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

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

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

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

3. Light-yield response of liquid scintillators using 2--6 MeV tagged neutrons

Author: Mauritzson, N., Fissum, K. G., Annand, J. R. M., Perrey, H., Jebali, R. Al, Backis, A., Hall-Wilton, R., Kanaki, K., Maulerova-Subert, V., Messi, F., Frost, R. J. W., Rofors, E., and Scherzinger, J.
Subjects: Physics - Instrumentation and Detectors, Nuclear Experiment
Abstract: Knowledge of the neutron light-yield response is crucial to the understanding of scintillator-based neutron detectors. In this work, neutrons from 2--6 MeV have been used to study the scintillation light-yield response of the liquid scintillators NE 213A, EJ 305, EJ 331 and EJ 321P using event-by-event waveform digitization. Energy calibration was performed using a GEANT model to locate the edge positions of the Compton distributions produced by gamma-ray sources. The simulated light yield for neutrons from a PuBe source was compared to measured recoil proton distributions, where neutron energy was selected by time-of-flight. This resulted in an energy-dependent Birks parametrization to characterize the non-linear response to the lower energy neutrons. The NE 213A and EJ 305 results agree very well with existing data and are reproduced nicely by the simulation. New results for EJ 331 and EJ 321P, where the simulation also reproduces the data well, are presented., Comment: 31 pages, 15 figures, 4 tables
Published: 2023

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

Author: A2 Collaboration, Ghosal, D., Sokhoyan, V., Fix, A., Lutterer, S., Abt, S., Achenbach, P., Afzal, F., Ahmed, Z., Annand, J. R. M., Bashkanov, M., Beck, R., Biroth, M., Borisov, N., Braghieri, A., Briscoe, W. J., Cividini, F., Collicot, C., Costanza, S., Denig, A., Dieterle, M., Dolzhikov, A. S., Downie, E. J., Drexler, P., Fegan, S., Gardner, S., Glazier, D. I., Gorodnov, I., Gradl, W., Günther, M., Gurevich, D., Heijkenskjöld, L., Hornidge, D., Huber, G. M., Jermann, N., Käser, A., Kashevarov, V. L., Korolija, M., Krusche, B., Lazarev, A., Livingston, K., MacGregor, I. J. D., Manley, D. M., Martel, P. P., Meier, Ch., Miskimen, R., Mocanu, M., Mornacchi, E., Mullen, C., Neganov, A., Neiser, A., Ostrick, M., Otte, P., Paudyal, D., Pedroni, P., Powell, A., Reicherz, G., Rostomyan, T., Spieker, K., Steffen, O., Strakovsky, I. I., Thiel, A., Thiel, M., Thomas, A., Unverzagt, M., Usov, Yu. A., Wagner, S., Walford, N. K., Watts, D. P., Werthmüller, D., Wettig, J., Witthauer, L., Wolfes, M., and Zachariou, N.
Subjects: Nuclear Experiment
Abstract: Photoproduction of $\pi^0\pi^{\pm}$-pairs from quasifree nucleons bound in the deuteron has been investigated to study the helicity dependence of this reaction. Measurements with a liquid deuterium target were used to extract the unpolarized cross sections for reactions on protons and neutrons. A deuterated, longitudinally polarized solid-butanol target, together with a circularly polarized photon beam, determined the double polarization observable $E$. From these results the spin-dependent cross sections $\sigma_{1/2}$ and $\sigma_{3/2}$, corresponding to the anti-parallel and parallel spin configurations of the beam photon and target nucleon, have been derived. The measurements were performed at the Mainz MAMI accelerator with tagged, circularly-polarized photon beams produced via bremsstrahlung from longitudinally polarized electron beams. The reaction products were detected with an almost $4\pi$ solid-angle covering calorimeter composed of the Crystal Ball and TAPS detectors, supplemented by plastic scintillation detectors for charged particle identification. The results are sensitive to sequential decays of nucleon resonances via intermediate states and also to the decay of nucleon resonances by emission of charged $\rho$ mesons, and are compared to recent model results., Comment: 9 pages, 6 figures
Published: 2023
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5. Neutron polarisation transfer, $C_{x'}^n$, in $\pi^+$ photoproduction off the proton

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

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

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

7. First measurement of polarisation transfer $C^n_{x'}$ in deuteron photodisintegration

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., Arends, H. J., Beck, R., Biroth, M., Borisov, N., Braghieri, A., Briscoe, W. J., Cividini, F., Collicott, C., Costanza, S., Denig, A., Downie, E. J., Drexler, P., Fegan, S., Fix, A., Gardner, S., Ghosal, D., Glazier, D. I., Gorodnov, I., Gradl, W., Guenther, M., Gurevich, D., Heijkenskjöld, L., Hornidge, D., Huber, G. M., Käser, A., Kashevarov, V. L., Korolija, M., Krusche, B., Lazarev, A., Livingston, K., Lutterer, S., MacGregor, I. J. D., 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., Powell, A., Prakhov, S. N., Sokhoyan, V., Spieker, K., Steffen, O., Strakovsky, I. I., Strub, T., Supek, I., Thiel, A., Thiel, M., Thomas, A., Usov, Yu. A., Wagner, S., Wettig, J., Wolfes, M., and Zachariou, N.
Subjects: Nuclear Experiment
Abstract: A first measurement of the polarisation transfer from a circularly-polarised photon to the final state neutron ($C^n_{x'}$) in deuterium photodisintegration has been carried out. This quantity is determined over the photon energy range 370~--~700~MeV and for neutron centre-of-mass breakup angles $\sim45-120^{\circ}$. The polarisation of the final state neutrons was determined by an ancillary large-acceptance nucleon polarimeter, surrounding a cryogenic liquid deuterium target within the Crystal Ball detector at MAMI. The polarimeter characterised $(n,p)$ charge exchange of the ejected neutrons to determine their polarisation. The new $C^n_{x'}$ data are also compared to a theoretical model based on nucleonic and nucleon resonance degrees of freedom constrained by the current world-database of deuterium photodisintegration measurements. Structures in $C^n_{x'}$ observed in the region of the $d^*(2380)$ could not be explained by conventional models of deuteron photodisintegration.
Published: 2022
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8. Technique for the measurement of intrinsic pulse-shape discrimination for organic scintillators using tagged neutrons

Author: Mauritzson, N., Fissum, K. G., Annand, J. R. M., Perrey, H., Frost, R. J. W., Jebali, R. Al, Backis, A., Hall-Wilton, R., Kanaki, K., Maulerova-Subert, V., Maurer, C., Messi, F., and Rofors, E.
Subjects: Physics - Instrumentation and Detectors, Nuclear Experiment
Abstract: Fast-neutron/gamma-ray pulse-shape discrimination has been performed for the organic liquid scintillators NE 213A and EJ 305 using a time-of-flight based neutron-tagging technique and waveform digitization on an event-by-event basis. Gamma-ray sources and a Geant4-based simulation were used to calibrate the scintillation-light yield. The difference in pulse shape for the neutron and gamma-ray events was analysed by integrating selected portions of the digitized waveform to produce a figure-of-merit for neutron/gamma-ray separation. This figure-of-merit has been mapped as a function of detector threshold and also of neutron energy determined from time-of-flight. It shows clearly that the well-established pulse-shape discrimination capabilities of NE 213A are superior to those of EJ 305. The extra information provided by the neutron-tagging technique has resulted in a far more detailed assessment of the pulse-shape discrimination capabilities of these organic scintillators., Comment: 22 pages, 12 figures, 2 tables
Published: 2022
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9. Proton spin structure and generalized polarizabilities in the strong quantum chromodynamics regime

Author: Ruth, D, Zielinski, R, Gu, C, Allada (Cummings), M, Badman, T, Huang, M, Liu, J, Zhu, P, Allada, K, Zhang, J, Camsonne, A, Chen, J-P, Slifer, K, Aniol, K, Annand, J, Arrington, J, Averett, T, Baghdasaryan, H, Bellini, V, Boeglin, W, Brock, J, Carlin, C, Chen, C, Cisbani, E, Crabb, D, Daniel, A, Day, D, Duve, R, Fassi, L El, Friedman, M, Fuchey, E, Gao, H, Gilman, R, Glamazdin, S, Gueye, P, Hafez, M, Han, Y, Hansen, O, Shabestari, M Hashemi, Hen, O, Higinbotham, D, Horn, T, Iqbal, S, Jensen, E, Kang, H, Keith, CD, Kelleher, A, Keller, D, Khanal, H, Korover, I, Kumbartzki, G, Li, W, Lichtenstadt, J, Lindgren, R, Long, E, Malace, S, Markowitz, P, Maxwell, J, Meekins, DM, Meziani, ZE, McLean, C, Michaels, R, Mihovilovič, M, Muangma, N, Camacho, C Munoz, Musson, J, Myers, K, Oh, Y, Carmignotto, M Pannunzio, Perdrisat, C, Phillips, S, Piasetzky, E, Pierce, J, Punjabi, V, Qiang, Y, Reimer, PE, Roblin, Y, Ron, G, Rondon, O, Russo, G, Saenboonruang, K, Sawatzky, B, Shahinyan, A, Shneor, R, Širca, S, Sjoegren, J, Solvignon-Slifer, P, Sparveris, N, Sulkosky, V, Wesselmann, F, Yan, W, Yang, H, Yao, H, Ye, Z, Yurov, M, Zhang, Y, Zhao, YX, and Zheng, X
Subjects: Mathematical Sciences, Physical Sciences, Fluids & Plasmas
Abstract: The strong interaction is not well understood at low energies or for interactions with low momentum transfer. Chiral perturbation theory gives testable predictions for the nucleonic generalized polarizabilities, which are fundamental quantities describing the nucleon’s response to an external field. We report a measurement of the proton’s generalized spin polarizabilities extracted with a polarized electron beam and a polarized solid ammonia target in the region where chiral perturbation theory is expected to be valid. The investigated structure function g2 characterizes the internal spin structure of the proton. From its moments, we extract the longitudinal–transverse spin polarizability δLT and twist-3 matrix element and polarizability d2¯. Our results provide discriminating power between existing chiral perturbation theory calculations and will help provide a better understanding of this strong quantum chromodynamics regime.
Published: 2022

10. The Proton Spin Structure Function $g_2$ and Generalized Polarizabilities in the Strong QCD Regime

Author: Ruth, D., Zielinski, R., Gu, C., Allada, M., Badman, T., Huang, M., Liu, J., Zhu, P., Allada, K., Zhang, J., Camsonne, A., Chen, J. P., Slifer, K., Aniol, K., Annand, J., Arrington, J., Averett, T., Baghdasaryan, H., Bellini, V., Boeglin, W., Brock, J., Carlin, C., Chen, C., Cisbani, E., Crabb, D., Daniel, A., Day, D., Duve, R., Fassi, L. El, Friedman, M., Fuchey, E., Gao, H., Gilman, R., Glamazdin, S., Gueye, P., Hafez, M., Han, Y., Hansen, O., Shabestari, M. Hashemi, Hen, O., Higinbotham, D., Horn, T., Iqbal, S., Jensen, E., Kang, H., Keith, C. D., Kelleher, A., Keller, D., Khanal, H., Korover, I., Kumbartzki, G., Li, W., Lichtenstadt, J., Lindgren, R., Long, E., Malace, S., Markowitz, P., Maxwell, J., Meekins, D. M., Meziani, Z. E., McLean, C., Michaels, R., Mihovilovic, M., Muangma, N., Camacho, C. Munoz, Musson, J., Myers, K., Oh, Y., Carmignotto, M. Pannunzio, Perdrisat, C., Phillips, S., Piasetzky, E., Pierce, J., Punjabi, V., Qiang, Y., Reimer, P. E., Roblin, Y., Ron, G., Rondon, O., Russo, G., Saenboonruang, K., Sawatzky, B., Shahinyan, A., Shneor, R., Sjoegren, J., Solvignon-Slifer, P., Sparveris, N., Sulkosky, V., Wesselmann, F., Yan, W., Yang, H., Yao, H., Ye, Z., Yurov, M., Zhang, Y., Zhao, Y. X., and Zheng, X.
Subjects: Nuclear Experiment, High Energy Physics - Experiment
Abstract: The strong interaction is not well understood at low energy, or for interactions with low momentum transfer $Q^2$, but one of the clearest insights we have comes from Chiral Perturbation Theory ($\chi$PT). This effective treatment gives testable predictions for the nucleonic generalized polarizabilities -- fundamental quantities describing the nucleon's response to an external field. We have measured the proton's generalized spin polarizabilities in the region where $\chi$PT is expected to be valid. Our results include the first ever data for the transverse-longitudinal spin polarizability $\delta_{LT}$, and also extend the coverage of the polarizability $\bar{d_2}$ to very low $Q^2$ for the first time. These results were extracted from moments of the structure function $g_2$, a quantity which characterizes the internal spin structure of the proton. Our experiment ran at Jefferson Lab using a polarized electron beam and a polarized solid ammonia (NH$_3$) target. The $\delta_{LT}$ polarizability has remained a challenging quantity for $\chi$PT to reproduce, despite its reduced sensitivity to higher resonance contributions; recent competing calculations still disagree with each other and also diverge from the measured neutron data at very low $Q^2$. Our proton results provide discriminating power between existing calculations, and will help provide a better understanding of this strong QCD regime.
Published: 2022

