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135 results on '"Zehr., F."'

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

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

2. Photoproduction of the $\omega$ meson off the proton near threshold

Author: Strakovsky, I. I., Prakhov, S., Azimov, Y. I., Aguar-Bartolome, P., Annand, J. R. M., Arends, H. J., Bantawa, K., Beck, R., Bekrenev, V., Berghaeuser, H., Braghieri, A., Briscoe, W. J., Brudvik, J., Cherepnya, S., Codling, R. F. B., Collicott, C., Costanza, S., Demissie, B. T., Downie, E. J., Drexler, P., Fil'kov, L. V., Glazier, D. I., Gregor, R., Hamilton, D. J., Heid, E., Hornidge, D., Jaegle, I., Jahn, O., Jude, T. C., Kashevarov, V. L., Keshelashvili, I., Kondratiev, R., Korolija, M., Kotulla, M., Koulbardis, A., Kruglov, S., Krusche, B., Lisin, V., Livingston, K., MacGregor, I. J. D., Maghrbi, Y., Manley, D. M., Marinides, Z., McGeorge, J. C., McNicoll, E. F., Mekterovic, D., Metag, V., Middleton, D. G., Mushkarenkov, A., Nefkens, B. M. K., Nikolaev, A., Novotny, R., Ortega, H., Ostrick, M., Otte, P. B., Oussena, B., Pedroni, P., Pheron, F., Polonski, A., Robinson, J., Rosner, G., Rostomyan, T., Schumann, S., Sikora, M. H., Starostin, A., Supek, I., Taragin, M. F., Tarbert, C. M., Thiel, M., Thomas, A., Unverzagt, M., Watts, D. P., Werthmueller, D., and Zehr, F.
Subjects: Nuclear Experiment, High Energy Physics - Experiment, High Energy Physics - Phenomenology
Abstract: An experimental study of $\omega$ photoproduction on the proton was conducted by using the Crystal Ball and TAPS multiphoton spectrometers together with the photon tagging facility at the Mainz Microtron MAMI. The $\gamma p\to\omega p$ differential cross sections are measured from threshold to the incident-photon energy $E_\gamma=1.40$ GeV ($W=1.87$ GeV for the center-of-mass energy) with 15-MeV binning in $E_\gamma$ and full production-angle coverage. The quality of the present data near threshold gives access to a variety of interesting physics aspects. As an example, an estimation of the $\omega N$ scattering length $\alpha_{\omega p}$ is provided., Comment: 8 pages, 5 figures. Published version; some typos were fixed
Published: 2014
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3. 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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4. Neutron skin of $^{208}$Pb from Coherent Pion Photoproduction

Author: Tarbert, C. M., Watts, D. P., Glazier, D. I., Aguar, P., Ahrens, J., Annand, J. R. M., Arends, H. J., Beck, R., Bekrenev, V., Boillat, B., Braghieri, A., Branford, D., Briscoe, W. J., Brudvik, J., Cherepnya, S., Codling, R., Downie, E. J., Foehl, K., Grabmayr, P., Gregor, R., Heid, E., Hornidge, D., Jahn, O., Kashevarov, V. L., Knezevic, A., Kondratiev, R., Korolija, M., Kotulla, M., Krambrich, D., Krusche, B., Lang, M., Lisin, V., Livingston, K., Lugert, S., MacGregor, I. J. D., Manley, D. M., Martinez, M., McGeorge, J. C., Mekterovic, D., Metag, V., Nefkens, B. M. K., Nikolaev, A., Novotny, R., Owens, R. O., Pedroni, P., Polonski, A., Prakhov, S. N., Price, J. W., Rosner, G., Rost, M., Rostomyan, T., Schadmand, S., Schumann, S., Sober, D., Starostin, A., Supek, I., Thomas, A., Unverzagt, M., Walcher, Th., and Zehr, F.
Subjects: Nuclear Experiment, Nuclear Theory
Abstract: Information on the size and shape of the neutron skin on $^{208}$Pb has been extracted from coherent pion photoproduction cross sections measured using the Crystal Ball together with the Glasgow tagger at the MAMI electron beam facility. On exploitation of an interpolated fit of a theoretical model to the measured cross sections the half-height radius and diffuseness of the neutron distribution are found to be 6.70$\pm 0.03(stat)$ fm and 0.55$\pm 0.01(stat)$$^{+0.02}_{-0.03}(sys)$ fm respectively, corresponding to a neutron skin thickness $\Delta r_{np}$=0.15$\pm 0.03(stat)$$^{+0.01}_{-0.03}(sys)$ fm. The results give the first successful extraction of a neutron skin with an electromagnetic probe and indicate the skin of $^{208}$Pb has a halo character. The measurement provides valuable new constraints on both the structure of nuclei and the equation of state for neutron-rich matter., Comment: 4 figures 5 pages. Version submitted to journal. Includes additional studies of systematic effects in the extracted diffuseness, which led to a small increase in the quoted systematic error. These additional studies are discussed in the revised manuscript. Also includes minor editorial improvements to the text
Published: 2013
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5. Measurement of the $^{1}H$($\vec{\gamma}$, $\vec{p}$)$\pi^{0}$ reaction using a novel nucleon spin polarimeter

Author: Watts, D. P., Glazier, D. I., Aguar-Bartolomé, P., Akasoy, L. K., Annand, J. R. M., Arends, H. J., Bantawa, K., Beck, R., Bekrenev, V. S., Berghäuser, H., Braghieri, A., Branford, D., Briscoe, W. J., Brudvik, J., Cherepnya, S., Codling, R. F. B., Demissie, B. T., Downie, E. J., Drexler, P., Fil'kov, L. V., Freehart, B., Gregor, R., Hamilton, D., Heid, E., Hornidge, D., Jaegle, I., Jahn, O., Jude, T. C., Kashevarov, V. L., Keshelashvili, I., Kondratiev, R., Korolija, M., Kotulla, M., Koulbardis, A. A., Kruglov, S. P., Krusche, B., Lisin, V., Livingston, K., MacGregor, I. J. D., Maghrbi, Y., Manley, D. M., Marinides, Z., Martinez, M., McGeorge, J. C., McKinnon, B., McNicoll, E. F., Mekterovic, D., Metag, V., Micanovic, S., Middleton, D. G., Mushkarenkov, A., Nefkens, B. M. K., Nikolaev, A., Novotny, R., Ostrick, M., Otte, P. B., Oussena, B., Pedroni, P., Pheron, F., Polonski, A., Prakhov, S., Robinson, J., Rosner, G., Rostomyan, T., Schumann, S., Sober, D. I., Starostin, A., Strakovsky, I. I., Suarez, I. M., Supek, I., Thiel, M., Thomas, A., Unverzagt, M., Werthmüller, D., Workman, R. L., Zamboni, I., and Zehr, F.
Subjects: Nuclear Experiment
Abstract: We report the first large-acceptance measurement of polarization transfer from a polarized photon beam to a recoiling nucleon, pioneering a novel polarimetry technique with wide application to future nuclear and hadronic physics experiments. The commissioning measurement of polarization transfer in the $^{1}H$($\vec{\gamma}$,$\vec{p}$)$\pi^{0}$ reaction in the range $0.4
Published: 2013
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6. A new determination of the eta transition form factor in the Dalitz decay eta -> e^+ e^- gamma 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., Costanza, S., Denig, A., Downie, E. J., Drexler, P., Fil'kov, L. V., Fix, A., Glazier, D. I., Gregor, R., Hamilton, D. J., Heid, E., Hornidge, 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., Manley, D. M., Masjuan, P., McGeorge, J. C., McNicoll, E. F., Mekterovic, D., Metag, V., Mushkarenkov, A., Nefkens, B. M. K., Nikolaev, A., Novotny, R., 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., and Zehr., F.
Subjects: High Energy Physics - Experiment, Nuclear Experiment
Abstract: The Dalitz decay eta -> e^+ e^- gamma has been measured in the gamma p -> eta p reaction with the Crystal Ball and TAPS multiphoton spectrometers, together with the photon tagging facility at the Mainz Microtron MAMI. The experimental statistic used in this work is one order of magnitude greater than in any previous measurement of eta -> e^+ e^- gamma. The value obtained for the slope parameter 1/Lambda^2 of the eta transition form factor, 1/Lambda^2 = (1.95 +/- 0.15_stat +/- 0.10_syst) [1/GeV^2], is in good agreement with recent measurements conducted in eta -> e^+ e^- gamma and eta -> mu^+ mu^- gamma decays, as well as with recent form-factor calculations. The uncertainty obtained in the value of 1/Lambda^2 is lower compared to results from previous measurements of the eta -> e^+ e^- gamma decay., Comment: 11 pages, 10 figures, 1 table
Published: 2013
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7. $K^+\Lambda$ 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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8. 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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9. Double pion photoproduction off nuclei - are there effects beyond final-state interaction?

