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372 results on '"Gurevich, G."'

1. 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

3. 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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4. 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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5. 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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6. 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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7. Study of the $\gamma p\to \pi^0\eta p$ reaction with the A2 setup at MAMI

Author

Sokhoyan, V., Prakhov, S., Fix, A., Abt, S., Achenbach, P., Adlarson, P., Afzal, F., Aguar-Bartolomé, P., Ahmed, Z., Ahrens, J., Annand, J. R. M., Arends, H. J., Bantawa, K., Bashkanov, M., Beck, R., Biroth, M., Borisov, N. S., Braghieri, A., Briscoe, W. J., Cherepnya, S., Cividini, F., Collicott, C., Costanza, S., Denig, A., Dieterle, M., Downie, E. J., Drexler, P., Bondy, M. I. Ferretti, Fil'kov, L. V., Gardner, S., Garni, S., Glazier, D. I., Glowa, D., Gorodnov, I., Gradl, W., Günther, M., Gurevich, G. M., Hamill, C. B., Heijkenskjöld, L., Hornidge, D., Huber, G. M., Jude, T. C., Käser, A., Kashevarov, V. L., Kay, S., Keshelashvili, I., Kondratiev, R., Korolija, M., Krusche, B., Lazarev, A., Linturi, J., Lisin, V., Livingston, K., Lutterer, S., MacGregor, I. J. D., Macrae, R., Manley, D. M., Martel, P. P., McGeorge, J. C., McNicoll, E. F., Middleton, D. G., Miskimen, R., Mornacchi, E., Mullen, C., Mushkarenkov, A., Neganov, A., Neiser, A., Nikolaev, A., Oberle, M., Ostrick, M., Ott, P., Otte, P. B., Paudyal, D., Pedroni, P., Polonski, A., Rajabi, A., Robinson, J., Ron, G., Rosner, G., Rostomyan, T., Sarty, A., Sfienti, C., Sikora, M. H., Spieker, K., Steffen, O., Strakovsky, I. I., Strandberg, B., Strub, Th., Supek, I., Thiel, A., Thiel, M., Thomas, A., Unverzagt, M., Usov, Yu. A., Wagner, S., Walford, N. K., Watts, D. P., Werthmüller, D., Wettig, J., Witthauer, L., Wolfes, M., and Zana, L. A.

Subjects
Nuclear Experiment
Abstract

The data available from the A2 Collaboration at MAMI were analyzed to select the $\gamma p\to \pi^0\eta p$ reaction on an event-by-event basis, which allows for partial-wave analyses of three-body final states to obtain more reliable results, compared to fits to measured distributions. These data provide the world's best statistical accuracy in the energy range from threshold to $E_{\gamma}=1.45$ GeV, allowing a finer energy binning in the measurement of all observables needed for understanding the reaction dynamics. The results obtained for the measured observables are compared to existing models, and the impact from the new data is checked by the fit with the revised Mainz model., Comment: 15 pages, 18 figures

Published
2018
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8. Measurement of the decay $\eta^{\prime}\to\pi^{0}\pi^{0}\eta$ at MAMI

Author

Adlarson, P., Afzal, F., Akondi, C. S., Annand, J. R. M., Arends, H. J., Beck, R., Borisov, N., Braghieri, A., Briscoe, W. J., Cividini, F., Collicott, C., Costanza, S., Denig, A., Downie, E. J., Dieterle, M., Bondy, M. I. Ferretti, Gardner, S., Garni, S., Glazier, D. I., Glowa, D., Gradl, W., Gurevich, G., Hamilton, D. J., Hornidge, D., Huber, G. M., Käser, A., Kashevarov, V. L., Kay, S., Keshelashvili, I., Kondratiev, R., Korolija, M., Krusche, B., Lazarev, A., Linturi, J., Livingston, K., MacGregor, I. J. D., Manley, D. M., Martel, P. P., McGeorge, J. C., Middleton, D. G., Miskimen, R., Mushkarenkov, A., Neganov, A., Neiser, A., Oberle, M., Ostrick, M., Ott, P., Otte, P. B., Oussena, B., Paudyal, D., Pedroni, P., Polonski, A., Prakhov, S., Rajabi, A., Ron, G., Rostomyan, T., Sarty, A., Sfienti, C., Sokhoyan, V., Spieker, K., Steffen, O., Strakovsky, I. I., Strub, T., Supek, I., Thiel, A., Thiel, M., Tiator, L., Thomas, A., Unverzagt, M., Usov, Y. A., Wagner, S., Watts, D. P., Werthmüller, D., Wettig, J., Witthauer, L., Wolfes, M., Workman, R. L., and Zana, L. A.

Subjects
High Energy Physics - Experiment
Abstract

An experimental study of the $\eta'\to \pi^0\pi^0\eta \to 6\gamma$ decay has been conducted with the best up-to-date statistical accuracy, by measuring $\eta'$ mesons produced in the $\gamma p \to \eta' p$ reaction with the A2 tagged-photon facility at the Mainz Microtron, MAMI. The results obtained for the standard parametrization of the $\eta'\to \pi^0\pi^0\eta$ matrix element are consistent with the most recent results for $\eta'\to\pi\pi\eta$ decays, but have smaller uncertainties. The available statistics and experimental resolution allowed, for the first time, an observation of a structure below the $\pi^+\pi^-$ mass threshold, the magnitude and sign of which, checked within the framework of the nonrelativistic effective-field theory, demonstrated good agreement with the cusp that was predicted based on the $\pi\pi$ scattering length combination, $a_0-a_2$, extracted from $K \to 3\pi$ decays., Comment: 15 pages, 8 figures, 2 tables, accepted for publication in Phys. Rev. D

Published
2017
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9. First measurement of the polarization observable $E$ and helicity-dependent cross sections in single $\pi^{0}$ photoproduction from quasi-free nucleons

Author

Dieterle, M., Witthauer, L., Cividini, F., Abt, S., Achenbach, P., Adlarson, P., Afzal, F., Ahmed, Z., Akondi, C. S., Annand, J. R. M., Arends, H. J., Bashkanov, M., Beck, R., Biroth, M., Borisov, N. S., Braghieri, A., Briscoe, W. J., Costanza, S., Collicott, C., Denig, A., Downie, E. J., Drexler, P., Ferretti-Bondy, M. I., Gardner, S., Garni, S., Glazier, D. I., Glowa, D., Gradl, W., Günther, M., Gurevich, G. M., Hamilton, D., Hornidge, D., Huber, G. M., Käser, A., Kashevarov, V. L., Kay, S., Keshelashvili, I., Kondratiev, R., Korolija, M., Krusche, B., Lazarev, A. B., Linturi, J. M., Lisin, V., Livingston, K., Lutterer, S., MacGregor, I. J. D., Mancell, J., Manley, D. M., Martel, P. P., Metag, V., Meyer, W., Miskimen, R., Mornacchi, E., Mushkarenkov, A., Neganov, A. B., Neiser, A., Oberle, M., Ostrick, M., Otte, P. B., Paudyal, D., Pedroni, P., Polonski, A., Prakhov, S. N., Rajabi, A., Reicherz, G., Ron, G., Rostomyan, T., Sarty, A., Sfienti, C., Sikora, M. H., Sokhoyan, V., Spieker, K., Steffen, O., Strakovsky, I. I., Strub, Th., Supek, I., Thiel, A., Thiel, M., Thomas, A., Unverzagt, M., Usov, Yu. A., Wagner, S., Watts, N. K. Walford D. P., Werthmüller, D., Wettig, J., Wolfes, M., and Zana, L.