11. Measurement of the helicity dependence for single $\pi^{0}$ photoproduction from the deuteron

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

12. Deeply virtual Compton scattering cross section at high Bjorken $x_B$

Author: Georges, F., Rashad, M. N. H., Stefanko, A., Dlamini, M., Karki, B., Ali, S. F., Lin, P-J., Ko, H-S, Israel, N., Adikaram, D., Ahmed, Z., Albataineh, H., Aljawrneh, B., Allada, K., Allison, S., Alsalmi, S., Androic, D., Aniol, K., Annand, J., Atac, H., Averett, T., Gayoso, C. Ayerbe, Bai, X., Bane, J., Barcus, S., Bartlett, K., Bellini, V., Beminiwattha, R., Bericic, J., Biswas, D., Brash, E., Bulumulla, D., Campbell, J., Camsonne, A., Carmignotto, M., Castellano, J., Chen, C., Chen, J-P., Chetry, T., Christy, M. E., Cisbani, E., Clary, B., Cohen, E., Compton, N., Cornejo, J. C., Dusa, S. Covrig, Crowe, B., Danagoulian, S., Danley, T., De Persio, F., Deconinck, W., Defurne, M., Desnault, C., Di, D., Duer, M., Duran, B., Ent, R., Fanelli, C., Franklin, G., Fuchey, E., Gal, C., Gaskell, D., Gautam, T., Glamazdin, O., Gnanvo, K., Gray, V. M., Gu, C., Hague, T., Hamad, G., Hamilton, D., Hamilton, K., Hansen, O., Hauenstein, F., Henry, W., Higinbotham, D. W., Holmstrom, T., Horn, T., Huang, Y., Huber, G. M., Hyde, C., Ibrahim, H., Jen, C-M., Jin, K., Jones, M., Kabir, A., Keppel, C., Khachatryan, V., King, P. M., Li, S., Li, W. B., Liu, J., Liu, H., Liyanage, A., Magee, J., Malace, S., Mammei, J., Markowitz, P., McClellan, E., Mazouz, M., Meddi, F., Meekins, D., Mesik, K., Michaels, R., Mkrtchyan, A., Montgomery, R., Camacho, C. Muñoz, Myers, L. S., Nadel-Turonski, P., Nazeer, S. J., Nelyubin, V., Nguyen, D., Nuruzzaman, N., Nycz, M., Obretch, O. F., Ou, L., Palatchi, C., Pandey, B., Park, S., Park, K., Peng, C., Pomatsalyuk, R., Pooser, E., Puckett, A. J. R., Punjabi, V., Quinn, B., Rahman, S., Reimer, P. E., Roche, J., Sapkota, I., Sarty, A., Sawatzky, B., Saylor, N. H., Schmookler, B., Shabestari, M. H., Shahinyan, A., Sirca, S., Smith, G. R., Sooriyaarachchilage, S., Sparveris, N., Spies, R., Su, T., Subedi, A., Sulkosky, V., Sun, A., Thorne, L., Tian, Y., Ton, N., Tortorici, F., Trotta, R., Urciuoli, G. M., Voutier, E., Waidyawansa, B., Wang, Y., Wojtsekhowski, B., Wood, S., Yan, X., Ye, L., Ye, Z., Yero, C., Zhang, J., Zhao, Y., and Zhu, P.
Subjects: High Energy Physics - Phenomenology, High Energy Physics - Experiment, Nuclear Experiment
Abstract: We report high-precision measurements of the Deeply Virtual Compton Scattering (DVCS) cross section at high values of the Bjorken variable $x_B$. DVCS is sensitive to the Generalized Parton Distributions of the nucleon, which provide a three-dimensional description of its internal constituents. Using the exact analytic expression of the DVCS cross section for all possible polarization states of the initial and final electron and nucleon, and final state photon, we present the first experimental extraction of all four helicity-conserving Compton Form Factors (CFFs) of the nucleon as a function of $x_B$, while systematically including helicity flip amplitudes. In particular, the high accuracy of the present data demonstrates sensitivity to some very poorly known CFFs.
Published: 2022
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13. Probing for high-momentum protons in He4 via the He4(e,e′p)X reactions

Author: Iqbal, S, Benmokhtar, F, Ivanov, M, See, N, Aniol, K, Higinbotham, DW, Boyd, C, Gadsby, A, Goodwill, JS, Finton, D, Boyer, A, Gilad, S, Saha, A, Udias, JM, Ye, Z, Solvignon, P, Aguilera, P, Ahmed, Z, Albataineh, H, Allada, K, Anderson, B, Anez, D, Annand, J, Arrington, J, Averett, T, Baghdasaryan, H, Bai, X, Beck, A, Beck, S, Bellini, V, Camsonne, A, Chen, C, Chen, J-P, Chirapatpimol, K, Cisbani, E, Dalton, MM, Daniel, A, Day, D, Deconinck, W, Defurne, M, Flay, D, Fomin, N, Friend, M, Frullani, S, Fuchey, E, Garibaldi, F, Gaskell, D, Gilman, R, Glamazdin, S, Gu, C, Guèye, P, Hanretty, C, Hansen, J-O, Shabestari, M Hashemi, Huang, M, Jin, G, Kalantarians, N, Kang, H, Kelleher, A, Korover, I, LeRose, J, Leckey, J, Lindgren, R, Long, E, Mammei, J, Margaziotis, DJ, Markowitz, P, Meekins, D, Meziani, Z, Michaels, R, Mihovilovic, M, Muangma, N, Camacho, C Munoz, Norum, B, Nuruzzaman, Pan, K, Phillips, S, Piasetzky, E, Pomerantz, I, Posik, M, Punjabi, V, Qian, X, Qiang, Y, Qiu, X, Reimer, PE, Rakhman, A, Riordan, S, Ron, G, Rondon-Aramayo, O, Selvy, L, Shahinyan, A, Shneor, R, Sirca, S, Slifer, K, Sparveris, N, Subedi, R, Sulkosky, V, Wang, D, Watson, JW, and Weinstein, LB
Subjects: Nuclear and Plasma Physics, Physical Sciences, Nuclear and plasma physics
Abstract: Experimental cross sections for the He4(e,e′p)X reactions in the missing energy range from 0.017 to 0.022 GeV and up to a missing momentum of 0.632 GeV/c at xB=1.24 and Q2=2 (GeV/c)2 are reported. The data are compared to relativistic distorted-wave impulse approximation calculations for the He4(e,e′p)H3 channel. Significantly more events are observed for pm≥0.45 GeV/c than are predicted by the theoretical model, and striking fluctuations in the ratio of data to the theoretical model around pm=0.3GeV/c are possible signals of initial-state multinucleon correlations.
Published: 2022

14. Deeply Virtual Compton Scattering Cross Section at High Bjorken x_{B}.

Author: Georges, F, Rashad, MNH, Stefanko, A, Dlamini, M, Karki, B, Ali, SF, Lin, P-J, Ko, H-S, Israel, N, Adikaram, D, Ahmed, Z, Albataineh, H, Aljawrneh, B, Allada, K, Allison, S, Alsalmi, S, Androic, D, Aniol, K, Annand, J, Atac, H, Averett, T, Ayerbe Gayoso, C, Bai, X, Bane, J, Barcus, S, Bartlett, K, Bellini, V, Beminiwattha, R, Bericic, J, Biswas, D, Brash, E, Bulumulla, D, Campbell, J, Camsonne, A, Carmignotto, M, Castellano, J, Chen, C, Chen, J-P, Chetry, T, Christy, ME, Cisbani, E, Clary, B, Cohen, E, Compton, N, Cornejo, JC, Covrig Dusa, S, Crowe, B, Danagoulian, S, Danley, T, De Persio, F, Deconinck, W, Defurne, M, Desnault, C, Di, D, Duer, M, Duran, B, Ent, R, Fanelli, C, Franklin, G, Fuchey, E, Gal, C, Gaskell, D, Gautam, T, Glamazdin, O, Gnanvo, K, Gray, VM, Gu, C, Hague, T, Hamad, G, Hamilton, D, Hamilton, K, Hansen, O, Hauenstein, F, Henry, W, Higinbotham, DW, Holmstrom, T, Horn, T, Huang, Y, Huber, GM, Hyde, CE, Ibrahim, H, Jen, C-M, Jin, K, Jones, M, Kabir, A, Keppel, C, Khachatryan, V, King, PM, Li, S, Li, WB, Liu, J, Liu, H, Liyanage, A, Magee, J, Malace, S, Mammei, J, Markowitz, P, McClellan, E, Mazouz, M, and Meddi, F
Subjects: Jefferson Lab Hall A Collaboration, Mathematical Sciences, Physical Sciences, Engineering, General Physics
Abstract: We report high-precision measurements of the deeply virtual Compton scattering (DVCS) cross section at high values of the Bjorken variable x_{B}. DVCS is sensitive to the generalized parton distributions of the nucleon, which provide a three-dimensional description of its internal constituents. Using the exact analytic expression of the DVCS cross section for all possible polarization states of the initial and final electron and nucleon, and final state photon, we present the first experimental extraction of all four helicity-conserving Compton form factors (CFFs) of the nucleon as a function of x_{B}, while systematically including helicity flip amplitudes. In particular, the high accuracy of the present data demonstrates sensitivity to some very poorly known CFFs.
Published: 2022

15. Measurement of Compton scattering at MAMI for the extraction of the electric and magnetic polarizabilities of the proton

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

16. Geant4-based calibration of an organic liquid scintillator

Author: Mauritzson, N., Fissum, K. G., Perrey, H., Annand, J. R. M., Frost, R. J. W., Hall-Wilton, R., Jebali, R. Al, Kanaki, K., Maulerova, V., Messi, F., and Rofors, E.
Subjects: Physics - Instrumentation and Detectors, Nuclear Experiment
Abstract: A light-yield calibration of an NE 213A organic liquid scintillator detector has been performed using both monoenergetic and polyenergetic gamma-ray sources. Scintillation light was detected in a photomultiplier tube, and the corresponding pulses were subjected to waveform digitization on an event-by-event basis. The resulting Compton edges have been analyzed using a Geant4 simulation of the detector which models both the interactions of the ionizing radiation as well as the transport of scintillation photons. The simulation is calibrated and also compared to well-established prescriptions used to determine the Compton edges, resulting ultimately in light-yield calibration functions. In the process, the simulation-based method produced information on the gain and intrinsic pulse-height resolution of the detector. It also facilitated a previously inaccessible understanding of the systematic uncertainties associated with the calibration of the scintillation-light yield. The simulation-based method was also compared to well-established numerical prescriptions for locating the Compton edges. Ultimately, the simulation predicted as much as 17% lower light-yield calibrations than the prescriptions. These calibrations indicate that approximately 35% of the scintillation light associated with a given gamma-ray reaches the photocathode. It is remarkable how well two 50 year old prescriptions for calibrating scintillation-light yield in organic scintillators have stood the test of time., Comment: 20 pages, 8 figures, 4 tables
Published: 2021
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17. Form Factors and Two-Photon Exchange in High-Energy Elastic Electron-Proton Scattering

