Author: "Oberle, M." - Searchworks@Jio Institute Digital Library Search Results

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417 results on '"Oberle, M."'

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

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

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

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

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

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

4. Single $\pi^0$ Production Off Neutrons Bound in Deuteron with Linearly Polarized Photons

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Author: Sokhoyan, V., Downie, E. J., Mornacchi, E., McGovern, J. A., Krupina, N., Afzal, F., Ahrens, J., Akondi, C. S., Annand, J. R. M., Arends, H. J., Beck, R., Braghieri, A., Briscoe, W. J., Cividini, F., Collicott, C., Costanza, S., Denig, A., Dieterle, M., Ferretti, M., Gardner, S., Garni, S., Glazier, D. I., Glowa, D., Gradl, W., Gurevich, G., Hamilton, D., Hornidge, D., Huber, G. M., Käser, A., Kashevarov, V. L., Keshelashvili, I., Kondratiev, R., Korolija, M., Krusche, B., Lensky, V., Linturi, J., Lisin, V., Livingston, K., MacGregor, I. J. D., Macrae, R., Manley, D. M., Martel, P. P., Middleton, D. G., Miskimen, R., Mushkarenkov, A., Neiser, A., Oberle, M., Spina, H. Ortega, Ostrick, M., Ott, P., Otte, P. B., Oussena, B., Paudyal, D., Pedroni, P., Polonski, A., Polyansky, V., Prakhov, S., Rajabi, A., Rostomyan, T., Sarty, A., Schumann, S., Steffen, O., Strakovsky, I. I., Strandberg, B., Strub, T., Supek, I., Thiel, M., Thomas, A., Unverzagt, M., Wagner, S., Watts, D. P., Wettig, J., Witthauer, L., Werthmüller, D., Wolfes, M., and Zana, L.
Subjects: Nuclear Experiment
Abstract: The scalar dipole polarizabilities, $\alpha_{E1}$ and $\beta_{M1}$, are fundamental properties related to the internal dynamics of the nucleon. The currently accepted values of the proton polarizabilities were determined by fitting to unpolarized proton Compton scattering cross section data. The measurement of the beam asymmetry $\Sigma_{3}$ in a certain kinematical range provides an alternative approach to the extraction of the scalar polarizabilities. At the Mainz Microtron (MAMI) the beam asymmetry was measured for Compton scattering below pion photoproduction threshold for the first time. The results are compared with model calculations and the influence of the experimental data on the extraction of the scalar polarizabilities is determined., Comment: 6 pages, 5 figures
Published: 2016
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20. Measurement of the omega -> pi^0 e^+e^- and eta -> e^+e^-g Dalitz decays with the A2 setup at MAMI

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

Author: Kaeser, A., Mueller, F., Ahrens, J., Annand, J. R. M., Arends, H. J., Bantawa, K., Bartolome, P. A., Beck, R., Braghieri, A., Briscoe, W. J., Cherepnya, S., Costanza, S., Dieterle, M., Downie, E. J., Drexler, P., Fil'kov, L. V., Fix, A., Garni, S., Glazier, D. I., Hamilton, D., Hornidge, D., Howdle, D., Huber, G. M., Jaegle, I., Jude, T. C., Kashevarov, V. L., Keshelashvili, I., Kondratiev, R., Korolija, M., Krusche, B., Lisin, V., Livingston, K., MacGregor, I. J. D., Maghrbi, Y., Mancell, J., Manley, D. M., Marinides, Z., McGeorge, J. C., McNicoll, E., Mekterovic, D., Metag, V., Micanovic, S., Middleton, D. G., Mushkarenkov, A., Nikolaev, A., Novotny, R., Oberle, M., Ostrick, M., Otte, P., Oussena, B., Pedroni, P., Pheron, F., Polonski, A., Prakhov, S., Robinson, J., Rostomyan, T., Schumann, S., Sikora, M. H., Sober, D., Starostin, A., Strub, Th., Supek, I., Thiel, M., Thomas, A., Unverzagt, M., Walford, N. K., Watts, D. P., Werthmueller, D., and Witthauer, L.
Subjects: Nuclear Experiment
Abstract: Quasi-free photoproduction of $\pi\eta$-pairs has been investigated from threshold up to incident photon energies of 1.4 GeV, respectively up to photon-nucleon invariant masses up to 1.9 GeV. Total cross sections, angular distributions, invariant-mass distributions of the $\pi\eta$ and meson-nucleon pairs, and beam-helicity asymmetries have been measured for the reactions $\gamma p\rightarrow p\pi^0\eta$, $\gamma n\rightarrow n\pi^0\eta$, $\gamma p\rightarrow n\pi^+\eta$, and $\gamma n\rightarrow p\pi^-\eta$ from nucleons bound inside the deuteron. For the $\gamma p$ initial state data for free protons have also been analyzed. Finally, the total cross sections for quasi-free production of $\pi^0\eta$ pairs from nucleons bound in $^3$He nuclei have been investigated in view of final state interaction (FSI) effects. The experiments were performed at the tagged photon beam facility of the Mainz MAMI accelerator using an almost $4\pi$ covering electromagnetic calorimeter composed of the Crystal Ball and TAPS detectors. The shapes of all differential cross section data and the asymmetries are very similar for protons and neutrons and agree with the conjecture that the reactions are dominated by the sequential $\Delta^{\star}3/2^-\rightarrow\eta\Delta(1232)\rightarrow\pi\eta N$ decay chain, mainly with $\Delta(1700)3/2^-$ and $\Delta(1940)3/2^-$. The ratios of the magnitude of the total cross sections also agree with this assumption. However, the absolute magnitudes of the cross sections are reduced by FSI effects with respect to free proton data., Comment: accepted for publication in Eur. Phys. J. A
Published: 2016
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22. Photon asymmetry measurements of $\overrightarrow{\gamma} \mathrm{p} \rightarrow \pi^{0} \mathrm{p}$ for E$_{\gamma}$=320$-$650 MeV