Subjects
Nuclear Experiment
Abstract

The double-polarization observable $E$ and the helicity-dependent cross sections $\sigma_{1/2}$ and $\sigma_{3/2}$ have been measured for the first time for single $\pi^{0}$ photoproduction from protons and neutrons bound in the deuteron at the electron accelerator facility MAMI in Mainz, Germany. The experiment used a circularly polarized photon beam and a longitudinally polarized deuterated butanol target. The reaction products, recoil nucleons and decay photons from the $\pi^0$ meson were detected with the Crystal Ball and TAPS electromagnetic calorimeters. Effects from nuclear Fermi motion were removed by a kinematic reconstruction of the $\pi^{0}N$ final state. A comparison to data measured with a free proton target showed that the absolute scale of the cross sections is significantly modified by nuclear final-state interaction (FSI) effects. However, there is no significant effect on the asymmetry $E$ since the $\sigma_{1/2}$ and $\sigma_{3/2}$ components appear to be influenced in a similar way. Thus, the best approximation of the two helicity-dependent cross sections for the free neutron is obtained by combining the asymmetry $E$ measured with quasi-free neutrons and the unpolarized cross section corrected for FSI effects under the assumption that the FSI effects are similar for neutrons and protons., Comment: accepted for publication in Phys. Lett. B

Published
2017
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10. Helicity-dependent cross sections and double-polarization observable E in eta photoproduction from quasi-free protons and neutrons

Author

Witthauer, L., Dieterle, M., Abt, S., Achenbach, P., Afzal, F., Ahmed, Z., Akondi, C. S., Annand, J. R. M., Arends, H. J., Bashkanov, M., Beck, R., Biroth, M., Borisov, N. S., Braghieri, A., Briscoe, W. J., Cividini, F., Costanza, S., Collicott, C., Denig, A., Downie, E. J., Drexler, P., Ferretti-Bondy, M. I., Gardner, S., Garni, S., Glazier, D. I., Glowa, D., Gradl, W., Günther, M., Gurevich, G. M., Hamilton, D., Hornidge, D., Huber, G. M., Käser, A., Kashevarov, V. L., Kay, S., Keshelashvili, I., Kondratiev, R., Korolija, M., Krusche, B., Lazarev, A. B., Linturi, J. M., Lisin, V., Livingston, K., Lutterer, S., MacGregor, I. J. D., Mancell, J., Manley, D. M., Martel, P. P., Metag, V., Meyer, W., Miskimen, R., Mornacchi, E., Mushkarenkov, A., Neganov, A. B., Neiser, A., Oberle, M., Ostrick, M., Otte, P. B., Paudyal, D., Pedroni, P., Polonski, A., Prakhov, S. N., Rajabi, A., Reicherz, G., Ron, G., Rostomyan, T., Sarty, A., Sfienti, C., Sikora, M. H., Sokhoyan, V., Spieker, K., Steffen, O., Strakovsky, I. I., Strub, Th., Supek, I., Thiel, A., Thiel, M., Thomas, A., Unverzagt, M., Usov, Yu. A., Wagner, S., Walford, N. K., Watts, D. P., Werthmüller, D., Wettig, J., Wolfes, M., and Zana, L.

Subjects
Nuclear Experiment
Abstract

Precise helicity-dependent cross sections and the double-polarization observable $E$ were measured for $\eta$ photoproduction from quasi-free protons and neutrons bound in the deuteron. The $\eta\rightarrow 2\gamma$ and $\eta\rightarrow 3\pi^0\rightarrow 6\gamma$ decay modes were used to optimize the statistical quality of the data and to estimate systematic uncertainties. The measurement used the A2 detector setup at the tagged photon beam of the electron accelerator MAMI in Mainz. A longitudinally polarized deuterated butanol target was used in combination with a circularly polarized photon beam from bremsstrahlung of a longitudinally polarized electron beam. The reaction products were detected with the electromagnetic calorimeters Crystal Ball and TAPS, which covered 98\% of the full solid angle. The results show that the narrow structure observed earlier in the unpolarized excitation function of $\eta$ photoproduction off the neutron appears only in reactions with antiparallel photon and nucleon spin ($\sigma_{1/2}$). It is absent for reactions with parallel spin orientation ($\sigma_{3/2}$) and thus very probably related to partial waves with total spin 1/2. The behavior of the angular distributions of the helicity-dependent cross sections was analyzed by fitting them with Legendre polynomials. The results are in good agreement with a model from the Bonn-Gatchina group, which uses an interference of $P_{11}$ and $S_{11}$ partial waves to explain the narrow structure., Comment: accepted for publication in Phys. Rev. C

Published
2017
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11. Insight into the narrow structure in {\boldmath{$\eta$}}-photoproduction on the neutron from helicity dependent cross sections

Author

Witthauer, L., Dieterle, M., Abt, S., Achenbach, P., Afzal, F., Ahmed, Z., Annand, J. R. M., Arends, H. J., Bashkanov, M., Beck, R., Biroth, M., Borisov, N. S., Braghieri, A., Briscoe, W. J., Cividini, F., Costanza, S., Collicott, C., Denig, A., Downie, E. J., Drexler, P., Ferretti-Bondy, M. I., Gardner, S., Garni, S., Glazier, D. I., Glowa, D., Gradl, W., Günther, M., Gurevich, G. M., Hamilton, D., Hornidge, D., Huber, G. M., Käser, A., Kashevarov, V. L., Kay, S., Keshelashvili, I., Kondratiev, R., Korolija, M., Krusche, B., Lazarev, A. B., Linturi, J. M., Lisin, V., Livingston, ., Lutterer, S., MacGregor, I. J. D., Mancell, J., Manley, D. M., Martel, P. P., Metag, V., Meyer, W., Miskimen, R., Mornacchi, E., Mushkarenkov, A., Neganov, A. B., Neiser, A., Oberle, M., Ostrick, M., Otte, P. B., Paudyal, D., Pedroni, P., Polonski, A., Prakhov, S. N., Rajabi, A., Reicherz, G., Ron, G., Rostomyan, T., Sarty, A., Sfienti, C., Sikora, M. H., Sokhoyan, V., Spieker, K., Steffen, O., Strakovsky, I. I., Strub, Th., Supek, I., Thiel, A., Thiel, M., Thomas, A., Unverzagt, M., Usov, Yu. A., Wagner, S., Walford, N. K., Watts, D. P., Werthmüller, D., Wettig, J., Wolfes, M., and Zana, L.

Subjects
Nuclear Experiment
Abstract

The double polarization observable $E$ and the helicity dependent cross sections $\sigma_{1/2}$ and $\sigma_{3/2}$ were measured for $\eta$ photoproduction from quasi-free protons and neutrons. The circularly polarized tagged photon beam of the A2 experiment at the Mainz MAMI accelerator was used in combination with a longitudinally polarized deuterated butanol target. The almost $4\pi$ detector setup of the Crystal Ball and TAPS is ideally suited to detect the recoil nucleons and the decay photons from $\eta\rightarrow 2\gamma$ and $\eta\rightarrow 3\pi^0$. The results show that the narrow structure previously observed in $\eta$ photoproduction from the neutron is only apparent in $\sigma_{1/2}$ and hence, most likely related to a spin-1/2 amplitude. Nucleon resonances that contribute to this partial wave in $\eta$ production are only $N1/2^-$ ($S_{11}$) and $N1/2^+$ ($P_{11}$). Furthermore, the extracted Legendre coefficients of the angular distributions for $\sigma_{1/2}$ are in good agreement with recent reaction model predictions assuming a narrow resonance in the $P_{11}$ wave as the origin of this structure.

