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1. First measurement of polarisation transfer In Deuteron Photodisintegration

Author

Bashkanov, M., Watts, D.P., Kay, S., 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., 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., 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.

Abstract

A first measurement of the polarisation transfer from a circularly-polarised photon to the final state neutron (Cx′n) 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 ∼45−120∘. 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 Cx′n 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 Cx′n observed in the region of the d⁎(2380) could not be explained by conventional models of deuteron photodisintegration.

Published
2023

2. 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 Theory, FOS: Physical sciences, Nuclear Experiment (nucl-ex), 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

3. Measurement of Compton Scattering at MAMI for the Extraction of the Electric and Magnetic Polarizabilities of the Proton

Author

Mornacchi, E., Martel, P. P., Abt, S., Achenbach, P., Adlarson, P., Afzal, F., Ahmed, Z., Annand, J. R. M., Arends, H. J., Bashkanov, M., Beck, R., Biroth, M., Borisov, N., Braghieri, A., Briscoe, W. J., Cividini, F., Collicott, C., Costanza, S., Denig, A., Dolzhikov, A. S., Downie, E. J., Drexler, P., Fegan, S., Gardner, S., Ghosal, D., Glazier, D. I., Gorodnov, I., Gradl, W., Günther, M., Gurevich, D., Heijkenskjöld, L., Hornidge, D., Huber, G. M., Käser, A., Kashevarov, V. L., Kay, S. J. D., Korolija, M., Krusche, B., Lazarev, A., Livingston, K., Lutterer, S., MacGregor, I. J. D., Manley, D. M., Miskimen, R., Mocanu, M., Mullen, C., Neganov, A., Neiser, A., Ostrick, M., Paudyal, D., Pedroni, P., Powell, A., Rostomyan, T., Sokhoyan, V., Spieker, K., Steffen, O., Strakovsky, I., Strub, T., Thiel, M., Thomas, A., Usov, Yu. A., Wagner, S., Watts, D. P., Werthmüller, D., Wettig, J., Wolfes, M., Zachariou, N., and Publica

Subjects
Electromagnetic transitions, Nuclear structure & decays, Photonuclear reactions, General Physics and Astronomy, Nuclear reactions
Abstract

A precise measurement of the differential cross sections \ud d\ud σ\ud /\ud d\ud Ω\ud and the linearly polarized photon beam asymmetry \ud Σ\ud 3\ud for Compton scattering on the proton below pion threshold has been performed with a tagged photon beam and almost \ud 4\ud π\ud detector at the Mainz Microtron. The incident photons were produced by the recently upgraded Glasgow-Mainz photon tagging facility and impinged on a cryogenic liquid hydrogen target, with the scattered photons detected in the Crystal Ball/TAPS setup. Using the highest statistics Compton scattering data ever measured on the proton along with two effective field theories (both covariant baryon and heavy-baryon) and one fixed-\ud t\ud dispersion relation model, constraining the fits with the Baldin sum rule, we have obtained the proton electric and magnetic polarizabilities with unprecedented precision: \ud α\ud E\ud 1\ud =\ud 10.99\ud ±\ud 0.16\ud ±\ud 0.47\ud ±\ud 0.17\ud ±\ud 0.34\ud , \ud β\ud M\ud 1\ud =\ud 3.14\ud ±\ud 0.21\ud ±\ud 0.24\ud ±\ud 0.20\ud ±\ud 0.35\ud ; in units of \ud 10\ud −\ud 4\ud \ud \ud fm\ud 3\ud where the errors are statistical, systematic, spin polarizability dependent, and model dependent.

Published
2022

4. 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 Theory, 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

5. Neutron polarisation transfer, $C_{x'}^n$, in $π^+$ photoproduction off the proton

Author

Bashkanov, M., Watts, D. P., Kay, S. J. D., Abt, S., Achenbach, P., Adlarson, P., Afzal, F., Ahmed, Z., Akondi, C. S., Annand, J. R. M., Beck, R., Biroth, M., Borisov, N., Braghieri, A., Briscoe, W. J., Cividini, F., Collicott, C., Costanza, S., Denig, A., Downie, E. J., Drexler, P., Fegan, S., Fix, A., Gardner, S., Ghosal, D., Glazier, D. I., Gorodnov, I., Gradl, W., Gurevich, D., Heijkenskjöld, L., Hornidge, D., Huber, G. M., Kashevarov, V. L., Korolija, M., Krusche, B., Lazarev, A., Livingston, K., Lutterer, S., MacGregor, I. J. D., Manley, D. M., Martel, P. P., Miskimen, R., Mornacchi, E., Mullen, C., Neganov, A., Neiser, A., Ostrick, M., Otte, P. B., Paudyal, D., Pedroni, P., Rostomyan, T., Sokhoyan, V., Spieker, K., Steffen, O., Strakovsky, I. I., Strub, T., Supek, I., Thiel, A., Thiel, M., Thomas, A., Usov, Yu. A., Wagner, S., Walford, N. K., Wettig, J., Wolfes, M., and Zachariou, N.

Subjects
FOS: Physical sciences, Nuclear Experiment (nucl-ex)
Abstract

We report a first measurement of the double-polarisation observable, $C_{x'}$, in $π^+$ photoproduction off the proton. The $C_{x'}$ double-polarisation observable represents the transfer of polarisation from a circularly polarised photon beam to the recoiling neutron. The MAMI circularly polarised photon beam impinged on a liquid deuterium target cell, with reaction products detected in the Crystal Ball calorimeter. Ancillary apparatus surrounding the target provided tracking, particle identification and determination of recoil nucleon polarisation. The $C_{x'}$ observable is determined for photon energies 800-1400 MeV, providing new constraints on models aiming to elucidate the spectrum and properties of nucleon resonances. This is the first determination of any polarisation observable from the beam-recoil group of observables for this reaction, providing a valuable constraint and systematic check of the current solutions of partial wave analysis based theoretical models.

Published
2022
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6. Measurement of the helicity dependence for single π0 photoproduction from the deuteron

Author

Cividini, Federico, Dieterle, Michael, Abt, S., Achenbach, Patrik, Adlarson, P., Afzal, F., Ahmed, Zafar, Annand, John R.M., Arends, Hans Jürgen, Bashkanov, Mikhail, Beck, Reinhard, M. Biroth, Borisov, N., Braghieri, A., Briscoe, W.J., Collicott, Cristina, Costanza, Susanna, Denig, A., Dolzhikov, A.S., Downie, E.J., Drexler, P., Fegan, Suzanne, 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., Paudyal, D., Pedroni, P., Powell, A., Rostomyan, T., Sokhoyan, V., Spieker, K., Steffen, O., Strakovsky, I., Strub, T., Thiel, A., Thiel, M., Thomas, A., Usov, Yu.A., Wagner, S., Watts, D.P., Werthmüller, D., Wettig, J., Witthauer, L., Wolfes, M., Zachariou, N., and Publica

Abstract

The helicity-dependent single π0 photoproduction cross section on the deuteron and the angular dependence of the double polarisation observable E for the quasi-free single π0 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 the 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.

Published
2022

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

Author

Metag, V., Nanova, M., Hartmann, J., Mahlberg, P., Afzal, F., Bartels, C., Bayadilov, D., Beck, R., Becker, M., Blanke, E., Brinkmann, K. -T., Ciupka, S., Crede, V., Dieterle, M., Dutz, H., Elsner, D., Frommberger, F., Gridnev, A., Gottschall, M., Grüner, M., Hammann, Ch., Hannappel, J., Hillert, W., Hoff, J., Hoffmeister, Ph., Honisch, Ch., Jude, T., Kalinowsky, H., Kalischewski, F., Keshelashvili, I., Ketzer, B., Klassen, P., Klein, F., Koop, K., Kroenert, P., Krusche, B., Lang, M., Lopatin, I., Messi, F., Meyer, W., Mitlasóczky, B., Müller, J., Müllers, J., Nikonov, V., Novinsky, V., Novotny, R., Piontek, D., Reicherz, G., Richter, L., Rostomyan, T., Runkel, S., Salisbury, B., Sarantsev, A., Schaab, D., Schmidt, Ch., Schmieden, H., Schultes, J., Seifen, T., Sokhoyan, V., Sowa, C., Spieker, K., Stausberg, N., Thiel, A., Thoma, U., Triffterer, T., Urban, M., Urff, G., van Pee, H., Wagner, M., Walther, D., Wendel, Ch., Werthmüller, D., Wiedner, U., Wilson, A., Winnebeck, A., Witthauer, L., and Wunderlich, Y.