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

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

24. The isospin structure of photoproduction of pi-eta pairs from the nucleon in the threshold region

Author: Käser, A., Ahrens, J., Annand, J. R. M., Arends, H. J., Bantawa, K., Bartolome, P. A., Beck, R., Bekrenev, V., Berghäuser, H., Braghieri, A., Branford, D., Briscoe, W. J., Brudvik, J., Cherepnya, S., Costanza, S., Demissie, B., Dieterle, M., Downie, E. J., Drexler, P., Fil'kov, L. V., Fix, A., Glazier, D. I., Hamilton, D., Heid, E., Hornidge, D., Howdle, D., Huber, G. M., Jahn, O., Jaegle, I., Jude, T. C., Kashevarov, V. L., Keshelashvili, I., Kondratiev, R., Korolija, M., Kruglov, S. P., Krusche, B., Lisin, V., Livingston, K., MacGregor, I. J. D., Maghrbi, Y., Mancell, J., Manley, D. M., Marinides, Z., McGeorge, J. C., McNicoll, E., Mekterovic, D., Metag, V., Micanovic, S., Middleton, D. G., Mushkarenkov, A., Nikolaev, A., Novotny, R., Oberle, M., Ostrick, M., Otte, P., Oussena, B., Pedroni, P., Pheron, F., Polonski, A., Prakhov, S. N., Robinson, J., Rosner, G., Rostomyan, T., Schumann, S., Sikora, M. H., Sober, D. I., Starostin, A., Supek, I., Thiel, M., Thomas, A., Unverzagt, M., Watts, D. P., Werthmüller, D., and Witthauer, L.
Subjects: Nuclear Experiment
Abstract: Photoproduction of $\pi\eta$-pairs from nucleons has been investigated from threshold up to incident photon energies of $\approx$~1.4~GeV. The quasi-free reactions $\gamma p\rightarrow p\pi^0\eta$, $\gamma n\rightarrow n\pi^0\eta$, $\gamma p\rightarrow n\pi^+\eta$, and $\gamma n\rightarrow p\pi^-\eta$ were for the first time measured from nucleons bound in the deuteron. The corresponding reactions from a free-proton target were also studied to investigate final-state interaction effects (for neutral pions the free-proton results could be compared to previous measurements; the $\gamma p\rightarrow n\pi^+\eta$ reaction was measured for the first time). For the $\pi^0\eta$ final state coherent production via the $\gamma d\rightarrow d\pi^0\eta$ reaction was also investigated. The experiments were performed at the tagged photon beam of the Mainz MAMI accelerator using an almost $4\pi$ coverage electromagnetic calorimeter composed of the Crystal Ball and TAPS detectors. The total cross sections for the four different final states obey the relation $\sigma(p\pi^0\eta)$ $\approx$ $\sigma(n\pi^0\eta)$ $\approx$ $2\sigma(p\pi^-\eta)$ $\approx$ $2\sigma(n\pi^+\eta)$ as expected for a dominant contribution from a $\Delta^{\star}\rightarrow\eta\Delta(1232)\rightarrow\pi\eta N$ reaction chain, which is also supported by the shapes of the invariant-mass distributions of nucleon-meson and $\pi$-$\eta$ pairs. The experimental results are compared to the predictions from an isobar reaction model., Comment: accepted for publication in Phys. Lett. B
Published: 2015

25. Measurement of pi^0 photoproduction on the proton at MAMI C

Author: Adlarson, P., Afzal, F., Akondi, C. S., Annand, J. R. M., Arends, H. J., Azimov, Ya. I., Beck, R., Borisov, N., Braghieri, A., Briscoe, W. J., Cherepnya, S., Cividini, F., Collicott, C., Costanza, S., Denig, A., Downie, E. J., Dieterle, M., Bondy, M. I. Ferretti, Fil'kov, L. V., Fix, A., Gardner, S., Garni, S., Glazier, D. I., Glowa, D., Gradl, W., Gurevich, G., Hamilton, D. J., Hornidge, D., Huber, G. M., Käser, A., Kashevarov, V. L., Kay, S., Keshelashvili, I., Kondratiev, R., Korolija, M., Krusche, B., Kulikov, V. V., Lazarev, A., Linturi, J., Lisin, V., Livingston, K., MacGregor, I. J. D., Manley, D. M., Martel, P. P., Martemianov, M., McGeorge, J. C., Meyer, W., Middleton, D. G., Miskimen, R., Mushkarenkov, A., Neganov, A., Neiser, A., Oberle, M., Ostrick, M., Ott, P., Otte, P. B., Oussena, B., Paudyal, D., Pedroni, P., Polonski, A., Polyanski, V. V., Prakhov, S., Rajabi, A., Reicherz, G., Ron, G., Rostomyan, T., Sarty, A., Schott, D. M., Schumann, S., Sfienti, C., Sokhoyan, V., Spieker, K., Steffen, O., Strakovsky, I. I., Strub, Th., Supek, I., Taragin, M. F., Thiel, A., Thiel, M., Tiator, L., Thomas, A., Unverzagt, M., Usov, Yu. A., Wagner, S., Watts, D. P., Werthmüller, D., Wettig, J., Witthauer, L., Wolfes, M., Workman, R. L., and Zana, L. A.
Subjects: High Energy Physics - Experiment, Nuclear Experiment
Abstract: Differential cross sections for the gamma p -> pi^0 p reaction have been measured with the A2 tagged-photon facilities at the Mainz Microtron, MAMI C, up to the center-of-mass energy W=1.9 GeV. The new results, obtained with a fine energy and angular binning, increase the existing quantity of pi^0 photoproduction data by ~47%. Owing to the unprecedented statistical accuracy and the full angular coverage, the results are sensitive to high partial-wave amplitudes. This is demonstrated by the decomposition of the differential cross sections in terms of Legendre polynomials and by further comparison to model predictions. A new solution of the SAID partial-wave analysis obtained after adding the new data into the fit is presented., Comment: 13 pages, 12 figures, 1 table
Published: 2015
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26. First measurement of target and beam-target asymmetries in the $\gamma p\to \pi^0\eta p$ reaction