Published
2017
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12. Study of $\eta$ and $\eta'$ photoproduction at MAMI

Author

Kashevarov, V. L., Ott, P., Prakhov, S., Adlarson, P., Afzal, F., Ahmed, Z., Akondi, C. S., Annand, J. R. M., Arends, H. J., Beck, R., Braghieri, A., Briscoe, W. J., Cividini, F., Codling, R., Collicott, C., Costanza, S., Denig, A., Downie, E. J., Dieterle, M., Bondy, M. I. Ferretti, Filkov, L. V., Fix, A., Gardner, S., Garni, S., Glazier, D. I., Glowa, D., Gradl, W., Gurevich, G., Hamilton, D. J., Hornidge, D., Howdle, D., Huber, G. M., Kaeser, A., Kay, S., Keshelashvili, I., Kondratiev, R., Korolija, M., Krusche, B., Linturi, J., Lisin, V., Livingston, K., MacGregor, I. J. D., MacRae, R., Mancell, J., Manley, D. M., Martel, P. P., McGeorge, J. C., McNicol, E., Middleton, D. G., Miskimen, R., Mornacchi, E., Mullen, C., Mushkarenkov, A., Neiser, A., Oberle, M., Ostrick, M., Otte, P. B., Oussena, B., Paudyal, D., Pedroni, P., Polyanski, V. V., Rajabi, A., Robinson, J., Rosner, G., Rostomyan, T., Sarty, A., Schott, D. M., Schumann, S., Sfienti, C., Sokhoyan, V., Spieker, K., Steffen, O., Strandberg, B., Strakovsky, I. I., Strub, Th., Supek, I., Taragin, M. F., Thiel, A., Thiel, M., Tiator, L., Thomas, A., Unverzagt, M., Wagner, S., Watts, D. P., Werthmueller, D., Wettig, J., Witthauer, L., Wolfes, M., Workman, R. L., and Zana, L.

Subjects
Nuclear Experiment, High Energy Physics - Experiment, High Energy Physics - Phenomenology
Abstract

The reactions $\gamma p\to \eta p$ and $\gamma p\to \eta' p$ have been measured from their thresholds up to the center-of-mass energy $W=1.96$GeV with the tagged-photon facilities at the Mainz Microtron, MAMI. Differential cross sections were obtained with unprecedented accuracy, providing fine energy binning and full production-angle coverage. A strong cusp is observed in the total cross section and excitation functions for $\eta$ photoproduction at the energies in vicinity of the $\eta'$ threshold, $W=1896$MeV ($E_\gamma=1447$MeV). This behavior is explained in a revised $\eta$MAID isobar model by a significant branching of the $N(1895)1/2^-$ nucleon resonance to both, $\eta p$ and $\eta' p$, confirming the existence and constraining the properties of this poorly known state.

Published
2017
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13. Measurement of the pi^0 -> e^+e^-gamma Dalitz decay at the Mainz Microtron

Author

Adlarson, P., Afzal, F., Aguar-Bartolomé, P., Ahmed, Z., Akondi, C. S., Annand, J. R. M., Arends, H. J., Bantawa, K., Beck, R., Berghäuser, H., Biroth, M., Borisov, N. S., Braghieri, A., Briscoe, W. J., Cherepnya, S., Cividini, F., Collicott, C., Costanza, S., Denig, A., Dieterle, M., Downie, E. J., Drexler, P., Bondy, M. I. Ferretti, Fil'kov, L. V., Gardner, S., Garni, S., Glazier, D. I., Glowa, D., Gradl, W., Gurevich, G. M., Hamilton, D. J., Hornidge, D., Huber, G. M., Jude, T. C., Käser, A., Kashevarov, V. L., Kay, S., Keshelashvili, I., Kondratiev, R., Korolija, M., Krusche, B., Kulikov, V. V., Lazarev, A., Linturi, J., Lisin, V., Livingston, K., MacGregor, I. J. D., Macrae, R., Manley, D. M., Martel, P. P., Martemianov, M., McGeorge, J. C., McNicoll, E. F., Metag, V., Middleton, D. G., Miskimen, R., Mornacchi, E., Mullen, C., Mushkarenkov, A., Neganov, A., Neiser, A., Nikolaev, A., Oberle, M., Ostrick, M., Ott, P., Otte, P. B., Paudyal, D., Pedroni, P., Polonski, A., Prakhov, S., Rajabi, A., Robinson, J., Ron, G., Rosner, G., Rostomyan, T., Sfienti, C., Sikora, M. H., Sokhoyan, V., Spieker, K., Steffen, O., Strakovsky, I. I., Strandberg, B., Strub, Th., Supek, I., Thiel, A., Thiel, M., Thomas, A., Unverzagt, M., Usov, Yu. A., Wagner, S., Walford, N., Watts, D. P., Werthmüller, D., Wettig, J., Witthauer, L., Wolfes, M., and Zana, L. A.

Subjects
High Energy Physics - Experiment, Nuclear Experiment
Abstract

The Dalitz decay pi^0 -> e^+e^-gamma has been measured in the gamma p -> pi^0 p reaction with the A2 tagged-photon facility at the Mainz Microtron, MAMI. The value obtained for the slope parameter of the pi^0 electromagnetic transition form factor, a_pi = 0.030+/-0.010_tot, is in agreement with existing measurements of this decay and with recent theoretical calculations. The uncertainty obtained in the value of a_pi is lower than in previous results based on the pi^0 -> e^+e^-gamma decay., Comment: 11 pages, 7 figures, 1 table

Published
2016
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14. Determination of the scalar polarizabilities of the proton using beam asymmetry $\Sigma_{3}$ in Compton scattering

Author

Sokhoyan, V., Downie, E. J., Mornacchi, E., McGovern, J. A., Krupina, N., Afzal, F., Ahrens, J., Akondi, C. S., Annand, J. R. M., Arends, H. J., Beck, R., Braghieri, A., Briscoe, W. J., Cividini, F., Collicott, C., Costanza, S., Denig, A., Dieterle, M., Ferretti, M., Gardner, S., Garni, S., Glazier, D. I., Glowa, D., Gradl, W., Gurevich, G., Hamilton, D., Hornidge, D., Huber, G. M., Käser, A., Kashevarov, V. L., Keshelashvili, I., Kondratiev, R., Korolija, M., Krusche, B., Lensky, V., Linturi, J., Lisin, V., Livingston, K., MacGregor, I. J. D., Macrae, R., Manley, D. M., Martel, P. P., Middleton, D. G., Miskimen, R., Mushkarenkov, A., Neiser, A., Oberle, M., Spina, H. Ortega, Ostrick, M., Ott, P., Otte, P. B., Oussena, B., Paudyal, D., Pedroni, P., Polonski, A., Polyansky, V., Prakhov, S., Rajabi, A., Rostomyan, T., Sarty, A., Schumann, S., Steffen, O., Strakovsky, I. I., Strandberg, B., Strub, T., Supek, I., Thiel, M., Thomas, A., Unverzagt, M., Wagner, S., Watts, D. P., Wettig, J., Witthauer, L., Werthmüller, D., Wolfes, M., and Zana, L.