Author: Maghrbi, Y., Gregor, R., Lugert, S., Ahrens, J., Annand, J. R. M., Arends, H. J., Beck, R., Bekrenev, V., Boillat, B., Braghieri, A., Branford, D., Briscoe, W. J., Brudvik, J., Cherepnya, S., Codling, R., Downie, E. J., Dexler, P., Fil'kov, L. V., Fix, A., Glazier, D. I., Heid, E., Hornidge, D., Jahn, O., Jaegle, I., Kashevarov, V. L., Keshelashvili, I., Knezevic, A., Kondratiev, A., Korolija, M., Kotulla, M., Krambrich, D., Krusche, B., Lang, M., Lisin, V., Livingston, K., MacGregor, I. J. D., Manley, D. M., Martinez, M., McGeorge, J. C., Mekterovic, D., Metag, V., Nefkens, B. M. K., Nikolaev, A., Novotny, R., Ostrick, M., Pedroni, P., Pheron, F., Polonski, A., Prakhov, S. N., Price, J. W., Rosner, G., Rost, M., Rostomyan, T., Schadmand, S., Schumann, S., Sober, D., Starostin, S., Supek, I., Thomas, A., Unverzagt, M., Watts, D. P., Werthmueller, D., and Zehr, F.
Subjects: Nuclear Experiment
Abstract: Photoproduction of $\pi^{0}\pi^{0}$ and $\pi^{0}\pi^{\pm}$ pairs from nuclei has been measured over a wide mass range ($^2$H, $^{7}$Li, $^{12}$C, $^{40}$Ca, and $^{\rm nat}$Pb) for photon energies from threshold to 600 MeV. The experiments were performed at the MAMI accelerator in Mainz, using the Glasgow photon tagging spectrometer and a 4$\pi$ electromagnetic calorimeter consisting of the Crystal Ball and TAPS detectors. A shift of the pion-pion invariant mass spectra for heavy nuclei to small invariant masses has been observed for $\pi^0$ pairs but also for the mixed-charge pairs. The precise results allow for the first time a model-independent analysis of the influence of pion final-state interactions. The corresponding effects are found to be large and must be carefully considered in the search for possible in-medium modifications of the $\sigma$-meson. Results from a transport model calculation reproduce the shape of the invariant-mass distributions for the mixed-charge pairs better than for the neutral pairs, but also for the latter differences between model results and experiment are not large, leaving not much room for $\sigma$-in-medium modification., Comment: accepted for publication in Phys. Lett. B
Published: 2013
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10. 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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11. Coherent photoproduction of pi^0- and eta-mesons off 7Li

Author: Maghrbi, Y., Krusche, B., Ahrens, J., Annand, J. R. M., Arends, H. J., Beck, R., Bekrenev, V., Boillat, B., Braghieri, A., Branford, D., Briscoe, W. J., Brudvik, J., Cherepnya, S., Codling, R. F. B., Downie, E. J., Drexler, P., Fil'kov, L. V., Fix, A., Glazier, D. I., Gregor, R., Heid, E., Hornidge, D., Jaegle, I., Jahn, O., Kashevarov, V. L., Keshelashvili, I., Knezevic, A., Kondratiev, R., Korolija, M., Krambrich, D., Lang, M., Lisin, V., Livingston, K., Lugert, S., MacGregor, I. J. D., Manley, D. M., Martinez, M., McGeorge, J. C., Mekterovic, D., Metag, V., Nefkens, B. M. K., Nikolaev, A., Novotny, R., Ostrick, M., Pedroni, P., Pheron, F., Polonski, A., Prakhov, S., Price, J. W., Rosner, G., Rost, M., Rostomyan, T., Schadmand, S., Schumann, S., Sober, D., Starostin, A., Supek, I., Tarbert, C. M., Thomas, A., Unverzagt, M., Watts, D. P., Werthmueller, D., and Zehr, F.
Subjects: Nuclear Experiment
Abstract: Coherent photoproduction of $\pi^0$-mesons from threshold ($E_{th} \approx$ 136 MeV) throughout the $\Delta$-resonance region and of $\eta$-mesons close to the production threshold ($E_{th} \approx$ 570 MeV for $\eta$) has been measured for $^7$Li nuclei. The experiment was performed using the tagged-photon beam of the Mainz MAMI accelerator with the Crystal Ball and TAPS detectors combined to give an almost 4$\pi$ solid-angle electromagnetic calorimeter. The reactions were identified by a combined invariant-mass and missing-energy analysis. A comparison of the pion data to plane-wave impulse modelling tests the nuclear mass form factor. So far coherent $\eta$-production had been only identified for the lightest nuclear systems ($^2$H and $^3$He). For $^3$He a large enhancement of the cross section above plane-wave approximations had been reported, indicating the formation of a quasi-bound state. The present Li-data for $\eta$-production agree with a plane-wave approximation. Contrary to $^3$He, neither a threshold enhancement of the total cross section nor a deviation of the angular distributions from the expected form-factor dependence were observed., Comment: accepted for publication in Eur. Phys. J. A
Published: 2013
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12. Determination of the {\eta} mass with the Crystal Ball at MAMI-B

Author: Nikolaev, A., Aguar-Bartolomé, P., Ahrens, J., Annand, J. R. M., Arends, H. J., Beck, R., Bekrenev, V., Boillat, B., Braghieri, A., Branford, D., Briscoe, W. J., Brudvik, J. W., Cherepnya, S., Codling, R., Dehn, M., Downie, E. J., Fil'kov, L. V., Glazier, D. I., Gregor, R., Heid, E., Hornidge, D., Jahn, O., Jankowiak, A., Kaiser, K. -H., Kashevarov, V. L., Kondratiev, R., Korolija, M., Kotulla, M., Krambrich, D., Krusche, B., Lang, M., Lisin, V., Livingston, K., Ludwig-Mertin, U., Lugert, S., MacGregor, I. J. D., Manley, D. M., Martinez-Fabregate, M., McGeorge, J. C., Mekterovic, D., Metag, V., Nefkens, B. M. K., Novotny, R., Owens, R. O., Pedroni, P., Polonski, A., Prakhov, S. N., Price, J. W., Reiter, A., Rosner, G., Rost, M., Rostomyan, T., Schumann, S., Sober, D., Starostin, A., Supek, I., Tarbert, C. M., Thomas, A., Unverzagt, M., Walcher, Th., Watts, D. P., and Zehr, F.
Subjects: Nuclear Experiment
Abstract: A new precise determination of the {\eta} meson mass is presented. It is based on a measurement of the threshold for the {\gamma}p -> p{\eta} reaction using the tagger focal-plane microscope detector at the MAMI-B facility in Mainz. The tagger microscope has a higher energy resolution than the standard tagging spectrometer and, hence, allowed an improvement in the accuracy compared to the previous {\eta} mass measurement at MAMI-B. The result m{\eta} = (547.851 +- 0.031 stat. +- 0.062 syst.) MeV agrees very well with the precise values of the NA48, KLOE and CLEO collaborations and deviates by about 5{\sigma} from the smaller, but also very precise value obtained by the GEM collaboration at COSY., Comment: Submitted for publication in EPJA
Published: 2012

13. Photoproduction of pi0pi0 and pi0pi+-pairs off the proton from threshold to the second resonance region

Author: Zehr, F., Krusche, B., Aguar, P., Ahrens, J., Annand, J. R. M., Arends, H. J., Beck, R., Bekrenev, V., Boillat, B., Braghieri, A., Branford, D., Briscoe, W. J., Brudvik, J., Cherepnya, S., Codling, R. F. B., Downie, E. J., Drexler, P., Glazier, D. I., Fil'kov, L. V., Gregor, R., Heid, E., Hornidge, D., Jaegle, I., Jahn, O., Kashevarov, V. L., Knezevic, A., Kondratiev, R., Korolija, M., Kotulla, M., Krambrich, D., Kulbardis, A., Lang, M., Lisin, V., Livingston, K., Lugert, S., MacGregor, I. J. D., Manley, D. M., Maghrbi, Y., Martinez, M., McGeorge, J. C., Mekterovic, D., Metag, V., Nefkens, B. M. K., Nikolaev, A., Ostrick, M., Pedroni, P., Pheron, F., Polonski, A., Prakhov, S., Price, J. W., Rosner, G., Rost, M., Rostomyan, T., Schumann, S., Sober, D., Starostin, A., Supek, I., Tarbert, C. M., Thomas, A., Unverzagt, M., Walcher, Th., and Watts, D. P.
Subjects: Nuclear Experiment
Abstract: Precise total cross-sections and invariant-mass distributions have been measured for photoproduction of pion pairs off the proton producing $p\pi^0\pi^0$ and $n\pi^+\pi^0$ final states from the threshold region up to 800 MeV incident photon energy. Additionally, beam helicity asymmetries have been measured in the second resonance region (550 MeV - 820 MeV). The experiment was performed at the tagged photon beam of the Mainz MAMI accelerator with the Crystal Ball and TAPS detectors combined to give an almost 4$\pi$ solid-angle electromagnetic calorimeter. The results are much more precise than any previous measurements and confirm the chiral perturbation theory predictions for the threshold behavior of these reactions. In the second resonance region, the invariant-mass distributions of meson-meson and meson-nucleon pairs are in reasonable agreement with model predictions, but none of the models reproduce the asymmetries for the mixed-charge channel., Comment: accepted for publication in Eur. Phys. J. A
Published: 2012
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14. Study of the gamma p --> pi0 pi0 p reaction with the Crystal Ball/TAPS at the Mainz

Author: Kashevarov, V. L., Fix, A., 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., Downie, E. J., Drexler, P., Fil'kov, L. V., Glazier, D. I., Gregor, R., Heid, E., Hornidge, D., Isaksson, L., Jaegle, I., Jahn, O., Jude, T. C., Keshelashvili, I., Kondratiev, R., Korolija, M., Kotulla, M., Koulbardis, A., Kruglov, S., Krusche, B., Lisin, V., Livingston, K., MacGregor, I. J. D., Maghrbi, Y., Manley, D. M., McGeorge, J. C., McNicoll, E. F., Mekterovic, D., Metag, V., Mushkarenkov, A., Nefkens, B. M. K., Nikolaev, A., Novotny, R., Ortega, H., Ostrick, M., Ott, P., Otte, P. B., Oussena, B., Pedroni, P., Pheron, F., Polonski, A., 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., and Zehr, F.
Subjects: Nuclear Experiment, High Energy Physics - Experiment, Nuclear Theory
Abstract: The gamma p --> pi0 pi0 p reaction has been measured from threshold to 1.4 GeV using the Crystal Ball and TAPS photon spectrometers together with the photon tagging facility at the Mainz Microtron. The experimental results include total and differential cross sections as well as specific angular distributions, which were used to extract partial-wave amplitudes. In particular, the energy region below the D13(1520) resonance was studied., Comment: 12 pages, 13 figures, corrected version, published in PRC
Published: 2012
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15. 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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16. First measurement of the circular beam asymmetry in the gamma p --> pi0 eta p reaction