Subjects
Nuclear Theory, Nuclear Experiment
Abstract

The reaction $\gamma p \rightarrow p \pi^0 \eta$ has been studied with the CBELSA/TAPS detector at the electron stretcher accelerator ELSA in Bonn for incident photon energies from threshold up to 3.1 GeV. This paper has been motivated by the recently claimed observation of a narrow structure in the M$_{N\eta}$ invariant mass distribution at a mass of 1678 MeV/$c^2$. The existence of this structure cannot be confirmed in the present work. Instead, for E$_{\gamma}$ = 1400 - 1500 MeV and the cut M$_{p\pi^0} \le 1190 $ MeV/$c^2$ a statistically significant structure in the M$_{p\eta}$ invariant mass distribution near 1700 MeV/$c^2$ is observed with a width of $\Gamma\approx 35$ MeV/$c^2$ while the mass resolution is $\sigma_{res}$ = 5 MeV/$c^2$. Increasing the incident photon energy from 1420 to 1540 MeV this structure shifts in mass from $\approx$ 1700MeV/c$^2$ to $\approx$ 1725 MeV/$c^2$; the width increases to about 50 MeV/$c^2$ and decreases thereafter. The cross section associated with this structure reaches a maximum of $\approx$ 100 nb around E$_{\gamma} \approx$ 1490 MeV (W $\approx $ 1920 MeV), which coincides with the $p a_0$ threshold. Three scenarios are discussed which might be the origin of this structure in the M$_{p\eta}$ invariant mass distribution. The most likely interpretation is that it is due to a triangular singularity in the $\gamma p \rightarrow p a_0 \rightarrow p \pi^0 \eta$ reaction, Comment: 16 pages, 18 figure

Published
2021

9. Single π0 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., Günther, M., Gurevic, G., Heijkenskjöld, 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., 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., Zachariou, N., and Publica

Subjects
deuteron, polarization, N(1440), partial wave, Nuclear Theory, photon: energy, Delta(1232), beam: asymmetry, Mainz Linac, kinematics, isospin: symmetry, calorimeter, electron: beam, pi0: photoproduction, Nuclear Experiment, photon: beam, Crystal Ball
Abstract

The quasifree γ→d→π0n(p) photon beam asymmetry, Σ, has been measured at photon energies, Eγ, 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∘. In this kinematic region, polarization observables are sensitive to contributions from the Δ(1232) and N(1440) resonances. The extracted values of Σ 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 Σ measurements, has also been performed. In addition, isospin symmetry is examined as a way to predict π0n photoproduction observables, based on fits to published data in the channels π0p, π+n and π-p.

Published
2021

10. Single \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\pi ^0$$\end{document}π0 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., Günther, M., Gurevic, G., Heijkenskjöld, 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., 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
Regular Article - Experimental Physics
Abstract

The quasifree \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\overrightarrow{\gamma } d\rightarrow \pi ^0n(p)$$\end{document}γ→d→π0n(p) photon beam asymmetry, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\varSigma $$\end{document}Σ, has been measured at photon energies, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$E_\gamma $$\end{document}Eγ, 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\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^\circ $$\end{document}∘ to 148\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^\circ $$\end{document}∘. In this kinematic region, polarization observables are sensitive to contributions from the \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\varDelta (1232)$$\end{document}Δ(1232) and N(1440) resonances. The extracted values of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\varSigma $$\end{document}Σ 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 \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\varSigma $$\end{document}Σ measurements, has also been performed. In addition, isospin symmetry is examined as a way to predict \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\pi ^0n$$\end{document}π0n photoproduction observables, based on fits to published data in the channels \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\pi ^0p$$\end{document}π0p, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\pi ^+n$$\end{document}π+n and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\pi ^-p$$\end{document}π-p.

Published
2021

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

Author

A2 Collaboration, Mornacchi, E., Martel, P. P., Abt, S., Achenbach, P., Adlarson, P., Afzal, F., Ahmed, Z., Annand, J. R. M., Arends, H. J., Bashkanov, M., Beck, R., Biroth, M., Borisov, N., Braghieri, A., Briscoe, W. J., Cividini, F., Collicott, C., Costanza, S., Denig, A., Dolzhikov, A. S., Downie, E. J., Drexler, P., Fegan, S., Gardner, S., Ghosal, D., Glazier, D. I., Gorodnov, I., Gradl, W., Günther, M., Gurevich, D., Heijkenskjöld, L., Hornidge, D., Huber, G. M., Käser, A., Kashevarov, V. L., Kay, S. J. D., Korolija, M., Krusche, B., Lazarev, A., Livingston, K., Lutterer, S., MacGregor, I. J. D., Manley, D. M., Miskimen, R., Mocanu, M., Mullen, C., Neganov, A., Neiser, A., Ostrick, M., Paudyal, D., Pedroni, P., Powell, A., Rostomyan, T., Sokhoyan, V., Spieker, K., Steffen, O., Strakovsky, I., Strub, T., Thiel, M., Thomas, A., Usov, Yu. A., Wagner, S., Watts, D. P., Werthmüller, D., Wettig, J., Wolfes, M., and Zachariou, N.

Subjects
Nuclear Theory (nucl-th), Nuclear Theory, FOS: Physical sciences, High Energy Physics::Experiment, Nuclear Experiment (nucl-ex), Nuclear Experiment
Abstract

A precise measurement of the differential cross-sections $d\sigma/d\Omega$ and the linearly polarized photon beam asymmetry $\Sigma_3$ for Compton scattering on the proton below pion threshold has been performed with a tagged photon beam and almost $4\pi$ detector at the Mainz Microtron. The incident photons were produced by the recently upgraded Glasgow-Mainz photon tagging facility and impinged on a cryogenic liquid hydrogen target, with the scattered photons detected in the Crystal Ball/TAPS set-up. Using the highest statistics Compton scattering data ever measured on the proton along with two effective field theories (both covariant baryon and heavy-baryon) and one fixed-$t$ dispersion relation model, constraining the fits with the Baldin sum rule, we have obtained the proton electric and magnetic polarizabilities with unprecedented precision: \begin{align*} &{}\alpha_{E1} = 10.99 \pm 0.16 \pm 0.47 \pm 0.17 \pm 0.34 &{}\beta_{M1} = 3.14 \pm 0.21 \pm 0.24 \pm 0.20 \pm 0.35 \end{align*} in units of $10^{-4}$\,fm$^3$ where the errors are statistical, systematic, spin polarizability dependent and model dependent.

Published
2021
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12. Observation of a structure in the M$_{p��}$ invariant mass distribution near 1700 MeV/$c^2$ in the $\mathbf{��p \rightarrow p ��^0 ��} $ reaction

Author

Metag, V., Nanova, M., Hartmann, J., Mahlberg, P., Afzal, F., Bartels, C., Bayadilov, D., Beck, R., Becker, M., Blanke, E., Brinkmann, K. -T., Ciupka, S., Crede, V., Dieterle, M., Dutz, H., Elsner, D., Frommberger, F., Gridnev, A., Gottschall, M., Gr��ner, M., Hammann, Ch., Hannappel, J., Hillert, W., Hoff, J., Hoffmeister, Ph., Honisch, Ch., Jude, T., Kalinowsky, H., Kalischewski, F., Keshelashvili, I., Ketzer, B., Klassen, P., Klein, F., Koop, K., Kroenert, P., Krusche, B., Lang, M., Lopatin, I., Messi, F., Meyer, W., Mitlas��czky, B., M��ller, J., M��llers, J., Nikonov, V., Novinsky, V., Novotny, R., Piontek, D., Reicherz, G., Richter, L., Rostomyan, T., Runkel, S., Salisbury, B., Sarantsev, A., Schaab, D., Schmidt, Ch., Schmieden, H., Schultes, J., Seifen, T., Sokhoyan, V., Sowa, C., Spieker, K., Stausberg, N., Thiel, A., Thoma, U., Triffterer, T., Urban, M., Urff, G., van Pee, H., Wagner, M., Walther, D., Wendel, Ch., Werthm��ller, D., Wiedner, U., Wilson, A., Winnebeck, A., Witthauer, L., and Wunderlich, Y.