Author: Christy, ME, Gautam, T, Ou, L, Schmookler, B, Wang, Y, Adikaram, D, Ahmed, Z, Albataineh, H, Ali, SF, Aljawrneh, B, Allada, K, Allison, SL, Alsalmi, S, Androic, D, Aniol, K, Annand, J, Arrington, J, Atac, H, Averett, T, Gayoso, C Ayerbe, Bai, X, Bane, J, Barcus, S, Bartlett, K, Bellini, V, Beminiwattha, R, Bericic, J, Bhatt, H, Bhetuwal, D, Biswas, D, Brash, E, Bulumulla, D, Camacho, CM, Campbell, J, Camsonne, A, Carmignotto, M, Castellanos, J, Chen, C, Chen, J-P, Chetry, T, Cisbani, E, Clary, B, Cohen, E, Compton, N, Cornejo, JC, Dusa, S Covrig, Crowe, B, Danagoulian, S, Danley, T, Deconinck, W, Defurne, M, Desnault, C, Di, D, Dlamini, M, Duer, M, Duran, B, Ent, R, Fanelli, C, Fuchey, E, Gal, C, Gaskell, D, Georges, F, Gilad, S, Glamazdin, O, Gnanvo, K, Gramolin, AV, Gray, VM, Gu, C, Habarakada, A, Hague, T, Hamad, G, Hamilton, D, Hamilton, K, Hansen, O, Hauenstein, F, Hernandez, AV, Henry, W, Higinbotham, DW, Holmstrom, T, Horn, T, Huang, Y, Huber, GM, Hyde, C, Ibrahim, H, Israel, N, Jen, C-M, Jin, K, Jones, M, Kabir, A, Karki, B, Keppel, C, Khachatryan, V, King, PM, Li, S, Li, W, Liu, H, Liu, J, Liyanage, AH, Mack, D, and Magee, J
Subjects: Nuclear and Plasma Physics, Particle and High Energy Physics, Physical Sciences, Mathematical Sciences, Engineering, General Physics, Mathematical sciences, Physical sciences
Abstract: We present new precision measurements of the elastic electron-proton scattering cross section for momentum transfer (Q^{2}) up to 15.75 (GeV/c)^{2}. Combined with existing data, these provide an improved extraction of the proton magnetic form factor at high Q^{2} and double the range over which a longitudinal or transverse separation of the cross section can be performed. The difference between our results and polarization data agrees with that observed at lower Q^{2} and attributed to hard two-photon exchange (TPE) effects, extending to 8 (GeV/c)^{2} the range of Q^{2} for which a discrepancy is established at >95% confidence. We use the discrepancy to quantify the size of TPE contributions needed to explain the cross section at high Q^{2}.
Published: 2022

18. Deeply virtual Compton scattering using a positron beam in Hall-C at Jefferson Lab

Author: Afanasev, A., Albayrak, I., Ali, S., Amaryan, M., Annand, J. R. M., Asaturyan, A., Bellini, V., Berdnikov, V. V., Boer, M., Brinkmann, K., Briscoe, W. J., Camsonne, A., Caudron, M., Causse, L., Carmignotto, M., Day, D., Defurne, M., Diehl, S., Ent, R., Chatagnon, P., Dupré, R., Dutta, D., Ehrhart, M., Fernando, M. A. I., Forest, T., Guidal, M., Grames, J., Gueye, P., Habet, S., Hamilton, D. J., Hobart, A., Horn, T., Hyde, C., Kalicy, G., Keller, D., Keppel, C., Kerver, M., Kinney, E., Ko, H. -S., Marchand, D., Markowitze, P., Mazouz, M., McCaughan, M., McKinnon, B., Mkrtchyan, A., Mkrtchyan, H., Muhoza, M., Camacho, C. Muñoz, Murphy, J., Nadel-Turonski, P., Niccolai, S., Niculescu, G., Novotny, R., Paremuzyan, R., Pegg, I., Price, K., Rashad, H., Roche, J., Rondon, R., Sawatzky, B., Sergeyeva, V., Širca, S., Somov, A., Strakovsky, I., Tadevosyan, V., Trotta, R., Voskanyan, H., Voutier, E., Wojtsekhowski, B., Wood, S., Zhamkochyan, S., Zhang, J., Zhao, S., and Zorn, C.
Subjects: Nuclear Experiment
Abstract: We propose to use the High Momentum Spectrometer of Hall C combined with the Neutral Particle Spectrometer (NPS) to perform high precision measurements of the Deeply Virtual Compton Scattering (DVCS) cross section using a beam of positrons. The combination of measurements with oppositely charged incident beams is the only unambiguous way to disentangle the contribution of the DVCS$^2$ term in the photon electroproduction cross section from its interference with the Bethe-Heitler amplitude. This provides a stronger way to constrain the Generalized Parton Distributions of the nucleon. A wide range of kinematics accessible with an 11 GeV beam off an unpolarized proton target will be covered. The $Q^2-$dependence of each contribution will be measured independently.
Published: 2021
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19. Single $\pi^0$ Production Off Neutrons Bound in Deuteron with Linearly Polarized Photons

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

Author: Christy, M. E., Gautam, T., Ou, L., Schmookler, B., Wang, Y., Adikaram, D., Ahmed, Z., Albataineh, H., Ali, S. F., Aljawrneh, B., Allada, K., Allison, S. L., Alsalmi, S., Androic, D., Aniol, K., Annand, J., Arrington, J., Atac, H., Averett, T., Gayoso, C. Ayerbe, Bai, X., Bane, J., Barcus, S., Bartlett, K., Bellini, V., Beminiwattha, R., Bericic, J., Bhatt, H., Bhetuwal, D., Biswas, D., Brash, E., Bulumulla, D., Camacho, C. M., Campbell, J., Camsonne, A., Carmignotto, M., Castellanos, J., Chen, C., Chen, J-P., Chetry, T., Cisbani, E., Clary, B., Cohen, E., Compton, N., Cornejo, J. C., Dusa, S. Covrig, Crowe, B., Danagoulian, S., Danley, T., Deconinck, W., Defurne, M., Desnault, C., Di, D., Dlamini, M., Duer, M., Duran, B., Ent, R., Fanelli, C., Fuchey, E., Gal, C., Gaskell, D., Georges, F., Gilad, S., Glamazdin, O., Gnanvo, K., Gramolin, A. V., Gray, V. M., Gu, C., Habarakada, A., Hague, T., Hamad, G., Hamilton, D., Hamilton, K., Hansen, O., Hauenstein, F., Hernandez, A. V., Henry, W., Higinbotham, D. W., Holmstrom, T., Horn, T., Huang, Y., Huber, G. M., Hyde, C., Ibrahim, H., Israel, N., Jen, C-M., Jin, K., Jones, M., Kabir, A., Karki, B., Keppel, C., Khachatryan, V., King, P. M., Li, S., Li, W., Liu, H., Liu, J., Liyanage, A. H., Mack, D., Magee, J., Malace, S., Mammei, J., Markowitz, P., Mayilyan, S., McClellan, E., Meddi, F., Meekins, D., Mesick, K., Michaels, R., Mkrtchyan, A., Moffit, B., Montgomery, R., Myers, L. S., Nadel-Turonski, P., Nazeer, S. J., Nelyubin, V., Nguyen, D., Nuruzzaman, N., Nycz, M., Obrecht, R. F., Ohanyan, K., Palatchi, C., Pandey, B., Park, K., Park, S., Peng, C., Persio, F. D., Pomatsalyuk, R., Pooser, E., Puckett, A. J. R., Punjabi, V., Quinn, B., Rahman, S., Rashad, M. N. H., Riordan, S., Roche, J., Sapkota, I., Sarty, A., Sawatzky, B., Saylor, N. H., Shabestari, M. H., Shahinyan, A., Sirca, S., Smith, G. R., Sooriyaarachchilage, S., Sparveris, N., Spies, R., Stefanko, A., Su, T., Subedi, A., Sulkosky, V., Sun, A., Tan, Y., Thorne, L., Ton, N., Tortorici, F., Trotta, R., Uniyal, R., Urciuoli, G. M., Voutier, E., Waidyawansa, B., Wojtsekhowski, B., Wood, S., Yan, X., Ye, L., Ye, Z. H., Yero, C., Zhang, J., Zhao, Y. X., and Zhu, P.
Subjects: Nuclear Experiment, High Energy Physics - Experiment
Abstract: We present new precision measurements of the elastic electron-proton scattering cross section for momentum transfer (Q$^2$) up to 15.75~\gevsq. Combined with existing data, these provide an improved extraction of the proton magnetic form factor at high Q$^2$ and double the range over which a longitudinal/transverse separation of the cross section can be performed. The difference between our results and polarization data agrees with that observed at lower Q$^2$ and attributed to hard two-photon exchange (TPE) effects, extending to 8~(GeV/c)$^2$ the range of Q$^2$ for which a discrepancy is established at $>$95\% confidence. We use the discrepancy to quantify the size of TPE contributions needed to explain the cross section at high Q$^2$., Comment: 7 pages, 2 figures
Published: 2021
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21. International Workshop on Next Generation Gamma-Ray Source

Author: Howell, C. R., Ahmed, M. W., Afanasev, A., Alesini, D., Annand, J. R. M., Aprahamian, A., Balabanski, D. L., Benson, S. V., Bernstein, A., Brune, C. R., Byrd, J., Carlsten, B. E., Champagne, A. E., Chattopadhyay, S., Davis, D., Downie, E. J., Durham, M. J., Feldman, G., Gao, H., Geddes, C. G. R., Griesshammer, H. W., Hajima, R., Hao, H., Hornidge, D., Isaak, J., Janssens, R. V. F., Kendellen, D. P., Kovash, M. A., Martel, P. P., Meissner, Ulf-G., Miskimen, R., Pasquini, B., Phillips, D. R., Pietralla, N., Savran, D., Schindler, M. R., Sikora, M. H., Snow, W. M., Springer, R. P., Sun, C., Tang, C., Tiburzi, B., Tonchev, A. P., Tornow, W., Ur, C. A., Wang, D., Weller, H. R., Werner, V., Wu, Y. K., Yan, J., Zhao, Z., Zilges, A., and Zomer, F.
Subjects: Nuclear Experiment, Nuclear Theory, Physics - Accelerator Physics
Abstract: A workshop on The Next Generation Gamma-Ray Sources sponsored by the Office of Nuclear Physics at the Department of Energy, was held November 17--19, 2016 in Bethesda, Maryland. The goals of the workshop were to identify basic and applied research opportunities at the frontiers of nuclear physics that would be made possible by the beam capabilities of an advanced laser Compton beam facility. To anchor the scientific vision to realistically achievable beam specifications using proven technologies, the workshop brought together experts in the fields of electron accelerators, lasers, and optics to examine the technical options for achieving the beam specifications required by the most compelling parts of the proposed research programs. An international assembly of participants included current and prospective $\gamma$-ray beam users, accelerator and light-source physicists, and federal agency program managers. Sessions were organized to foster interactions between the beam users and facility developers, allowing for information sharing and mutual feedback between the two groups. The workshop findings and recommendations are summarized in this whitepaper.
Published: 2020