Author: Kashevarov, V. L., Fix, A., Aguar-Bartolomé, P., Akasoy, L. K., Annand, J. R. M., Arends, H. J., Bantawa, K., Beck, R., Bekrenev, V., Berghäuser, H., Braghieri, A., Branford, D., Briscoe, W. J., Brudvik, J., Cherepnya, S., Codling, R. F. B., Demissie, B. T., Downie, E. J., Drexler, P., Fil'kov, L. V., Glazier, D. I., Gregor, R., Hamilton, D., Heid, E., Hornidge, D., Jaegle, I., Jahn, O., Jude, T. C., Kellie, J. D., Keshelashvili, I., Kondratiev, R., Korolija, M., Kotulla, M., Koulbardis, A., Kruglov, S., Krusche, B., Lisin, V., Livingston, K., MacGregor, I. J. D., Maghrbi, Y., Manley, D. M., Martinez-Fabregate, M., McGeorge, J. C., McNicoll, E. F., Mekterovic, D., Metag, V., Micanovic, S., Middleton, D., Mushkarenkov, A., Nefkens, B. M. K., Nikolaev, A., Novotny, R., Ostrick, M., Otte, P. B., Oussena, B., Pedroni, P., Pheron, F., Polonski, A., Prakhov, S. N., Robinson, J., Rosner, G., Rostomyan, T., Schumann, S., Sikora, M. H., Sober, D., Starostin, A., Stakovsky, I. I., Suarez, I. M., Supek, I., Tarbert, C., Thiel, M., Thomas, A., Unverzagt, M., Watts, D. P., Werthmüller, D., Zamboni, I., and Zehr., F.
Subjects: Nuclear Experiment, High Energy Physics - Experiment, Nuclear Theory
Abstract: The circular photon asymmetry for pi0 eta photoproduction on the proton was measured for the first time at the tagged photon facility of the MAMI C accelerator using the Crystal Ball/TAPS photon spectrometer. The experimental results are interpreted within a phenomenological isobar model that confirms the dominant role of the Delta(1700)D33 resonance. The measured asymmetry allows us to identify small contributions from positive-parity resonances via interference terms with the dominant D33 amplitude., Comment: 11 pages, 3 figures, submitted to Phys.Lett. B
Published: 2010
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17. Study of the gp-->etap reaction with the Crystal Ball detector at the Mainz Microtron(MAMI-C)

Author: McNicoll, E. F., Prakhov, S., Strakovsky, I. I., Aguar-Bartolomepmainz, P., Akasoy, L. K., Annand, J. R. M., Arends, H. J., Arndt, R. A., Azimov, Ya. I., Bantawa, K., Beck, R., Bekrenev, V. S., Berghaeuser, H., Braghieri, A., Branford, D., Briscoe, W. J., Brudvik, J., Cherepnya, S., Codling, R. F. B., Demissie, B. T., Downie, E. J., Drexler, P., Fil'kov, L. V., Fix, A., Freehart, B., Glazier, D. I., Gregor, R., Hamilton, D., Heid, E., Hornidge, D., Jaegle, I., Jahn, O., Jude, T. C., Kashevarov, V. L., Kellie, J. D., Keshelashvili, I., Kondratiev, R., Korolija, M., Kotulla, M., Koulbardis, A. A., Kruglov, S. P., Krusche, B., Lisin, V., Livingston, K., MacGregor, I. J. D., Maghrbi, Y., Manley, D. M., Marinides, Z., Martinez, M., McGeorge, J. C., McKinnon, B., Mekterovic, D., Metag, V., Micanovic, S., Middleton, D., Mushkarenkov, A., Nefkens, B. M. K., Nikolaev, A., Novotny, R., Ostrick, M., Otte, P. B., Oussena, B., Paris, M. W., Pedroni, P., Pheron, F., Polonski, A., Robinson, J., Rosner, G., Rostomyan, T., Schumann, S., Sikora, M. H., Sober, D. I., Starostin, A., Suarez, I. M., Supek, I., Thiel, M., Thomas, A., Tiator, L., Unverzagt, M., Watts, D. P., Werthmueller, D., Workman, R. L., Zamboni, I., and Zehr, F.
Subjects: Nuclear Experiment, High Energy Physics - Experiment, High Energy Physics - Phenomenology, Nuclear Theory
Abstract: The gp-->etap reaction has been measured with the Crystal Ball and TAPS multiphoton spectrometers in the energy range from the production threshold of 707 MeV to 1.4 GeV (1.49 =< W >= 1.87 GeV). Bremsstrahlung photons produced by the 1.5-GeV electron beam of the Mainz Microtron MAMI-C and momentum analyzed by the Glasgow Tagging Spectrometer were used for the eta-meson production. Our accumulation of 3.8 x 10^6 gp-->etap-->3pi0p-->6gp events allows a detailed study of the reaction dynamics. The gp-->etap differential cross sections were determined for 120 energy bins and the full range of the production angles. Our data show a dip near W = 1680 MeV in the total cross section caused by a substantial dip in eta production at forward angles. The data are compared to predictions of previous SAID and MAID partial-wave analyses and to thelatest SAID and MAID fits that have included our data., Comment: 15 pages, 12 figures
Published: 2010
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18. Radiative pi0 photoproduction on protons in the Delta+(1232) region

Author: Schumann, S., Boillat, B., Downie, E. J., Aguar-Bartolomé, P., Ahrens, J., Annand, J. R. M., Arends, H. J., Beck, R., Bekrenev, V., Braghieri, A., Branford, D., Briscoe, W. J., Brudvik, J. W., Cherepnya, S., Codling, R., Drexler, P., Fil'kov, L. V., Glazier, D. I., Gregor, R., Heid, E., Hornidge, D., Jahn, O., Kashevarov, V. L., Kondratiev, R., Korolija, M., Kotulla, M., Krambrich, D., Krusche, B., Lang, M., Lisin, V., Livingston, K., Lugert, S., MacGregor, I. J. D., Manley, D. M., Martinez-Fabregate, M., McGeorge, J. C., Mekterovic, D., Metag, V., Nefkens, B. M. K., Nikolaev, A., Novotny, R., Ostrick, M., Owens, R. O., Pedroni, P., Polonski, A., Prakhov, S. N., Price, J. W., Rosner, G., Rost, M., Rostomyan, T., Sober, D., Starostin, A., Supek, I., Tarbert, C. M., Thomas, A., Unverzagt, M., Walcher, Th., Watts, D. P., and Zehr, F.
Subjects: High Energy Physics - Experiment
Abstract: The reaction gamma p -> p pi0 gamma' has been measured with the Crystal Ball / TAPS detectors using the energy-tagged photon beam at the electron accelerator facility MAMI-B. Energy and angular differential cross sections for the emitted photon gamma' and angular differential cross sections for the pi0 have been determined with high statistics in the energy range of the Delta+(1232) resonance. Cross sections and the ratio of the cross section to the non-radiative process gamma p -> p pi0 are compared to theoretical reaction models, having the anomalous magnetic moment kappa_Delta+ as free parameter. As the shape of the experimental distributions is not reproduced in detail by the model calculations, currently no extraction of kappa_Delta+ is feasible., Comment: 14 pages, 19 figures
Published: 2010
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19. Beam-Helicity Asymmetries in Double Pion Photoproduction off the Proton

Author: Krambrich, D., Zehr, F., Fix, A., Roca, L., Aguar, P., Ahrens, J., Annand, J. R. M., Arends, H. J., Beck, R., Bekrenev, V., Boillat, B., Braghieri, A., Branford, D., Briscoe, W. J., Brudvik, J., Cherepnya, S., Codling, R., Downie, E. J., Dexler, P., Glazier, D. I., Grabmayr, P., Gregor, R., Heid, E., Hornidge, D., Jahn, O., Kashevarov, V. L., Knezevic, A., Kondratiev, R., Korolija, M., Kotulla, M., Krusche, B., Kulbardis, A., Lang, M., Lisin, V., Livingston, K., Lugert, S., MacGregor, I. J. D., Manley, D. M., Martinez, M., McGeorge, J. C., Mekterovic, D., Metag, V., Nefkens, B. M. K., Nikolaev, A., Pedroni, P., Pheron, F., Polonski, A., Prakhov, S. N., Price, J. W., Rosner, G., Rost, M., Rostomyan, T., Schumann, S., Sober, D., Starostin, A., Supek, I., Tarbert, C. M., Thomas, A., Unverzagt, M., Walcher, Th., and Watts, D. P.
Subjects: Nuclear Experiment
Abstract: Beam-helicity asymmetries have been measured at the MAMI accelerator in Mainz in the three isospin channels $\vec{\gamma}p\to \pi^{+}\pi^0n$, $\vec{\gamma}p\to \pi^{0}\pi^0p$ and $\vec{\gamma}p\to \pi^{+}\pi^{-}p$ . The circularly polarized photons, produced from bremsstrahlung of longitudinally polarized electrons, were tagged with the Glasgow magnetic spectrometer. Charged pions and the decay photons of $\pi^0$ mesons were detected in a $~4\pi$ electromagnetic calorimeter which combined the Crystal Ball detector with the TAPS detector. The precisely measured asymmetries are very sensitive to details of the production processes and are thus key observables in the modeling of the reaction dynamics., Comment: accepted for publication in Phys. Rev. Lett
Published: 2009
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20. Photoproduction of pi^0 eta on protons and the Delta(1700)D_{33} resonance