Subjects
Nuclear Theory (nucl-th), Nuclear Theory, Physics::Accelerator Physics, FOS: Physical sciences, Nuclear Experiment (nucl-ex), Nuclear Experiment
Abstract

The reaction $��p \rightarrow p ��^0 ��$ has been studied with the CBELSA/TAPS detector at the electron stretcher accelerator ELSA in Bonn for incident photon energies from threshold up to 3.1 GeV. This paper has been motivated by the recently claimed observation of a narrow structure in the M$_{N��}$ invariant mass distribution at a mass of 1678 MeV/$c^2$. The existence of this structure cannot be confirmed in the present work. Instead, for E$_��$ = 1400 - 1500 MeV and the cut M$_{p��^0} \le 1190 $ MeV/$c^2$ a statistically significant structure in the M$_{p��}$ invariant mass distribution near 1700 MeV/$c^2$ is observed with a width of $��\approx 35$ MeV/$c^2$ while the mass resolution is $��_{res}$ = 5 MeV/$c^2$. Increasing the incident photon energy from 1420 to 1540 MeV this structure shifts in mass from $\approx$ 1700MeV/c$^2$ to $\approx$ 1725 MeV/$c^2$; the width increases to about 50 MeV/$c^2$ and decreases thereafter. The cross section associated with this structure reaches a maximum of $\approx$ 100 nb around E$_�� \approx$ 1490 MeV (W $\approx $ 1920 MeV), which coincides with the $p a_0$ threshold. Three scenarios are discussed which might be the origin of this structure in the M$_{p��}$ invariant mass distribution. The most likely interpretation is that it is due to a triangular singularity in the $��p \rightarrow p a_0 \rightarrow p ��^0 ��$ reaction, 16 pages, 18 figure

Published
2021
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13. Single $��^0$ Production Off Neutrons Bound in Deuteron with Linearly Polarized Photons

Author

Mullen, C., Gardner, S., Glazier, D. I., Kay, S. J. D., Livingston, K., Strakovsky, I. I., Workman, R. L., Abt, S., Achenbach, P., Afzal, F., Ahmed, Z., Akondi, C. S., Annand, J. R. M., Bashkanov, M., Beck, R., Biroth, M., Borisov, N. S., Braghieri, A., Briscoe, W. J., Cividini, F., Collicott, C., Costanza, S., Denig, A., Dieterle, M., Downie, E. J., Drexler, P., Fegan, S., Ferretti-Bondy, M. I., Ghosal, D., Gorodnov, I., Gradl, W., Gunther, M., Gurevic, G., Heijkenskjold, L., Hornidge, D., Huber, G. M., Jermann, N., Kaeser, A., Korolija, M., Kashevarov, V. L, Krusche, B., Kulikov, V. V., Lazarev, A., Lutterer, S., MacGregor, I. J. D., Manley, D. M., Martel, P. P., Martemianov, M. A., Meier, C., Miskimen, R., Mocanu, M., Mornacchi, E., Neganov, A., Oberle, M., Ostrick, M., Otte, P., Paudyal, D., Pedroni, P., Powell, A., Prakhov, S. N., Reicherz, G., Ron, G., Rostomyan, T., Sfienti, C., Sokhoyan, V., Spieker, K., Steffen, O., Strub, Th., Supek, I., Thie, A., Thiel, M., Thomas, A., Unverzagt, M., Usov, Yu. A., Wagner, S., Walford, N. K., Watts, D. P., Werthmuller, D., Wettig, J., Witthauer, L., Wolfes, M., and Zachariou, N.

Subjects
Nuclear Theory (nucl-th), High Energy Physics - Experiment (hep-ex), High Energy Physics - Phenomenology (hep-ph), Nuclear Theory, FOS: Physical sciences, Nuclear Experiment (nucl-ex), Nuclear Experiment
Abstract

The quasifree $\overrightarrow�� d\to��^0n(p)$ photon beam asymmetry, $��$, has been measured at photon energies, $E_��$, from 390 to 610 MeV, corresponding to center of mass energy from 1.271 to 1.424 GeV, for the first time. The data were collected in the A2 hall of the MAMI electron beam facility with the Crystal Ball and TAPS calorimeters covering pion center-of-mass angles from 49 to 148$^\circ$. In this kinematic region, polarization observables are sensitive to contributions from the $��(1232)$ and $N(1440)$ resonances. The extracted values of $��$ have been compared to predictions based on partial-wave analyses (PWAs) of the existing pion photoproduction database. Our comparison includes the SAID, MAID, and Bonn-Gatchina analyses; while a revised SAID fit, including the new $��$ measurements, has also been performed. In addition, isospin symmetry is examined as a way to predict $��^0n$ photoproduction observables, based on fits to published data in the channels $��^0p$, $��^+n$, and $��^-p$., 11 pages, 9 figures, 5 tables; fixed 2 glitches

Published
2021
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14. Helicity-dependent cross sections for the photoproduction of π0 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., 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
Physics, Proton, spin polarization, neutron, photodisintegration, Crystal Ball at MAMI, Nuclear Theory, Bremsstrahlung, General Physics and Astronomy, Electron, 7. Clean energy, 01 natural sciences, Resonance (particle physics), Helicity, Nuclear physics, 0103 physical sciences, Neutron, 010306 general physics, Nucleon, Nuclear Experiment, Crystal Ball
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

15. Signatures of the d*(2380) Hexaquark in d(γ,pn→)

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., 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., 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 Theory, Nuclear Experiment
Abstract

We report a measurement of the spin polarization of the recoiling neutron in deuterium photodisintegration, utilizing 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 polarization 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 polarization in a narrow structure centered around \ud E\ud γ\ud ∼\ud 570\ud \ud \ud MeV\ud is observed, which is inconsistent with current theoretical predictions employing nucleon resonance degrees of freedom. A Legendre polynomial decomposition suggests this behavior could be related to the excitation of the \ud d\ud ∗\ud (\ud 2380\ud )\ud hexaquark.

Published
2020

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

Author

Fegan, Stuart, Fix, A., 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, Dominik, Wettig, J., Wolfes, M., Zachariou, Nick, and Zana, L A

Subjects
Nuclear Theory, 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
2020

17. Measurement of the beam-helicity asymmetry in photoproduction of 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., Ferretti Bondy, M.I., 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.

Abstract

The beam-helicity asymmetry was measured, for the first time, in photoproduction of π0η 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 π0η pairs on nuclei is similar to photoproduction on a free nucleon. This process is dominated by the D33 partial wave with the ηΔ(1232) intermediate state.

Published
2020

18. Helicity-dependent cross sections for the photoproduction of $��^0$ pairs from nucleons

Author

Dieterle, M., Witthauer, L., Fix, A., Abt, S., Achenbach, P., Adlarson, P., Afzal, F., Bartolome, P. Aguar, Ahmed, Z., Annand, J. R. M., Arends, H. J., Bashkanov, M., Beck, R., Biroth, M., Borisov, N., Braghieri, A., Briscoe, W. J., Cividini, F., Collicott, C., Costanza, S., Denig, A., Dolzhikov, A. S., Downie, E. J., Drexler, P., Gardner, S., Ghosal, D., Glazier, D. I., Gorodnov, I., Gradl, W., G{��, M., Nther, Gurevich, D., Heijkenskj{��, L., Hornidge, D., Huber, G. M., K{��, A., Ser, Kashevarov, V. L., Kay, S., Keshelashvili, I., Kondratiev, R., Korolija, M., Krusche, B., Lazarev, A., Lisin, V., Livingston, K., Lutterer, S., MacGregor, I. J. D., Manley, D. M., Martel, P. P., Metag, V., Meyer, W., Middleton, D. G., Miskimen, R., Mornacchi, E., Mullen, C., Mushkarenkov, A., Neganov, A., Neiser, A., Oberle, M., Ostrick, M., Otte, P. B., Paudyal, D., Pedroni, P., Polonski, A., Powell, A., Prakhov, S. N., Reicherz, G., Ron, G., Rostomyan, T., Sarty, A., Sfienti, C., Sokhoyan, V., Spieker, K., Steffen, O., Strakovsky, I. I., Strub, T., Supek, I., Thiel, A., Thiel, M., Thomas, A., Unverzagt, M., Usov, Yu. A., Wagner, S., Walford, N. K., Watts, D. P., Werthm��ller, D., Wettig, J., Wolfes, M., and Zana, L. A.