22. Deep Exclusive Electroproduction of π0 at High Q2 in the Quark Valence Regime

Author: Dlamini, M, Karki, B, Ali, SF, Lin, P-J, Georges, F, Ko, H-S, Israel, N, Rashad, MNH, Stefanko, A, Adikaram, D, Ahmed, Z, Albataineh, H, Aljawrneh, B, Allada, K, Allison, S, Alsalmi, S, Androic, D, Aniol, K, Annand, J, Atac, H, Averett, T, Ayerbe Gayoso, C, Bai, X, Bane, J, Barcus, S, Bartlett, K, Bellini, V, Beminiwattha, R, Bericic, J, Biswas, D, Brash, E, Bulumulla, D, Campbell, J, Camsonne, A, Carmignotto, M, Castellano, J, Chen, C, Chen, J-P, Chetry, T, Christy, ME, Cisbani, E, Clary, B, Cohen, E, Compton, N, Cornejo, JC, Covrig Dusa, S, Crowe, B, Danagoulian, S, Danley, T, De Persio, F, Deconinck, W, Defurne, M, Desnault, C, Di, D, Duer, M, Duran, B, Ent, R, Fanelli, C, Franklin, G, Fuchey, E, Gal, C, Gaskell, D, Gautam, T, Glamazdin, O, Gnanvo, K, Gray, VM, Gu, C, Hague, T, Hamad, G, Hamilton, D, Hamilton, K, Hansen, O, Hauenstein, F, Henry, W, Higinbotham, DW, Holmstrom, T, Horn, T, Huang, Y, Huber, GM, Hyde, C, Ibrahim, H, Jen, C-M, Jin, K, Jones, M, Kabir, A, Keppel, C, Khachatryan, V, King, PM, Li, S, Li, W, Liu, J, Liu, H, Liyanage, A, Magee, J, Malace, S, Mammei, J, Markowitz, P, McClellan, E, Meddi, F, and Meekins, D
Subjects: Jefferson Lab Hall A Collaboration, Mathematical Sciences, Physical Sciences, Engineering, General Physics
Abstract: We report measurements of the exclusive neutral pion electroproduction cross section off protons at large values of x_{B} (0.36, 0.48, and 0.60) and Q^{2} (3.1 to 8.4 GeV^{2}) obtained from Jefferson Lab Hall A experiment E12-06-014. The corresponding structure functions dσ_{T}/dt+εdσ_{L}/dt, dσ_{TT}/dt, dσ_{LT}/dt, and dσ_{LT^{'}}/dt are extracted as a function of the proton momentum transfer t-t_{min}. The results suggest the amplitude for transversely polarized virtual photons continues to dominate the cross section throughout this kinematic range. The data are well described by calculations based on transversity generalized parton distributions coupled to a helicity flip distribution amplitude of the pion, thus providing a unique way to probe the structure of the nucleon.
Published: 2021

23. Deep exclusive electroproduction of $\pi^0$ at high $Q^2$ in the quark valence regime

Author: The Jefferson Lab Hall A Collaboration, Dlamini, M., Karki, B., Ali, S. F., Lin, P-J., Georges, F., Ko, H-S, Israel, N., Rashad, M. N. H., Stefanko, A., Adikaram, D., Ahmed, Z., Albataineh, H., Aljawrneh, B., Allada, K., Allison, S., Alsalmi, S., Androic, D., Aniol, K., Annand, J., Atac, H., Averett, T., Gayoso, C. Ayerbe, Bai, X., Bane, J., Barcus, S., Bartlett, K., Bellini, V., Beminiwattha, R., Bericic, J., Biswas, D., Brash, E., Bulumulla, D., Campbell, J., Camsonne, A., Carmignotto, M., Castellano, J., Chen, C., Chen, J-P., Chetry, T., Christy, M. E., Cisbani, E., Clary, B., Cohen, E., Compton, N., Cornejo, J. C., Dusa, S. Covrig, Crowe, B., Danagoulian, S., Danley, T., De Persio, F., Deconinck, W., Defurne, M., Desnault, C., Di, D., Duer, M., Duran, B., Ent, R., Fanelli, C., Franklin, G., Fuchey, E., Gal, C., Gaskell, D., Gautam, T., Glamazdin, O., Gnanvo, K., Gray, V. M., Gu, C., Hague, T., Hamad, G., Hamilton, D., Hamilton, K., Hansen, O., Hauenstein, F., Henry, W., Higinbotham, D. W., Holmstrom, T., Horn, T., Huang, Y., Huber, G. M., Hyde, C., Ibrahim, H., Jen, C-M., Jin, K., Jones, M., Kabir, A., Keppel, C., Khachatryan, V., King, P. M., Li, S., Li, W., Liu, J., Liu, H., Liyanage, A., Magee, J., Malace, S., Mammei, J., Markowitz, P., McClellan, E., Meddi, F., Meekins, D., Mesik, K., Michaels, R., Mkrtchyan, A., Montgomery, R., Camacho, C. Munoz, Myers, L. S., Nadel-Turonski, P., Nazeer, S. J., Nelyubin, V., Nguyen, D., Nuruzzaman, N., Nycz, M., Obretch, O. F., Ou, L., Palatchi, C., Pandey, B., Park, S., Park, K., Peng, C., Pomatsalyuk, R., Pooser, E., Puckett, A. J. R., Punjabi, V., Quinn, B., Rahman, S., Reimer, P. E., Roche, J., Sapkota, I., Sarty, A., Sawatzky, B., Saylor, N. H., Schmookler, B., Shabestari, M. H., Shahinyan, A., Sirca, S., Smith, G. R., Sooriyaarachchilage, S., Sparveris, N., Spies, R., Su, T., Subedi, A., Sulkosky, V., Sun, A., Thorne, L., Tian, Y., Ton, N., Tortorici, F., Trotta, R., Urciuoli, G. M., Voutier, E., Waidyawansa, B., Wang, Y., Wojtsekhowski, B., Wood, S., Yan, X., Ye, L., Ye, Z., Yero, C., Zhang, J., Zhao, Y., and Zhu, P.
Subjects: High Energy Physics - Experiment, Nuclear Experiment
Abstract: We report measurements of the exclusive neutral pion electroproduction cross section off protons at large values of $x_B$ (0.36, 0.48 and 0.60) and $Q^2$ (3.1 to 8.4 GeV$^2$) obtained from Jefferson Lab Hall A experiment E12-06-014. The corresponding structure functions $d\sigma_L/dt+\epsilon d\sigma_T/dt$, $d\sigma_{TT}/dt$, $d\sigma_{LT}/dt$ and $d\sigma_{LT'}/dt$ are extracted as a function of the proton momentum transfer $t-t_{min}$. The results suggest the amplitude for transversely polarized virtual photons continues to dominate the cross-section throughout this kinematic range. The data are well described by calculations based on transversity Generalized Parton Distributions coupled to a helicity flip Distribution Amplitude of the pion, thus providing a unique way to probe the structure of the nucleon.
Published: 2020
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24. Simulation of the Response of the Solid State Neutron Detector for the European Spallation Source

Author: Boyd, L., Rofors, E., Annand, J. R. M., Fissum, K. G., Hall-Wilton, R., Jebali, R. Al, Kanaki, K., Livingston, K., Maulerova, V., Mauritzson, N., Montgomery, R., Perrey, H., and Seitz, B.
Subjects: Physics - Instrumentation and Detectors, Physics - Computational Physics
Abstract: The characteristics of the Solid-state Neutron Detector, under development for neutron-scattering measurements at the European Spallation Source, have been simulated with a Geant4-based computer code. The code models the interations of thermal neutrons and ionising radiation in the 6Li-doped scintillating glass of the detector, the production of scintillation light and the transport of optical, scintillation photons through the the scintillator, en route to the photo-cathode of the attached multi-anode photomultiplier. Factors which affect the optical-photon transport, such as surface finish, pixelation of the glass sheet, provision of a front reflector and optical coupling media are compared. Predictions of the detector response are compared with measurements made with neutron and gamma-ray sources, a collimated alpha source and finely collimated beams of 2.5 MeV protons and deuterons., Comment: Preprint 22 pages, 12 figures, published in NIM A
Published: 2020
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25. Response of a Li-glass/multi-anode photomultiplier detector to collimated thermal-neutron beams

Author: Rofors, E., Mauritzson, N., Perrey, H., Jebali, R. Al, Annand, J. R. M., Boyd, L., Christensen, M. J., Clemens, U., Desert, S., Engels, R., Fissum, K. G., Frielinghaus, H., Gheorghe, C., Hall-Wilton, R., Jaksch, S., Kanaki, K., Kazi, S., Kemmerling, G., Jansa, I. Llamas, Maulerova, V., Montgomery, R., Richter, T., Scherzinger, J., Seitz, B., and Shetty, M.
Subjects: Physics - Instrumentation and Detectors, Nuclear Experiment
Abstract: The response of a position-sensitive Li-glass scintillator detector being developed for thermal-neutron detection with 6 mm position resolution has been investigated using collimated beams of thermal neutrons. The detector was moved perpendicularly through the neutron beams in 0.5 to 1.0 mm horizontal and vertical steps. Scintillation was detected in an 8 X 8 pixel multi-anode photomultiplier tube on an event-by-event basis. In general, several pixels registered large signals at each neutron-beam location. The number of pixels registering signal above a set threshold was investigated, with the maximization of the single-hit efficiency over the largest possible area of the detector as the primary goal. At a threshold of ~50% of the mean of the full-deposition peak, ~80% of the events were registered in a single pixel, resulting in an effective position resolution of ~5 mm in X and Y. Lower thresholds generally resulted in events demonstrating higher pixel multiplicities, but these events could also be localized with ~5 mm position resolution., Comment: 23 pages, 8 figures
Published: 2020
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26. An experimental program with high duty-cycle polarized and unpolarized positron beams at Jefferson Lab