Author: Kashevarov, V. L., Fix, A., Aguar-Bartolome, P., Akasoy, L. K., Annand, J. R. M., Arends, H. J., Bantawa, K., Beck, R., Bekrenev, V., Berghauser, H., Boillat, B., Braghieri, A., Branford, D., Briscoe, W. J., Brudvik, J., Cherepnya, S., Downie, E. J., Drexler, P., Fil'kov, L. V., Glazier, D. I., Gregor, R., Heid, E., Hornidge, D., Jahn, O., Jude, T. C., Knezevic, A., Kondratiev, R., Korolija, M., Kotulla, M., Koulbardis, A., Kruglov, S., Krusche, B., Lisin, V., Livingston, K., MacGregor, I. J. D., Maghrbi, Y., Manley, D. M., Martinez-Fabregate, M., McGeorge, J. C., McNicoll, E. F., Mekterovic, D., Metag, V., Micanovic, S., Nefkens, B. M. K., Nikolaev, A., Novotny, R., Ostrick, M., Owens, R. O., Pedroni, P., Pheron, F., Polonski, A., Robinson, J., Prakhov, S. N., Rosner, G., Rostomyan, T., Schumann, S., Sober, D., Starostin, A., Suarez, I. M., Supek, I., Tarbert, C. M., Thiel, M., Thomas, A., Unverzagt, M., Watts, D. P., Zamboni, I., and Zehr, F.
Subjects: High Energy Physics - Experiment
Abstract: Total and differential cross sections for the reaction gamma p -> pi^o eta p have been measured with the Crystal Ball/TAPS detector using the tagged photon facility at the MAMI C accelerator in Mainz. In the energy range E_gamma=0.95-1.4 GeV the reaction is dominated by the excitation and sequential decay of the Delta(1700)D33 resonance. Angular distributions measured with high statistics allow us to determine the ratio of hadronic decay widths \Gamma_{\eta \Delta}/\Gamma_{\pi S11} and the ratio of the helicity amplitudes A_{3/2}/A_{1/2} for this resonance., Comment: 9 pages, 11 figures
Published: 2009
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21. Determination of the Dalitz plot parameter alpha for the decay eta->3pi^0 with the Crystal Ball at MAMI-B

Author: Unverzagt, M., Aguar-Bartolome, P., Ahrens, J., Annand, J. R. M., Arends, H. J., Beck, R., Bekrenev, V., Boillat, B., Braghieri, A., Branford, D., Briscoe, W. J., Brudvik, J. W., Cherepnya, S., Codling, R., Downie, E. J., Filkov, L. V., Glazier, D. I., Gregor, R., Heid, E., Hornidge, D., Jahn, O., Kashevarov, V. L., Kondratiev, R., Korolija, M., Kotulla, M., Krambrich, D., Krusche, B., Lang, M., Lisin, V., Livingston, K., Lugert, S., MacGregor, I. J. D., Manley, D. M., Martinez-Fabregate, M., McGeorge, J. C., Mekterovic, D., Metag, V., Nefkens, B. M. K., Nikolaev, A., Novotny, R., Owens, R. O., Pedroni, P., Polonski, A., Prakhov, S. N., Price, J. W., Rosner, G., Rost, M., Rostomyan, T., Schumann, S., Sober, D., Starostin, A., Supek, I., Tarbert, C. M., Thomas, A., Walcher, Th., Watts, D. P., and Zehr, F.
Subjects: High Energy Physics - Experiment
Abstract: A precise measurement of the Dalitz plot parameter, alpha, for the eta->3pi^0 decay is presented. The experiment was performed with the Crystal Ball and TAPS large acceptance photon detectors at the tagged photon beam facility of the MAMI-B electron accelerator in Mainz. High statistics of 1.8*10^6 eta->3pi^0 events were obtained, giving the result alpha = -0.032 +/- 0.002(stat) +/- 0.002(syst)., Comment: 9 pages, 6 figures, published in the online-first section of EPJ A, included changes referees asked for, added DOI
Published: 2008
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22. Measurement of the Slope Parameter $\alpha$ for the $\eta\to 3\pi^0$ decay with the Crystal Ball detector at the Mainz Microtron (MAMI-C)

Author: Prakhov, S., Nefkens, B. M. K., Aguar-Bartolome, P., Akasoy, L. K., Annand, J. R. M., Arends, H. J., Bantawa, K., Beck, R., Bekrenev, V., Berghauser, H., Boillat, B., Braghieri, A., Branford, D., Briscoe, W. J., Brudvik, J., Cherepnya, S., Codling, R. F. B., Downie, E. J., Drexler, P., Fil'kov, L. V., Glazier, D. I., Gregor, R., Heid, E., Hornidge, D., Jahn, O., Jude, T. C., Kashevarov, V. L., Kellie, J. D., Kondratiev, R., Korolija, M., Kotulla, M., Koulbardis, A., Krambrich, D., Kruglov, S., Krusche, B., Lang, M., Lisin, V., Livingston, K., MacGregor, I. J. D., Maghrbi, Y., Manley, D. M., Martinez, M., McGeorge, J. C., McNicoll, E. F., Mekterovic, D., Metag, V., Micanovic, S., Nikolaev, A., Novotny, R., Ostrick, M., Otte, P. B., Pedroni, P., Pheron, F., Polonski, A., Robinson, J., Rosner, G., Rost, M., Rostomyan, T., Schumann, S., Sikora, M. H., Sober, D. I., Starostin, A., Suarez, I. M., Supek, I., Tarbert, C. M., Thiel, M., Thomas, A., Unverzagt, M., Watts, D. P., Zamboni, I., and Zehr, F.
Subjects: High Energy Physics - Experiment
Abstract: The dynamics of the $\eta\to 3\pi^0$ decay have been studied with the Crystal Ball multiphoton spectrometer and the TAPS calorimeter. Bremsstrahlung photons produced by the 1.5-GeV electron beam of the Mainz microtron MAMI-C and tagged by the Glasgow photon spectrometer were used for $\eta$-meson production. The analysis of $3 \times 10^6$ $\gamma p \to \eta p \to 3\pi^0 p \to 6\gamma p$ events yields the value $\alpha=-0.032\pm0.003$ for the $\eta\to 3\pi^0$ slope parameter, which agrees with the majority of recent experimental results and has the smallest uncertainty. The $\pi^0\pi^0$ invariant-mass spectrum was investigated for the occurrence of a cusplike structure in the vicinity of the $\pi^+\pi^-$ threshold. The observed effect is small and does not affect our measured value for the slope parameter.
Published: 2008
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23. Incoherent pion photoproduction on $^{12}$C

Author: Tarbert, C. M., Watts, D. P., Aguar, P., Ahrens, J., Annand, J. R. M., Arends, H. J., Beck, R., Bekrenev, V., Boillat, B., Braghieri, A., Branford, D., Briscoe, W. J., Brudvik, J., Cherepnya, S., Codling, R., Downie, E. J., Foehl, K., Glazier, D. I., Grabmayr, P., Gregor, R., Heid, E., Hornidge, D., Jahn, O., Kashevarov, V. L., Knezevic, A., Kondratiev, R., Korolija, M., Kotulla, M., Krambrich, D., Krusche, B., Lang, M., Lisin, V., Livingston, K., Lugert, S., MacGregor, I. J. D., Manley, D. M., Martinez, M., McGeorge, J. C., Mekterovic, D., Metag, V., Nefkens, B. M. K., Nikolaev, A., Novotny, R., Owens, R. O., Pedroni, P., Polonski, A., Prakhov, S. N., Price, J. W., Rosner, G., Rost, M., Rostomyan, T., Schadmand, S., Schumann, S., Sober, D., Starostin, A., Supek, I., Thomas, A., Unverzagt, M., Walcher, Th., and Zehr, F.
Subjects: Nuclear Experiment
Abstract: We present the first detailed measurement of incoherent photoproduction of neutral pions to a discrete state of a residual nucleus. The $^{12}$C$(\gamma,\pi^{0})^{12}$C$^{*}_{4.4MeV}$ reaction has been studied with the Glasgow photon tagger at MAMI employing a new technique which uses the large solid angle Crystal Ball detector both as a $\pi^{0}$ spectrometer and to detect decay photons from the excited residual nucleus. The technique has potential applications to a broad range of future nuclear measurements with the Crystal Ball and similar detector systems elsewhere. The data are sensitive to the propagation of the $\Delta$ in the nuclear medium and will give the first information on matter transition form factors from measurements with an electromagnetic probe. The incoherent cross sections are compared to two theoretical predictions including a $\Delta$-hole model., Comment: 4 pages, 8 figures, submitted to Physical Review Letters
Published: 2007
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24. Target and beam-target asymmetries for the $γp \to π^0 π^0 p$ reaction

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

Author: Nikolaev, A., Aguar-Bartolomé, P., Ahrens, J., Annand, J. R. M., Arends, H. J., Beck, R., Bekrenev, V., Boillat, B., Braghieri, A., Branford, D., Briscoe, W. J., Brudvik, J. W., Cherepnya, S., Codling, R., Dehn, M., Downie, E. J., Fil’kov, L. V., Glazier, D. I., Gregor, R., Heid, E., Hornidge, D., Jahn, O., Jankowiak, A., Kaiser, K. -H., Kashevarov, V. L., Kondratiev, R., Korolija, M., Kotulla, M., Krambrich, D., Krusche, B., Lang, M., Lisin, V., Livingston, K., Ludwig-Mertin, U., Lugert, S., MacGregor, I. J. D., Manley, D. M., Martinez-Fabregate, M., McGeorge, J. C., Mekterovic, D., Metag, V., Nefkens, B. M. K., Novotny, R., Owens, R. O., Pedroni, P., Polonski, A., Prakhov, S. N., Price, J. W., Reiter, A., Rosner, G., Rost, M., Rostomyan, T., Schumann, S., Sober, D., Starostin, A., Supek, I., Tarbert, C. M., Thomas, A., Unverzagt, M., Walcher, Th., Watts, D. P., Zehr, F., and The Crystal Ball at MAMI, TAPS and A2 Collaborations
Published: 2014
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26. The LHCb VELO analogue transmission line

Author: Bay, A., Borel, J., Buytaert, J., De Laere, S., Frei, R., Haefeli, G., Koppenburg, P., Locatelli, L., Schneider, O., and Zehr, F.
Published: 2010
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27. Determination of the Dalitz plot parameter $ \pi^{0}_{}$ with the Crystal Ball at MAMI-B