Subjects
Nuclear Experiment
Abstract

The scalar dipole polarizabilities, $\alpha_{E1}$ and $\beta_{M1}$, are fundamental properties related to the internal dynamics of the nucleon. The currently accepted values of the proton polarizabilities were determined by fitting to unpolarized proton Compton scattering cross section data. The measurement of the beam asymmetry $\Sigma_{3}$ in a certain kinematical range provides an alternative approach to the extraction of the scalar polarizabilities. At the Mainz Microtron (MAMI) the beam asymmetry was measured for Compton scattering below pion photoproduction threshold for the first time. The results are compared with model calculations and the influence of the experimental data on the extraction of the scalar polarizabilities is determined., Comment: 6 pages, 5 figures

Published
2016
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15. Measurement of the omega -> pi^0 e^+e^- and eta -> e^+e^-g Dalitz decays with the A2 setup at MAMI

Author

Adlarson, P., Afzal, F., Aguar-Bartolomé, P., Ahmed, Z., Annand, J. R. M., Arends, H. J., Bantawa, K., Beck, R., Berghäuser, H., Biroth, M., Borisov, N. S., Braghieri, A., Briscoe, W. J., Cherepnya, S., Cividini, F., Collicott, C., Costanza, S., Danilkin, I. V., Denig, A., Dieterle, M., Downie, E. J., Drexler, P., Bondy, M. I. Ferretti, Fil'kov, L. V., Gardner, S., Garni, S., Glazier, D. I., Glowa, D., Gradl, W., Gurevich, G. M., Hamilton, D. J., Hornidge, D., Huber, G. M., Jude, T. C., Käser, A., Kashevarov, V. L., Kay, S., Keshelashvili, I., Kondratiev, R., Korolija, M., Krusche, B., Lazarev, A., Linturi, J., Lisin, V., Livingston, K., MacGregor, I. J. D., Macrae, R., Manley, D. M., Martel, P. P., McGeorge, J. C., McNicoll, E. F., Metag, V., Middleton, D. G., Miskimen, R., Mornacchi, E., Mullen, C., Mushkarenkov, A., Neganov, A., Neiser, A., Nikolaev, A., Oberle, M., Ostrick, M., Ott, P., Otte, P. B., Paudyal, D., Pedroni, P., Polonski, A., Prakhov, S., Rajabi, A., Robinson, J., Ron, G., Rosner, G., Rostomyan, T., Sfienti, C., Sikora, M. H., Sokhoyan, V., Spieker, K., Steffen, O., Strakovsky, I. I., Strandberg, B., Strub, Th., Supek, I., Thiel, A., Thiel, M., Thomas, A., Unverzagt, M., Usov, Yu. A., Wagner, S., Walford, N., Watts, D. P., Werthmüller, D., Wettig, J., Witthauer, L., Wolfes, M., and Zana, L. A.

Subjects
High Energy Physics - Experiment, Nuclear Experiment
Abstract

The Dalitz decays eta -> e^+e^-g and omega -> pi^0 e^+e^- have been measured in the g p -> eta p and g p -> omega p reactions, respectively, with the A2 tagged-photon facility at the Mainz Microtron, MAMI. The value obtained for the slope parameter of the electromagnetic transition form factor of eta, Lambda^{-2}_eta=(1.97+/-0.11_tot) GeV^{-2}, is in good agreement with previous measurements of the eta -> e^+e^-g and eta -> mu^+mu^-g decays. The uncertainty obtained in the value of Lambda^{-2}_eta is lower than in previous results based on the eta -> e^+e^-g decay. The value obtained for the omega slope parameter, Lambda^{-2}_omega_pi^0 = (1.99+/-0.21_tot) GeV^{-2}, is somewhat lower than previous measurements based on omega -> pi^0 mu^+mu^-, but the results for the omega transition form factor are in better agreement with theoretical calculations, compared to earlier experiments., Comment: 19 figures, 2 tables

Published
2016
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16. Photon asymmetry measurements of $\overrightarrow{\gamma} \mathrm{p} \rightarrow \pi^{0} \mathrm{p}$ for E$_{\gamma}$=320$-$650 MeV

Author

Gardner, S., Howdle, D., Sikora, M. H., Wunderlich, Y., Abt, S., Achenbach, P., Afzal, F., Aguar-Bartolome, P., Ahmed, Z., Annand, J. R. M., Arends, H. J., Bantawa, K., Bashkanov, M., Beck, R., Biroth, M., Borisov, N. S., Braghieri, A., Briscoe, W. J., Cherepnya, S., Cividini, F., Costanza, S., Collicott, C., Demissie, B. T., Denig, A., Dieterle, M., Downie, E. J., Drexler, P., Ferretti-Bondy, M. I., Filkov, L. V., Glazier, D. I., Garni, S., Gradl, W., Günther, M., Gurevich, G. M., Hamilton, D., Heid, E., Hornidge, D., Huber, G. M., Jahn, O., Jude, T. C., Käser, A., Kay, S., Kashevarov, V. L., Keshelashvili, I., Kondratiev, R., Korolija, M., Krusche, B., Linturi, J. M., Lisin, V., Livingston, K., Lutterer, S., MacGregor, I. J. D., Macrae, R., Mancell, J., Manley, D. M., Martel, P. P., McGeorge, J. C., McNicoll, E. F., Middleton, D. G., Miskimen, R., Mullen, C., Mushkarenkov, A., Neganov, A. B., Neiser, A., Nikolaev, A., Oberle, M., Ostrick, M., Owens, R. O., Otte, P. B., Oussena, B., Paudyal, D., Pedroni, P., Polonski, A., Prakhov, S., Rajabi, A., Robinson, J., Rosner, G., Rostomyan, T., Sarty, A., Schumann, S., Sokhoyan, V., Spieker, K., Steffen, O., Sfienti, C., Strakovsky, I. I., Strandberg, B., Strub, Th., Supek, I., Tarbert, C. M., Thiel, A., Thiel, M., Thomas, A., Unverzagt, M., Usov, Yu. A., Watts, D. P., Werthmüller, D., Wettig, J., Wolfes, M., Witthauer, L., and Zana, L.

Subjects
Nuclear Experiment
Abstract

High statistics measurements of the photon asymmetry $\mathrm{\Sigma}$ for the $\overrightarrow{\gamma}$p$\rightarrow\pi^{0}$p reaction have been made in the center of mass energy range W=1214-1450 MeV. The data were measured with the MAMI A2 real photon beam and Crystal Ball/TAPS detector systems in Mainz, Germany. The results significantly improve the existing world data and are shown to be in good agreement with previous measurements, and with the MAID, SAID, and Bonn-Gatchina predictions. We have also combined the photon asymmetry results with recent cross-section measurements from Mainz to calculate the profile functions, $\check{\mathrm{\Sigma}}$ (= $\sigma_{0}\mathrm{\Sigma}$), and perform a moment analysis. Comparison with calculations from the Bonn-Gatchina model shows that the precision of the data is good enough to further constrain the higher partial waves, and there is an indication of interference between the very small $F$-waves and the $N(1520) 3/2^{-}$ and $N(1535) 1/2^{-}$ resonances.