Subjects
Nuclear Theory, FOS: Physical sciences, Nuclear Experiment (nucl-ex), Nuclear Experiment
Abstract

The double-polarization observable $E$ and helicity-dependent cross sections $��_{1/2}$, $��_{3/2}$ have been measured for the photoproduction of $��^0$ pairs off quasi-free protons and neutrons at the Mainz MAMI accelerator with the Crystal Ball/TAPS setup. A circularly polarized photon beam was produced by bremsstrahlung from longitudinally polarized electrons and impinged on a longitudinally polarized deuterated butanol target. The reaction products were detected with an almost $4��$ covering calorimeter. The results reveal for the first time the helicity- and isospin-dependent structure of the $��N\rightarrow N��^0��^0$ reaction. They are compared to predictions from reaction models in view of nucleon resonance contributions and also to a refit of one model that predicted results for the proton and for the neutron target. The comparison of the prediction and the refit demonstrate the large impact of the new data., Submitted to Phys. Rev. Lett

Published
2020
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19. Coda-Q in the 2.5-20 s period band from seismic noise : application to the greater Alpine area

Author

Soergel, D., Pedersen, H. A., Stehly, L., Margerin, L., Paul, A., Hetenyi, G., Abreu, R., Allegretti, I., Apoloner, M. T., Aubert, C., De Berc, M. B., Bokelmann, G., Brunel, D., Capello, M., Carman, M., Cavaliere, A., Cheze, J., Chiarabba, C., Clinton, J., Cougoulat, G., Crawford, W., Cristiano, L., Czifra, T., D'Alema, E., Danesi, S., Daniel, R., Dasovic, I., Deschamps, A., Dessa, J. X., Doubre, C., Egdorf, S., Fiket, T., Fischer, K., Friederich, W., Fuchs, F., Funke, S., Giardini, D., Govoni, A., Graczer, Z., Groschl, G., Heimers, S., Heit, B., Herak, D., Herak, M., Huber, J., Jaric, D., Jedlicka, P., Jia, Y., Jund, H., Kissling, E., Klingen, S., Klotz, B., Kolinsky, P., Korn, M., Kotek, J., Kuhne, L., Kuk, K., Loos, J., Malengros, D., Margheriti, L., Maron, C., Martin, X., Massa, M., Mazzarini, F., Meier, T., Metral, L., Molinari, I., Moretti, M., Munzarova, H., Nardi, A., Pahor, J., Pequegnat, C., Pesaresi, D., Piccinini, D., Piromallo, C., Plenefisch, T., Plomerova, J., Pondrelli, S., Prevolnik, S., Racine, R., Régnier, Marc, Reiss, M., Ritter, J., Rumpker, G., Salimbeni, S., Schulte-Kortnack, D., Scherer, W., Schippkus, S., Sipka, V., Spallarossa, D., Spieker, K., Stipcevic, J., Strollo, A., Sule, B., Szanyi, G., Szucs, E., Thomas, C., Tilmann, F., Ueding, S., Vallocchia, M., Vecsey, L., Voigt, R., Wassermann, J., Weber, Z., Weidle, C., Wesztergom, V., Weyland, G., Wiemer, S., Wolyniec, D., Zieke, T., Zivvic, M., and AlpArray Working Group

Subjects
Europe, surface waves and free oscillations, Coda waves, seismic attenuation, seismic noise, wave scattering and diffraction
Abstract

Coda-Q is used to estimate the attenuation and scattering properties of the Earth. So far focus has been on earthquake data at frequencies above 1 Hz, as the high noise level in the first and second microseismic peak, and possibly lower scattering coefficient, hinder stable measurements at lower frequencies. In this work, we measure and map coda-Q in the period bands 2.5-5 s, 5-10 s and 10-20 s in the greater Alpine region using noise cross-correlations between station pairs, based on data from permanent seismic stations and from the temporary AlpArray experiment. The observed coda-Q for short interstation distances is independent of azimuth so there is no indication of influence of the directivity of the incoming noise field on our measurements. In the 2.5-5 s and 5-10 s period bands, our measurements are self-consistent, and we observe stable geographic patterns of low and high coda-Q in the period bands 2.5-5 s and 5-10 s. In the period band 10-20 s, the dispersion of our measurements increases and geographic patterns become speculative. The coda-Q maps show that major features are observed with high resolution, with a very good geographical resolution of for example low coda-Q in the Po Plain. There is a sharp contrast between the Po Plain and the Alps and Apennines where coda-Q is high, with the exception a small area in the Swiss Alps which may be contaminated by the low coda-Q of the Po Plain. The coda of the correlations is too short to make independent measurements at different times within the coda, so we cannot distinguish between intrinsic and scattering Q. Measurements on more severely selected data sets and longer time-series result in identical geographical patterns but lower numerical values. Therefore, high coda-Q values may be overestimated, but the geographic distribution between high and low coda-Q areas is respected. Our results demonstrate that noise correlations are a promising tool for extending coda-Q measurements to frequencies lower than those analysed with earthquake data.

Published
2020

20. 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 Theory, 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

21. Experimental study of the γp→K0Σ+, γn→K0Λ, and γn→K0Σ0 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., Ferretti Bondy, M. I., 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.

Abstract

This work measured dσ/dΩ for neutral kaon photoproduction reactions from threshold up to a c.m. energy of 1855MeV, focussing specifically on the γp→K0Σ+, γn→K0Λ, and γn→K0Σ0 reactions. Our results for γn→K0Σ0 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 πN 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.

Published
2019

22. 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
High Energy Physics - Phenomenology, Nuclear Theory, Nuclear Experiment, High Energy Physics - Experiment
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

23. Measurement of the Helicity Asymmetry $E$ for the reaction $ \gamma p\to \pi^0 p$

Author

collaboration, CBELSA/TAPS, Gottschall, M., Afzal, F., Anisovich, A. V., Bayadilov, D., Beck, R., Bichow, M., Brinkmann, K. -Th., Crede, V., Dieterle, M., Dietz, F., Dutz, H., Eberhardt, H., Elsner, D., Ewald, R., Fornet-Ponse, K., Friedrich, St., Frommberger, F., Gridnev, A., Grüner, M., Gutz, E., Hammann, Ch., Hannappel, J., Hartmann, J., Hillert, W., Hoffmeister, Ph., Honisch, Ch., Jude, T., Kammer, S., Kalinowsky, H., Keshelashvili, I., Klassen, P., Klein, F., Klempt, E., Koop, K., Krusche, B., Kube, M., Lang, M., Lopatin, I., Mahlberg, P., Makonyi, K., Metag, V., Meyer, W., Müller, J., Müllers, J., Nanova, M., Nikonov, V., Novotny, R., Piontek, D., Reicherz, G., Rostomyan, T., Sarantsev, A., Schmidt, Ch., Schmieden, H., Seifen, T., Sokhoyan, V., Spieker, K., Thiel, A., Thoma, U., Urban, M., van Pee, H., Walther, D., Wendel, Ch., Werthmüller, D., Wiedner, U., Wilson, A., Winnebeck, A., Witthauer, L., and Wunderlich, Y.

Subjects
Nuclear Theory, Physics::Accelerator Physics, Nuclear Experiment
Abstract

A measurement of the double-polarization observable $E$ for the reaction $\gamma p\to \pi^0 p$ is reported. The data were taken with the CBELSA/TAPS experiment at the ELSA facility in Bonn using the Bonn frozen-spin butanol (C$_4$H$_9$OH) target, which provided longitudinally-polarized protons. Circularly-polarized photons were produced via bremsstrahlung of longitudinally-polarized electrons. The data cover the photon energy range from $E_\gamma =600$~MeV to $E_\gamma =2310$~MeV and nearly the complete angular range. The results are compared to and have been included in recent partial wave analyses., Comment: 21 pages

Published
2019

24. Deuteron photodisintegration by polarized photons in the region of the d⁎ (2380)

Author

Paudyal, D., Pedroni, P., Powell, A, Prakhov, S., Ron, G., Rostomyan, T., Sarty, A. J., 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, Dominik, Wettig, J., Wolfes, M., and Zana, L. A.