Author: Unverzagt, M., Aguar-Bartolomé, P., Ahrens, J., Annand, J. R. M., Arends, H. J., Beck, R., Bekrenev, V., Boillat, B., Braghieri, A., Branford, D., Briscoe, W. J., Brudvik, J. W., Cherepnya, S., Codling, R., Downie, E. J., Fil’kov, L. V., Glazier, D. I., Gregor, R., Heid, E., Hornidge, D., Jahn, O., Kashevarov, V. L., Kondratiev, R., Korolija, M., Kotulla, M., Krambrich, D., Krusche, B., Lang, M., Lisin, V., Livingston, K., Lugert, S., MacGregor, I. J. D., Manley, D. M., Martinez-Fabregate, M., McGeorge, J. C., Mekterovic, D., Metag, V., Nefkens, B. M. K., Nikolaev, A., Novotny, R., Owens, R. O., Pedroni, P., Polonski, A., Prakhov, S. N., Price, J. W., Rosner, G., Rost, M., Rostomyan, T., Schumann, S., Sober, D., Starostin, A., Supek, I., Tarbert, C. M., Thomas, A., Walcher, Th., Watts, D. P., Zehr, F., and Crystal Ball at MAMI, TAPS and A2 Collaborations
Published: 2009
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28. Measurement of the beam-helicity asymmetry I⊙ in the photoproduction of $ \pi^{0}$ $ \pi^{\pm}$ pairs off protons and off neutrons

Author: Oberle, M., Ahrens, J., Annand, J., Arends, H., Bantawa, K., Bartolome, P., Beck, R., Bekrenev, V., Berghäuser, H., Braghieri, A., Branford, D., Briscoe, W., Brudvik, J., Cherepnya, S., Demissie, B., Dieterle, M., Downie, E., Drexler, P., Fil'kov, L., Fix, A., Glazier, D., Heid, E., Hornidge, D., Howdle, D., Huber, G., Jahn, O., Jaegle, I., Jude, T., Käser, A., Kashevarov, V., Keshelashvili, I., Kondratiev, R., Korolija, M., Kruglov, S., Krusche, B., Kulbardis, A., Lisin, V., Livingston, K., MacGregor, I., Maghrbi, Y., Mancell, J., Manley, D., Marinides, Z., Martinez, M., McGeorge, J., McNicoll, E., Mekterovic, D., Metag, V., Micanovic, S., Middleton, D., Mushkarenkov, A., Nefkens, B., Nikolaev, A., Novotny, R., Ostrick, M., Oussena, B., Pedroni, P., Pheron, F., Polonski, A., Prakhov, S., Robinson, J., Rosner, G., Rostomyan, T., Schumann, S., Sikora, M., Sober, D., Starostin, A., Supek, I., Thiel, M., Thomas, A., Unverzagt, M., Watts, D., Werthmüller, D., Witthauer, L., Zehr, F., Oberle, M., Ahrens, J., Annand, J., Arends, H., Bantawa, K., Bartolome, P., Beck, R., Bekrenev, V., Berghäuser, H., Braghieri, A., Branford, D., Briscoe, W., Brudvik, J., Cherepnya, S., Demissie, B., Dieterle, M., Downie, E., Drexler, P., Fil'kov, L., Fix, A., Glazier, D., Heid, E., Hornidge, D., Howdle, D., Huber, G., Jahn, O., Jaegle, I., Jude, T., Käser, A., Kashevarov, V., Keshelashvili, I., Kondratiev, R., Korolija, M., Kruglov, S., Krusche, B., Kulbardis, A., Lisin, V., Livingston, K., MacGregor, I., Maghrbi, Y., Mancell, J., Manley, D., Marinides, Z., Martinez, M., McGeorge, J., McNicoll, E., Mekterovic, D., Metag, V., Micanovic, S., Middleton, D., Mushkarenkov, A., Nefkens, B., Nikolaev, A., Novotny, R., Ostrick, M., Oussena, B., Pedroni, P., Pheron, F., Polonski, A., Prakhov, S., Robinson, J., Rosner, G., Rostomyan, T., Schumann, S., Sikora, M., Sober, D., Starostin, A., Supek, I., Thiel, M., Thomas, A., Unverzagt, M., Watts, D., Werthmüller, D., Witthauer, L., and Zehr, F.
Abstract: Beam-helicity asymmetries have been measured at the MAMI accelerator in Mainz for the photoproduction of mixed-charge pion pairs in the reactions $ \gamma p\rightarrow n\pi^{0}\pi^{+}$ off free protons and $ \gamma d \rightarrow (p)p\pi^{0}\pi^{-}$ and $ \gamma d\rightarrow (n)n\pi^{0}\pi^{+}$ off quasi-free nucleons bound in the deuteron for incident photon energies up to 1.4GeV. 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.
Published: 2019

29. K+Λ and K+Σ0 photoproduction with fine center-of-mass energy resolution

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

Author: Strakovsky, I. I., Prakhov, S., Azimov, Ya. I., 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., Demissie, B. T., Downie, E. J., Drexler, P., Fil'kov, L. V., Glazier, D. I., Gregor, R., Hamilton, D. J., Heid, E., Hornidge, D., Jaegle, I., Jahn, O., Jude, T. C., Kashevarov, V. L., Keshelashvili, I., Kondratiev, R., Korolija, M., Kotulla, M., Koulbardis, A., Kruglov, S., Krusche, B., Lisin, V., Livingston, K., MacGregor, I. J. D., Maghrbi, Y., Manley, D. M., Marinides, Z., McGeorge, J. C., McNicoll, E. F., Mekterovic, D., Metag, V., Middleton, D. G., Mushkarenkov, A., Nefkens, B. M. K., Nikolaev, A., Novotny, R., Ortega, H., Ostrick, M., Otte, P. B., Oussena, B., Pedroni, P., Pheron, F., Polonski, A., Robinson, J., Rosner, G., Rostomyan, T., Schumann, S., Sikora, M. H., Starostin, A., Supek, I., Taragin, M. F., Tarbert, C. M., Thiel, M., Thomas, A., Unverzagt, M., Watts, D. P., Werthmüller, D., and Zehr, F.
Subjects: Nuclear Experiment
Abstract: An experimental study of ω photoproduction on the proton was conducted by using the Crystal Ball and TAPS multiphoton spectrometers together with the photon tagging facility at the Mainz Microtron MAMI. The γp→ωp differential cross sections are measured from threshold to the incident-photon energy Eγ=1.40 GeV (W=1.87 GeV for the center-of-mass energy) with 15-MeV binning in Eγ and full production-angle coverage. The quality of the present data near threshold gives access to a variety of interesting physics aspects. As an example, an estimation of the ωN scattering length αωp is provided.
Published: 2015

31. [formula omitted] and [formula omitted] photoproduction with fine center-of-mass energy resolution

Author: Jude, T.C., Glazier, D.I., Watts, D.P., Aguar-Bartolomé, P., Akasoy, L.K., Annand, J.R.M., Arends, H.J., Bantawa, K., Beck, R., Bekrenev, V.S., Berghäuser, H., Braghieri, A., Branford, D., Briscoe, W.J., Brudvik, J., Cherepnya, S., Demissie, B.T., Dieterle, M., Downie, E.J., Fil'kov, L.V., Gregor, R., Heid, E., Hornidge, D., Jaegle, I., Jahn, O., Kashevarov, V.L., Keshelashvili, I., Kondratiev, R., Korolija, M., Koulbardis, A.A., Kruglov, S.P., Krusche, B., Lisin, V., Livingston, K., MacGregor, I.J.D., Maghrbi, Y., Manley, D.M., Marinides, Z., Mart, T., Martinez, M., McGeorge, J.C., McNicoll, E.F., Middleton, D.G., Mushkarenkov, A., Nefkens, B.M.K., Nikolaev, A., Nikonov, V.A., Oberle, M., Ostrick, M., Otte, P.B., Oussena, B., Pedroni, P., Pheron, F., Polonski, A., Prakhov, S., Robinson, J., Rosner, G., Rostomyan, T., Sarantsev, A.V., Schumann, S., Sikora, M.H., Sober, D.I., Starostin, A., Strakovsky, I., Suarez, I.M., Supek, I., Thiel, M., Thomas, A., Unverzagt, M., Werthmüller, D., Witthauer, L., and Zehr, F.
Published: 2014
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32. <math altimg='si1.gif' xmlns='http://www.w3.org/1998/Math/MathML'><msup><mrow><mi>K</mi></mrow><mrow><mo>+</mo></mrow></msup><mi>Λ</mi></math> and <math altimg='si2.gif' xmlns='http://www.w3.org/1998/Math/MathML'><msup><mrow><mi>K</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>Σ</mi></mrow><mrow><mn>0</mn></mrow></msup></math> photoproduction with fine center-of-mass energy resolution

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

33. K+ Lambda and K+ Sigma(0) photoproduction with fine center-of-mass energy resolution

Author: Jude, T. C., Korolija, Marina, Supek, Ivan, and Zehr, F.
Subjects: photoproduction, strangeness, baryon spectroscopy, Physics, High Energy Physics::Experiment
Abstract: Measurements of gamma p -> K+ Lambda and gamma p -> 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.
Published: 2014

34. Neutron skin of 208Pb from Coherent Pion Photoproduction

Author: Tarbert, C.M., Knežević, Andrea, Korolija, Milorad, Mekterović, Darko, Supek, Ivan, and Zehr, F.
Subjects: neutron skin, 208Pb, pion photoproduction cross sections, CB, MAMI, integumentary system, High Energy Physics::Experiment, Nuclear Experiment
Abstract: Information on the size and shape of the neutron skin on 208Pb is extracted from coherent pion photoproduction cross sections measured using the Crystal Ball detector together with the Glasgow tagger at the MAMI electron beam facility. On exploitation of an interpolated fit of a theoretical model to the measured cross sections the half-height radius and diffuseness of the neutron distribution are found to be cn=6.70±0.03(stat.)fm and an=0.55±0.01(stat.)+0.02−0.03(sys.)fm respectively, corresponding to a neutron skin thickness ∆r(np)=0.15±0.03(stat.)+0.01−0.03(sys.)fm. The results give the first successful extraction of a neutron skin thickness with an electromagnetic probe and indicate that the skin of 208Pb has a halo character. The measurement provides valuable new constraints on both the structure of nuclei and the equation of state for neutron rich matter.
Published: 2014

