Krusche, B., Kulbardis, A., Lisin, V., Livingston, K., MacGregor, I. J. D., Maghrbi, Y., Mancell, J., Manley, D. M., Marinides, Z., Martinez, M., McGeorge, J. C., McNicoll, E., Mekterovic, D., Metag, V., Micanovic, S., Middleton, D. G., Mushkarenkov, A., Nefkens, B. M. K., Nikolaev, A., Novotny, R., Oberle, M., Ostrick, M., Oussena, B., Pedroni, P., Pheron, F., Polonski, A., Prakhov, S. N., Robinson, J., Rosner, G., Rostomyan, T., Schumann, S., Sikora, M. H., Sober, D., Starostin, A., Supek, I., Thiel, M., Thomas, A., Unverzagt, M., Watts, D. P., Werthmueller, D., and Witthauer, L.
Subjects: Nuclear Theory, FOS: Physical sciences, Nuclear Experiment (nucl-ex), Nuclear Experiment
Abstract: Precise angular distributions have been measured for the first time for the photoproduction of $\pi^{0}$-mesons off neutrons bound in the deuteron. The effects from nuclear Fermi motion have been eliminated by a complete kinematic reconstruction of the final state. The influence of final-state-interaction effects has been estimated by a comparison of the reaction cross section for quasi-free protons bound in the deuteron to the results for free protons and then applied as a correction to the quasi-free neutron data. The experiment was performed at the tagged photon facility of the Mainz Microtron MAMI with the Crystal Ball and TAPS detector setup for incident photon energies between $0.45$~GeV and $1.4$~GeV. The results are compared to the predictions from reaction models and partial-wave analyses based on data from other isospin channels. The model predictions show large discrepancies among each other and the present data will provide much tighter constraints. This is demonstrated by the results of a new analysis in the framework of the Bonn-Gatchina coupled-channel analysis which included the present data., Comment: accepted for publication in Phys; Rev. Lett
Published: 2014
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45. Measurement of the beam-helicity asymmetry $I^{\odot}$ in the photoproduction of $��^0��^{\pm}$-pairs off protons and off neutrons

Author: Oberle, M., Ahrens, J., Annand, J. R. M., Arends, H. J., Bantawa, K., Bartolome, P. A., Beck, R., Bekrenev, V., Berghaeuser, H., Braghieri, A., Branford, D., Briscoe, W. J., Brudvik, J., Cherepnya, S., Demissie, B., Dieterle, M., Downie, E. J., Drexler, P., Fil'kov, L. V., Fix, A., Glazier, D. I., Heid, E., Hornidge, D., Howdle, D., Huber, G. M., Jahn, O., Jaegle, I., Jude, T. C., Kaeser, A., Kashevarov, V. L., Keshelashvili, I., Kondratiev, R., Korolija, M., Kruglov, S. P., Krusche, B., Kulbardis, A., Lisin, V., Livingston, K., MacGregor, I. J. D., Maghrbi, Y., Mancell, J., Manley, D. M., Marinides, Z., Martinez, M., McGeorge, J. C., McNicoll, E., Mekterovic, D., Metag, V., Micanovic, S., Middleton, D. G., Mushkarenkov, A., Nefkens, B. M. K., Nikolaev, A., Novotny, R., Ostrick, M., Oussena, B., Pedroni, P., Pheron, F., Polonski, A., Prakhov, S. N., Robinson, J., Rosner, G., Rostomyan, T., Schumann, S., Sikora, M. H., Sober, D. I., Starostin, A., Supek, I., Thiel, M., Thomas, A., Unverzagt, M., Watts, D. P., Werthmueller, D., Witthauer, L., and Zehr, F.