Abstract

We report the first large-acceptance measurement of the beam–spin asymmetry for deuteron photodisintegration (γ→d→pn) in the photon energy range 420

Published
2019

25. Experimental study of the gamma p -> K-0 Sigma(+), gamma n -> K-0 Lambda, and gamma n -> 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., Ferretti Bondy, M. I., 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, Milorad, 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, Ivan, 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
photon energies, photoproduction, proton, lambda
Abstract

This work measured ds/dO for neutral kaon photoproduction reactions from threshold up to a c.m. energy of 1855MeV, focussing specifically on the.p. K0S+, .n. K0., and.n. K 0 S 0 reactions. Our results for.n. K0S0 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 pN 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.

Published
2019

26. Measurement of the beam-helicity asymmetry in photoproduction of $��^{0}��$ pairs on carbon, aluminum, and lead

Author

Sokhoyan, V., Prakhov, S., Fix, A., Abt, S., Achenbach, P., Adlarson, P., Afzal, F., Aguar-Bartolom��, P., Ahmed, Z., Altangerel, K., Annand, J. R. M., Arends, H. J., Bantawa, K., Bashkanov, M., Beck, R., Biroth, M., Borisov, N. S., Braghieri, A., Briscoe, W. J., Cherepnya, S., Cividini, F., Collicott, C., Costanza, S., Denig, A., Dieterle, M., Downie, E. J., Drexler, P., Bondy, M. I. Ferretti, Fil'kov, L. V., Gardner, S., Garni, S., Glazier, D. I., Gorodnov, I., Gradl, W., G��nther, M., Gurevich, G. M., Heijkenskj��ld, L., Hornidge, D., Huber, G. M., K��ser, A., Kashevarov, V. L., Kay, S., Keshelashvili, I., Kondratiev, R., Korolija, M., Krusche, B., Lazarev, A., Livingston, K., Lutterer, S., MacGregor, I. J. D., Macrae, R., Manley, D. M., Martel, P. P., McGeorge, J. C., Middleton, D. G., Miskimen, R., Mornacchi, E., Mullen, C., Mushkarenkov, A., Neganov, A., Neiser, A., Oberle, M., Ostrick, M., Otte, P. B., Paudyal, D., Pedroni, P., Powell, A., Rickert, E., Ron, G., Rostomyan, T., Sarty, A., Sfienti, C., Spieker, K., Steffen, O., Strakovsky, I. I., Strandberg, B., Strub, Th., Supek, I., Thiel, A., Thiel, M., Thomas, A., Unverzagt, M., Usov, Yu. A., Wagner, S., Walford, N. K., Watts, D. P., Werthm��ller, D., Wettig, J., Witthauer, L., Wolfes, M., and Zachariou, N.

Subjects
Nuclear Theory, FOS: Physical sciences, High Energy Physics::Experiment, Nuclear Experiment (nucl-ex), Nuclear Experiment
Abstract

The beam-helicity asymmetry was measured, for the first time, in photoproduction of $��^{0}��$ pairs on carbon, aluminum, and lead, with the A2 experimental setup at MAMI. The results are compared to an earlier measurement on a free proton and to the corresponding theoretical calculations. The Mainz model is used to predict the beam-helicity asymmetry for the nuclear targets. The present results indicate that the photoproduction mechanism for $��^{0}��$ pairs on nuclei is similar to photoproduction on a free nucleon. This process is dominated by the $D_{33}$ partial wave with the $����(1232)$ intermediate state., Accepted for publication in Physics Letters B (2020)

Published
2019
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27. Cross section for γn→π0n measured at the Mainz A2 experiment

Author

Briscoe, W. J., Hadžimehmedović, M., Kudryavtsev, A. E., Kulikov, V. V., Martemianov, M. A., Strakovsky, I. I., Švarc, Alfred, Tarasov, V. E., Workman, R. L., Abt, S., Achenbach, P., Akondi, C. S., Afzal, F., Aguar-Bartolomé, 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., Ferretti Bondy, M. I., 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., Korolija, Milorad, 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., Osmanović, H., Omerović, R., Oussena, B., Paudyal, D., Pedroni, P., Powell, A., Prakhov, S. N., Ron, G., Rostomyan, T., Sarty, A., Sfienti, C., Sokhoyan, V., Spieker, K., Stahov, J., Steffen, O., Supek, Ivan, Thiel, A., Thiel, M., Thomas, A., Tiator, L., Unverzagt, M., Usov, Yu. A., Walford, N. K., Watts, D. P., Wagner, S., Werthmüller, D., Wettig, J., Wolfes, M., and Zachariou, N.

Subjects
Physics, Nuclear Theory, neutral pion-photoproduction, tagged photon spectrometer, microtron, Nuclear Experiment
Abstract

The gamma n -> 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 degrees to 162 degrees, making use of model-dependent nuclear corrections to extract pi(0) 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 pi(0)-meson production. Our accumulation of 3.6 x 10(6) gamma n -> 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 with 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* -> gamma n at the resonance poles are determined for the first time.

Published
2019

28. Spin polarizabilities of the proton by measurement of Compton double-polarization observables

Author

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

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

The Compton double-polarization observable $\Sigma_{2z}$ has been measured for the first time in the $\Delta(1232)$ resonance region using a circularly polarized photon beam incident on a longitudinally polarized target at the Mainz Microtron. This paper reports these results, together with the model-dependent extraction of four proton spin polarizabilities from fits to additional asymmetry data using dispersion relation and chiral perturbation theory calculations, with the former resulting in: $\gamma_{E1E1} = -3.18 \pm 0.52$, $\gamma_{M1M1} = 2.98 \pm 0.43$, $\gamma_{E1M2} = -0.44 \pm 0.67$ and $\gamma_{M1E2} = 1.58 \pm 0.43$, in units of $10^{-4}~\mathrm{fm}^{4}$., Comment: 7 pages, 5 figures, 2 tables, accepted for publication in PRC

Published
2019
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29. Signatures of the $d^*(2380)$ hexaquark in d($��$,$p\vec{n}$)

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., G��nther, M., Gurevich, D., Heijkenskj��ld, L., Hornidge, D., Huber, G. M., K��ser, 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., Werthm��ller, D., Wettig, J., Wolfes, M., Zachariou, N., and Zana, L. A.

Subjects
Nuclear Theory, FOS: Physical sciences, Nuclear Experiment (nucl-ex), 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 $E_��\sim$~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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30. Measurement of the Helicity Asymmetry $E$ for the reaction $ ��p\to ��^0 p$

Author

TAPS Collaboration, Gottschall, M., Afzal, F., Anisovich, A. V., Bayadilov, D., Beck, R., Bichow, M., Brinkmann, K. -Th., Crede, V., Dieterle, M., Dietz, F., Dutz, H., Eberhardt, H., Elsner, D., Ewald, R., Fornet-Ponse, K., Friedrich, St., Frommberger, F., Gridnev, A., Gr��ner, M., Gutz, E., Hammann, Ch., Hannappel, J., Hartmann, J., Hillert, W., Hoffmeister, Ph., Honisch, Ch., Jude, T., Kammer, S., Kalinowsky, H., Keshelashvili, I., Klassen, P., Klein, F., Klempt, E., Koop, K., Krusche, B., Kube, M., Lang, M., Lopatin, I., Mahlberg, P., Makonyi, K., Metag, V., Meyer, W., M��ller, J., M��llers, J., Nanova, M., Nikonov, V., Novotny, R., Piontek, D., Reicherz, G., Rostomyan, T., Sarantsev, A., Schmidt, Ch., Schmieden, H., Seifen, T., Sokhoyan, V., Spieker, K., Thiel, A., Thoma, U., Urban, M., van Pee, H., Walther, D., Wendel, Ch., Werthm��ller, D., Wiedner, U., Wilson, A., Winnebeck, A., Witthauer, L., and Wunderlich, Y.

