Coherent photoproduction of eta-mesons off He-3 - search for eta-mesic nuclei

F. Pheron, J. Ahrens, J. R. M. Annand, H. J. Arends, K. Bantawa, P. A. Bartolome, R. Beck, V. Bekrenev, H. Berghaeuser, B. Boillat, A. Braghieri, D. Branford, W. J. Briscoe, J. Brudvik, S. Cherepnya, B. Demissie, M. Dieterle, E. J. Downie, P. Drexler, D. I. GlazierE. Heid, L. V. Fil'kov, D. Hornidge, D. Howdle, O. Jahn, I. Jaegle, T. C. Jude, V. L. Kashevarov, I. Keshelashvili, R. Kondratiev, M. Korolija, M. Kotulla, A. Kulbardis, S. P. Kruglov, B. Krusche, V. Lisin, K. Livingston, I. J. D. MacGregor, Y. Maghrbi, J. Mancell, D. M. Manley, Z. Marinides, M. Martinez, J. C. McGeorge, E. McNicoll, D. Mekterovic, V. Metag, S. Micanovic, D. G. Middleton, A. Mushkarenkov, B. M. K. Nefkens, A. Nikolaev, R. Novotny, M. Oberle, M. Ostrick, B. Oussena, P. Pedroni, A. Polonski, S. N. Prakhov, J. Robinson, G. Rosner, T. Rostomyan, S. Schumann, M. H. Sikora, D. I. Sober, A. Starostin, I. Supek, M. Thiel, A. Thomas, M. Unverzagt, D. P. Watts, D. Werthmueller, L. Witthauer, F. Zehr

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Coherent photoproduction of eta-mesons off He-3, i.e. the reaction gamma He-3 -> eta He-3, 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 -> gamma gamma and eta -> 3 pi(0) -> 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 He-3 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 He-3 -> pi(0)pX reaction revealed a very complicated structure of the background and could not support previous conclusions. (C) 2012 Elsevier B.V. All rights reserved.

Original languageEnglish
Pages (from-to)21-27
Number of pages7
JournalPhysics Letters B
Issue number1-2
Publication statusPublished - 13 Mar 2012

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