Author: Accardi, A., Afanasev, A., Albayrak, I., Ali, S. F., Amaryan, M., Annand, J. R. M., Arrington, J., Asaturyan, A., Atac, H., Avakian, H., Averett, T., Gayoso, C. Ayerbe, Bai, X., Barion, L., Battaglieri, M., Bellini, V., Beminiwattha, R., Benmokhtar, F., Berdnikov, V. V., Bernauer, J. C., Bertone, V., Bianconi, A., Biselli, A., Bisio, P., Blunden, P., Boer, M., Bondì, M., Brinkmann, K. -T., Briscoe, W. J., Burkert, V., Cao, T., Camsonne, A., Capobianco, R., Cardman, L., Carmignotto, M., Caudron, M., Causse, L., Celentano, A., Chatagnon, P., Chen, J. -P., Chetry, T., Ciullo, G., Cline, E., Cole, P. L., Contalbrigo, M., Costantini, G., D'Angelo, A., Darmé, L., Day, D., Defurne, M., De Napoli, M., Deur, A., De Vita, R., D'Hose, N., Diehl, S., Diefenthaler, M., Dongwi, B., Dupré, R., Dutrieux, H., Dutta, D., Ehrhart, M., Fassi, L. El, Elouadrhiri, L., Ent, R., Erler, J., Fernando, I. P., Filippi, A., Flay, D., Forest, T., Fuchey, E., Fucini, S., Furletova, Y., Gao, H., Gaskell, D., Gasparian, A., Gautam, T., Girod, F. -X., Gnanvo, K., Grames, J., Grauvoge, G. N., Gueye, P., Guidal, M., Habet, S., Hague, T. J., Hamilton, D. J., Hansen, O., Hasell, D., Hattawy, M., Higinbotham, D. W., Hobart, A., Horn, T., Hyde, C. E., Ibrahim, H., Ilyichev, A., Italiano, A., Joo, K., Joosten, S. J., Khachatryan, V., Kalantarians, N., Kalicy, G., Karky, B., Keller, D., Keppel, C., Kerver, M., Khandaker, M., Kim, A., Kim, J., King, P. M., Kinney, E., Klimenko, V., Ko, H. -S., Kohl, M., Kozhuharov, V., Kriesten, B. T., Krnjaic, G., Kubarovsky, V., Kutz, T., Lanza, L., Leali, M., Lenisa, P., Liyanage, N., Liu, Q., Liuti, S., Mammei, J., Mantry, S., Marchand, D., Markowitz, P., Marsicano, L., Mascagna, V., Mazouz, M., McCaughan, M., McKinnon, B., McNulty, D., Melnitchouk, W., Metz, A., Meziani, Z. -E., Migliorati, S., Mihovilovic, M., Milner, R., Mkrtchyan, A., Mkrtchyan, H., Movsisyan, A., Moutarde, H., Muhoza, M., Camacho, C. Muñoz, Murphy, J., Nadel-Turonski, P., Nardi, E., Nazeer, J., Niccolai, S., Niculescu, G., Novotny, R., Owens, J. F., Paolone, M., Pappalardo, L., Paremuzyan, R., Pasquini, B., Pasyuk, E., Patel, T., Pegg, I., Peng, C., Perera, D., Poelker, M., Price, K., Puckett, A. J. R., Raggi, M., Randazzo, N., Rashad, M. N. H., Rathnayake, M., Raue, B., Reimer, P. E., Rinaldi, M., Rizzo, A., Roblin, Y., Roche, J., Rondon-Aramayo, O., Sabatié, F., Salmè, G., Santopinto, E., Estrada, R. Santos, Sawatzky, B., Schmidt, A., Schweitzer, P., Scopetta, S., Sergeyeva, V., Shabestari, M., Shahinyan, A., Sharabian, Y., Širca, S., Smith, E. S., Sokhan, D., Somov, A., Sparveris, N., Spata, M., Spiesberger, H., Spreafico, M., Stepanyan, S., Stoler, P., Strakovsky, I., Suleiman, R., Suresh, M., Sznajder, P., Szumila-Vance, H., Tadevosyan, V., Tadepalli, A. S., Thomas, A. W., Tiefenback, M., Trotta, R., Ungaro, M., Valente, P., Vanderhaeghen, M., Venturelli, L., Voskanyan, H., Voutier, E., Wojtsekhowski, B., Wood, M. H., Wood, S., Xie, J., Xiong, W., Ye, Z., Yurov, M., Zaunick, H. -G., Zhamkochyan, S., Zhang, J., Zhang, S., Zhao, S., Zhao, Z. W., Zheng, X., Zhou, J., and Zorn, C.
Subjects: Nuclear Experiment, High Energy Physics - Experiment, High Energy Physics - Phenomenology
Abstract: Positron beams, both polarized and unpolarized, are identified as essential ingredients for the experimental programs at the next generation of lepton accelerators. In the context of the hadronic physics program at Jefferson Lab (JLab), positron beams are complementary, even essential, tools for a precise understanding of the electromagnetic structure of nucleons and nuclei, in both the elastic and deep-inelastic regimes. For instance, elastic scattering of polarized and unpolarized electrons and positrons from the nucleon enables a model independent determination of its electromagnetic form factors. Also, the deeply-virtual scattering of polarized and unpolarized electrons and positrons allows unambiguous separation of the different contributions to the cross section of the lepto-production of photons and of lepton-pairs, enabling an accurate determination of the nucleons and nuclei generalized parton distributions, and providing an access to the gravitational form factors. Furthermore, positron beams offer the possibility of alternative tests of the Standard Model of particle physics through the search of a dark photon, the precise measurement of electroweak couplings, and the investigation of charged lepton flavor violation. This document discusses the perspectives of an experimental program with high duty-cycle positron beams at JLab., Comment: 18 pages, 7 figures This version superseeds the previous version which scientific content was decomposed into several more elaborated articles. All of these articles will be collected in the EPJ A Topical Issue about "Positron beam and physics at Jefferson Lab (e+@Jlab)"
Published: 2020
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27. Helicity-dependent cross sections for the photoproduction of $\pi^0$ pairs from nucleons

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

Author: Rofors, E., Pallon, J., Jebali, R. Al, Annand, J. R. M., Boyd, L., Christensen, M. J., Clemens, U., Desert, S., Elfman, M., Engels, R., Fissum, K. G., Frielinghaus, H., Frost, R., Gardner, S., Gheorghe, C., Hall-Wilton, R., Jaksch, S., Kanaki, K., Kemmerling, G., Kristiansson, P., Livingston, K., Maulerova, V., Mauritzson, N., Montgomery, R., Perrey, H., Richter, T., Scherzinger, J., Seitz, B., and Shetty, M.
Subjects: Physics - Instrumentation and Detectors, Nuclear Experiment
Abstract: The response of a position-sensitive Li-glass based scintillation detector to focused beams of 2.5 MeV protons and deuterons has been investigated. The beams were scanned across the detector in 0.5 mm horizontal and vertical steps perpendicular to the beams. Scintillation light was registered using an 8 by 8 pixel multi-anode photomultiplier tube. The signal amplitudes were recorded for each pixel on an event-by-event basis. Several pixels generally registered considerable signals at each beam location. The number of pixels above set thresholds were investigated, with the optimization of the single-hit efficiency over the largest possible area as the goal. For both beams, at a threshold of ~50% of the mean of the full-deposition peak, ~80% of the events were registered in a single pixel, resulting in an effective position resolution of ~5 mm in X and Y., Comment: 22 pages, 8 figures, to be submitted to Nucl. Instr. and Meth. in Phys. Res. A
Published: 2020
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29. Novel observation of isospin structure of short-range correlations in calcium isotopes

Author: Nguyen, D., Ye, Z., Aguilera, P., Ahmed, Z., Albataineh, H., Allada, K., Anderson, B., Anez, D., Aniol, K., Annand, J., Arrington, J., Averett, T., Baghdasaryan, H., Bai, X., Beck, A., Beck, S., Bellini, V., Benmokhtar, F., Camsonne, A., Chen, C., Chen, J. -P., Chirapatpimol, K., Cisbani, E., Dalton, M. M., Daniel, A., Day, D., Deconinck, W., Defurne, M., Flay, D., Fomin, N., Friend, M., Frullani, S., Fuchey, E., Garibaldi, F., Gaskell, D., Gilad, S., Gilman, R., Glamazdin, S., Gu, C., Guèye, P., Hanretty, C., Hansen, J. -O., Shabestari, M. Hashemi, Higinbotham, D. W., Huang, M., Iqbal, S., Jin, G., Kalantarians, N., Kang, H., her, A. Kelle, Korover, I., LeRose, J., Leckey, J., Li, S., Lindgren, R., Long, E., Mammei, J., Margaziotis, D. J., Markowitz, P., Meekins, D., Meziani, Z. -E., Michaels, R., Mihovilovi\v, M., Muangma, N., Camacho, C. Munoz, Norum, B. E., Nuruzzaman, Pan, K., Phillips, S., Piasetzky, E., Pomerantz, I., Posik, M., Punjabi, V., Qian, X., Qiang, Y., Qiu, X., Reimer, P. E., Rakhman, A., Riordan, S., Ron, G., Rondon-Aramayo, O., Saha, A., Selvy, L., Shahinyan, A., Shneor, R., \v, S., Slifer, K., Solvignon, P., Sparveris, N., Subedi, R., Sulkosky, V., Wang, D., Watson, J. W., Weinstein, L. B., Wojtsekhowski, B., Wood, S. A., Yaron, I., Zhan, X., Zhang, J., Zhang, Y. W., Zhao, B., Zheng, X., Zhu, P., and Zielinski, R.
Subjects: Nuclear Experiment
Abstract: Short Range Correlations (SRCs) have been identified as being responsible for the high momentum tail of the nucleon momentum distribution, n(k). Hard, short-range interactions of nucleon pairs generate the high momentum tail and imprint a universal character on n(k) for all nuclei at large momentum. Triple coincidence experiments have shown a strong dominance of np pairs, but these measurements involve large final state interactions. This paper presents the results from Jefferson Lab experiment E08014 which measured inclusive electron scattering cross-section from Ca isotopes. By comparing the inclusive cross section from 48Ca to 40Ca in a kinematic region dominated by SRCs we provide a new way to study the isospin structure of SRCs., Comment: 7 pages, 3 figures
Published: 2020
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30. Form Factors and Two-Photon Exchange in High-Energy Elastic Electron-Proton Scattering

Author: Christy, ME, Gautam, T, Ou, L, Schmookler, B, Wang, Y, Adikaram, D, Ahmed, Z, Albataineh, H, Ali, SF, Aljawrneh, B, Allada, K, Allison, SL, Alsalmi, S, Androic, D, Aniol, K, Annand, J, Arrington, J, Atac, H, Averett, T, Gayoso, C Ayerbe, Bai, X, Bane, J, Barcus, S, Bartlett, K, Bellini, V, Beminiwattha, R, Bericic, J, Bhatt, H, Bhetuwal, D, Biswas, D, Brash, E, Bulumulla, D, Camacho, CM, Campbell, J, Camsonne, A, Carmignotto, M, Castellanos, J, Chen, C, Chen, J-P, Chetry, T, Cisbani, E, Clary, B, Cohen, E, Compton, N, Cornejo, JC, Dusa, S Covrig, Crowe, B, Danagoulian, S, Danley, T, Deconinck, W, Defurne, M, Desnault, C, Di, D, Dlamini, M, Duer, M, Duran, B, Ent, R, Fanelli, C, Fuchey, E, Gal, C, Gaskell, D, Georges, F, Gilad, S, Glamazdin, O, Gnanvo, K, Gramolin, AV, Gray, VM, Gu, C, Habarakada, A, Hague, T, Hamad, G, Hamilton, D, Hamilton, K, Hansen, O, Hauenstein, F, Hernandez, AV, Henry, W, Higinbotham, DW, Holmstrom, T, Horn, T, Huang, Y, Huber, GM, Hyde, C, Ibrahim, H, Israel, N, Jen, C-M, Jin, K, Jones, M, Kabir, A, Karki, B, Keppel, C, Khachatryan, V, King, PM, Li, S, Li, W, Liu, H, Liu, J, Liyanage, AH, Mack, D, and Magee, J
Subjects: nucl-ex, hep-ex
Abstract: We present new precision measurements of the elastic electron-protonscattering cross section for momentum transfer (Q$^2$) up to 15.75~\gevsq.Combined with existing data, these provide an improved extraction of the protonmagnetic form factor at high Q$^2$ and double the range over which alongitudinal/transverse separation of the cross section can be performed. Thedifference between our results and polarization data agrees with that observedat lower Q$^2$ and attributed to hard two-photon exchange (TPE) effects,extending to 8~(GeV/c)$^2$ the range of Q$^2$ for which a discrepancy isestablished at $>$95\% confidence. We use the discrepancy to quantify the sizeof TPE contributions needed to explain the cross section at high Q$^2$.
Published: 2021