Subjects: Nuclear Theory, FOS: Physical sciences, High Energy Physics::Experiment, Nuclear Experiment (nucl-ex), Nuclear Experiment
Abstract: Beam-helicity asymmetries have been measured at the MAMI accelerator in Mainz for the photoproduction of mixed-charge pion pairs in the reactions $\boldsymbol��p\rightarrow n��^0��^+$ off free protons and $\boldsymbol��d\rightarrow (p)p��^0��^-$ and $\boldsymbol��d\rightarrow (n)n��^0��^+$ off quasi-free nucleons bound in the deuteron for incident photon energies up to 1.4 GeV. Circularly polarized photons were produced from bremsstrahlung of longitudinally polarized electrons and tagged with the Glasgow-Mainz magnetic spectrometer. The charged pions, recoil protons, recoil neutrons, and decay photons from $��^0$ mesons were detected in the 4$��$ electromagnetic calorimeter composed of the Crystal Ball and TAPS detectors. Using a complete kinematic reconstruction of the final state, excellent agreement was found between the results for free and quasi-free protons, suggesting that the quasi-free neutron results are also a close approximation of the free-neutron asymmetries. A comparison of the results to the predictions of the Two-Pion-MAID reaction model shows that the reaction mechanisms are still not well understood, in particular at low incident photon energies in the second nucleon-resonance region., accepted for publication in Eur. phys. J. A
Published: 2014
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46. Photoproduction of the $��$ meson off the proton near threshold

Author: Strakovsky, I. I., Prakhov, S., Azimov, Y. I., Aguar-Bartolome, P., Annand, J. R. M., Arends, H. J., Bantawa, K., Beck, R., Bekrenev, V., Berghaeuser, H., Braghieri, A., Briscoe, W. J., Brudvik, J., Cherepnya, S., Codling, R. F. B., Collicott, C., Costanza, S., Demissie, B. T., Downie, E. J., Drexler, P., Fil'kov, L. V., Glazier, D. I., Gregor, R., Hamilton, D. J., Heid, E., Hornidge, D., Jaegle, I., Jahn, O., Jude, T. C., Kashevarov, V. L., Keshelashvili, I., Kondratiev, R., Korolija, M., Kotulla, M., Koulbardis, A., Kruglov, S., Krusche, B., Lisin, V., Livingston, K., MacGregor, I. J. D., Maghrbi, Y., Manley, D. M., Marinides, Z., McGeorge, J. C., McNicoll, E. F., Mekterovic, D., Metag, V., Middleton, D. G., Mushkarenkov, A., Nefkens, B. M. K., Nikolaev, A., Novotny, R., Ortega, H., Ostrick, M., Otte, P. B., Oussena, B., Pedroni, P., Pheron, F., Polonski, A., Robinson, J., Rosner, G., Rostomyan, T., Schumann, S., Sikora, M. H., Starostin, A., Supek, I., Taragin, M. F., Tarbert, C. M., Thiel, M., Thomas, A., Unverzagt, M., Watts, D. P., Werthmueller, D., and Zehr, F.
Subjects: High Energy Physics - Experiment (hep-ex), High Energy Physics - Phenomenology (hep-ph), FOS: Physical sciences, Nuclear Experiment (nucl-ex), Nuclear Experiment
Abstract: An experimental study of $��$ photoproduction on the proton was conducted by using the Crystal Ball and TAPS multiphoton spectrometers together with the photon tagging facility at the Mainz Microtron MAMI. The $��p\to��p$ differential cross sections are measured from threshold to the incident-photon energy $E_��=1.40$ GeV ($W=1.87$ GeV for the center-of-mass energy) with 15-MeV binning in $E_��$ and full production-angle coverage. The quality of the present data near threshold gives access to a variety of interesting physics aspects. As an example, an estimation of the $��N$ scattering length $��_{��p}$ is provided., 8 pages, 5 figures. Published version; some typos were fixed
Published: 2014
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47. Measurement of the transverse target and beam-target asymmetries in $��$ meson photoproduction at MAMI

Author: Akondi, C. S., Annand, J. R. M., Arends, H. J., Beck, R., Bernstein, A., Borisov, N., Braghieri, A., Briscoe, W. J., Cherepnya, S., Collicott, C., Costanza, S., Downie, E. J., Dieterle, M., Fix, A., Fil'kov, L. V., Garni, S., Glazier, D. I., Gradl, W., Gurevich, G., Barrientos, P. Hall, Hamilton, D., Hornidge, D., Howdle, D., Huber, G. M., Kashevarov, V. L., Keshelashvili, I., Kondratiev, R., Korolija, M., Krusche, B., Lazarev, A., Lisin, V., Livingston, K., MacGregor, I. J. D., Mancel, J., Manley, D. M., Martel, P., McNicoll, E. F., Meyer, W., Middleton, D., Miskimen, R., Mushkarenkov, A., Nefkens, B. M. K., Neganov, A., Nikolaev, A., Oberle, M., Ostrick, M., Ortega, H., Ott, P., Otte, P. B., Oussena, B., Pedroni, P., Polonski, A., Polyanski, V. V., Prakhov, S., Reicherz, G., Rostomyan, T., Sarty, A., Schumann, S., Steffen, O., Strakovsky, I. I., Strub, Th., Supek, I., Tiator, L., Thomas, A., Unverzagt, M., Usov, Yu. A., Watts, D. P., Werthm��ller, D., Witthauer, L., and Wolfes, M.