Author: Annand, J. R. M., Arends, H. J., Beck, R., Borisov, N., Braghieri, A., Briscoe, W. J., Cherepnya, S., Collicott, C., Costanza, S., Downie, E. J., Dieterle, M., Fix, A., Fil'kov, L. V., Garni, S., Glazier, D. I., Gradl, W., Gurevich, G., Barrientos, P. H., Hamilton, D., Hornidge, D., Howdle, D., Huber, G. M., Kashevarov, V. L., Keshelashvili, I., Kondratiev, R., Korolija, M., Krusche, B., Lazarev, A., Lisin, V., Livingston, K., MacGregor, I. J. D., Mancel, J., Manley, D. M., Martel, P., McNicoll, E. F., Meyer, W., Middleton, D., Miskimen, R., Mushkarenkov, A., Neganov, A., Nikolaev, A., Oberle, M., Ortega, H., Ostrick, M., Ott, P., Otte, P. B., Oussena, B., Pedroni, P., Polonski, A., Polyanski, V. V., Prakhov, S., Reicherz, G., Rostomyan, T., Sarty, A., Schumann, S., Steffen, O., Strakovsky, I. I., Strub, T., Supek, I., Tiator, L., Thomas, A., Unverzagt, M., Usov, Y. A., Watts, D. P., Werthmüller, D., Witthauer, L., and Wolfes, M.
Subjects: Nuclear Experiment, High Energy Physics - Experiment, Nuclear Theory
Abstract: The first data on target and beam-target asymmetries for the $\gamma p\to\pi^0\eta p$ reaction at photon energies from 1050 up to 1450 MeV are presented. The measurements were performed using the Crystal Ball and TAPS detector setup at the Glasgow tagged photon facility of the Mainz Microtron MAMI. The general assumption that the reaction is dominated by the $\Delta 3/2^-$ amplitude is confirmed. The data are in particular sensitive to small contributions from other partial waves., Comment: 9 pages, 9 figures
Published: 2015
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27. A new measurement of the neutron detection efficiency for the NaI Crystal Ball detector

Author: Martemianov, M., Kulikov, V., Demissie, B. T., Marinides, Z., Akondi, C. S., Annand, J. R. M., Arends, H. J., Beck, R., Borisov, N., Braghieri, A., Briscoe, W. J., Cherepnya, S., Collicott, C., Costanza, S., Downie, E. J., Dieterle, M., Bondy, M. I. Ferretti, Filkov, L. V., Garni, S., Glazier, D. I., Glowa, D., Gradl, W., Gurevich, G., Hornidge, D., Huber, G. M., Kaeser, A., Kashevarov, V. L., Keshelashvili, I., Kondratiev, R., Korolija, M., Krusche, B., Lazarev, A., Linturi, J. M., Lisin, V., Livingston, K., MacGregor, I. J. D., Manley, D. M., Martel, P. P., Middleton, D. G., Miskimen, R., Mushkarenkov, A., Neganov, A., Neiser, A., Oberle, M., Ostrick, M., Ott, P., Otte, P. B., Oussena, B., Pedroni, P., Polonski, A., Prakhov, S., Ron, G., Rostomyan, T., Sarty, A., Schott, D. M., Schumann, S., Sokhoyan, V., Steffen, O., Strakovsky, I. I., Strub, Th., Supek, I., Thiel, M., Thomas, A., Unverzagt, M., Usov, Yu. A., Wagner, S., Watts, D. P., Wettig, J., Werthmuller, D., Witthauer, L., and Wolfes, M.
Subjects: Physics - Instrumentation and Detectors, High Energy Physics - Experiment, Nuclear Experiment
Abstract: We report on a measurement of the neutron detection efficiency in NaI crystals in the Crystal Ball detector obtained from a study of single p0 photoproduction on deuterium using the tagged photon beam at the Mainz Microtron. The results were obtained up to a neutron energy of 400 MeV. They are compared to previous measurements made more than 15 years ago at the pion beam at the BNL AGS.
Published: 2015
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28. Measurement of the transverse target and beam-target asymmetries in $\eta$ meson photoproduction at MAMI

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

Author: Martel, P. P., Miskimen, R., Aguar-Bartolome, P., Ahrens, J., Akondi, C. S., Annand, J. R. M., Arends, H. J., Barnes, W., Beck, R., Bernstein, A., Borisov, N., Braghieri, A., Briscoe, W. J., Cherepnya, S., Collicott, C., Costanza, S., Denig, A., Dieterle, M., Downie, E. J., Fil'kov, L. V., Garni, S., Glazier, D. I., Gradl, W., Gurevich, G., Barrientos, P. Hall, Hamilton, D., Hornidge, D., Howdle, D., Huber, G. M., Jude, T. C., Kaeser, A., Kashevarov, V. L., Keshelashvili, I., Kondratiev, R., Korolija, M., Krusche, B., Lazarev, A., Lisin, V., Livingston, K., MacGregor, I. J. D., Mancell, J., Manley, D. M., Meyer, W., Middleton, D. G., Mushkarenkov, A., Nefkens, B. M. K., Neganov, A., Nikolaev, A., Oberle, M., Spina, H. Ortega, Ostrick, M., Ott, P., Otte, P. B., Oussena, B., Pedroni, P., Polonski, A., Polyansky, V., Prakhov, S., Rajabi, A., Reicherz, G., Rostomyan, T., Sarty, A., Schrauf, S., Schumann, S., Sikora, M. H., Starostin, A., Steffen, O., Strakovsky, I. I., Strub, T., Supek, I., Thiel, M., Tiator, L., Thomas, A., Unverzagt, M., Usov, Y., Watts, D. P., Witthauer, L., Werthmüller, D., and Wolfes, M.
Subjects: Nuclear Experiment
Abstract: The spin polarizabilities of the nucleon describe how the spin of the nucleon responds to an incident polarized photon. The most model-independent way to measure the nucleon spin polarizabilities is through polarized Compton scattering. Double-polarized Compton scattering asymmetries on the proton were measured in the $\Delta(1232)$ region using circularly polarized incident photons and a transversely polarized proton target at the Mainz Microtron. Fits to asymmetry data were performed using a dispersion model calculation and a baryon chiral perturbation theory calculation, and a separation of all four proton spin polarizabilities in the multipole basis was achieved. The analysis based on a dispersion model calculation yields $\gamma_{E1E1} = -3.5 \pm 1.2$, $\gamma_{M1M1}= 3.16 \pm 0.85$, $\gamma_{E1M2} = -0.7 \pm 1.2$, and $\gamma_{M1E2} = 1.99 \pm 0.29$, in units of $10^{-4}$ fm$^4$., Comment: 5 pages, 3 figures, 2 tables
Published: 2014
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30. Quasifree photoproduction of $\eta$ mesons off protons and neutrons