Subjects
Nuclear Theory, Physics::Accelerator Physics, FOS: Physical sciences, Nuclear Experiment (nucl-ex), Nuclear Experiment
Abstract

A measurement of the double-polarization observable $E$ for the reaction $��p\to ��^0 p$ is reported. The data were taken with the CBELSA/TAPS experiment at the ELSA facility in Bonn using the Bonn frozen-spin butanol (C$_4$H$_9$OH) target, which provided longitudinally-polarized protons. Circularly-polarized photons were produced via bremsstrahlung of longitudinally-polarized electrons. The data cover the photon energy range from $E_��=600$~MeV to $E_��=2310$~MeV and nearly the complete angular range. The results are compared to and have been included in recent partial wave analyses., 21 pages

Published
2019
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31. Cross Section for $��n \to ��^0 n$ measured at Mainz/A2

Author

Briscoe, W. J., Hadzimehmedovi, M., Kudryavtsev, A. E., Kulikov, V. V., Martemianov, M. A., Strakovsky, I. I., Svarc, A., Tarasov, V. E., Workman, R. L., Abt, S., Achenbach, P., Akondi, C. S., Afzal, F., Aguar-Bartolome, P., Ahmed, Z., Annand, J. R. M., Arends, H. J., Bantawa, K., Bashkanov, M., Beck, R., Biroth, M., Borisov, N., Braghieri, A., Bulychjov, S. A., Cividini, F., Collicott, C., Costanza, S., Denig, A., Downie, E. J., Drexler, P., Fegan, S., Bondy, M. I. Ferretti, Gardner, S., Ghosal, D., Glazier, D. I., Gorodnov, I., Gradl, W., Gunther, M., Gurevich, D., Heijkenskjold, L., Hornidge, D., Huber, G. M., Kaeser, M., Kashevarov, V. L., Kay, S., Korolija, M., Krusche, B., Lazarev, A., Livingston, K., Lutterer, S., MacGregor, I. J. D., Macrae, R., Manley, D. M., Martel, P. P., McGeorge, J. C., Middleton, D. G., Miskimen, R., Mornacchi, E., Mushkarenkov, A., Mullen, C., Neganov, A., Neiser, A., Ostrick, M., Otte, P. B., Osmanovic, H., Oussena, R. Omerovic B., Paudyal, D., Pedroni, P., Powell, A., Prakhov, S. N., Ron, G., Rostomyan, T., Sarty, A., Senti, C., Sokhoyan, V., Spieker, K., Stahov, J., Steffen, O., Supek, I., Thiel, A., Thiel, M., Thomas, A., Tiator, L., Unverzagt, M., Usov, Yu. A., Walford, N. K., Watts, D. P., Wagner, S., Werthmueller, D., Wettig, J., Wolfes, M., and Zachariou, N.

Subjects
Nuclear Theory (nucl-th), High Energy Physics - Experiment (hep-ex), High Energy Physics - Phenomenology (hep-ph), Nuclear Theory, FOS: Physical sciences, Nuclear Experiment (nucl-ex), Nuclear Experiment
Abstract

The $��n \to ��^0 n$ differential cross section evaluated for 27 energy bins span the photon-energy range 290-813 MeV (W = 1.195-1.553 GeV) and the pion c.m. polar production angles, ranging from 18 deg to 162 deg, making use of model-dependent nuclear corrections to extract pi0 production data on the neutron from measurements on the deuteron target. Additionally, the total photoabsorption cross section was measured. The tagged photon beam produced by the 883-MeV electron beam of the Mainz Microtron MAMI was used for the 0-meson production. Our accumulation of 3.6 x 10^6 $��n \to ��^0 n$ events allowed a detailed study of the reaction dynamics. Our data are in reasonable agreement with previous A2 measurements and extend them to lower energies. The data are compared to predictions of previous SAID, MAID, and BnGa partial-wave analyses and to the latest SAID fit MA19 that included our data. Selected photon decay amplitudes $N^* \to ��n$ at the resonance poles are determined for the first time., 16 pages, 12 figures, 3 tables

Published
2019
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32. Experimental study of the gamma p -> K-0 Sigma(+), gamma n -> K-0 Lambda, and gamma n -> 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., Ferretti Bondy, M. I., 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, Milorad, 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, Ivan, 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
Physics
Abstract

This work measured ds/dO for neutral kaon photoproduction reactions from threshold up to a c.m. energy of 1855MeV, focussing specifically on the.p. K0S+, .n. K0., and.n. K 0 S 0 reactions. Our results for.n. K0S0 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 pN 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.

Published
2019

33. First measurement of helicity-dependent cross sections in 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.

Abstract

The helicity-dependent cross sections for the photoproduction of π0η 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 σ1/2 (photon and target spin antiparallel) and σ3/2 (parallel spins) components to be measured for quasi-free production of π0η 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, A1/2n,p and A3/2n,p. Identical couplings for protons and neutrons are typical for Δ resonances and identical A1/2 and A3/2 components are only possible for J≥3/2 states, which constrains possible contributions of nucleon resonances.

Published
2018

34. The {\eta}'-carbon potential at low meson momenta

Author

Nanova, M., Friedrich, S., Metag, V., Paryev, E. Ya., Afzal, F. N., Bayadilov, D., Bantes, B., Beck, R., Becker, M., Böse, S., Brinkmann, K. -T., Crede, V., Drexler, P., Eberhardt, H., Elsner, D., Frommberger, F., Funke, Ch., Gottschall, M., Grüner, M., Gutz, E., Hammann, Ch., Hannappel, J., Hartmann, J., Hillert, W., Hoffmeister, Ph., Honisch, Ch., Jude, T., Kaiser, D., Kalischewski, F., Keshelashvili, I., Klein, F., Koop, K., Krusche, B., Lang, M., Makonyi, K., Messi, F., Müller, J., Müllers, J., Piontek, D., Rostomyan, T., Schaab, D., Schmidt, Ch., Schmieden, H., Schmitz, R., Seifen, T., Sokhoyan, V., Sowa, C., Spieker, K., Thiel, A., Thoma, U., Triffterer, T., Urban, M., van Pee, H., Walther, D., Wendel, Ch., Werthmüller, D., Wiedner, U., Wilson, A., Witthauer, L., Wunderlich, Y., and Zaunick, H. -G.

Subjects
High Energy Physics::Experiment, Nuclear Experiment
Abstract

The production of $\eta^\prime$ mesons in coincidence with forward-going protons has been studied in photon-induced reactions on $^{12}$C and on a liquid hydrogen (LH$_2$) target for incoming photon energies of 1.3-2.6 GeV at the electron accelerator ELSA. The $\eta^\prime$ mesons have been identified via the $\eta^\prime\rightarrow \pi^0 \pi^0\eta \rightarrow 6 \gamma$ decay registered with the CBELSA/TAPS detector system. Coincident protons have been identified in the MiniTAPS BaF$_2$ array at polar angles of $2^{\circ} \le \theta _{p} \le 11^{\circ}$. Under these kinematic constraints the $\eta^\prime$ mesons are produced with relatively low kinetic energy ($\approx$ 150 MeV) since the coincident protons take over most of the momentum of the incident-photon beam. For the C-target this allows the determination of the real part of the $\eta^\prime$-carbon potential at low meson momenta by comparing with collision model calculations of the $\eta^\prime$ kinetic energy distribution and excitation function. Fitting the latter data for $\eta^\prime$ mesons going backwards in the center-of-mass system yields a potential depth of V = $-$(44 $\pm$ 16(stat)$\pm$15(syst)) MeV, consistent with earlier determinations of the potential depth in inclusive measurements for average $\eta^\prime$ momenta of $\approx$ 1.1 GeV/$c$. Within the experimental uncertainties, there is no indication of a momentum dependence of the $\eta^\prime$-carbon potential. The LH$_2$ data, taken as a reference to check the data analysis and the model calculations, provide differential and integral cross sections in good agreement with previous results for $\eta^\prime$ photoproduction off the free proton., Comment: 9 pages, 13 figures. arXiv admin note: text overlap with arXiv:1608.06074

Published
2018

35. Measurement of the decay <math><mrow><msup><mrow><mi>η</mi></mrow><mrow><mo>′</mo></mrow></msup><mo>→</mo><msup><mrow><mi>π</mi></mrow><mrow><mn>0</mn></mrow></msup><msup><mrow><mi>π</mi></mrow><mrow><mn>0</mn></mrow></msup><mi>η</mi></mrow></math> at MAMI

Author

Adlarson, P., Afzal, F., Ahmed, Z., 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., Ferretti Bondy, M. I., 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.

Abstract

An experimental study of the η′→π0π0η→6γ decay has been conducted with the best up-to-date statistical accuracy, by measuring η′ mesons produced in the γp→η′p reaction with the A2 tagged-photon facility at the Mainz Microtron, MAMI. The results obtained for the standard parametrization of the η′→π0π0η matrix element are consistent with the most recent results for η′→ππη decays, but have smaller uncertainties. The available statistics and experimental resolution allowed, for the first time, an observation of a structure below the π+π− 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 ππ scattering length combination, a0−a2, extracted from K→3π decays.