Published
2016
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17. Measurement of pi^0 photoproduction on the proton at MAMI C

Author

Adlarson, P., Afzal, F., Akondi, C. S., Annand, J. R. M., Arends, H. J., Azimov, Ya. I., Beck, R., Borisov, N., Braghieri, A., Briscoe, W. J., Cherepnya, S., Cividini, F., Collicott, C., Costanza, S., Denig, A., Downie, E. J., Dieterle, M., Bondy, M. I. Ferretti, Fil'kov, L. V., Fix, A., Gardner, S., Garni, S., Glazier, D. I., Glowa, D., Gradl, W., Gurevich, G., Hamilton, D. J., Hornidge, D., Huber, G. M., Käser, A., Kashevarov, V. L., Kay, S., Keshelashvili, I., Kondratiev, R., Korolija, M., Krusche, B., Kulikov, V. V., Lazarev, A., Linturi, J., Lisin, V., Livingston, K., MacGregor, I. J. D., Manley, D. M., Martel, P. P., Martemianov, M., McGeorge, J. C., Meyer, W., Middleton, D. G., Miskimen, R., Mushkarenkov, A., Neganov, A., Neiser, A., Oberle, M., Ostrick, M., Ott, P., Otte, P. B., Oussena, B., Paudyal, D., Pedroni, P., Polonski, A., Polyanski, V. V., Prakhov, S., Rajabi, A., Reicherz, G., Ron, G., Rostomyan, T., Sarty, A., Schott, D. M., Schumann, S., Sfienti, C., Sokhoyan, V., Spieker, K., Steffen, O., Strakovsky, I. I., Strub, Th., Supek, I., Taragin, M. F., Thiel, A., Thiel, M., Tiator, L., Thomas, A., Unverzagt, M., Usov, Yu. A., Wagner, S., Watts, D. P., Werthmüller, D., Wettig, J., Witthauer, L., Wolfes, M., Workman, R. L., and Zana, L. A.

Subjects
High Energy Physics - Experiment, Nuclear Experiment
Abstract

Differential cross sections for the gamma p -> pi^0 p reaction have been measured with the A2 tagged-photon facilities at the Mainz Microtron, MAMI C, up to the center-of-mass energy W=1.9 GeV. The new results, obtained with a fine energy and angular binning, increase the existing quantity of pi^0 photoproduction data by ~47%. Owing to the unprecedented statistical accuracy and the full angular coverage, the results are sensitive to high partial-wave amplitudes. This is demonstrated by the decomposition of the differential cross sections in terms of Legendre polynomials and by further comparison to model predictions. A new solution of the SAID partial-wave analysis obtained after adding the new data into the fit is presented., Comment: 13 pages, 12 figures, 1 table

Published
2015
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18. First measurement of target and beam-target asymmetries in the $\gamma p\to \pi^0\eta p$ reaction

Author

Annand, J. R. M., Arends, H. J., Beck, R., Borisov, N., Braghieri, A., Briscoe, W. J., Cherepnya, S., Collicott, C., Costanza, S., Downie, E. J., Dieterle, M., Fix, A., Fil'kov, L. V., Garni, S., Glazier, D. I., Gradl, W., Gurevich, G., Barrientos, P. H., Hamilton, D., Hornidge, D., Howdle, D., Huber, G. M., Kashevarov, V. L., Keshelashvili, I., Kondratiev, R., Korolija, M., Krusche, B., Lazarev, A., Lisin, V., Livingston, K., MacGregor, I. J. D., Mancel, J., Manley, D. M., Martel, P., McNicoll, E. F., Meyer, W., Middleton, D., Miskimen, R., Mushkarenkov, A., Neganov, A., Nikolaev, A., Oberle, M., Ortega, H., Ostrick, M., Ott, P., Otte, P. B., Oussena, B., Pedroni, P., Polonski, A., Polyanski, V. V., Prakhov, S., Reicherz, G., Rostomyan, T., Sarty, A., Schumann, S., Steffen, O., Strakovsky, I. I., Strub, T., Supek, I., Tiator, L., Thomas, A., Unverzagt, M., Usov, Y. A., Watts, D. P., Werthmüller, D., Witthauer, L., and Wolfes, M.

Subjects
Nuclear Experiment, High Energy Physics - Experiment, Nuclear Theory
Abstract

The first data on target and beam-target asymmetries for the $\gamma p\to\pi^0\eta p$ reaction at photon energies from 1050 up to 1450 MeV are presented. The measurements were performed using the Crystal Ball and TAPS detector setup at the Glasgow tagged photon facility of the Mainz Microtron MAMI. The general assumption that the reaction is dominated by the $\Delta 3/2^-$ amplitude is confirmed. The data are in particular sensitive to small contributions from other partial waves., Comment: 9 pages, 9 figures

Published
2015
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19. A new measurement of the neutron detection efficiency for the NaI Crystal Ball detector

Author

Martemianov, M., Kulikov, V., Demissie, B. T., Marinides, Z., Akondi, C. S., Annand, J. R. M., Arends, H. J., Beck, R., Borisov, N., Braghieri, A., Briscoe, W. J., Cherepnya, S., Collicott, C., Costanza, S., Downie, E. J., Dieterle, M., Bondy, M. I. Ferretti, Filkov, L. V., Garni, S., Glazier, D. I., Glowa, D., Gradl, W., Gurevich, G., Hornidge, D., Huber, G. M., Kaeser, A., Kashevarov, V. L., Keshelashvili, I., Kondratiev, R., Korolija, M., Krusche, B., Lazarev, A., Linturi, J. M., Lisin, V., Livingston, K., MacGregor, I. J. D., Manley, D. M., Martel, P. P., Middleton, D. G., Miskimen, R., Mushkarenkov, A., Neganov, A., Neiser, A., Oberle, M., Ostrick, M., Ott, P., Otte, P. B., Oussena, B., Pedroni, P., Polonski, A., Prakhov, S., Ron, G., Rostomyan, T., Sarty, A., Schott, D. M., Schumann, S., Sokhoyan, V., Steffen, O., Strakovsky, I. I., Strub, Th., Supek, I., Thiel, M., Thomas, A., Unverzagt, M., Usov, Yu. A., Wagner, S., Watts, D. P., Wettig, J., Werthmuller, D., Witthauer, L., and Wolfes, M.

Subjects
Physics - Instrumentation and Detectors, High Energy Physics - Experiment, Nuclear Experiment
Abstract

We report on a measurement of the neutron detection efficiency in NaI crystals in the Crystal Ball detector obtained from a study of single p0 photoproduction on deuterium using the tagged photon beam at the Mainz Microtron. The results were obtained up to a neutron energy of 400 MeV. They are compared to previous measurements made more than 15 years ago at the pion beam at the BNL AGS.

Published
2015
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22. Measurement of the transverse target and beam-target asymmetries in $\eta$ meson photoproduction at MAMI

Author

Akondi, C. S., Annand, J. R. M., Arends, H. J., Beck, R., Bernstein, A., Borisov, N., Braghieri, A., Briscoe, W. J., Cherepnya, S., Collicott, C., Costanza, S., Downie, E. J., Dieterle, M., Fix, A., Fil'kov, L. V., Garni, S., Glazier, D. I., Gradl, W., Gurevich, G., Barrientos, P. Hall, Hamilton, D., Hornidge, D., Howdle, D., Huber, G. M., Kashevarov, V. L., Keshelashvili, I., Kondratiev, R., Korolija, M., Krusche, B., Lazarev, A., Lisin, V., Livingston, K., MacGregor, I. J. D., Mancel, J., Manley, D. M., Martel, P., McNicoll, E. F., Meyer, W., Middleton, D., Miskimen, R., Mushkarenkov, A., Nefkens, B. M. K., Neganov, A., Nikolaev, A., Oberle, M., Ostrick, M., Ortega, H., Ott, P., Otte, P. B., Oussena, B., Pedroni, P., Polonski, A., Polyanski, V. V., Prakhov, S., Reicherz, G., Rostomyan, T., Sarty, A., Schumann, S., Steffen, O., Strakovsky, I. I., Strub, Th., Supek, I., Tiator, L., Thomas, A., Unverzagt, M., Usov, Yu. A., Watts, D. P., Werthmüller, D., Witthauer, L., and Wolfes, M.

