Photoproduction of -mesons on protons in the resonance region: The background problem and the third S 11-resonance
Institute for Nuclear Physics, Tomsk Polytechnic University, P.O. Box 25, 634050, Tomsk, Russia
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We have constructed an isobar model for the -photoproduction on the proton in the energy region up to the photon lab energy K 0 = 3 GeV. The database involved into the fitting procedure includes precise results for the cross-section and for the T-asymmetry of the process near threshold obtained at MAMI and ELSA as well as recent results for the -asymmetry and for the angular distribution measured at higher energies in Grenoble and also more recent measurements performed at JLab for the photon energies up to 2 GeV. The model includes twelve nucleon resonances: S 11(1535), S 11(1650), S 11(1825), P 11(1440), P 13(1720), D 13(1520), D 15(1675), F 15(1680), F 17(1990), G 17(2190), G 19(2250), H 19(2220), and the background consisting of the nucleon pole term and the vector meson exchange in the t-channel. To explain the observed energy dependence of the integrated cross-section, two s-wave resonances, S 11(1650) and S 11(1825), have to be taken into account along with the dominating S 11(1535). The integrated cross-section as well as the angular distribution and -asymmetry predicted by the model are in good agreement with the data. Above the photon energy K 0 = 2 GeV, the calculated cross-section exhibits an appreciable dependence on the - and -meson contribution, whose coupling with nucleons is not well defined. Several versions of extending the model to higher energies are considered.
© Società Italiana di Fisica and Springer-Verlag, 2004