35. Measurement of the H1(γ, p→)π0 reaction using a novel nucleon spin polarimeter

Author: Sikora, M.H., Watts, D.P., Glazier, D.I., 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., Codling, R.F.B., Demissie, B.T., Downie, E.J., Drexler, P., Fil'kov, L.V., Freehart, B., Gregor, R., Hamilton, D., Heid, E., Hornidge, D., Howdle, D.A., Jaegle, I., Jahn, O., Jude, T.C., Kashevarov, V.L., Keshelashvili, I., Kondratiev, R., Korolija, M., Kotulla, M., Koulbardis, A.A., Kruglov, S.P., Krusche, B., Lisin, V., Livingston, K., MacGregor, I.J.D., Maghrbi, Y., Manley, D.M., Marinides, Z., Martinez, M., McGeorge, J.C., McKinnon, B., McNicoll, E.F., Mekterovic, D., Metag, V., Micanovic, S., Middleton, D.G., Mushkarenkov, A., Nefkens, B.M.K., Nikolaev, A., Novotny, R., Ostrick, M., Otte, P.B., Oussena, B., Pedroni, P., Pheron, F., Polonski, A., Prakov, S., Robinson, J., Rosner, G., Rostomyan, T., Schumann, S., Sober, D.I., Starostin, A., Strakovsky, I.I., Suarez, I.M., Supek, I., Thiel, M., Thomas, A., Unversagt, M., Werthmueller, D., Workman, R.L., Zamboni, I., and Zehr, F.
Subjects: Nuclear Theory, Nuclear Experiment, QC
Abstract: We report the first large-acceptance measurement of polarization transfer from a polarized photon beam to a recoiling nucleon. The measurement pioneers a novel polarimetry technique, which can be applied to many other nuclear and hadron physics experiments. The commissioning reaction of H1(γ→, p⃗)π0 in the range 0.4
Published: 2014

36. 'Measurement of the 1H(γ, p)π0 reaction using a novel nucleon spin polarimeter'

Author: Sikora, M.H., Korolija, Milorad, Mekterović, Darko, Mićanović, S., Supek, Ivan, Zamboni, Ivana, and Zehr, F.
Subjects: polarization transfer, polarized photon beam, MAMI, Nuclear Experiment
Abstract: We report the first large-acceptance measurement of polarization transfer from a polarized photon beam to a recoiling nucleon, pioneering a novel polarimetry technique with wide application to future nuclear and hadronic physics experiments. The commissioning measurement of polarization transfer in the 1H(~γ, ~p)π0 reaction in the range 0.4< Eγ < 1.4 GeV is highly selective regarding the basic parametrization used in partial wave analyses to extract the nucleon excitation spectrum. The new data strongly favor the recently proposed Chew-Mandelstam formalism.
Published: 2014
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37. Coherent photoproduction of π0- and η-mesons off 7Li

Author: Maghrbi, Y., Krusche, B., Ahrens, J., Annand, J. R. M., Arends, H. J., Beck, R., Bekrenev, V., Boillat, B., Braghieri, A., Branford, D., Briscoe, W. J., Brudvik, J., Cherepnya, S., Codling, R. F. B., Downie, E. J., Drexler, P., Fil’kov, L. V., Fix, A., Glazier, D. I., Gregor, R., Heid, E., Hornidge, D., Jaegle, I., Jahn, O., Kashevarov, V. L., Keshelashvili, I., Knezevic, A., Kondratiev, R., Korolija, M., Krambrich, D., Lang, M., Lisin, V., Livingston, K., Lugert, S., MacGregor, I. J. D., Manley, D. M., Martinez, M., McGeorge, J. C., Mekterovic, D., Metag, V., Nefkens, B. M. K., Nikolaev, A., Novotny, R., Ostrick, M., Pedroni, P., Pheron, F., Polonski, A., Prakhov, S., Price, J. W., Rosner, G., Rost, M., Rostomyan, T., Schadmand, S., Schumann, S., Sober, D., Starostin, A., Supek, I., Tarbert, C. M., Thomas, A., Unverzagt, M., Watts, D. P., Werthmüller, D., and Zehr, F.
Subjects: Nuclear Theory, Nuclear Experiment
Abstract: Coherent photoproduction of π0-mesons from threshold (E th ≈ 136 MeV) throughout the Δ-resonance region and of η-mesons close to the production threshold (E th ≈ 570 MeV for η has been measured for 7Li nuclei. The experiment was performed using the tagged-photon beam of the Mainz MAMI accelerator with the Crystal Ball and TAPS detectors combined to give an almost 4π solid-angle electromagnetic calorimeter. The reactions were identified by a combined invariant-mass and missing-energy analysis. A comparison of the pion data to plane-wave impulse modelling tests the nuclear mass form factor. So far coherent η production had been only identified for the lightest nuclear systems (2H and 3He . For 3He a large enhancement of the cross section above plane-wave approximations had been reported, indicating the formation of a quasi-bound state. The present Li data for η production agree with a plane-wave approximation. Contrary to 3He , neither a threshold enhancement of the total cross section nor a deviation of the angular distributions from the expected form factor dependence were observed
Published: 2013

38. Measurement of the γ p→K0 Σ+ reaction with the Crystal Ball/TAPS detectors at the Mainz Microtron

Author: P. Aguar-Bartolomé, P. ..., Korolija, Milorad, Mekterović, Darko, Supek, Ivan, and Zehr, F.
Subjects: γp → K0 Σ+ reaction, partial-wave scattering amplitudes, Crystal Ball, TAPS, MAMI
Abstract: The γp→K0 Σ+ reaction has been measured from threshold to Eγ=1.45 GeV (WCM = 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 3π0p final state. The experimental results include total and differential cross sections as well as the polarization of the recoil hyperon. The new data significantly improve the empirical knowledge about the γp → K0 Σ+ reaction in the measured energy range. The results are compared to previous measurements and model predictions.
Published: 2013

39. A new determination of the eta transition form factor in the Dalitz decay eta -> e^+ e^- gamma with the Crystal Ball/TAPS detectors at the Mainz Microtron

Author: Aguar-Bartolom��, P., Annand, J. R. M., Arends, H. J., Bantawa, K., Beck, R., Bekrenev, V., Bergh��user, H., Braghieri, A., Briscoe, W. J., Brudvik, J., Cherepnya, S., Codling, R. F. B., Collicott, C., Costanza, S., Denig, A., Downie, E. J., Drexler, P., Fil'kov, L. V., Fix, A., Glazier, D. I., Gregor, R., Hamilton, D. J., Heid, E., Hornidge, 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., Manley, D. M., Masjuan, P., McGeorge, J. C., McNicoll, E. F., Mekterovic, D., Metag, V., Mushkarenkov, A., Nefkens, B. M. K., Nikolaev, A., Novotny, R., 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., Werthm��ller, D., and Zehr., F.
Subjects: High Energy Physics - Experiment (hep-ex), FOS: Physical sciences, High Energy Physics::Experiment, Nuclear Experiment (nucl-ex), Nuclear Experiment
Abstract: The Dalitz decay eta -> e^+ e^- gamma has been measured in the gamma p -> eta p reaction with the Crystal Ball and TAPS multiphoton spectrometers, together with the photon tagging facility at the Mainz Microtron MAMI. The experimental statistic used in this work is one order of magnitude greater than in any previous measurement of eta -> e^+ e^- gamma. The value obtained for the slope parameter 1/Lambda^2 of the eta transition form factor, 1/Lambda^2 = (1.95 +/- 0.15_stat +/- 0.10_syst) [1/GeV^2], is in good agreement with recent measurements conducted in eta -> e^+ e^- gamma and eta -> mu^+ mu^- gamma decays, as well as with recent form-factor calculations. The uncertainty obtained in the value of 1/Lambda^2 is lower compared to results from previous measurements of the eta -> e^+ e^- gamma decay., 11 pages, 10 figures, 1 table
Published: 2013
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40. Measurement of the beam-helicity asymmetry Io in the photoproduction of π0-pairs off the proton and off the neutron

Author: Oberle, M., Korolija, Milorad, Mekterović, Darko, Mićanović, Saša, Supek, Ivan, and Zehr, F.
Subjects: Nuclear Theory, Beam-helicity asymmetries, MAMI accelerator, photoproduction of neutral pion pairs, High Energy Physics::Experiment, 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 ~γp→pπ0 π0 and ~γd→(n)pπ0π0, ~γd → (p)nπ0π0 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 π0 mesons, recoil protons, and recoil neutrons were detected in the 4π 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
Published: 2013

41. Measurement of the g p -> K^0 Sigma^+ reaction with the Crystal Ball/TAPS detectors at the Mainz Microtron

Author: Aguar-Bartolom��, P., Annand, J. R. M., Arends, H. J., Bantawa, K., Beck, R., Bekrenev, V., Bergh��user, H., Braghieri, A., Briscoe, W. J., Brudvik, J., Cherepnya, S., Codling, R. F. B., Collicott, C., 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., Werthm��ller, D., Witthauer, L., and Zehr., F.
Subjects: High Energy Physics - Experiment (hep-ex), FOS: Physical sciences, Nuclear Experiment (nucl-ex)
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., 12 pages, 10 figures, 4 tables
Published: 2013
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42. Determination of the �� mass with the Crystal Ball at MAMI-B