Subjects: Nuclear Theory (nucl-th), High Energy Physics - Experiment (hep-ex), Nuclear Theory, FOS: Physical sciences, High Energy Physics::Experiment, Nuclear Experiment (nucl-ex), Nuclear Experiment
Abstract: We present new data for the transverse target asymmetry T and the very first data for the beam-target asymmetry F in the $\vec ��\vec p\to��p$ reaction up to a center-of-mass energy of W=1.9 GeV. The data were obtained with the Crystal-Ball/TAPS detector setup at the Glasgow tagged photon facility of the Mainz Microtron MAMI. All existing model predictions fail to reproduce the new data indicating a significant impact on our understanding of the underlying dynamics of $��$ meson photoproduction. The peculiar nodal structure observed in existing T data close to threshold is not confirmed., 5 pages, 3 figures, accepted for publication in PRL
Published: 2014
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48. Experimental constraints on the $��$-nucleus real potential

Author: Friedrich, S., Makonyi, K., Metag, V., Bayadilov, D., Bantes, B., Beck, R., Beloglazov, Y. A., B��se, S., Brinkmann, K. -T., Challand, Th., Crede, V., Dahlke, T., Dietz, F., Drexler, P., Eberhardt, H., Elsner, D., Ewald, R., Fornet-Ponse, K., Frommberger, F., Funke, Ch., Gottschall, M., Gridnev, A., Gr��ner, M., Gutz, E., Hammann, Ch., Hammann, D., Hannappel, J., Hartmann, J., Hillert, W., Hirenzaki, S., Hoffmeister, P., Honisch, Ch., Jaegle, I., Kaiser, D., Kalinowsky, H., Kammer, S., Keshelashvili, I., Kleber, V., Klein, F., Krusche, B., Lang, M., Lopatin, I. V., Maghrbi, Y., Nanova, M., Nagahiro, H., M��ller, J., Odenthal, T., Piontek, D., Rostomyan, T., Schaepe, S., Schmidt, Ch., Schmieden, H., Schmitz, R., Seifen, T., Thiel, A., Thoma, U., van Pee, H., Walther, D., Weil, J., Wendel, Ch., Wiedner, U., Wilson, A., Winnebeck, A., and Zenke, F.
Subjects: Nuclear Theory, FOS: Physical sciences, High Energy Physics::Experiment, Nuclear Experiment (nucl-ex), Nuclear Experiment
Abstract: In a search for $��$ mesic states, the production of $��$-mesons in coincidence with forward going protons has been studied in photon induced reactions on $^{12}$C for incident photon energies of 1250 - 3100 MeV. The $��^0 ��$ pairs from decays of bound or quasi-free $��$-mesons have been measured with the CBELSA/TAPS detector system in coincidence with protons registered in the MiniTAPS forward array. Structures in the total energy distribution of the $��^0 ��$ pairs, which would indicate the population and decay of bound $��~^{11}$B states, are not observed. The $��^0 ��$ cross section of 0.3 nb/MeV/sr observed in the bound state energy regime between -100 and 0 MeV may be accounted for by yield leaking into the bound state regime because of the large in-medium width of the $��$-meson. A comparison of the measured total energy distribution with calculations suggests the real part $V_0$ of the $��~^{11}$B potential to be small and only weakly attractive with $V_0(��=��_0) = -15\pm$ 35(stat) $\pm$20(syst) MeV in contrast to some theoretical predictions of attractive potentials with a depth of 100 - 150 MeV., 13 pages, 8 figures
Published: 2014
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49. The N(1520) 3/2- helicity amplitudes from an energy-independent multipole analysis based on new polarization data on photoproduction of neutral pions