Subjects
Nuclear Experiment, High Energy Physics - Experiment, Nuclear Theory
Abstract

We present new data for the transverse target asymmetry T and the very first data for the beam-target asymmetry F in the $\vec \gamma \vec p\to\eta p$ reaction up to a center-of-mass energy of W=1.9 GeV. The data were obtained with the Crystal-Ball/TAPS detector setup at the Glasgow tagged photon facility of the Mainz Microtron MAMI. All existing model predictions fail to reproduce the new data indicating a significant impact on our understanding of the underlying dynamics of $\eta$ meson photoproduction. The peculiar nodal structure observed in existing T data close to threshold is not confirmed., Comment: 5 pages, 3 figures, accepted for publication in PRL

Published
2014
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23. Measurements of Double-Polarized Compton Scattering Asymmetries and Extraction of the Proton Spin Polarizabilities

Author

Martel, P. P., Miskimen, R., Aguar-Bartolome, P., Ahrens, J., Akondi, C. S., Annand, J. R. M., Arends, H. J., Barnes, W., Beck, R., Bernstein, A., Borisov, N., Braghieri, A., Briscoe, W. J., Cherepnya, S., Collicott, C., Costanza, S., Denig, A., Dieterle, M., Downie, E. J., Fil'kov, L. V., Garni, S., Glazier, D. I., Gradl, W., Gurevich, G., Barrientos, P. Hall, Hamilton, D., Hornidge, D., Howdle, D., Huber, G. M., Jude, T. C., Kaeser, A., Kashevarov, V. L., Keshelashvili, I., Kondratiev, R., Korolija, M., Krusche, B., Lazarev, A., Lisin, V., Livingston, K., MacGregor, I. J. D., Mancell, J., Manley, D. M., Meyer, W., Middleton, D. G., Mushkarenkov, A., Nefkens, B. M. K., Neganov, A., Nikolaev, A., Oberle, M., Spina, H. Ortega, Ostrick, M., Ott, P., Otte, P. B., Oussena, B., Pedroni, P., Polonski, A., Polyansky, V., Prakhov, S., Rajabi, A., Reicherz, G., Rostomyan, T., Sarty, A., Schrauf, S., Schumann, S., Sikora, M. H., Starostin, A., Steffen, O., Strakovsky, I. I., Strub, T., Supek, I., Thiel, M., Tiator, L., Thomas, A., Unverzagt, M., Usov, Y., Watts, D. P., Witthauer, L., Werthmüller, D., and Wolfes, M.

Subjects
Nuclear Experiment
Abstract

The spin polarizabilities of the nucleon describe how the spin of the nucleon responds to an incident polarized photon. The most model-independent way to measure the nucleon spin polarizabilities is through polarized Compton scattering. Double-polarized Compton scattering asymmetries on the proton were measured in the $\Delta(1232)$ region using circularly polarized incident photons and a transversely polarized proton target at the Mainz Microtron. Fits to asymmetry data were performed using a dispersion model calculation and a baryon chiral perturbation theory calculation, and a separation of all four proton spin polarizabilities in the multipole basis was achieved. The analysis based on a dispersion model calculation yields $\gamma_{E1E1} = -3.5 \pm 1.2$, $\gamma_{M1M1}= 3.16 \pm 0.85$, $\gamma_{E1M2} = -0.7 \pm 1.2$, and $\gamma_{M1E2} = 1.99 \pm 0.29$, in units of $10^{-4}$ fm$^4$., Comment: 5 pages, 3 figures, 2 tables

Published
2014
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24. Deuteron frozen spin polarized target for nd experiements at the VdG accelerator of Charles University

Author

Borisov, N. S., Bazhanov, N. A., Belyaev, A. A., Broz, J., Cerny, J., Dolezal, Z., Fedorov, A. N., Gurevich, G. M., Ivanov, M. P., Kodys, P., Kubik, P., Kuzmin, E. S., Lazarev, A. B., Lehar, F., Lukhanin, O. O., Matafonov, V. N., Neganov, A. B., Pisarev, I. L., Svejda, J., Shilov, S. N., Usov, Yu. A., and Wilhelm, I.

Subjects
Nuclear Experiment
Abstract

A frozen spin polarized deuteron target cooled by the 3He/4He dilution refrigerator is described. Fully deuterated 1,2-propanediol was used as a target material. Deuteron vector polarization about 40% was obtained for the target in the shape of a cylinder of 2 cm diameter and 6 cm length. The target is intended for a study of 3N interactions at the polarized neutron beam generated by the Van de Graaff accelerator at the Charles University in Prague.

Published
2007
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28. Determination of the scalar polarizabilities of the proton using beam asymmetry Σ 3 in Compton scattering

Author

Sokhoyan, V., Downie, E. J., Mornacchi, E., McGovern, J. A., Krupina, N., Afzal, F., Ahrens, J., Akondi, C. S., Annand, J. R. M., Arends, H. J., Beck, R., Braghieri, A., Briscoe, W. J., Cividini, F., Collicott, C., Costanza, S., Denig, A., Dieterle, M., Ferretti, M., Gardner, S., Garni, S., Glazier, D. I., Glowa, D., Gradl, W., Gurevich, G., Hamilton, D., Hornidge, D., Huber, G. M., Käser, A., Kashevarov, V. L., Keshelashvili, I., Kondratiev, R., Korolija, M., Krusche, B., Lensky, V., Linturi, J., Lisin, V., Livingston, K., MacGregor, I. J. D., Macrae, R., Manley, D. M., Martel, P. P., Middleton, D. G., Miskimen, R., Mushkarenkov, A., Neiser, A., Oberle, M., Ortega Spina, H., Ostrick, M., Ott, P., Otte, P. B., Oussena, B., Paudyal, D., Pedroni, P., Polonski, A., Prakhov, S., Rajabi, A., Rostomyan, T., Sarty, A., Schumann, S., Spieker, K., Steffen, O., Strakovsky, I. I., Strandberg, B., Strub, T., Supek, I., Thiel, A., Thiel, M., Thomas, A., Unverzagt, M., Wagner, S., Watts, D. P., Wettig, J., Witthauer, L., Werthmüller, D., Wolfes, M., Zana, L., and The A2 Collaboration

Published
2017
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29. Target and beam-target asymmetries for the $γp \to π^0 π^0 p$ reaction

Author

Garni, S., Kashevarov, V. L., Fix, A., Abt, S., Afzal, F., Bartolome, P. Aguar, Ahmed, Z., Ahrens, J., Annand, J. R. M., Arends, H. J., Bashkanov, M., Beck, R., Biroth, M., Borisov, N., Braghieri, A., Briscoe, W. J., Cherepnya, S., Cividini, F., Collicott, C., Costanza, S., Denig, A., Downie, E. J., Dolzhikov, A. S., Drexler, P., Filkov, L. V., Glazier, D. I., Gorodnov, I., Gradl, W., Günther, M., Gurevich, G., Heijkenskjöld, L., Hornidge, D., Huber, G. M., Käser, A., Kay, S., Keshelashvili, I., Kondratiev, R., Korolija, M., Krusche, B., Lazarev, A., Lisin, V., Livingston, K., Lutterer, S., MacGregor, I. J. D., Maghrbi, Y., Manley, D. M., Martel, P. P., McGeorge, J. C., Middleton, D. G., Miskimen, R., Mornacchi, E., Mushkarenkov, A., Neganov, A., Neiser, A., Oberle, M., Ostrick, M., Otte, P. B., Oussena, B., Paudyal, D., Pedroni, P., Pheron, F., Polonski, A., Prakhov, S. N., Ron, G., Rostomyan, T., Sarty, A., Sfienti, C., Sokhoyan, V., Spieker, K., Steffen, O., Strakovsky, I. I., Supek, I., Thiel, A., Thiel, M., Thomas, A., Unverzagt, M., Usov, Yu. A., Wagner, S., Walford, N. K., Watts, D. P., Wettig, J., Wolfes, M., Zana, L. A., and Zehr, F.