Author: Nikolaev, A., Aguar-Bartolom��, P., Ahrens, J., Annand, J. R. M., Arends, H. J., Beck, R., Bekrenev, V., Boillat, B., Braghieri, A., Branford, D., Briscoe, W. J., Brudvik, J. W., Cherepnya, S., Codling, R., Dehn, M., Downie, E. J., Fil'kov, L. V., Glazier, D. I., Gregor, R., Heid, E., Hornidge, D., Jahn, O., Jankowiak, A., Kaiser, K. -H., Kashevarov, V. L., Kondratiev, R., Korolija, M., Kotulla, M., Krambrich, D., Krusche, B., Lang, M., Lisin, V., Livingston, K., Ludwig-Mertin, U., Lugert, S., MacGregor, I. J. D., Manley, D. M., Martinez-Fabregate, M., McGeorge, J. C., Mekterovic, D., Metag, V., Nefkens, B. M. K., Novotny, R., Owens, R. O., Pedroni, P., Polonski, A., Prakhov, S. N., Price, J. W., Reiter, A., Rosner, G., Rost, M., Rostomyan, T., Schumann, S., Sober, D., Starostin, A., Supek, I., Tarbert, C. M., Thomas, A., Unverzagt, M., Walcher, Th., Watts, D. P., and Zehr, F.
Subjects: FOS: Physical sciences, High Energy Physics::Experiment, Nuclear Experiment (nucl-ex), Nuclear Experiment
Abstract: A new precise determination of the �� meson mass is presented. It is based on a measurement of the threshold for the ��p -> p�� reaction using the tagger focal-plane microscope detector at the MAMI-B facility in Mainz. The tagger microscope has a higher energy resolution than the standard tagging spectrometer and, hence, allowed an improvement in the accuracy compared to the previous �� mass measurement at MAMI-B. The result m�� = (547.851 +- 0.031 stat. +- 0.062 syst.) MeV agrees very well with the precise values of the NA48, KLOE and CLEO collaborations and deviates by about 5�� from the smaller, but also very precise value obtained by the GEM collaboration at COSY., Submitted for publication in EPJA
Published: 2012
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43. Determination of the eta-transition form factor in the gamma p -< p eta -< p gamma e(+)e(-) reaction

Author: Berghaeuser, H., Metag, V., Starostin, A., Bartolome, P. Aguar, Akasoy, L. K., 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. T., Downie, E. J., Drexler, P., Dieterle, M., Fil`kov, L. V., Fix, A., Glazier, D. I., Heid, E., Hornidge, D., Jahn, O., Jude, T. C., Kashevarov, V. L., Knezevic, A., Kondratiev, R., Korolija, M., Kotulla, M., Koulbardis, A., Kruglov, S., Krusche, B., Lemmer, B., Lisin, V., Livingston, K., MacGregor, I. J. D., Maghrbi, Y., Manley, D. M., Martinez-Fabregate, M., McGeorge, J. C., McNicoll, E. F., Mekterovic, D., Micanovic, S., Mushkarenkov, A., Nefkens, B. M. K., Nikolaev, A., Novotny, R., Ostrick, M., Owens, R. O., Pedroni, P., Pheron, F., Polonski, A., Robinson, J., Prakhov, S. N., Rosner, G., Rostomyan, T., Schumann, S., Sober, D., Suarez, I. M., Supek, I., Tarbert, C. M., Thiel, M., Thomas, A., Unverzagt, M., Watts, D. P., Werthmueller, D., Zamboni, I., and Zehr, F.
Subjects: High Energy Physics::Experiment, Nuclear Experiment
Abstract: The Dalitz decay eta -> gamma e(+)e(-) has been measured using the combined Crystal Ball and TAPS photon detector setup at the electron accelerator MAMI-C. Compared to the most recent transition form-factor measurement in the e(+)e(-) channel, statistics have been improved by one order of magnitude. The e(+)e(-)invariant mass distribution shows a deviation from the QED prediction for a point-like particle, which can be described by a form-factor. Using the usual monopole transition form-factor parameterization, F(m(2)) = (1 - m(2)/Lambda(2))(-1), a value of Lambda(-2) = (1.92 +/- 0.35(stat) +/- 0.13(syst)) GeV(-2) has been determined. This value is in good agreement with a recent measurement of the eta Dalitz decay in the mu(+)mu(-) channel and with recent form-factor calculations. An improved value of the branching ratio BR(eta -> gamma e(+)e(-)) = (6.6 +/- 0.4(stat) +/- 0.4(syst)) . 10(-3) has been determined. (C) 2011 Elsevier B.V. All rights reserved.
Published: 2011
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44. Determination of the η-transition form factor in the γp→pη→pγe+e− reaction

Author: Berghäuser, H., Metag, V., Starostin, A., Aguar Bartolomé, P., Akasoy, L.K., 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.T., Downie, E.J., Drexler, P., Dieterle, M., Fil’kov, L.V., Fix, A., Glazier, D.I., Heid, E., Hornidge, D., Jahn, O., Jude, T.C., Kashevarov, V.L., Knežević, Andrea, Kondratiev, R., Korolija, Milorad, Kotulla, M., Koulbardis, A., Kruglov, S., Krusche, B., Lemmer, B., Lisin, V., Livingston, K., MacGregor, I.J.D., Maghrbi, Y., Manley, D.M., Martinez-Fabregate, M., McGeorge, J.C., McNicoll, E.F., Mekterović, Darko, Mićanović, Saša, Mushkarenkov, A., Nefkens, B.M.K., Nikolaev, A., Novotny, R., Ostrick, M., Owens, R.O., Pedroni, P., Pheron, F., Polonski, A., Prakhov, S.N., Robinson, J., Rosner, G., Rostomyan, T., Schumann, S., Sober, D. I., Suarez, I.M., Supek, Ivan, Tarbert, C.M., Thiel, M., Thomas, A., Unverzagt, M., Watts, D.P., Werthmüller, D., Zamboni, Ivana, and Zehr, F.
Subjects: High Energy Physics::Experiment, Nuclear Experiment, Meson decays, Transition form factor
Abstract: The Dalitz decay η→γe+e− has been measured using the combined Crystal Ball and TAPS photon detector setup at the electron accelerator MAMI-C. Compared to the most recent transition form-factor measurement in the e+e− channel, statistics have been improved by one order of magnitude. The e+e− invariant mass distribution shows a deviation from the QED prediction for a point-like particle, which can be described by a form-factor. Using the usual monopole transition form-factor parameterization, F(m^2)=(1−m^2/Λ^2)^−1, a value of Λ^−2=(1.92±0.35(stat)±0.13(syst)) GeV^−2 has been determined. This value is in good agreement with a recent measurement of the η Dalitz decay in the μ+μ− channel and with recent form-factor calculations. An improved value of the branching ratio BR(η→γe+e−)=(6.6±0.4(stat)±0.4(syst))•10^−3 has been determined.
Published: 2011
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45. First measurement of the circular beam asymmetry in the γp→π0ηp reaction

Author: Kashevarov, V.L., Fix, A., Aguar-Bartolomé, P., Akasoy, L.K., Annand, J.R.M., Arends, H.J., Bantawa, K., Beck, R., Bekrenev, V., Berghäuser, H., Braghieri, A., Branford, D., Briscoe, W.J., Brudvik, J., Cherepnya, S., Codling, R.F.B., Demissie, B.T., Downie, E.J., Drexler, P., Fil'kov, L.V., Glazier, D.I., Gregor, R., Hamilton, D., Heid, E., Hornidge, D., Jaegle, I., Jahn, O., Jude, T.C., Kellie, J.D., Keshelashvili, I., Kondratiev, R., Korolija, Milorad, Kotulla, M., Koulbardis, A., Kruglov, S., Krusche, B., Lisin, V., Livingston, K., MacGregor, I.J.D., Maghrbi, Y., Manley, D.M., Martinez-Fabregate, M., McGeorge, J.C., McNicoll, E.F., Mekterović, Darko, Metag, V., Mićanović, Saša, Nefkens, B.M.K., Nikolaev, A., Novotny, R., 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. I., Starostin, A., Stakovsky, I.I., Suarez, I.M., Supek, Ivan, Tarbert, C.M., Thiel, M., Thomas, A., Unverzagt, M., Watts, D.P., Werthmüller, D., Zamboni, Ivana, and Zehr, F.
Subjects: Nuclear Experiment, Pseudoscalar meson photoproduction, Baryon resonances, Polarization observables
Abstract: The circular photon asymmetry for π0η photoproduction on the proton was measured for the first time at the tagged photon facility of the MAMI C accelerator using the Crystal Ball/TAPS photon spectrometer. The experimental results are interpreted within a phenomenological isobar model that confirms the dominant role of the Δ(1700)D33 resonance. The measured asymmetry allows us to identify small contributions from positive-parity resonances via interference terms with the dominant D33 amplitude.
Published: 2010

46. Experimental study of the γp→ηp reaction with the Crystal Ball detector at the Mainz Microtron (MAMI-C)

Author: McNicoll, E.F., Prakhov, S., Strakovsky, I.I., Aguar-Bartolomé, P., Akasoy, L.K., Annand, J.R.M., Arends, H.J., Arndt, R.A., Azimov, Ya.I., Bantawa, K., Beck, R., Bekrenev, V., Berghäuser, H., Braghieri, A., Branford, D., Briscoe, W.J., Brudvik, J., Cherepnya, S., Codling, R.F.B., Demissie, B.T., Downie, E.J., Drexler, P., Fil'kov, L.V., Fix, A., Glazier, D.I., Gregor, R., Hamilton, D., Heid, E., Hornidge, D., Jaegle, I., Jahn, O., Jude, T.C., Kashevarov, V.L., Kellie, J.D., Keshelashvili, I., Kondratiev, R., Korolija, Milorad, Kotulla, M., Koulbardis, A., Kruglov, S.P., Krusche, B., Lisin, V., Livingston, K., MacGregor, I.J.D., Maghrbi, Y., Manley, D.M., Marinides, Z., Martinez, M., McGeorge, J.C., McKinnon, B., Mekterović, Darko, Metag, V., Mićanović, Saša, Middleton, D., Mushkarenkov, A., Nefkens, B.M.K., Nikolaev, A., Novotny, R., Ostrick, M., Otte, P.B., Oussena, B., Paris, M.W., Pedroni, P., Pheron, F., Polonski, A., Robinson, J., Rosner, G., Rostomyan, T., Schumann, S., Sikora, M.H., Sober, D.I., Starostin, A., Suarez, I.M., Supek, Ivan, Thiel, M., Thomas, A., Tiator, L, Unverzagt, M., Watts, D.P., Werthmüller, D., Workman, R.L., Zamboni, Ivana, and Zehr, F.
Subjects: Crystal Ball, TAPS, γp→ηp reaction
Abstract: The γp → ηp reaction has been measured with the Crystal Ball and TAPS multiphoton spectrometers in the energy range from the production threshold of 707 MeV to 1.4 GeV (1.49
Published: 2010
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47. Determination of the Dalitz plot parameter α for the decay η → 3 π 0 with the Crystal Ball at MAMI-B