Author: Hartmann, J., Dutz, H., Anisovich, A. V., Bayadilov, D., Beck, R., Becker, M., Beloglazov, Y., Berlin, A., Bichow, M., Böse, S., Brinkmann, K. -Th., Crede, V., Dieterle, M., Eberhardt, H., Elsner, D., Fornet-Ponse, K., Friedrich, St., Frommberger, F., Funke, Ch., Gottschall, M., Gridnev, A., Grüner, M., Gutz, E., Hammann, Ch., Hannappel, J., Hannen, V., 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., Kube, M., Lang, M., Lopatin, I., Makonyi, K., Messi, F., Metag, V., Meyer, W., Müller, J., Nanova, M., Nikonov, V., Novinski, D., Novotny, R., Piontek, D., Rosenbaum, C., Roth, B., Reicherz, G., Rostomyan, T., Sarantsev, A., Schmidt, Ch., Schmieden, H., Schmitz, R., Seifen, T., Sokhoyan, V., Thämer, Ph., Thiel, A., Thoma, U., Urban, M., van Pee, H., Walther, D., Wendel, Ch., Wiedner, U., Wilson, A., Winnebeck, A., Witthauer, L., and Wunderlich, Y.
Subjects: FOS: Physical sciences, Nuclear Experiment (nucl-ex), Nuclear Experiment
Abstract: New data on the polarization observables T, P, and H for the reaction $\gamma p \to p\pi^0$ are reported. The results are extracted from azimuthal asymmetries when a transversely polarized butanol target and a linearly polarized photon beam are used. The data were taken at the Bonn electron stretcher accelerator ELSA using the CBELSA/TAPS detector. These and earlier data are used to perform a truncated energy-independent partial wave analysis in sliced-energy bins. This energy-independent analysis is compared to the results from energy-dependent partial wave analyses.
Published: 2014
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50. Measurement of the $^{1}H$($\vec��$, $\vec{p}$)$��^{0}$ reaction using a novel nucleon spin polarimeter

Author: Watts, D. P., Glazier, D. I., Aguar-Bartolom��, P., Akasoy, L. K., Annand, J. R. M., Arends, H. J., Bantawa, K., Beck, R., Bekrenev, V. S., Bergh��user, H., Braghieri, A., Branford, D., Briscoe, W. J., Brudvik, J., Cherepnya, S., Codling, R. F. B., Demissie, B. T., Downie, E. J., Drexler, P., Fil'kov, L. V., Freehart, B., Gregor, R., Hamilton, D., Heid, E., Hornidge, D., Jaegle, I., Jahn, O., Jude, T. C., Kashevarov, V. L., Keshelashvili, I., Kondratiev, R., Korolija, M., Kotulla, M., Koulbardis, A. A., Kruglov, S. P., Krusche, B., Lisin, V., Livingston, K., MacGregor, I. J. D., Maghrbi, Y., Manley, D. M., Marinides, Z., Martinez, M., McGeorge, J. C., McKinnon, B., McNicoll, E. F., Mekterovic, D., Metag, V., Micanovic, S., Middleton, D. G., Mushkarenkov, A., Nefkens, B. M. K., Nikolaev, A., Novotny, R., Ostrick, M., Otte, P. B., Oussena, B., Pedroni, P., Pheron, F., Polonski, A., Prakhov, S., Robinson, J., Rosner, G., Rostomyan, T., Schumann, S., Sober, D. I., Starostin, A., Strakovsky, I. I., Suarez, I. M., Supek, I., Thiel, M., Thomas, A., Unverzagt, M., Werthm��ller, D., Workman, R. L., Zamboni, I., and Zehr, F.
Subjects: Nuclear Theory, FOS: Physical sciences, Nuclear Experiment (nucl-ex), Nuclear Experiment
Abstract: We report the first large-acceptance measurement of polarization transfer from a polarized photon beam to a recoiling nucleon, pioneering a novel polarimetry technique with wide application to future nuclear and hadronic physics experiments. The commissioning measurement of polarization transfer in the $^{1}H$($\vec��$,$\vec{p}$)$��^{0}$ reaction in the range $0.4, 6 pages, 4 figures
Published: 2013
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