Subjects
High Energy Physics - Experiment (hep-ex), FOS: Physical sciences
Abstract

Background: Photoproduction of pion pairs allows to study sequential decays of nucleon resonances via excited intermediate states. Such decays are important e.g. for states which in the quark model have both oscillators excited and de-excite them in a two-step process. However, analyses of multi-meson final states is difficult and requires more than unpolarized cross section measurements. Purpose: Experimental study and model analysis in view of resonant contributions of target and beam-target polarization observables for the reaction $γp \to π^0 π^0 p$. Methods: Investigated were target (single) and beam-target (double) polarization asymmetries in dependence of several parameters. The experiments were performed at the Mainz Microtron (MAMI) using circularly polarized photon beams and transversally polarized solid-state butanol targets. The reaction products were analyzed with the Crystal Ball and TAPS detectors. Results: Studied were the polarization observables Py (unpolarized beam, target polarized in y direction) and Px (circularly polarized beam, target polarized in x direction), which are similar to T (target asymmetry) and F (beam-target asymmetry) for single pion production. The asymmetries were analyzed with three independent methods, revealing systematic uncertainties., 16 pages, 12 figures, 5 tables

Published
2022
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34. The new frozen spin target at MAMI

Author

Thomas, A., Borisov, N. S., Arends, H. -J., Fedorov, A. N., Gurevich, G. M., Kondratiev, R. L., Korolija, M., Lazarev, A. B., Martinez, M., Meyer, W., Mironov, S. V., Neganov, A. B., Pavlov, V. N., Ortega, H., Reicherz, G., and Usov, Yu. A.

Published
2013
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37. Measurements of the total-cross-section difference Δσ L(np) at 1.39, 1.69, 1.89, and 1.99 GeV

Author

Sharov, V. I., Anischenko, N. G., Antonenko, V. G., Averichev, S. A., Azhgirey, L. S., Bartenev, V. D., Bazhanov, N. A., Belyaev, A. A., Blinov, N. A., Borisov, N. S., Borzakov, S. B., Borzunov, Yu. T., Bushuev, Yu. P., Chernenko, L. P., Chernykh, E. V., Chumakov, V. F., Dolgii, S. A., Fedorov, A. N., Fimushkin, V. V., Finger, M., Finger, Jr., M., Golovanov, L. B., Gurevich, G. M., Janata, A., Kirillov, A. D., Kolomiets, V. G., Komogorov, E. V., Kovalenko, A. D., Kovalev, A. I., Krasnov, V. A., Krstonoshich, P., Kuzmin, E. S., Ladygin, V. P., Lazarev, A. B., Lehar, F., de Lesquen, A., Liburg, M. Yu., Livanov, A. N., Lukhanin, A. A., Maniakov, P. K., Matafonov, V. N., Matyushevsky, E. A., Moroz, V. D., Morozov, A. A., Neganov, A. B., Nikolaevsky, G. P., Nomofilov, A. A., Panteleev, Tz., Pilipenko, Yu. K., Pisarev, I. L., Plis, Yu. A., Polunin, Yu. P., Prokofiev, A. N., Prytkov, V. Yu., Rukoyatkin, P. A., Schedrov, V. A., Schevelev, O. N., Shilov, S. N., Shindin, R. A., Slunečka, M., Slunečková, V., Starikov, A. Yu., Stoletov, G. D., Strunov, L. N., Svetov, A. L., Usov, Yu. A., Vasiliev, T., Volkov, V. I., Vorobiev, E. I., Yudin, I. P., Zaitsev, I. V., Zhdanov, A. A., and Zhmyrov, V. N.

Published
2005
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38. Measurements of energy behaviour of spin-dependentnp—observables over 1.2–3.7 GeV energy region Dubna “Delta-Sigma” Experiment

Author

Sharov, V. I., Anischenko, N. G., Antonenko, V. G., Averichev, S. A., Azhgirey, L. S., Bartenev, V. D., Bazhanov, N. A., Belyaev, A. A., Blinov, N. A., Borisov, N. S., Borzakov, S. B., Borzunov, Yu. T., Bushuev, Yu. P., Chernenko, L. P., Chernykh, E. V., Chumakov, V. F., Dolgh, S. A., Fedorov, A. N., Fimushkin, V. V., Finger, M., Finger, Jr., M., Golovanov, L. B., Gurevich, G. M., Guriev, D. K., Janata, A., Kirillov, A. D., Kolomiets, V. G., Komogorov, E. V., Kovalenko, A. D., Kovalev, A. I., Krasnov, V. A., Krstonoshich, P., Kuzmin, E. S., Kuzmin, N. A., Ladygin, V. P., Lazarev, A. B., Lehar, F., de Lesquen, A., Liburg, M. Yu., Livanov, A. N., Lukhanin, A. A., Maniakov, P. K., Matafonov, V. N., Matyushevsky, E. A., Moroz, V. D., Morozov, A. A., Neganov, A. B., Nikolaevsky, G. P., Nomofilov, A. A., Panteleev, Tz., Pillpenko, Yu. K., Pisarev, I. L., Plis, Yu. A., Polunin, Yu. P., Prokofiev, A. N., Prytkov, V. Yu., Rukoyatkin, P. A., Schedrov, V. A., Schevelev, O. N., Shilov, S. N., Shindin, R. A., Slunecka, M., Slunečková, V., Starikov, A. Yu., Stoletov, G. D., Strunov, L. N., Svetov, A. L., Usov, Yu. A., Vasiliev, T., Volkov, V. I., Vorobiev, E. I., Yudin, I. P., Zaitsev, I. V., Zhdanov, A. A., and Zhmyrov, V. N.