Published
2018

36. High-statistics measurement of the η → 3π0 decay at MAMI

Author

Prakhov, S., Abt, S., Adlarson, P., Afzal, F., Aguar-Bartolome, P., Ahmed, |., 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., Ferretti Bondy, M.I., Fil'kov, L.V., Fix, A., Gardner, S., Garni, S., Glazier, D.I., Gordonov, I., Gradl, W., 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., 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., Sarty, A., 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.

Abstract

The largest, at the moment, statistics of 7×106 η→3π0 decay s, based on 6.2×107 η mesons produced in the γp→ηp r eaction, has been accumulated by the A2 Collaboration at the Mainz Microtron, MAMI. It allowed a detailed study of the η→3π0 dynamics beyond its conventional parametrization with just the quadratic slope parameter α and enabled, for the first time, a measurement of the second-order ter m 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.

Published
2018

37. 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, High Energy Physics - 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

38. 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

39. High-statistics measurement of the eta->3pi^0 decay at the Mainz Microtron

Author

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

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

The largest, at the moment, statistics of 7x10^6 eta->3pi^0 decays, based on 6.2x10^7 eta mesons produced in the gamma p -> eta p reaction, has been accumulated by the A2 Collaboration at the Mainz Microtron, MAMI. It allowed a detailed study of the eta->3pi^0 dynamics beyond its conventional parametrization with just the quadratic slope parameter alpha and enabled, for the first time, a measurement of the second-order term and a better understanding of the cusp structure in the neutral decay. The present data are also compared to recent theoretical calculations that predict a nonlinear dependence along the quadratic distance from the Dalitz-plot center., 11 pages, 6 figures, 1 table

Published
2018
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40. Experimental study of the $��p\rightarrow K^0��^+$, $��n\rightarrow K^0��$, and $��n\rightarrow K^0 ��^0$ reactions at the Mainz Microtron

Author

Akondi, C. S., Bantawa, K., Manley, D. M., Abt, S., Achenbach, P., Afzal, F., Aguar-Bartolom��, P., Ahmed, Z., Annand, J. R. M., Arends, H. J., Bashkanov, M., Beck, R., Biroth, M., Borisov, N., Braghieri, A., Briscoe, W. J., Cividini, F., Collicott, C., Costanza, S., Denig, A., Dieterle, M., Downie, E. J., Drexler, P., Bondy, M. I. Ferretti, Gardner, S., Glazier, D. I., Gorodnov, I., Gradl, W., G��nther, M., Gurevich, D., Kay, S., Heijkenskj��ld, L., Hornidge, D., Huber, G. M., K��ser, M., Kashevarov, V. L., Korolija, M., Krusche, B., Lazarev, A., Livingston, K., Lutterer, S., McGeorge, J. C., MacGregor, I. J. D., Martel, P. P., Middleton, D. G., Miskimen, R., Mornacchi, E., Mushkarenkov, A., Mullen, C., Neganov, A., Neiser, A., Oberle, M., Ostrick, M., Otte, P. B., Oussena, B., Paudyal, D., Pedroni, P., Powell, A., Prakhov, S. N., Ron, G., Rostomyan, T., Sarty, A., Sfienti, C., Sokhoyan, V., Spieker, K., Steffen, O., Strakovsky, I. I., Strub, Th., Supek, I., Thiel, A., Thiel, M., Thomas, A., Unverzagt, M., Usov, Yu. A., Walford, N. K., Watts, D. P., Wagner, S., Werthm��ller, D., Wettig, J., Witthauer, L., and Wolfes, M.

Subjects
FOS: Physical sciences, Nuclear Experiment (nucl-ex), Nuclear Experiment
Abstract

This work measured $d��/d��$ for neutral kaon photoproduction reactions from threshold up to a c.m.\ energy of 1855MeV, focussing specifically on the $��p\rightarrow K^0��^+$, $��n\rightarrow K^0��$, and $��n\rightarrow K^0 ��^0$ reactions. Our results for $��n\rightarrow K^0 ��^0$ are the first-ever measurements for that reaction. These data will provide insight into the properties of $N^*$ resonances and, in particular, will lead to an improved knowledge about those states that couple only weakly to the $��N$ channel. Integrated cross sections were extracted by fitting the differential cross sections for each reaction as a series of Legendre polynomials and our results are compared with prior experimental results and theoretical predictions., 16 pages, 13 figures, 7 tables

Published
2018
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41. Experimental study of the γp→π0ηp reaction with the A2 setup at the Mainz Microtron

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., Ferretti Bondy, M. I., Fil'kov, L. V., Gardner, S., Garni, S., Glazier, D. I., Gorodnov, I., Gradl, W., Günther, M., 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, Milorad, 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., Sarty, A., Sfienti, C., Spieker, K., Steffen, O., Strakovsky, I. I., Strandberg, B., Strub, Th., Supek, Ivan, 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., Zana, L. A., and A2 Collaboration at MAMI

Subjects
tagged photon spectrometer, high-statistics, partial-wave, I-S, photoproduction, resonances, mami, Pi(0)-pairs, P-Pi(0)eta, nucleon, Nuclear Experiment
Abstract

The data available from the A2 Collaboration at MAMI were analyzed to select the gamma p -> 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 themeasured observables are compared to existing models, and the impact from the new data is checked by the fit with the revised Mainz model.

Published
2018

42. Photoproduction of {\boldmath{$��^{0}$}} Mesons off Protons and Neutrons in the Second and Third Nucleon Resonance Region

Author

Dieterle, M., Werthm��ller, D., Abt, S., Afzal, F., Bartolome, P. Aguar, Ahmed, Z., Ahrens, J., Annand, J. R. M., Arends, H. J., Bashkanov, M., Beck, R., Biroth, M., Borisov, N., Braghieri, A., Briscoe, W. J., Cherepnya, S., Cividini, F., Collicott, C., Costanza, S., Denig, A., Downie, E. J., Drexler, P., Fil'kov, L. V., Garni, S., Glazier, D. I., Gorodnov, I., Gradl, W., G��nther, M., Gurevich, D., Heijkenskj��ld, L., Hornidge, D., Huber, G. M., K��ser, A., Kashevarov, V. L., Kay, S., Keshelashvili, I., Kondratiev, R., Korolija, M., Krusche, B., Lazarev, A., Lisin, V., Livingston, K., Lutterer, S., MacGregor, I. J. D., Manley, D. M., Martel, P. P., McGeorge, J. C., Metag, V., Middleton, D. G., Miskimen, R., Mornacchi, E., Mushkarenkov, A., Neganov, A., Neiser, A., Oberle, M., Ostrick, M., Otte, P. B., Oussena, B., Paudyal, D., Pedroni, P., Polonski, A., Prakhov, S. N., Ron, G., Rostomyan, T., Sarty, A., Sfienti, C., Sokhoyan, V., Spieker, K., Steffen, O., Strakovsky, I. I., Strub, T., Supek, I., Thiel, A., Thiel, M., Thomas, A., Unverzagt, M., Usov, Yu. A., Wagner, S., Walford, N. K., Watts, D. P., Wettig, J., Witthauer, L., Wolfes, M., and Zana, L. A.

Subjects
Nuclear Theory, FOS: Physical sciences, Nuclear Experiment (nucl-ex), Nuclear Experiment
Abstract

Photoproduction of mesons off quasi-free nucleons bound in the deuteron allows to study the electromagnetic excitation spectrum of the neutron and the isospin structure of the excitation of nucleon resonances. The database for such reactions is much more sparse than for free proton targets. Single $��^0$ photoproduction off quasi-free nucleons from the deuteron was experimentally studied. Nuclear effects were investigated by a comparison of the results for free protons and quasi-free protons and used as a correction for the quasi-free neutron data. The experiment was performed at the tagged photon beam of the Mainz MAMI accelerator for photon energies between 0.45~GeV and 1.4~GeV, using an almost $4��$ electromagnetic calorimeter composed of the Crystal Ball and TAPS detectors. A complete kinematic reconstruction of the final state removed the effects of Fermi motion. Reaction model predictions and PWA for $��n\rightarrow n��^{0}$, based on fits to data for the other isospin channels, disagreed between themselves and no model provided a good description of the new data. The results demonstrate clearly the importance of a measurement of the fully neutral final state for the isospin decomposition of the cross section. Model refits, for example from the Bonn-Gatchina analysis, show that the new and the previous data for the other three isospin channels can be simultaneously described when the contributions of several partial waves are modified. The results are also relevant for the suppression of the higher resonance bumps in total photoabsorption on nuclei, which are not well understood., excepted for publication in Phys. Rev. C

Published
2018
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43. Measurement of the decay η ′ → π 0 π 0 η at MAMI

Author

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

Subjects
ddc:530
Abstract

An experimental study of the η′→π0π0η→6γ decay has been conducted with the best up-to-date statistical accuracy, by measuring η′ mesons produced in the γp→η′p reaction with the A2 tagged-photon facility at the Mainz Microtron, MAMI. The results obtained for the standard parametrization of the η′→π0π0η matrix element are consistent with the most recent results for η′→ππη decays, but have smaller uncertainties. The available statistics and experimental resolution allowed, for the first time, an observation of a structure below the π+π− 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 ππ scattering length combination, a0−a2, extracted from K→3π decays.