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

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

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

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

Author: Oberle, M. and Krusche, B.
Subjects: Physics - Accelerator Physics, High Energy Physics - Experiment, Nuclear Experiment
Abstract: Beam-helicity asymmetries and mass-differential cross sections have been measured at the MAMI accelerator in Mainz for the photoproduction of neutral and mixed-charge pion pairs in the reactions $\boldsymbol{\gamma}p\rightarrow n\pi^0\pi^+$ and $\boldsymbol{\gamma}p\rightarrow p\pi^0\pi^0$ off free protons and $\boldsymbol{\gamma}d \rightarrow (p)p\pi^0\pi^-$, $\boldsymbol{\gamma}d\rightarrow (n)p\pi^0\pi^0$ and $\boldsymbol{\gamma}d\rightarrow (n)n\pi^0\pi^+$, $\boldsymbol{\gamma}d\rightarrow (p)n \pi^0\pi^0$ off quasi-free nucleons bound in the deuteron for incident photon energies up to 1.4 GeV. Circularly polarized photons were produced in bremsstrahlung processes of longitudinally polarized electrons and tagged with the Glasgow-Mainz magnetic spectrometer. The decay products (photons, protons, neutrons, and charged pions) were detected in the $4\pi$ electromagnetic calorimeter composed of the Crystal Ball and TAPS detectors. Using a full kinematic reconstruction of the final state, excellent agreement was found between the results for free and quasi-free protons, indicating that the quasi-free neutron results are also a close approximation of the free-neutron results. Comparisons of the results to predictions from model calculations suggest that especially the reaction mechanisms in the production of the mixed-charge final states are still not well understood, in particular at low incident photon energies in the second nucleon resonance region., Comment: 4 pages, 2 figures, Physics of Excited Nucleons (NSTAR 2013). International Journal of Modern Physics: Conference Series 2013
Published: 2014
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35. Quasi-free photoproduction of eta-mesons off 3He nuclei

Author: Witthauer, L., Werthmueller, D., Keshelashvili, I., Aguar-Bartolome, P., Ahrens, J., Annand, J. R. M., Arends, H. J., Bantawa, K., Beck, R., Bekrenev, V., Braghieri, A., Branford, D., Briscoe, W. J., Brudvik, J., Cherepnya, S., Demissie, B., Dieterle, M., Downie, E. J., Drexler, P., Fil'kov, L. V., Fix, A., Glazier, D. I., Hamilton, D., Heid, E., Hornidge, D., Howdle, D., Huber, G. M., Jaegle, I., Jahn, O., Jude, T. C., Kaeser, A., Kashevarov, V. L., Kondratiev, R., Korolija, M., Kruglov, S. P., Krusche, B., Kulbardis, A., Lisin, V., Livingston, K., MacGregor, I. J. D., Maghrbi, Y., Mancell, J., Manley, D. M., Marinides, Z., Martinez, M., McGeorge, J. C., McNicoll, E., Metag, V., Middleton, D. G., Mushkarenkov, A., Nefkens, B. M. K., Nikolaev, A., Novotny, R., Oberle, M., Ostrick, M., Oussena, B., Pedroni, P., Pheron, F., Polonski, A., Prakhov, S., Robinson, J., Rosner, G., Rost, M., Rostomyan, T., Schumann, S., Sikora, M. H., Sober, D., Starostin, A., Supek, I., Thiel, M., Thomas, A., Unverzagt, M., and Watts, D. P.
Subjects: Nuclear Experiment
Abstract: Quasi-free photoproduction of $\eta$-mesons has been measured off nucleons bound in $^3$He nuclei for incident photon energies from the threshold region up to 1.4 GeV. The experiment was performed at the tagged photon facility of the Mainz MAMI accelerator with an almost $4\pi$ covering electromagnetic calorimeter, combining the TAPS and Crystal Ball detectors. The $\eta$-mesons were detected in coincidence with the recoil nucleons. This allowed a comparison of the production cross section off quasi-free protons and quasi-free neutrons and a full kinematic reconstruction of the final state, eliminating effects from nuclear Fermi motion. In the $S_{11}$(1535) resonance peak, the data agree with the neutron/proton cross section ratio extracted from measurements with deuteron targets. More importantly, the prominent structure observed in photoproduction off quasi-free neutrons bound in the deuteron is also clearly observed. Its parameters (width, strength) are consistent with the expectations from the deuteron results. On an absolute scale the cross sections for both quasi-free protons and neutrons are suppressed with respect to the deuteron target pointing to significant nuclear final state interaction effects., Comment: accepted for publication in Eur. Phys. J. A
Published: 2013
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36. A narrow structure in the excitation function of eta-photoproduction off the neutron