Published
2005
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39. Measurement of the np total cross section difference $\Delta\sigma_{\mathrm L}(np)$ at 1.39, 1.69, 1.89 and 1.99 GeV

Author

Sharov, V. I., Anischenko, N. G., Antonenko, V. G., Averichev, S. A., Azhgirey, L. S., Bartenev, V. D., Bazhanov, N. A., Belyaev, A. A., Blinov, N. A., Borisov, N. S., Borzakov, S. B., Borzunov, Yu T., Bushuev, Yu P., Chernenko, L. P., Chernykh, E. V., Chumakov, V. F., Dolgii, S. A., Fedorov, A. N., Fimushkin, V. V., Finger, M., Finger, Jr., M., Golovanov, L. B., Gurevich, G. M., Janata, A., Kirillov, A. D., Kolomiets, V. G., Komogorov, E. V., Kovalenko, A. D., Kovalev, A. I., Krasnov, V. A., Krstonoshich, P., Kuzmin, E. S., Ladygin, V. P., Lazarev, A. B., Lehar, F., de Lesquen, A., Liburg, M. Yu, Livanov, A. N., Lukhanin, A. A., Maniakov, P. K., Matafonov, V. N., Matyushevsky, E. A., Moroz, V. D., Morozov, A. A., Neganov, A. B., Nikolaevsky, G. P., Nomofilov, A. A., Panteleev, Tz, Pilipenko, Yu K., Pisarev, I. L., Plis, Yu A., Polunin, Yu P., Prokofiev, A. N., Prytkov, V. Yu, Rukoyatkin, P. A., Schedrov, V. A., Schevelev, O. N., Shilov, S. N., Shindin, R. A., Slunečka, M., Slunečková, V., Starikov, A. Yu, Stoletov, G. D., Strunov, L. N., Svetov, A. L., Usov, Yu A., Vasiliev, T., Volkov, V. I., Vorobiev, E. I., Yudin, I. P., Zaitsev, I. V., Zhdanov, A. A., and Zhmyrov, V. N.

Published
2004
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42. New results of ΔσL(np) at high energies

Author

Sharov, V. I., Adiasevich, B. P., Anischenko, N. G., Antonenko, V. G., Averichev, S. A., Azhgirey, L. S., Bartenev, V. D., Bazhanov, N. A., Belyaev, A. A., Blinov, N. A., Borisov, N. S., Borzakov, S. B., Borzunov, Yu. T., Bushuev, Yu. P., Chernenko, L. P., Chernykh, E. V., Chumakov, V. F., Dolgh, S. A., Fedorov, A. N., Fimushkin, V. V., Finger, M., Finger, Jr., M., Golovanov, L. B., Gurevich, G. M., Janata, A., Kirillov, A. D., Kolomiets, V. G., Komogorov, E. V., Kopylov, S. A., Kovalenko, A. D., Kovalev, A. I., Krasnov, V. A., Krstonoshich, P., Kuzmin, E. S., Ladygin, V. P., Lazarev, A. B., Lehar, F., de Lesquen, A., Liburg, M. Yu., Livanov, A. N., Lukhanin, A. A., Maniakov, P. K., Matafonov, V. N., Matyushevsky, E. A., Moroz, V. D., Morozov, A. A., Neganov, A. B., Nikolaevsky, G. P., Nomofilov, A. A., Panteleev, Tz., Pilipenko, Yu. K., Pisarev, I. L., Plis, Yu. A., Polunin, Yu. P., Prokofiev, A. N., Prytkov, V. Yu., Rukoyatkin, P. A., Schedrov, V. A., Schevelev, O. N., Shilov, S. N., Shishov, Yu. A., Shutov, V. B., Slunečka, M., Slunečková, V., Starikov, A. Yu., Stoletov, G. D., Strunov, L. N., Svetov, A. L., Usov, Yu. A., Vasiliev, T., Volkov, V. I., Vorobiev, E. I., Yudin, I. P., Zaitsev, I. V., Zhdanov, A. A., and Zhmyrov, V. N.

Published
2002
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43. Measurements of energy behaviour of spin-dependent np observables over a GeV region. Results and prospects. Dubna “DELTA—SIGMA” experiment

Author

Sharov, V. I., Adiasevich, B. P., Anischenko, N. G., Antonenko, V. G., Averichev, S. A., Azhgirey, L. S., Bartenev, V. D., Bazhanov, N. A., Blinov, N. A., Borisov, N. S., Borzakov, S. B., Borzunov, Yu. T., Borzunova, T. N., Bunyatova, E. I., Burinov, V. F., Bushuev, Yu. P., Chernenko, L. P., Chernykh, E. V., Chumakov, V. F., Dolgii, S. A., Drobin, V. M., Durand, G., Dzyubak, A. P., Fedorov, A. N., Fimushkin, V. V., Finger, M., Finger, Jr., M., Golovanov, L. B., Gurevich, G. M., Janata, A., Khachaturov, B. A., Kirillov, A. D., Kochelev, N. I., Kolomiets, V. G., Konskii, I. G., Kovalenko, A. D., Kovalev, A. I., Kuzmin, E. S., Ladygin, V. P., Lazarev, A. B., Lehar, F., de Lesquen, A., Lukhanin, A. A., Maniakov, P. K., Matafonov, V. N., Matyushevsky, E. A., Motina, Z. P., Neganov, A. B., Nikolaevsky, G. P., Nomofilov, A. A., Orlova, V. V., Panteleev, Tz., Pavlova, T. F., Pilipenko, Yu. K., Pisarev, I. L., Plis, Yu. A., Polunin, Yu. P., Polyakova, R. V., Prokofiev, A. N., Prytkov, V. Yu., Rukoyatkin, P. A., Schedrov, V. A., Schevelev, O. N., Shavrina, T. V., Shilov, S. N., Starikov, Yu. A., Shutov, V. B., Slunecka, M., Slunečková, V., Starikov, A. Yu., Stoletov, G. D., Strunov, L. N., Svetov, A. L., Usov, Yu. A., Volkov, V. I., Vorobiev, E. I., Yershov, V. P., Yudin, I. P., Zaitsev, I. V., Zaporozhets, S. A., Zhdanov, A. A., and Zhmyrov, V. N.

Published
2001
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46. Measurements of the neutron-proton total cross section difference Δσ p (np) at 1.59, 1.79 and 2.20 GeVat 1.59, 1.79 and 2.20 GeV

Author

Sharov, V. I., Zaporozhets, S. A., Anischenko, N. G., Bartenev, V. D., Blinov, N. A., Borzunov, Yu. T., Bushuev, Yu. P., Chernykh, E. V., Dolgii, S. A., Drobin, V. M., Fimushkin, V. V., Golovanov, L. B., Karpunin, A. V., Kirillov, A. D., Kovalenko, A. D., Ladygin, V. P., Maniakov, P. K., Nikolaevsky, G. P., Nomofilov, A. A., Pilipenko, Yu. K., Piskunov, N. M., Rukoyatkin, P. A., Shishov, Yu. A., Shutov, V. B., Starikov, A. Yu., Strunov, L. N., Svetov, A. L., Tsvinev, A. P., Volkov, V. I., Yershov, V. P., Azhgirey, L. S., Borisov, N. S., Budkin, L. V., Burinov, V. F., Fedorov, A. N., Finger, M., Finger, Jr., M., Janata, A., Khachaturov, B. A., Kolomiets, V. G., Kuzmin, E. S., Lazarev, A. B., Matafonov, V. N., Neganov, A. B., Pisarev, I. L., Plis, Yu. A., Shchevelev, O. N., Shilov, S. N., Slunecka, M., Slunečková, V., Stoletov, G. D., Usov, Yu. A., Zhmyrov, V. N., Borzakov, S. B., Chernenko, L. P., Panteleev, Tz., Bazhanov, N. A., Kovalev, A. I., Prokofiev, A. N., Shchedrov, V. A., Zhdanov, A. A., Adiasevich, B. P., Antonenko, V. G., Polunin, Yu. P., Gurevich, G. M., Kochetkov, A. A., Nikitina, M. S., Dzyubak, A. P., Lukhanin, A. A., Durand, G., Lehar, F., and de Lesquen, A.

Published
2000
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