Quasi-free photoproduction of η -mesons off the deuteron
Jaegle, I. ; Krusche, B. ; Anisovich, A. ; Bacelar, J. ; Bantes, B. ; Bartholomy, O. ; Bayadilov, D. ; Beck, R. ; Beloglazov, Y. ; Castelijns, R. ; Crede, V. ; Dieterle, M. ; Dutz, H. ; Elsner, D. ; Ewald, R. ; Frommberger, F. ; Funke, C. ; Gothe, R. ; Gregor, R. ; Gridnev, A. ; Gutz, E. ; Hillert, W. ; Höffgen, S. ; Hoffmeister, P. ; Horn, I. ; Junkersfeld, J. ; Kalinowsky, H. ; Kammer, S. ; Keshelashvili, I. ; Kleber, V. ; Klein, Frank ; Klein, Friedrich ; Klempt, E. ; Konrad, M. ; Kotulla, M. ; Lang, M. ; Löhner, H. ; Lopatin, I. ; Lugert, S. ; Maghrbi, Y. ; Menze, D. ; Mertens, T. ; Messchendorp, J. ; Metag, V. ; Nikonov, V. ; Nanova, M. ; Novinski, D. ; Novotny, R. ; Oberle, M. ; Ostrick, M. ; Pant, L. ; van Pee, H. ; Pfeiffer, M. ; Pheron, F. ; Roy, A. ; Sarantsev, A. ; Schadmand, S. ; Schmidt, C. ; Schmieden, H. ; Schoch, B. ; Shende, S. ; Sokhoyan, V. ; Süle, A. ; Sumachev, V. ; Szczepanek, T. ; Thoma, U. ; Trnka, D. ; Varma, R. ; Walther, D. ; Wendel, C. ; Werthmüller, D. ; Witthauer, L.
In: The European Physical Journal A, 2011, vol. 47, no. 8, p. 1-25
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- Abstract.: Precise data for quasi-free photoproduction of η-mesons off the deuteron have been measured at the Bonn ELSA accelerator with the combined Crystal Barrel/TAPS detector for incident photon energies up to 2.5GeV. The η-mesons have been detected in coincidence with recoil protons and neutrons. Possible nuclear effects like Fermi motion and re-scattering can be studied via a comparison of the quasi-free reaction off the bound proton to η-production off the free proton. No significant effects beyond the folding of the free cross-section with the momentum distribution of the bound protons have been found. These Fermi motion effects can be removed by an analysis using the invariant mass of the η-nucleon pairs reconstructed from the final-state four-momenta of the particles. The total cross-section for quasi-free η-photoproduction off the neutron reveals even without correction for Fermi motion a pronounced bump-like structure around 1GeV of incident photon energy, which is not observed for the proton. This structure is even narrower in the invariant-mass spectrum of the η-neutron pairs. Position and width of the peak in the invariant-mass spectrum are W ≈ 1665 MeV and FWHM Γ ≈ 25 MeV. The data are compared to the results of different models