Measurement of the beam-helicity asymmetry I⊙ in the photoproduction of pi0 pi±- pairs off the protons and off the neutrons

Oberle, M. et al. (2014) Measurement of the beam-helicity asymmetry I⊙ in the photoproduction of pi0 pi±- pairs off the protons and off the neutrons. European Physical Journal A, 50, p. 54. (doi: 10.1140/epja/i2014-14054-5)

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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 -> n pi0 pi+ off free protons and gamma d -> (p)p pi0 pi- and gamma d -> (n) n pi0 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 pi0 mesons were detected in the 4pi 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.

Item Type:Articles
Glasgow Author(s) Enlighten ID:Middleton, Dr Duncan and Glazier, Dr Derek and McGeorge, Dr John and Robinson, Mr Jamie and Downie, Dr Evangeline and MacGregor, Professor Douglas and Livingston, Dr Kenneth and Howdle, Mr David and McNicoll, Miss Eilidh and Mancell, Mr Joe and Annand, Dr John and Rosner, Professor Guenther
Authors: Oberle, M., Ahrens, J., Annand, J., Arends, H., Bantawa, K., Bartomolme, P., Beck, R., Bekrenev, V., Berghaeuser, 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., Kaeser, 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., Unversagt, M., Watts, D., Werthmueller, D., Witthauer, L., and Zehr, F.
Subjects:Q Science > QC Physics
College/School:College of Science and Engineering > School of Physics and Astronomy
Research Group:Nuclear Physics
Journal Name:European Physical Journal A
ISSN (Online):1434-601X
Copyright Holders:Copyright © 2014 The Authors
First Published:First published in European Physical Journal A 50:54
Publisher Policy:Reproduced under a Creative Commons License

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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
570711Nuclear Physics GroupDavid IrelandScience & Technologies Facilities Council (STFC)ST/J000175/1P&A - PHYSICS & ASTRONOMY
507271Illuminating strongly interacting matterI MacgregorScience & Technologies Facilities Council (STFC)ST/G008604/1P&A - PHYSICS & ASTRONOMY