31. Novel observation of isospin structure of short-range correlations in calcium isotopes

Author: Nguyen, D, Ye, Z, Aguilera, P, Ahmed, Z, Albataineh, H, Allada, K, Anderson, B, Anez, D, Aniol, K, Annand, J, Arrington, J, Averett, T, Baghdasaryan, H, Bai, X, Beck, A, Beck, S, Bellini, V, Benmokhtar, F, Camsonne, A, Chen, C, Chen, JP, Chirapatpimol, K, Cisbani, E, Dalton, MM, Daniel, A, Day, D, Deconinck, W, Defurne, M, Flay, D, Fomin, N, Friend, M, Frullani, S, Fuchey, E, Garibaldi, F, Gaskell, D, Gilad, S, Gilman, R, Glamazdin, S, Gu, C, Guèye, P, Hanretty, C, Hansen, JO, Shabestari, MH, Higinbotham, DW, Huang, M, Iqbal, S, Jin, G, Kalantarians, N, Kang, H, Kelleher, A, Korover, I, Lerose, J, Leckey, J, Li, S, Lindgren, R, Long, E, Mammei, J, Margaziotis, DJ, Markowitz, P, Meekins, D, Meziani, ZE, Michaels, R, Mihovilovic, M, Muangma, N, Camacho, CM, Norum, BE, Nuruzzaman, Pan, K, Phillips, S, Piasetzky, E, Pomerantz, I, Posik, M, Punjabi, V, Qian, X, Qiang, Y, Qiu, X, Reimer, PE, Rakhman, A, Riordan, S, Ron, G, Rondon-Aramayo, O, Saha, A, Selvy, L, Shahinyan, A, Shneor, R, Širca, S, Slifer, K, Solvignon, P, Sparveris, N, Subedi, R, Sulkosky, V, Wang, D, Watson, JW, Weinstein, LB, Wojtsekhowski, B, Wood, SA, Yaron, I, Zhan, X, Zhang, J, and Zhang, YW
Subjects: nucl-ex
Abstract: Short-range correlations (SRCs) have been identified as being responsible for the high-momentum tail of the nucleon momentum distribution, n(k). Hard, short-range interactions of nucleon pairs generate the high-momentum tail and imprint a universal character on n(k) for all nuclei at large momentum. Triple coincidence experiments have shown a strong dominance of np pairs, but these measurements involve large final-state interactions. This paper presents the results from Jefferson Lab experiment E08014 which measured inclusive electron scattering cross section from Ca isotopes. By comparing the inclusive cross section from Ca48 to Ca40 in a kinematic region dominated by SRCs we provide a new way to study the isospin structure of SRCs.
Published: 2020

32. Signatures of the $d^*(2380)$ hexaquark in d($\gamma$,$p\vec{n}$)

Author: Bashkanov, M., Watts, D. P., Kay, S. J. D., Abt, S., Achenbach, P., Adlarson, P., Afzal, F., Bartolome, P. Aguar, Ahmed, Z., Akondi, C. S., Annand, J. R. M., Arends, H. J., Beck, R., Biroth, M., Borisov, N., Braghieri, A., Briscoe, W. J., Cividini, F., Collicott, C., Costanza, S., Denig, A., Dieterle, M., Downie, E. J., Drexler, P., Garni, 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., Korolija, M., Krusche, B., Lazarev, A., Livingston, K., Lutterer, S., MacGregor, I. J. D., Manley, D. M., Martel, P. P., McGeorge, J. C., Miskimen, R., Mornacchi, E., Mullen, C., Neganov, A., Neiser, A., Ostrick, M., Otte, P. B., Paudyal, D., Pedroni, P., Powell, A., Prakhov, S. N., Ron, G., Sarty, A., Sfienti, C., Sokhoyan, V., Spieker, K., Steffen, O., Strakovsky, I. I., Strub, T., Supek, I., Thiel, A., Thiel, M., Thomas, A., Usov, Yu. A., Wagner, S., Walford, N. K., Werthmüller, D., Wettig, J., Wolfes, M., Zachariou, N., and Zana, L. A.
Subjects: Nuclear Experiment
Abstract: We report a measurement of the spin polarisation of the recoiling neutron in deuterium photodisintegration, utilising a new large acceptance polarimeter within the Crystal Ball at MAMI. The measured photon energy range of 300~--~700~MeV provides the first measurement of recoil neutron polarisation at photon energies where the quark substructure of the deuteron plays a role, thereby providing important new constraints on photodisintegration mechanisms. A very high neutron polarisation in a narrow structure centred around $E_{\gamma}\sim$~570~MeV is observed, which is inconsistent with current theoretical predictions employing nucleon resonance degrees of freedom. A Legendre polynomial decomposition suggests this behaviour could be related to the excitation of the $d^*(2380)$ hexaquark.
Published: 2019
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33. Spin polarizabilities of the proton by measurement of Compton double-polarization observables

Author: Paudyal, D., Martel, P. P., Huber, G. M., Hornidge, D., Abt, S., Achenbach, P., Adlarson, P., Afzal, F., Ahmed, Z., Akondi, C. S., Annand, J. R. M., Arends, H. J., Bashkanov, M., Beck, R., Biroth, M., Borisov, N. S., Braghieri, A., Briscoe, W. J., Cividini, F., Costanza, S., Collicott, C., Denig, A., Dieterle, M., Downie, E. J., Drexler, P., Ferretti-Bondy, M. I., Gardner, S., Garni, S., Glazier, D. I., Glowa, D., Gorodnov, I., Gradl, W., Günther, S., Gurevich, G. M., Hamilton, D., Heijkenskjöld, L., Käser, A., Kashevarov, V. L., Kay, S., Keshelashvili, I., Kondratiev, R., Korolija, M., Krusche, B., Lazarev, A. B., Linturi, J. M., Lisin, V., Livingston, K., Lutterer, S., MacGregor, I. J. D., Macrae, R., Mancell, J., Manley, D. M., Metag, V., Meyer, W., Miskimen, R., Mornacchi, E., Mullen, C., Mushkarenkov, A., Neganov, A. B., Neiser, A., Oberle, M., Ostrick, M., Otte, P. B., Pedroni, P., Polonski, A., Powell, A., Prakhov, S. N., Rajabi, A., Reicherz, G., Ron, G., Rostomyan, T., Sarty, A., Sfienti, C., Sikora, M. H., Sokhoyan, V., Spieker, K., Steffen, O., Strakovsky, I. I., Strub, Th., Supek, I., Thiel, A., Thiel, M., Thomas, A., Unverzagt, M., Usov, Yu. A., Wagner, S., Walford, N. K., Watts, D. P., Werthmüller, D., Wettig, J., Witthauer, L., Wolfes, M., and Zana, L.
Subjects: Nuclear Experiment
Abstract: The Compton double-polarization observable $\Sigma_{2z}$ has been measured for the first time in the $\Delta(1232)$ resonance region using a circularly polarized photon beam incident on a longitudinally polarized target at the Mainz Microtron. This paper reports these results, together with the model-dependent extraction of four proton spin polarizabilities from fits to additional asymmetry data using dispersion relation and chiral perturbation theory calculations, with the former resulting in: $\gamma_{E1E1} = -3.18 \pm 0.52$, $\gamma_{M1M1} = 2.98 \pm 0.43$, $\gamma_{E1M2} = -0.44 \pm 0.67$ and $\gamma_{M1E2} = 1.58 \pm 0.43$, in units of $10^{-4}~\mathrm{fm}^{4}$., Comment: 7 pages, 5 figures, 2 tables, accepted for publication in PRC
Published: 2019
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34. Measurement of neutron and proton analyzing powers on $C$, $CH$, $CH_2$ and $Cu$ targets in the momentum region 3-4.2 GeV/c

Author: Basilev, S. N., Bushuev, Yu. P., Gavrishchuk, O. P., Glagolev, V. V., Kirillov, D. A., Kostayeva, N. V., Kovalenko, A. D., Legostaeva, K. S., Livanov, A. N., Philippov, I. A., Piskunov, N. M., Povtoreiko, A. A., Rukoyatkin, P. A., Shindin, R. A., Shipunov, A. V., Shutov, A. V., Sitnik, I. M., Slepnev, V. M., Slepnev, I. V., Terletskiy, A. V., Hamilton, K., Montgomery, R., Annand, J. R. M., Marchand, D., Wang, Y., Tomasi-Gustafsson, E., Perdrisat, C. F., Punjabi, V., Martinska, G., Urban, J., and Mušinsky, J.
Subjects: Nuclear Experiment, High Energy Physics - Experiment
Abstract: The analyzing powers for proton elastic scattering ($\vec p A\to pX$) and neutron charge exchange ($\vec n A\to p X$) reactions on nuclei have been measured on $ C$, $CH$, $CH_2$ and $Cu$ targets at incident neutron momenta 3.0 - 4.2 GeV/c by detecting one charged particle in forward direction. The polarized neutron measurements are the first of their kind. The experiment was performed using the Nuclotron accelerator in JINR Dubna, where polarized neutrons and protons were obtained from breakup of a polarized deuteron beam which has a maximum momentum of 13 GeV/c. The polarimeter ALPOM2 was used to obtain the analyzing power dependence on the transverse momentum of the final-state nucleon. These data have been used to estimate the figure of merit of a proposed experiment at Jefferson Laboratory to measure the recoiling neutron polarization in the quasi-elastic $^2H(\vec e,e'\vec n)$ reaction, which yields information on the charge and magnetic elastic form factors of the neutron., Comment: 14 pages and 19 figures
Published: 2019
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35. Cross Section for $\gamma n \to \pi^0 n$ measured at Mainz/A2

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

Author: Sokhoyan, V., Prakhov, S., Fix, A., Abt, S., Achenbach, P., Adlarson, P., Afzal, F., Aguar-Bartolomé, P., Ahmed, Z., Altangerel, K., Annand, J. R. M., Arends, H. J., Bantawa, K., Bashkanov, M., Beck, R., Biroth, M., Borisov, N. S., Braghieri, A., Briscoe, W. J., Cherepnya, S., Cividini, F., Collicott, C., Costanza, S., Denig, A., Dieterle, M., Downie, E. J., Drexler, P., Bondy, M. I. Ferretti, Fil'kov, L. V., Gardner, S., Garni, S., Glazier, D. I., Gorodnov, I., Gradl, W., Günther, M., Gurevich, G. M., Heijkenskjöld, L., Hornidge, D., Huber, G. M., Käser, A., Kashevarov, V. L., Kay, S., Keshelashvili, I., Kondratiev, R., Korolija, M., Krusche, B., Lazarev, A., Livingston, K., Lutterer, S., MacGregor, I. J. D., Macrae, R., Manley, D. M., Martel, P. P., McGeorge, J. C., Middleton, D. G., Miskimen, R., Mornacchi, E., Mullen, C., Mushkarenkov, A., Neganov, A., Neiser, A., Oberle, M., Ostrick, M., Otte, P. B., Paudyal, D., Pedroni, P., Powell, A., Rickert, E., Ron, G., Rostomyan, T., Sarty, A., Sfienti, C., Spieker, K., Steffen, O., Strakovsky, I. I., Strandberg, B., Strub, Th., Supek, I., Thiel, A., Thiel, M., Thomas, A., Unverzagt, M., Usov, Yu. A., Wagner, S., Walford, N. K., Watts, D. P., Werthmüller, D., Wettig, J., Witthauer, L., Wolfes, M., and Zachariou, N.
Subjects: Nuclear Experiment
Abstract: The beam-helicity asymmetry was measured, for the first time, in photoproduction of $\pi^{0}\eta$ pairs on carbon, aluminum, and lead, with the A2 experimental setup at MAMI. The results are compared to an earlier measurement on a free proton and to the corresponding theoretical calculations. The Mainz model is used to predict the beam-helicity asymmetry for the nuclear targets. The present results indicate that the photoproduction mechanism for $\pi^{0}\eta$ pairs on nuclei is similar to photoproduction on a free nucleon. This process is dominated by the $D_{33}$ partial wave with the $\eta\Delta(1232)$ intermediate state., Comment: Accepted for publication in Physics Letters B (2020)
Published: 2019
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37. Physics with Positron Beams at Jefferson Lab 12 GeV