Author: Werthmueller, D., Witthauer, L., Keshelashvili, I., Aguar-Bartolome, P., Ahrens, J., Annand, J. R. M., Arends, H. J., Bantawa, K., Beck, R., Bekrenev, V., Braghieri, A., Branford, D., Briscoe, W. J., Brudvik, J., Cherepnya, S., Demissie, B., Dieterle, M., Downie, E. J., Drexler, P., Fil'kov, L. V., Fix, A., Glazier, D. I., Hamilton, D., Heid, E., Hornidge, D., Howdle, D., Huber, G. M., Jaegle, I., Jahn, O., Jude, T. C., Kaeser, A., Kashevarov, V. L., Kondratiev, R., Korolija, M., Kruglov, S. P., Krusche, B., Kulbardis, A., Lisin, V., Livingston, K., MacGregor, I. J. D., Maghrbi, Y., Mancell, J., Manley, D. M., Marinides, Z., Martinez, M., McGeorge, J. C., McNicoll, E. F., Metag, V., Middleton, D. G., Mushkarenkov, A., Nefkens, B. M. K., Nikolaev, A., Novotny, R., Oberle, M., Ostrick, M., Oussena, B., Pedroni, P., Pheron, F., Polonski, A., Prakhov, S. N., Robinson, J., Rosner, G., Rostomyan, T., Schumann, S., Sikora, M. H., Sober, D., Starostin, A., Supek, I., Thiel, M., Thomas, A., Unverzagt, M., and Watts, D. P.
Subjects: Nuclear Experiment
Abstract: The photoproduction of $\eta$-mesons off nucleons bound in $^2$H and $^3$He has been measured in coincidence with recoil protons and recoil neutrons for incident photon energies from threshold up to 1.4 GeV. The experiments were performed at the Mainz MAMI accelerator, using the Glasgow tagged photon facility. Decay photons from the $\eta\rightarrow 2\gamma$ and $\eta\rightarrow 3\pi^0$ decays and the recoil nucleons were detected with an almost $4\pi$ electromagnetic calorimeter combining the Crystal Ball and TAPS detectors. The data from both targets are of excellent statistical quality and show a narrow structure in the excitation function of $\gamma n\rightarrow n\eta$. The results from the two measurements are consistent taking into account the expected effects from nuclear Fermi motion. The best estimates for position and intrinsic width of the structure are $W$ = (1670$\pm$5) MeV and $\Gamma$ =(30$\pm$15) MeV. For the first time precise results for the angular dependence of this structure have been extracted., Comment: Accepted for publication in Phys. Rev. Lett
Published: 2013
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37. $K^+\Lambda$ and $K^+\Sigma^0$ photoproduction with fine center-of-mass energy resolution

Author: Jude, T. C., Glazier, D. I., Watts, D. P., Aguar-Bartolome, P., Akasoy, L. K., Annand, J. R. M., Arends, H. J., Bantawa, K., Beck, R., Bekrenev, V. S., Berghauser, H., Braghieri, A., Branford, D., Briscoe, W. J., Brudvik, J., Cherepnya, S., Demissie, B. T., Dieterle, M., Downie, E. J., Fil'kov, L. V., Gregor, R., Heid, E., Hornidge, D., Jaegle, I., Jahn, O., Kashevarov, V. L., Keshelashvili, I., Kondratiev, R., Korolija, M., Koulbardis, A. A., Kruglov, S. P., Krusche, B., Lisin, V., Livingston, K., MacGregor, I. J. D., Maghrbi, Y., Manley, D. M., Marinides, Z., Mart, T., Martinez, M., McGeorge, J. C., McNicoll, E. F., Middleton, D. G., Mushkarenkov, A., Nefkens, B. M. K., Nikolaev, A., Nikonov, V. A., Oberle, M., Ostrick, M., Otte, P. B., Oussena, B., Pedroni, P., Pheron, F., Polonski, A., Prakhov, S., Robinson, J., Rosner, G., Rostomyan, T., Sarantsev, A. V., Schumann, S., Sikora, M. H., Sober, D. I., Starostin, A., Strakovsky, I., Suarez, I. M., Supek, I., Thiel, M., Thomas, A., Unverzagt, M., Werthmueller, D., Witthauer, L., and Zehr, F.
Subjects: Nuclear Experiment
Abstract: Measurements of $\gamma p \rightarrow K^{+} \Lambda$ and $\gamma p \rightarrow K^{+} \Sigma^0$ cross-sections have been obtained with the photon tagging facility and the Crystal Ball calorimeter at MAMI-C. The measurement uses a novel $K^+$ meson identification technique in which the weak decay products are characterized using the energy and timing characteristics of the energy deposit in the calorimeter, a method that has the potential to be applied at many other facilities. The fine center-of-mass energy ($W$) resolution and statistical accuracy of the new data results in a significant impact on partial wave analyses aiming to better establish the excitation spectrum of the nucleon. The new analyses disfavor a strong role for quark-diquark dynamics in the nucleon., Comment: 7 pages, 8 figures
Published: 2013
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38. Measurement of the g p -> K^0 Sigma^+ reaction with the Crystal Ball/TAPS detectors at the Mainz Microtron

Author: Aguar-Bartolomé, P., Annand, J. R. M., Arends, H. J., Bantawa, K., Beck, R., Bekrenev, V., Berghäuser, H., Braghieri, A., Briscoe, W. J., Brudvik, J., Cherepnya, S., Codling, R. F. B., Collicott, C., Demissie, B., Dieterle, M., Downie, E. J., Drexler, P., Fil'kov, L. V., Fix, A., Glazier, D. I., Gregor, R., Hamilton, D., Heid, E., Hornidge, D., Howdle, D., Isaksson, L., Jaegle, I., Jahn, O., Jude, T. C., Kashevarov, V. L., Keshelashvili, I., Kondratiev, R., Korolija, M., Kotulla, M., Koulbardis, A., Kruglov, S., Krusche, B., Lisin, V., Livingston, K., MacGregor, I. J. D., Maghrbi, Y., Mancel, J., Manley, D. M., McNicoll, E. F., Mekterovic, D., Metag, V., Mushkarenkov, A., Nefkens, B. M. K., Nikolaev, A., Novotny, R., Oberle, M., Ortega, H., Ostrick, M., Ott, P., Otte, P. B., Oussena, B., Pedroni, P., Pheron, F., Polonski, A., Prakhov, S., Robinson, J., Rosner, G., Rostomyan, T., Schumann, S., Sikora, M. H., Sober, D. I., Starostin, A., Strakovsky, I. I., Suarez, I. M., Supek, I., Tarbert, C. M., Thiel, M., Thomas, A., Unverzagt, M., Watts, D. P., Werthmüller, D., Witthauer, L., and Zehr., F.
Subjects: High Energy Physics - Experiment, Nuclear Experiment
Abstract: The g p -> K^0 Sigma^+ reaction has been measured from threshold to Eg=1.45 GeV (W_cm=1.9 GeV) using the Crystal Ball and TAPS multiphoton spectrometers together with the photon tagging facility at the Mainz Microtron MAMI. In the present experiment, this reaction was searched for in the 3pi^0 p final state, by assuming K^0_S -> pi^0 pi^0 and Sigma^+ -> pi^0 p. The experimental results include total and differential cross sections as well as the polarization of the recoil hyperon. The new data significantly improve empirical knowledge about the g p -> K^0 Sigma^+ reaction in the measured energy range. The results are compared to previous measurements and model predictions. It is demonstrated that adding the present g p -> K^0 Sigma^+ results to existing data allowed a better description of this reaction with various models., Comment: 12 pages, 10 figures, 4 tables
Published: 2013
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39. Measurement of the beam-helicity asymmetry $I^{\odot}$ in the photoproduction of $\pi^0$-pairs off the proton and off the neutron

