Quasifree photoproduction of eta mesons off protons and neutrons

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

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Differential and total cross sections for the quasifree reactions gamma p -> eta p and gamma n -> eta n have been determined at the MAMI-C electron accelerator by using a liquid deuterium target. Photons were produced via bremsstrahlung from the 1.5 GeV incident electron beam and energy tagged with the Glasgow photon tagger. Decay photons of the neutral decay modes eta -> 2 gamma and eta -> 3 pi(0) -> 6 gamma and coincident recoil nucleons were detected in a combined setup of the Crystal Ball and the TAPS calorimeters. The eta-production cross sections were measured in coincidence with recoil protons, recoil neutrons, and in an inclusive mode without a condition on recoil nucleons, which allowed a check of the internal consistency of the data. The effects from nuclear Fermi motion were removed by a kinematic reconstruction of the final-state invariant mass and possible nuclear effects on the quasifree cross section were investigated by a comparison of free and quasifree-proton data. The results, which represent a significant improvement in statistical quality compared to previous measurements, agree with the known neutron-to-proton cross-section ratio in the peak of the S-11(1535) resonance and confirm a peak in the neutron cross section, which is absent for the proton, at a center-of-mass energy W = (1670 +/- 5) MeV with an intrinsic width of Gamma approximate to 30 MeV.

Original languageEnglish
Article number015205
Number of pages21
JournalPhysical Review C
Issue number1
Publication statusPublished - 25 Jul 2014




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