Author: Afanasev, A., Albayrak, I., Ali, S., Amaryan, M., D'Angelo, A., Annand, J., Arrington, J., Asaturyan, A., Avakian, H., Averett, T., Barion, L., Battaglieri, M., Bellini, V., Berdnikov, V., Bernauer, J., Biselli, A., Boer, M., Bondì, M., Brinkmann, K. -T., Briscoe, B., Burkert, V., Camsonne, A., Cao, T., Cardman, L., Carmignotto, M., Causse, L., Celentano, A., Chatagnon, P., Ciullo, G., Contalbrigo, M., Day, D., Defurne, M., Diehl, S., Dongwi, B., Dupré, R., Dutta, D., Ehrhart, M., Elouadrhiri, L., Ent, R., Fernando, I., Filippi, A., Furletova, Y., Gao, H., Gasparian, A., Gaskell, D., Georges, F., Girod, F. -X., Grames, J., Gu, C., Guidal, M., Hamilton, D., Hasell, D., Higinbotham, D., Hoballah, M., Horn, T., Hyde, C., Italiano, A., Kalantarians, N., Kalicy, G., Keller, D., Keppel, C., Kerver, M., King, P., Kinney, E., Ko, H. -S., Kohl, M., Kubarovsky, V., Lanza, L., Lenisa, P., Liyanage, N., Liuti, S., Mamei, J., Marchand, D., Markowitz, P., Marsicano, L., Mazouz, M., McCaughan, M., McKinnon, B., Mihovilovič, M., Milner, R., Mkrtchyan, A., Mkrtchyan, H., Movsisyan, A., Camacho, C. Muñoz, Nadel-Turońs, P., De Napoli, M., Nazeer, J., Niccolai, S., Niculescu, G., Novotny, R., Pappalardo, L., Paremuzyan, R., Pasyuk, E., Patel, T., Pegg, I., Perera, D., Puckett, A., Randazzo, N., Rashad, M., Rathnayake, M., Rizzo, A., Roche, J., Rondon, O., Schmidt, A., Shabestari, M., Sharabian, Y., Širca, S., Sokhan, D., Somov, A., Sparveris, N., Stepanyan, S., Strakovsky, I., Tadevosyan, V., Tiefenback, M., Trotta, R., De Vita, R., Voskanyan, H., Voutier, E., Wang, R., Wojtsekhowski, B., Wood, S., Zaunick, H. -G., Zhamkochyan, S., Zhang, J., Zhao, S., Zheng, X., and Zorn, C.
Subjects: Nuclear Experiment, High Energy Physics - Experiment
Abstract: Positron beams, both polarized and unpolarized, are identified as essential ingredients for the experimental program at the next generation of lepton accelerators. In the context of the Hadronic Physics program at the Jefferson Laboratory (JLab), positron beams are complementary, even essential, tools for a precise understanding of the electromagnetic structure of the nucleon, in both the elastic and the deep-inelastic regimes. For instance, elastic scattering of (un)polarized electrons and positrons off the nucleon allows for a model independent determination of the electromagnetic form factors of the nucleon. Also, the deeply virtual Compton scattering of (un)polarized electrons and positrons allows us to separate unambiguously the different contributions to the cross section of the lepto-production of photons, enabling an accurate determination of the nucleon Generalized Parton Distributions (GPDs), and providing an access to its Gravitational Form Factors. Furthermore, positron beams offer the possibility of alternative tests of the Standard Model through the search of a dark photon or the precise measurement of electroweak couplings. This letter proposes to develop an experimental positron program at JLab to perform unique high impact measurements with respect to the two-photon exchange problem, the determination of the proton and the neutron GPDs, and the search for the $A^{\prime}$ dark photon., Comment: Letter-of-Intent to Jefferson Lab PAC46
Published: 2019

38. Measurement of the single-spin asymmetry $A_y^0$ in quasi-elastic $^3$He$^\uparrow$($e,e'n$) scattering at $0.4 < Q^2 < 1.0$ GeV$/c^2$

Author: Long, E., Zhang, Y. W., Mihoviloviv, M., Jin, G., Sulkosky, V., Kelleher, A., Anderson, B., Higinbotham, D. W., Sirca, S., Allada, K., Annand, J. R. M., Averett, T., Bertozzi, W., Boeglin, W., Bradshaw, P., Camsonne, A., Canan, M., Cates, G. D., Chen, C., Chen, J. -P., Chudakov, E., De Leo, R., Deng, X., Deur, A., Dutta, C., Fassi, L. El, Flay, D., Frullani, S., Garibaldi, F., Gao, H., Gilad, S., Gilman, R., Glamazdin, O., Golge, S., Gomez, J., Hansen, J. -O., Holmstrom, T., Huang, J., Ibrahim, H., de Jager, C. W., Jensen, E., Jiang, X., Jones, M., Kang, H., Katich, J., Khanal, H. P., King, P. M., Korsch, W., LeRose, J., Lindgren, R., Lu, H. -J., Luo, W., Markowitz, P., Meziane, M., Michaels, R., Moffit, B., Monaghan, P., Muangma, N., Nanda, S., Norum, B. E., Pan, K., Parno, D., Piasetzky, E., Posik, M., Punjabi, V., Puckett, A. J. R., Qian, X., Qiang, Y., Qui, X., Riordan, S., Saha, A., Sawatzky, B., Shabestari, M., Shahinyan, A., Shoenrock, B., John, J. St., Subedi, R., Tobias, W. A., Tireman, W., Urciuoli, G. M., Wang, D., Wang, K., Wang, Y., Watson, J., Wojtsekhowski, B., Ye, Z., Zhan, X., Zhang, Y., Zheng, X., Zhao, B., and Zhu, L.
Subjects: Nuclear Experiment
Abstract: Due to the lack of free neutron targets, studies of the structure of the neutron are typically made by scattering electrons from either $^2$H or $^3$He targets. In order to extract useful neutron information from a $^3$He target, one must understand how the neutron in a $^3$He system differs from a free neutron by taking into account nuclear effects such as final state interactions and meson exchange currents. The target single spin asymmetry $A_y^0$ is an ideal probe of such effects, as any deviation from zero indicates effects beyond plane wave impulse approximation. New measurements of the target single spin asymmetry $A_y^0$ at $Q^2$ of 0.46 and 0.96 (GeV/$c)^2$ were made at Jefferson Lab using the quasi-elastic $^3\mathrm{He}^{\uparrow}(e,e'n)$ reaction. Our measured asymmetry decreases rapidly, from $>20\%$ at $Q^2=0.46$ (GeV/$c)^2$ to nearly zero at $Q^2=0.96$ (GeV$/c)^2$, demonstrating the fall-off of the reaction mechanism effects as $Q^2$ increases. We also observed a small $\epsilon$-dependent increase in $A_y^0$ compared to previous measurements, particularly at moderate $Q^2$. This indicates that upcoming high $Q^2$ measurements from the Jefferson Lab 12 GeV program can cleanly probe neutron structure from polarized $^3$He using plane wave impulse approximation., Comment: 6 pages, 5 figures
Published: 2019
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39. Probing for high momentum protons in $^4$He via the $^4He(e,e'p)X$ reaction

Author: Iqbal, S., Benmokhtar, F., Ivanov, M., See, N., Aniol, K., Higinbotham, D. W., Boyd, C., Gadsby, A., Gilad, S., Saha, A., Udias, J. M., Goodwill, J. S., Finton, D., Boyer, A., Ye, Z., Solvignon, P., Aguilera, P., Ahmed, Z., Albataineh, H., Allada, K., Anderson, B., Anez, D., Annand, J., Arrington, J., Averett, T., Baghdasaryan, H., Bai, X., Beck, A., Beck, S., Bellini, V., Camsonne, A., Chen, C., Chen, J. -P., Chirapatpimol, K., Cisbani, E., Dalton, M. M., Daniel, A., Day, D., Deconinck, W., Defurne, M., Flay, D., Fomin, N., Friend, M., Frullani, S., Fuchey, E., Garibaldi, F., Gaskell, D., Gilman, R., Glamazdin, S., Gu, C., Gueye, P., Hanretty, C., Hansen, J. -O., Shabestari, M. Hashemi, Huang, M., Jin, G., Kalantarians, N., Kang, H., Kelleher, A., Korover, I., LeRose, J., Leckey, J., Lindgren, R., Long, E., Mammei, J., Margaziotis, D. J., Markowitz, P., Meekins, D., Meziani, Z., Michaels, R., Mihovilovic, M., Muangma, N., Camacho, C. Munoz, Norum, B., Nuruzzaman, Nuruzzaman, Pan, K., Phillips, S., Piasetzky, E., Pomerantz, I., Posik, M., Punjabi, V., Qian, X., Qiang, Y., Qiu, X., Reimer, P. E., Rakhman, A ., Riordan, S., Ron, G., Rondon-Aramayo, O., Selvy, L., Shahinyan, A., Shneor, R., Sirca, S., Slifer, K., Sparveris, N., Subedi, R., Sulkosky, V., Wang, D., Watson, J. W., Weinstein, L. B., Wojtsekhowski, B., Wood, S. A., Yaron, I., Zhan, X., Zhang, J., Zhang, Y. W., Zhao, B., Zheng, X., Zhu, P., and Zielinski, R.
Subjects: Nuclear Experiment
Abstract: Experimental cross sections for the $^4He(e,e'p)X$ reaction up to a missing momentum of 0.632 GeV/$c$ at $x_B=1.24$ and $Q^2$=2(GeV/$c$)$^2$ are reported. The data are compared to Relativistic Distorted Wave Impulse Approximation(RDWIA) calculations for $^4He(e,e'p)^3H$ channel. Significantly more events in the triton mass region are measured for $p_{m}$$>$0.45 GeV/$c$ than are predicted by the theoretical model, suggesting that the effects of initial-state multi-nucleon correlations are stronger than expected by the RDWIA model., Comment: Submitted to PRC
Published: 2019

40. Decay pion spectroscopy: a new approach

Author: Margaryan, A., Ajvazyan, R., Grigoryan, N., Kakoyan, V., Khacatryan, V., Vardanyan, H., Zhamkochyan, S., Achenbach, P., Pochodzalla, J., Nakamura, S. N., Nagao, S., Toyama, Y., Annand, J. R. M., Livingston, K., and Montgomery, R.
Subjects: Nuclear Experiment
Abstract: We propose a new experiment for decay pion spectroscopy of light hypernuclei at electron- and proton-beam facilities, using the recoil distance technique for separation of produced hypernuclei and a magnetic spectrometer for precise measurement of the decay pion momentum. Low-pressure MWPCs are advocated for low-energy recoil detection as they provide position and time information and are highly insensitive to gamma-ray and electron background. The position and timing characteristics of such a recoil detector were studied using ~5 MeV {\alpha}-particles. By using the present proposed approach the rate of the detected hypernuclei can be increased by one-to-two orders of magnitude compared to a recent experiment carried out at the MAMI electron accelerator in Mainz. The possibility of realizing a high luminosity decay pion spectroscopy experiment with proton beams is also discussed., Comment: 29 pages, 15 figures
Published: 2019
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41. Deep exclusive electroproduction of $π^0$ at high $Q^2$ in the quark valence regime