Author: Oberle, M., Krusche, B., Ahrens, J., Annand, J. R. M., Arends, H. J., Bantawa, K., Bartolome, P. A., Beck, R., Bekrenev, V., Berghaeuser, H., Braghieri, A., Branford, D., Briscoe, W. J., Brudvik, J., Cherepnya, S., Demissie, B., Dieterle, M., Downie, E. J., Drexler, P., Fil'kov, L. V., Fix, A., Glazier, D. I., Heid, E., Hornidge, D., Howdle, D., Huber, G. M., Jahn, O., Jaegle, I., Jude, T. C., Kaeser, A., Kashevarov, V. L., Keshelashvili, I., Kondratiev, R., Korolija, M., Kruglov, S. P., Kulbardis, A., Lisin, V., Livingston, K., MacGregor, I. J. D., Maghrbi, Y., Mancell, J., Manley, D. M., Marinides, Z., Martinez, M., McGeorge, J. C., McNicoll, E., Mekterovic, D., Metag, V., Micanovic, S., Middleton, D. G., Mushkarenkov, A., Nefkens, B. M. K., Nikolaev, A., Novotny, R., Ostrick, M., Oussena, B., Pedroni, P., Pheron, F., Polonski, A., Prakhov, S. N., Robinson, J., Rosner, G., Rostomyan, T., Schumann, S., Sikora, M. H., Sober, D. I., Starostin, A., Supek, I., Thiel, M., Thomas, A., Unverzagt, M., Watts, D. P., Werthmueller, D., Witthauer, L., and Zehr, F.
Subjects: Nuclear Experiment
Abstract: Beam-helicity asymmetries have been measured at the MAMI accelerator in Mainz for the photoproduction of neutral pion pairs in the reactions $\vec{\gamma}p\rightarrow p\pi^0\pi^0$ and $\vec{\gamma}d\rightarrow (n)p\pi^0\pi^0$, $\vec{\gamma}d\rightarrow (p)n\pi^0\pi^0$ off free protons and off quasi-free nucleons bound in the deuteron for incident photon energies up to 1.4 GeV. Circularly polarized photons were produced from bremsstrahlung of longitudinally polarized electrons and tagged with the Glasgow magnetic spectrometer. Decay photons from the $\pi^0$ mesons, recoil protons, and recoil neutrons were detected in the 4$\pi$ covering electromagnetic calorimeter composed of the Crystal Ball and TAPS detectors. After kinematic reconstruction of the final state, excellent agreement was found between the results for free and quasi-free protons. This demonstrates that the free-nucleon behavior of such observables can be extracted from measurements with quasi-free nucleons, which is the only possibility for the neutron. Contrary to expectations, the measured asymmetries are very similar for reactions off protons and neutrons. The results are compared to the predictions from the Two-Pion-MAID reaction model and (for the proton) also to the Bonn-Gatchina coupled channel analysis., Comment: accepted for publication in Phys. Lett. B
Published: 2013
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40. In vivo – determination of the fat content in mirror carps (Cyprinus carpio) using ultrasound, microwave and linear measurements

Author: Maas, P., Grzegrzółka, B., Kreß, P., Oberle, M., and Kremer-Rücker, P.V.
Published: 2019
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41. Accurate Test of Chiral Dynamics in the \boldmath$\vec{\gamma} p \rightarrow \pi^0p$ Reaction

Author: Hornidge, D., Bartolome, P. Aguar, Annand, J. R. M., Arends, H. J., Beck, R., Bekrenev, V., Berghaeuser, H., Bernstein, A. M., Braghieri, A., Briscoe, W. J., Cherepnya, S., Dieterle, M., Downie, E. J., Drexler, P., Fernandez-Ramirez, C., Filkov, L. V., Glazier, D. I., Barrientos, P. Hall, Heid, E., Hilt, M., Jaegle, I., Jahn, O., Jude, T. C., Kashevarov, V. L., Keshelashvili, I., Kondratiev, R., Korolija, M., Koulbardis, A., Krambrich, D., Kruglov, S., Krusche, B., Laffoley, A. T., Lisin, V., Livingston, K., MacGregor, I. J. D., Mancell, J., Manley, D. M., McNicoll, E. F., Mekterovic, D., Metag, V., Micanovic, S., Middleton, D. G., Moores, K. W., Mushkarenkov, A., Nefkens, B. M. K., Oberle, M., Ostrick, M., Otte, P. B., Oussena, B., Pedroni, P., Pheron, F., Polonski, A., Prakhov, S., Robinson, J., Rostomyan, T., Scherer, S., Schumann, S., Sikora, M. H., Starostin, A., Supek, I., Thiel, M., Thomas, A., Tiator, L., Unverzagt, M., Watts, D. P., Werthmueller, D., and Witthauer, L.
Subjects: Nuclear Experiment
Abstract: A precision measurement of the differential cross sections $d\sigma/d\Omega$ and the linearly polarized photon asymmetry $\Sigma \equiv (d\sigma_\perp - d\sigma_\parallel) \slash (d\sigma_\perp + d\sigma_\parallel)$ for the $\vec{\gamma} p \rightarrow \pi^0p$ reaction in the near-threshold region has been performed with a tagged photon beam and almost $4\pi$ detector at the Mainz Microtron. The Glasgow-Mainz photon tagging facility along with the Crystal Ball/TAPS multi-photon detector system and a cryogenic liquid hydrogen target were used. These data allowed for a precise determination of the energy dependence of the real parts of the $S$- and all three $P$-wave amplitudes for the first time and provide the most stringent test to date of the predictions of Chiral Perturbation Theory and its energy region of agreement with experiment., Comment: 5 pages, 2 figures
Published: 2012
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42. Coherent photoproduction of eta-mesons off 3He - search for eta-mesic nuclei

