Photoproduction of -mesons on protons in the resonance region: The background problem and the third S 11-resonance

V. A. Tryasuchev

doi:10.1140/epja/i2004-10024-x

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2023 Impact factor 2.6

Hadrons and Nuclei

Eur. Phys. J. A (2004) 22: 97-104
https://doi.org/10.1140/epja/i2004-10024-x

Photoproduction of $\eta$ -mesons on protons in the resonance region: The background problem and the third S ₁₁-resonance

V. A. Tryasuchev^*

Institute for Nuclear Physics, Tomsk Polytechnic University, P.O. Box 25, 634050, Tomsk, Russia

^* e-mail: trs@npi.tpu.ru

Abstract

We have constructed an isobar model for the $\eta$ -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 $\gamma p\to\eta p$ near threshold obtained at MAMI and ELSA as well as recent results for the $\Sigma$ -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 $\Sigma$ -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 $\rho$ - and $\omega$ -meson contribution, whose coupling with nucleons is not well defined. Several versions of extending the model to higher energies are considered.