Author: Collaboration, The Jefferson Lab Hall A, Dlamini, M, Karki, B, Ali, SF, Lin, P-J, Georges, F, Ko, H-S, Israel, N, Rashad, MNH, Stefanko, A, Adikaram, D, Ahmed, Z, Albataineh, H, Aljawrneh, B, Allada, K, Allison, S, Alsalmi, S, Androic, D, Aniol, K, Annand, J, Atac, H, Averett, T, Gayoso, C Ayerbe, Bai, X, Bane, J, Barcus, S, Bartlett, K, Bellini, V, Beminiwattha, R, Bericic, J, Biswas, D, Brash, E, Bulumulla, D, Campbell, J, Camsonne, A, Carmignotto, M, Castellano, J, Chen, C, Chen, J-P, Chetry, T, Christy, ME, Cisbani, E, Clary, B, Cohen, E, Compton, N, Cornejo, JC, Dusa, S Covrig, Crowe, B, Danagoulian, S, Danley, T, Persio, F De, Deconinck, W, Defurne, M, Desnault, C, Di, D, Duer, M, Duran, B, Ent, R, Fanelli, C, Franklin, G, Fuchey, E, Gal, C, Gaskell, D, Gautam, T, Glamazdin, O, Gnanvo, K, Gray, VM, Gu, C, Hague, T, Hamad, G, Hamilton, D, Hamilton, K, Hansen, O, Hauenstein, F, Henry, W, Higinbotham, DW, Holmstrom, T, Horn, T, Huang, Y, Huber, GM, Hyde, C, Ibrahim, H, Jen, C-M, Jin, K, Jones, M, Kabir, A, Keppel, C, Khachatryan, V, King, PM, Li, S, Li, W, Liu, J, Liu, H, Liyanage, A, Magee, J, Malace, S, Mammei, J, Markowitz, P, McClellan, E, and Meddi, F
Subjects: hep-ex, nucl-ex
Abstract: We report measurements of the exclusive neutral pion electroproduction crosssection off protons at large values of $x_B$ (0.36, 0.48 and 0.60) and $Q^2$(3.1 to 8.4 GeV$^2$) obtained from Jefferson Lab Hall A experiment E12-06-014.The corresponding structure functions $d\sigma_L/dt+\epsilon d\sigma_T/dt$,$d\sigma_{TT}/dt$, $d\sigma_{LT}/dt$ and $d\sigma_{LT'}/dt$ are extracted as afunction of the proton momentum transfer $t-t_{min}$. The results suggest theamplitude for transversely polarized virtual photons continues to dominate thecross-section throughout this kinematic range. The data are well described bycalculations based on transversity Generalized Parton Distributions coupled toa helicity flip Distribution Amplitude of the pion, thus providing a unique wayto probe the structure of the nucleon.
Published: 2020

42. Response of a Li-glass/multi-anode photomultiplier detector to $\alpha$-particles from $^{241}$Am

Author: Rofors, E., Perrey, H., Jebali, R. Al, Annand, J. R. M., Boyd, L., Clemens, U., Desert, S., Engels, R., Fissum, K. G., Frielinghaus, H., Gheorghe, C., Hall-Wilton, R., Jaksch, S., Jalgén, A., Kanaki, K., Kemmerling, G., Maulerova, V., Mauritzson, N., Montgomery, R., Scherzinger, J., and Seitz, B.
Subjects: Physics - Instrumentation and Detectors, Nuclear Experiment
Abstract: The response of a position-sensitive Li-glass scintillator detector to $\alpha$-particles from a collimated $^{241}$Am source scanned across the face of the detector has been measured. Scintillation light was read out by an 8 X 8 pixel multi-anode photomultiplier and the signal amplitude for each pixel has been recorded for every position on a scan. The pixel signal is strongly dependent on position and in general several pixels will register a signal (a hit) above a given threshold. The effect of this threshold on hit multiplicity is studied, with a view to optimize the single-hit efficiency of the detector., Comment: 23 pages, 7 figures, to be submitted to Nuclear Instruments and Methods in Physics Research Section A
Published: 2018
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43. Near-threshold $\pi^-$ photoproduction on the deuteron

Author: Strandberg, B., Fissum, K. G., Annand, J. R. M., Briscoe, W. J., Brudvik, J., Cividini, F., Clark, L., Downie, E. J., England, K., Feldman, G., Glazier, D. I., Hamilton, K., Hansen, K., Isaksson, L., Jebali, R. Al, Kovash, M. A., Kudryavtsev, A. E., Lensky, V., Lipschutz, S., Lundin, M., Meshkian, M., Middleton, D. G., Myers, L. S., O'Donnell, D., O'Rielly, G. V., Oussena, B., Preston, M. F., Schröder, B., Seitz, B., Strakovsky, I. I., Taragin, M., and Tarasov, V. E.
Subjects: Nuclear Experiment
Abstract: The first experimental investigation of the near-threshold cross section for incoherent $\pi^-$ photoproduction on the deuteron $\gamma$ d -> $\pi^-$ pp is presented. The experimental technique involved detection of the ~131 MeV gamma ray resulting from the radiative capture of photoproduced $\pi^-$ in the target. The total cross section has been measured using an unpolarized tagged-photon beam, a liquid-deuterium target, and three very large NaI(Tl) spectrometers. The data are compared to theoretical models that give insight into the elementary reaction $\gamma$ n -> $\pi^-$ p and pion-nucleon and nucleon-nucleon final-state interactions., Comment: 8 pages, 6 figures, to be submitted to Physical Review C
Published: 2018
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44. Experimental study of the $\gamma p\rightarrow K^0\Sigma^+$, $\gamma n\rightarrow K^0\Lambda$, and $\gamma n\rightarrow K^0 \Sigma^0$ reactions at the Mainz Microtron

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

Author: Käser, A., Dieterle, M., Witthauer, L., Abt, S., Achenbach, P., Adlarson, P., Afzal, F., Ahmed, Z., Ahrens, J., Annand, J. R. M., Arends, H. J., Bashkanov, M., Beck, R., Biroth, M., Borisov, N. S., Braghieri, A., Briscoe, W. J., Cividini, F., Collicott, C., Costanza, S., Denig, A., Downie, E. J., Drexler, P., Fix, A., Garni, S., Glazier, D. I., Gorodnov, I., Gradl, W., Günther, M., Gurevich, G. M., Heijkenskjöld, L., Hornidge, D., Huber, G. M., Kashevarov, V. L., Kay, S., Keshelashvili, I., Kondratiev, R., Korolija, M., Krusche, B., Lazarev, A. B., Lisin, V., Livingston, K., Lutterer, S., MacGregor, I. J. D., Manley, D. M., Martel, P. P., Metag, V., Meyer, W., Miskimen, R., Mornacchi, E., Mushkarenkov, A., Neganov, A. B., Neiser, A., Oberle, M., Ostrick, M., Otte, P. B., Paudyal, D., Pedroni, P., Polonski, A., Prakhov, S. N., Reicherz, G., Ron, G., Rostomyan, T., Sarty, A., Sfienti, C., Sokhoyan, V., Spieker, K., Steffen, O., Strakovsky, I. I., Strub, Th., Supek, I., Thiel, A., Thiel, M., Thomas, A., Unverzagt, M., Usov, Yu. A., Wagner, S., Walford, N. K., Watts, D. P., Werthmüller, D., Wettig, J., Wolfes, M., and Zana, L.
Subjects: Nuclear Experiment
Abstract: The helicity-dependent cross sections for the photoproduction of $\pi^0\eta$ pairs have been measured for the first time. The experiment was performed at the tagged photon facility of the Mainz MAMI accelerator with the combined Crystal Ball - TAPS calorimeter. The experiment used a polarized deuterated butanol target and a circularly polarized photon beam. This arrangement allowed the $\sigma_{1/2}$ (photon and target spin antiparallel) and $\sigma_{3/2}$ (parallel spins) components to be measured for quasi-free production of $\pi^0\eta$ pairs off protons and neutrons. The main finding is that the two helicity components contribute identically, within uncertainties, for both participant protons and neutrons. The absolute couplings for protons and neutrons are also identical. This means that nucleon resonances contributing to this reaction in the investigated energy range have almost equal electromagnetic helicity couplings, $A_{1/2}^{n,p}$ and $A_{3/2}^{n,p}$. Identical couplings for protons and neutrons are typical for $\Delta$ resonances and identical $A_{1/2}$ and $A_{3/2}$ components are only possible for $J\geq 3/2$ states, which constrains possible contributions of nucleon resonances., Comment: accepted for publication in Phys. Lett. B
Published: 2018
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46. Deuteron photodisintegration by polarized photons in the region of the $d^*(2380)$

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

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

Author: Mihovilovič, M., Jin, G., Long, E., Zhang, Y. -W., Allada, K., Anderson, B., Annand, J. R. M., Averett, T., Bertozzi, W., Boeglin, W., Bradshaw, P., Camsonne, A., Canan, M., Cates, G. D., Chen, C., Chen, J. P., Chudakov, E., De Leo, R., Deng, X., Deltuva, A., Deur, A., Dutta, C., Fassi, L. El, Flay, D., Frullani, S., Garibaldi, F., Gao, H., Gilad, S., Gilman, R., Glamazdin, O., Golak, J., Golge, S., Gomez, J., Hansen, O., Higinbotham, D. W., Holmstrom, T., Huang, J., Ibrahim, H., de Jager, C. W., Jensen, E., Jiang, X., Jones, M., Kamada, H., Kang, H., Katich, J., Khanal, H. P., Kievsky, A., King, P., Korsch, W., LeRose, J., Lindgren, R., Lu, H. -J., Luo, W., Marcucci, L. E., Markowitz, P., Meziane, M., Michaels, R., Moffit, B., Monaghan, P., Muangma, N., Nanda, S., Norum, B. E., Pan, K., Parno, D. S., Piasetzky, E., Posik, M., Punjabi, V., Puckett, A. J. R., Qian, X., Qiang, Y., Qui, X., Riordan, S., Saha, A., Sauer, P. U., Sawatzky, B., Schiavilla, R., Schoenrock, B., Shabestari, M., Shahinyan, A., Širca, S., Skibiński, R., John, J. St., Subedi, R., Sulkosky, V., Tireman, W., Tobias, W. A., Topolnicki, K., Urciuoli, G. M., Viviani, M., Wang, D., Wang, K., Wang, Y., Watson, J., Wojtsekhowski, B., Witała, H., Ye, Z., Zhan, X., Zhang, Y., Zheng, X., Zhao, B., Zhu, L., and Collaboration, The Jefferson Lab Hall A
Subjects: Nuclear Experiment
Abstract: We report on a precise measurement of double-polarization asymmetries in electron-induced breakup of $^3\mathrm{He}$ proceeding to $\mathrm{pd}$ and $\mathrm{ppn}$ final states, performed in quasi-elastic kinematics at $Q^2 = 0.25\,(\mathrm{GeV}/c)^2$ for missing momenta up to $250\,\mathrm{MeV}/c$. These observables represent highly sensitive tools to investigate the electromagnetic and spin structure of $^3\mathrm{He}$ and the relative importance of two- and three-body effects involved in the breakup reaction dynamics. The measured asymmetries cannot be satisfactorily reproduced by state-of-the-art calculations of $^3\mathrm{He}$ unless their three-body segment is adjusted, indicating that the spin-dependent part of the nuclear interaction governing the three-body breakup process is much smaller than previously thought., Comment: 5 pages, 3 figures, submitted to Phys. Rev. Lett
Published: 2018
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49. Compton Scattering from the Deuteron above Pion-Production Threshold

Author: Strandberg, B., Annand, J. R. M., Briscoe, W., Brudvik, J., Cividini, F., Clark, L., Downie, E. J., England, K., Feldman, G., Fissum, K. G., Glazier, D. I., Hamilton, K., Hansen, K., Isaksson, L., Jebali, R. Al, Kovash, M. A., Lipschutz, S., Lundin, M., Meshkian, M., Middleton, D. G., Myers, L. S., O'Donnell, D., O'Rielly, G., Oussena, B., Preston, M. F., Schröder, B., Seitz, B., Strakovsky, I., and Taragin, M.
Subjects: Nuclear Experiment
Abstract: The electromagnetic polarizabilities of the nucleon are fundamental nucleon-structure observables that characterize its response to external electromagnetic fields. The neutron polarizabilities can be accessed from Compton-scattering data on light nuclear targets. Recent measurements of the differential cross section for Compton scattering on the deuteron below the pion-production threshold have decreased the uncertainties in the neutron polarizabilities, yet the proton polarizabilities remain known substantially more accurately. As the sensitivity of the cross section to the polarizabilities increases with incident photon energy, measurements above the pion threshold may offer a way for an improved determination of the neutron polarizabilities. In this article, the first measurement of the cross section for Compton scattering on the deuteron above the pion-production threshold is presented., Comment: 6 pages, 4 figures, to be submitted to Physical Review C Rapid Communications
Published: 2018
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50. High-statistics measurement of the eta->3pi^0 decay at the Mainz Microtron

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