Author: Pheron, F., Ahrens, J., Annand, J. R. M., Arends, H. J., Bantawa, K., Bartolome, P. A., Beck, R., Bekrenev, V., Berghaeuser, H., Boillat, B., Braghieri, A., Branford, D., Briscoe, W. J., Brudvik, J., Cherepnya, S., Demissie, B., Dieterle, M., Downie, E. J., Drexler, P., Glazier, D. I., Heid, E., Fil'kov, L. V., Hornidge, D., Howdle, D., Jahn, O., Jaegle, I., Jude, T. C., Kashevarov, V. L., Keshelashvili, I., Kondratiev, R., Korolija, M., Kotulla, M., Kulbardis, A., Kruglov, S. P., Krusche, B., Lisin, V., Livingston, K., MacGregor, I. J. D., Maghrbi, Y., Mancell, J., Manley, D. M., Marinides, Z., Martinez, M., McGeorge, J. C., McNicoll, E., Mekterovic, D., Metag, V., Micanovic, S., Middleton, D. G., Mushkarenkov, A., Nefkens, B. M. K., Nikolaev, A., Novotny, R., Oberle, M., Ostrick, M., Oussena, B., Pedroni, P., Polonski, A., Prakhov, S. N., Robinson, J., Rosner, G., Rostomyan, T., Schumann, S., Sikora, M. H., Sober, D. I., Starostin, A., Supek, I., Thiel, M., Thomas, A., Unverzagt, M., Watts, D. P., Werthmueller, D., Witthauer, L., and Zehr, F.
Subjects: Nuclear Experiment
Abstract: Coherent photoproduction of $\eta$-mesons off $^3$He, i.e. the reaction $\gamma ^3{He}\rightarrow \eta ^3{He}$, has been investigated in the near-threshold region. The experiment was performed at the Glasgow tagged photon facility of the Mainz MAMI accelerator with the combined Crystal Ball - TAPS detector. Angular distributions and the total cross section were measured using the $\eta\rightarrow \gamma\gamma$ and $\eta\rightarrow 3\pi^0\rightarrow 6\gamma$ decay channels. The observed extremely sharp rise of the cross section at threshold and the behavior of the angular distributions are evidence for a strong $\eta {^3{He}}$ final state interaction, pointing to the existence of a resonant state. The search for further evidence of this state in the excitation function of $\pi^0$-proton back-to-back emission in the $\gamma ^3{He}\rightarrow \pi^0 pX$ reaction revealed a very complicated structure of the background and could not support previous conclusions., Comment: accepted for publication in Phys. Lett. B
Published: 2012
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43. SH—It happens: S–H bonds as intrinsic 2D-IR labels in proteins.

Author: Deniz, E., Schmidt-Engler, J. M., Ulrich, K., Oberle, M., Wille, G., and Bredenbeck, J.
Subjects: ESCHERICHIA coli, PROTEINS, EXCITED states, HYDROGEN bonding, ANHARMONIC motion
Abstract: Cysteine S–H bonds have a spectroscopically convenient stretching frequency of ∼2550 cm−1. However, their cross section is low, and the band can be strongly broadened in heterogeneous environments, making detection very challenging. With two-dimensional infrared (2D-IR) setups achieving ever higher sensitivities in recent years, systematic use of the weak cysteine sulfhydryls (Cys–SHs) absorption band is now within reach, even at low millimolar protein concentrations. Here, we demonstrate the capabilities of Cys–SH as an intrinsic 2D-IR label in pyruvate oxidase from E. coli, an enzyme with ten cysteines in its native sequence. 1D-IR measurements on the wild-type and individual cysteine knock-out variants show that two such residues have especially narrow SH signatures, caused by their intrahelical hydrogen bonding. 2D-IR analysis of these bands reveals an extraordinarily high anharmonicity (∼110 cm−1) and a long vibrational lifetime (∼4 ps). This allows monitoring spectral diffusion via center line slope analysis for up to 10 ps—separately for both the ground and excited states. The unique spectroscopic features and its ease of introduction make Cys–SH a useful IR spectroscopic label. [ABSTRACT FROM AUTHOR]
Published: 2022
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44. Quasi-free photoproduction of eta-mesons off the deuteron

Author: Jaegle, I., Krusche, B., Anisovich, A. V., Bacelar, J. C. S., Bantes, B., Bartholomy, O., Bayadilov, D. E., Beck, R., Beloglazov, Y. A., Castelijns, R., Crede, V., Dieterle, M., Dutz, H., Elsner, D., Ewald, R., Frommberger, F., Funke, C., Gothe, R., Gregor, R., Gridnev, A. B., Gutz, E., Hillert, W., Hoeffgen, S., Hoffmeister, P., Horn, I., Junkersfeld, J., Kalinowsky, H., Kammer, S., Keshelashvili, I., Kleber, V., Klein, Frank, Klein, Friedrich, Klempt, E., Konrad, M., Kotulla, M., Lang, M., Loehner, H., Lopatin, I. V., Lugert, S., Maghrbi, Y., Menze, D., Mertens, T., Messchendorp, J. G., Metag, V., Nikonov, V. A., Nanova, M., Novinski, D. V., Novotny, R., Oberle, M., Ostrick, M., Pant, L. M., van Pee, H., Pfeiffer, M., Pheron, F., Roy, A., Sarantsev, A. V., Schadmand, S., Schmidt, C., Schmieden, H., Schoch, B., Shende, S. V., Sokhoyan, V., Suele, A., Sumachev, V. V., Szczepanek, T., Thoma, U., Trnka, D., Varma, R., Walther, D., Wendel, C., Werthmueller, D., and Witthauer, L.
Subjects: Nuclear Experiment
Abstract: Precise data for quasi-free photoproduction of $\eta$ mesons off the deuteron have been measured at the Bonn ELSA accelerator with the combined Crystal Barrel/TAPS detector for incident photon energies up to 2.5 GeV. The $\eta$-mesons have been detected in coincidence with recoil protons and neutrons. Possible nuclear effects like Fermi motion and re-scattering can be studied via a comparison of the quasi-free reaction off the bound proton to $\eta$-production off the free proton. No significant effects beyond the folding of the free cross section with the momentum distribution of the bound protons have been found. These Fermi motion effects can be removed by an analysis using the invariant mass of the $\eta$-nucleon pairs reconstructed from the final state four-momenta of the particles. The total cross section for quasi-free $\eta$-photoproduction off the neutron reveals even without correction for Fermi motion a pronounced bump-like structure around 1 GeV of incident photon energy, which is not observed for the proton. This structure is even narrower in the invariant mass spectrum of the $\eta$-neutron pairs. Position and width of the peak in the invariant mass spectrum are $W\approx 1665$ MeV and FWHM $\Gamma\approx 25$ MeV. The data are compared to the results of different models., Comment: accepted for publication in Eur. Phys. J. A
Published: 2011
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45. Measurement of 3pi^0 photoproduction on the proton from threshold to 1.4 GeV