Author: Manley, D., Nefkens, B., Mcgeorge, J., Gregor, R., Mekterovic, D., Aguar-Bartolome, P., Zehr, F., Annand, J., Watts, D., Metag, V., Nikolaev, A., Novotny, R., Owens, R., Pedroni, P., Polonski, A., Prakhov, S., Price, J., Rost, M., Rosner, G., Heidari, E., Hornidge, D., Jahn, O., Kashevarov, V., Kondratiev, R., Glazier, D., FilKov, L., Downie, E., Codling, R., Cherepnya, S., Brudvik, J., Briscoe, W., Branford, D., Korolija, M., Kotulla, M., Walcher, Th., Thomas, A., Tarbert, C., Boillat, B., Filkov, L., Heid, E., Macgregor, I., Braghieri, A., Boillat., B., Bekrenev, V., Beck, R., Supek, I., Starostin, A., Sober, D., Schumann, S., Rostomyan, T., Arends, H., Ahrens, J., Aguar-Bartolomé, P., Unverzagt, M., Krambrich, D., Krusche, B., Lang, M., Lisin, V., Livingston, K., Lugert, S., and Martinez-Fabregate, M.
Subjects: Physics, Nuclear and High Energy Physics, Particle physics, bepress|Physical Sciences and Mathematics|Physics, Photon detector, Dalitz plot, Particle accelerator, n, K and η mesons, Alpha (navigation), law.invention, High Energy Physics - Experiment, law, High Energy Physics::Experiment, Photon beam, Nuclear Experiment, Crystal Ball
Abstract: A precise measurement of the Dalitz plot parameter, alpha, for the eta->3pi^0 decay is presented. The experiment was performed with the Crystal Ball and TAPS large acceptance photon detectors at the tagged photon beam facility of the MAMI-B electron accelerator in Mainz. High statistics of 1.8*10^6 eta->3pi^0 events were obtained, giving the result alpha = -0.032 +/- 0.002(stat) +/- 0.002(syst)., Comment: 9 pages, 6 figures, published in the online-first section of EPJ A, included changes referees asked for, added DOI
Published: 2009

48. Measurement of the Slope Parameter α for the eta-->3pi^0 decay with the Crystal Ball detector at the Mainz Microtron (MAMI-C)

Author: Prakhov, S., Nefkens, B. M. K., Aguar-Bartolomé, P., Akasoy, L. K., Annand, J. R. M., Arends, H. J., Bantawa, K., Beck, R., Bekrenev, V., Berghäuser, H., Boillat, B., Braghieri, A., Branford, D., Briscoe, W. J., Brudvik, J., Cherepnya, S., Codling, R. F. B., Downie, E. J., Drexler, P., Fil'kov, L. V., Glazier, D. I., Gregor, R., Heid, E., Hornidge, D., Jahn, O., Jude, T. C., Kashevarov, V. L., Kellie, J. D., Kondratiev, R., Korolija, Milorad, Kotulla, M., Koulbardis, A., Krambrich, D., Kruglov, S., Krusche, B., Lang, M., Lisin, V., Livingston, K., MacGregor, I. J. D., Maghrbi, Y., Manley, D. M., Martinez, M., McGeorge, J. C., McNicoll, E. F., Mekterović, Darko, Metag, V., Mićanović, Saša, Nikolaev, A., Novotny, R., Ostrick, M., Otte, P. B., Pedroni, P., Pheron, F., Polonski, A., Robinson, J., Rosner, G., Rost, M., Rostomyan, T., Schumann, S., Sikora, M. H., Sober, D. I., Starostin, A., Suarez, I. M., Supek, Ivan, Tarbert, C. M., Thiel, M., Thomas, A., Unverzagt, M., Watts, D. P., Zamboni, Ivana, and Zehr, F.
Subjects: High Energy Physics::Experiment, Nuclear Experiment, tagged photon spectrometer, eta-meson decay, slope parameter alpha
Abstract: The dynamics of the eta→ 3pi^0 decay have been studied with the Crystal Ball multiphoton spectrometer and the TAPS calorimeter. Bremsstrahlung photons produced by the 1.5-GeV electron beam of the Mainz microtron MAMI-C and tagged by the Glasgow photon spectrometer were used for eta-meson production. The analysis of 3×10^6 gamma p→ eta p→ 3 pi^0 p→ 6 gama p events yields the value alpha = -0.032 +/- 0.003 for the eta→ 3pi^0 slope parameter, which agrees with the majority of recent experimental results and has the smallest uncertainty. The pi^0pi^0 invariant-mass spectrum was investigated for the occurrence of a cusplike structure in the vicinity of the pi^+pi^-threshold. The observed effect is small and does not affect our measured value for the slope parameter.
Published: 2009
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49. Photoproduction of pi^0 eta on protons and the Delta(1700)D_33 resonance

Author: Kashevarov, V.L., Fix, A., Aguar-Bartolomé, P., Akasoy, L.K., Annand, J.R.M., Arends, H.J., Bantawa, K., Beck, R., Bekrenev, V., Berghäuser, H., Boillat, B., Braghieri, A., Branford, D., Briscoe, W.J., Brudvik, J., Cherepnya, S., Downie, E.J., Drexler, P., Fil'kov, L.V., Glazier, D.I., Gregor, R., Heid, E., Hornidge, D., Jahn, O., Jude, T.C., Knežević, Andrea, Kondratiev, R., Korolija, Milorad, Kotulla, M., Koulbardis, A., Kruglov, S., Krusche, B., Lisin, V., Livingston, K., MacGregor, I.J.D., Maghrbi, Y., Manley, D.M., Martinez, M., McGeorge, J.C., McNicoll, E.F., Mekterović, Darko, Metag, V., Mićanović, Saša, Nefkens, B.M.K., Novotny, R., Ostrick, M., Owens, R.O., Pedroni, P., Pheron, F., Polonski, A., Prakhov, S, Robinson, J., Rosner, G., Rostomyan, T., Schumann, S., Sober, D.I., Starostin, A., Suarez, I.M., Supek, Ivan, Tarbert, C.M., Thiel, M., Thomas, A., Unverzagt, M., Watts, D.P., Zamboni, Ivana, and Zehr, F.
Subjects: photoproduction, Crystal Ball, Delta resonance, High Energy Physics::Experiment, Nuclear Experiment
Abstract: Total and differential cross sections for the reaction gamma p -> pi^0 eta p have been measured with the Crystal Ball/TAPS detector using the tagged photon facility at the MAMI C accelerator in Mainz. In the energy range E_gamma=0.95-1.4 GeV the reaction is dominated by the excitation and sequential decay of the Delta(1700)D_33 resonance. Angular distributions measured with high statistics allow us to determine the ratio of hadronic decay widths Gamma_(eta Delta)/Gamma_(pi S11) and the ratio of the helicity amplitudes A_(3/2)/A_(1/2) for this resonance.
Published: 2009

50. Measurement of theγp→K0Σ+reaction with the Crystal Ball/TAPS detectors at the Mainz Microtron

Author: Aguar-Bartolomé, P., primary, Annand, J. R. M., additional, Arends, H. J., additional, Bantawa, K., additional, Beck, R., additional, Bekrenev, V., additional, Berghäuser, H., additional, Braghieri, A., additional, Briscoe, W. J., additional, Brudvik, J., additional, Cherepnya, S., additional, Codling, R. F. B., additional, Collicott, C., additional, Demissie, B., additional, Dieterle, M., additional, Downie, E. J., additional, Drexler, P., additional, Fil'kov, L. V., additional, Fix, A., additional, Glazier, D. I., additional, Gregor, R., additional, Hamilton, D., additional, Heid, E., additional, Hornidge, D., additional, Howdle, D., additional, Isaksson, L., additional, Jaegle, I., additional, Jahn, O., additional, Jude, T. C., additional, Kashevarov, V. L., additional, Keshelashvili, I., additional, Kondratiev, R., additional, Korolija, M., additional, Kotulla, M., additional, Koulbardis, A., additional, Kruglov, S., additional, Krusche, B., additional, Lisin, V., additional, Livingston, K., additional, MacGregor, I. J. D., additional, Maghrbi, Y., additional, Mancel, J., additional, Manley, D. M., additional, McNicoll, E. F., additional, Mekterovic, D., additional, Metag, V., additional, Mushkarenkov, A., additional, Nefkens, B. M. K., additional, Nikolaev, A., additional, Novotny, R., additional, Oberle, M., additional, Ortega, H., additional, Ostrick, M., additional, Ott, P., additional, Otte, P. B., additional, Oussena, B., additional, Pedroni, P., additional, Pheron, F., additional, Polonski, A., additional, Prakhov, S., additional, Robinson, J., additional, Rosner, G., additional, Rostomyan, T., additional, Schumann, S., additional, Sikora, M. H., additional, Sober, D. I., additional, Starostin, A., additional, Strakovsky, I. I., additional, Suarez, I. M., additional, Supek, I., additional, Tarbert, C. M., additional, Thiel, M., additional, Thomas, A., additional, Unverzagt, M., additional, Watts, D. P., additional, Werthmüller, D., additional, Witthauer, L., additional, and Zehr, F., additional
Published: 2013
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