Published
2018

44. High-statistics measurement of the η → 3 π 0 decay at the Mainz Microtron

Author

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

Subjects
High Energy Physics::Experiment, ddc:530, Nuclear Experiment
Abstract

The largest, at the moment, statistics of 7×106η→3π0 decays, based on 6.2×107η mesons produced in the γp→ηp reaction, has been accumulated by the A2 Collaboration at the Mainz Microtron, MAMI. It allowed a detailed study of the η→3π0 dynamics beyond its conventional parametrization with just the quadratic slope parameter α 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.

Published
2018

45. The $\eta^{\prime}$η-carbon potential at low meson momenta

Author

Nanova, M., Friedrich, S., Brinkmann, K. -T., Crede, V., Drexler, P., Eberhardt, H., Elsner, D., Frommberger, F., Funke, Ch., Gottschall, M., Grüner, M., Gutz, E., Metag, V., Hammann, Ch., Hannappel, J., Hartmann, J., Hillert, W., Hoffmeister, Ph., Honisch, Ch., Jude, T., Kaiser, D., Kalischewski, F., Keshelashvili, I., Paryev, E. Ya., Klein, F., Koop, K., Krusche, B., Lang, M., Makonyi, K., Messi, F., Müller, J., Müllers, J., Piontek, D., Rostomyan, T., Afzal, F. N., Schaab, D., Schmidt, Ch., Schmieden, H., Schmitz, R., Seifen, T., Sokhoyan, V., Sowa, C., Spieker, K., Thiel, A., Thoma, U., Bayadilov, D., Triffterer, T., Urban, M., van Pee, H., Walther, D., Wendel, Ch., Werthmüller, D., Wiedner, U., Wilson, A., Witthauer, L., Wunderlich, Y., Bantes, B., Zaunick, H. -G., Beck, R., Becker, M., and Böse, S.

Subjects
Nuclear Theory, High Energy Physics::Experiment, ddc:530, Nuclear Experiment
Abstract

The production of η′ mesons in coincidence with forward-going protons has been studied in photon-induced reactions on 12C and on a liquid hydrogen (LH2) target for incoming photon energies of 1.3-2.6 GeV at the electron accelerator ELSA. The η′ mesons have been identified via the η′→π0π0η→6γ decay registered with the CBELSA/TAPS detector system. Coincident protons have been identified in the MiniTAPS BaF2 array at polar angles of 2∘≤θp≤11∘. Under these kinematic constraints the η′ mesons are produced with relatively low kinetic energy (≈150 MeV) since the coincident protons take over most of the momentum of the incident-photon beam. For the C-target this allows the determination of the real part of the η′-carbon potential at low meson momenta by comparing with collision model calculations of the η′ kinetic energy distribution and excitation function. Fitting the latter data for η′ mesons going backwards in the center-of-mass system yields a potential depth of V=−(44±16(stat)±15(syst)) MeV, consistent with earlier determinations of the potential depth in inclusive measurements for average η′ momenta of ≈1.1 GeV/c. Within the experimental uncertainties, there is no indication of a momentum dependence of the η′-carbon potential. The LH2 data, taken as a reference to check the data analysis and the model calculations, provide differential and integral cross sections in good agreement with previous results for η′ photoproduction off the free proton.

Published
2018

46. Measurement of the decay η′→π0π0η at MAMI

Author

Adlarson, P., Afzal, F., Ahmed, Z., 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., Ferretti Bondy, M.I., 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., Werthmueller, D., Wettig, J., Witthauer, L., Wolfes, M., Workman, R.L., and Zana, L.A.

Subjects
Physics, High Energy Physics::Experiment, Nuclear Experiment, matrix-element, mass, microtron, 3-Pi(0), cusps, ratio
Abstract

An experimental study of the eta' -> pi(0)pi(0)eta -> 6 gamma decay has been conducted with the best up-to-date statistical accuracy, by measuring. 0 mesons produced in the gamma p -> eta'p reaction with the A2 tagged-photon facility at the Mainz Microtron, MAMI. The results obtained for the standard parametrization of the eta' -> pi(0)pi(0)eta matrix element are consistent with the most recent results for eta' -> 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(-) thorn p-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 -> 3 pi decays.

Published
2018

47. Study of the $��p\to ��^0��p$ reaction with the A2 setup at MAMI

Author

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

Subjects
FOS: Physical sciences, Nuclear Experiment (nucl-ex), Nuclear Experiment
Abstract

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

Published
2018
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48. Experimental study of the γ p → π 0 η p reaction with the A2 setup at the Mainz Microtron

Author

Sokhoyan, V., Prakhov, S., 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., Fix, A., Cividini, F., Collicott, C., Costanza, S., Denig, A., Dieterle, M., Downie, E. J., Drexler, P., Ferretti Bondy, M. I., Fil'kov, L. V., Gardner, S., Abt, S., Garni, S., Glazier, D. I., Gorodnov, I., Gradl, W., Günther, M., Gurevich, G. M., Hamill, C. B., Heijkenskjöld, L., Hornidge, D., Huber, G. M., Achenbach, P., Käser, A., Kashevarov, V. L., Kay, S., Keshelashvili, I., Kondratiev, R., Korolija, M., Krusche, B., Lazarev, A., Lisin, V., Livingston, K., Adlarson, P., 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., Afzal, F., Neiser, A., Oberle, M., Ostrick, M., Otte, P. B., Paudyal, D., Pedroni, P., Polonski, A., Ron, G., Rostomyan, T., Sarty, A., Aguar-Bartolomé, P., Sfienti, C., Spieker, K., Steffen, O., Strakovsky, I. I., Strandberg, B., Strub, Th., Supek, I., Thiel, A., Thiel, M., Thomas, A., Ahmed, Z., Unverzagt, M., Usov, Yu. A., Wagner, S., Walford, N. K., Watts, D. P., Werthmüller, D., Wettig, J., Witthauer, L., Wolfes, M., Zana, L. A., and Ahrens, J.

Subjects
ddc:530, Nuclear Experiment
Abstract

The data available from the A2 Collaboration at MAMI were analyzed to select the γp→π0ηp 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 Eγ=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.

Published
2018

49. 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, Nuclear Experiment, 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

50. Helicity-dependent cross sections and double-polarization observable E in η photoproduction\ud from quasifree 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 Theory, Nuclear Experiment
Abstract

Precise helicity-dependent cross sections and the double-polarization observable E were measured for η\ud photoproduction from quasifree protons and neutrons bound in the deuteron. The η → 2γ and η → 3π0 → 6γ\ud decay modes were used to optimize the statistical quality of the data and to estimate systematic uncertainties. The\ud measurement used the A2 detector setup at the tagged photon beam of the electron accelerator MAMI in Mainz.\ud A longitudinally polarized deuterated butanol target was used in combination with a circularly polarized photon\ud beam from bremsstrahlung of a longitudinally polarized electron beam. The reaction products were detected with\ud the electromagnetic calorimeters Crystal Ball and TAPS, which covered 98% of the full solid angle. The results\ud show that the narrow structure observed earlier in the unpolarized excitation function of η photoproduction off\ud the neutron appears only in reactions with antiparallel photon and nucleon spin (σ1/2). It is absent for reactions\ud with parallel spin orientation (σ3/2) and thus very probably related to partial waves with total spin 1/2. The\ud 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\ud uses an interference of P11 and S11 partial waves to explain the narrow structure.

Published
2017

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