Author: Starostin, A., Suarez, I. M., Nefkens, B. M. K., Ahrens, J., Annand, J. R. M., Arends, H. J., Bantawa, K., Bartolome, P. A., Beck, R., Bekrenev, V., Braghieri, A., Branford, D., Briscoe, W. J., Brudvik, J., Cherepnya, S., Dieterle, M., Downie, E. J., Fil'kov, L. V., Glazier, D. I., Gregor, R., Heid, E., Hornidge, D., Jaegle, I., Jahn, O., Jude, T. C., Kashevarov, V. L., Keshelashvili, I., Kondratiev, R., Korolija, M., Koulbardis, A., Kruglov, S., Krusche, B., Lisin, V., Livingston, K., MacGregor, I. J. D., Manley, D. M., Martinez, M., McGeorge, J. C., McNicoll, E. F., Metag, V., Mushkarenkov, A., Oberle, M., Ostrick, M., Pedroni, P., Polonski, A., Prakhov, S., Robinson, J., Rosner, G., Rostomyan, T., Schumann, S., Sikora, M. H., Sober, D., Supek, I., Thiel, M., Thomas, A., Unverzagt, M., Watts, D. P., Wertmueller, D., and Witthauer, L.
Subjects: Nuclear Experiment
Abstract: The total cross section for gamma p -> 3pi0 p has been measured for the first time from threshold to 1.4 GeV using the tagged photon beam of the Mainz Microtron. The equipment utilized the Crystal Ball multiphoton spectrometer, the TAPS forward detector and a particle identification detector. The gamma p -> 3pi0 p total cross section has two broad enhancements at sqrt{s}~1.5 GeV and 1.7 GeV. We obtained the ratio of the total cross sections gamma p -> 3pi0 p to gamma p -> eta p equal to 0.014 \pm 0.001 at sqrt{s}~1.5 GeV., Comment: submitted to Physical Review C
Published: 2011

46. Detection of Delayed Cerebral Ischemia (DCI) in Subarachnoid Haemorrhage Applying Near-Infrared Spectroscopy: Elimination of the Extracerebral Signal by Transcutaneous and Intraparenchymatous Measurements in Parallel

Author: Keller, Emanuela, Froehlich, J., Baumann, D., Böcklin, C., Sikorski, C., Oberle, M., Muser, M., Steiger, Hans-Jakob, Series editor, Fandino, Javier, editor, Marbacher, Serge, editor, Fathi, Ali-Reza, editor, Muroi, Carl, editor, and Keller, Emanuela, editor
Published: 2015
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47. Experimental study of the γp→K0Σ+γn→K0Λγn→K0Σ0, γp→K0Σ+γn→K0Λγn→K0Σ0, and γp→K0Σ+γn→K0Λγn→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.
Published: 2019
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48. Determination of the scalar polarizabilities of the proton using beam asymmetry Σ 3 in Compton scattering

Author: Sokhoyan, V., Downie, E. J., Mornacchi, E., McGovern, J. A., Krupina, N., Afzal, F., Ahrens, J., Akondi, C. S., Annand, J. R. M., Arends, H. J., Beck, R., Braghieri, A., Briscoe, W. J., Cividini, F., Collicott, C., Costanza, S., Denig, A., Dieterle, M., Ferretti, M., Gardner, S., Garni, S., Glazier, D. I., Glowa, D., Gradl, W., Gurevich, G., Hamilton, D., Hornidge, D., Huber, G. M., Käser, A., Kashevarov, V. L., Keshelashvili, I., Kondratiev, R., Korolija, M., Krusche, B., Lensky, V., Linturi, J., Lisin, V., Livingston, K., MacGregor, I. J. D., Macrae, R., Manley, D. M., Martel, P. P., Middleton, D. G., Miskimen, R., Mushkarenkov, A., Neiser, A., Oberle, M., Ortega Spina, H., Ostrick, M., Ott, P., Otte, P. B., Oussena, B., Paudyal, D., Pedroni, P., Polonski, A., Prakhov, S., Rajabi, A., Rostomyan, T., Sarty, A., Schumann, S., Spieker, K., Steffen, O., Strakovsky, I. I., Strandberg, B., Strub, T., Supek, I., Thiel, A., Thiel, M., Thomas, A., Unverzagt, M., Wagner, S., Watts, D. P., Wettig, J., Witthauer, L., Werthmüller, D., Wolfes, M., Zana, L., and The A2 Collaboration
Published: 2017
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49. Unterarm

Author: Oberle, M., Schlickewei, W., Dietz, H. G., editor, Illing, P., editor, Schmittenbecher, P. P., editor, Slongo, Th., editor, and Sommerfeldt, D. W., editor
Published: 2011
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50. Piloting a Student-Led Bingocize® Nutrition Workshop for Marginalized Community-Dwelling Older Adults

Author: OoNorasak, K., primary, Corrone, R., additional, Kinnarney, M., additional, Oberle, M., additional, Yokokura, K., additional, Crandall, K., additional, and Ickes, M., additional
Published: 2022
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