Study of the ηN scattering amplitude through the associated photoproduction of ϕ- and η-mesons in the region of the N∗(1535) resonance Original Research Article

The γp→ϕηp reaction is studied in the kinematic region where the ηp final state originates dominantly from the decay of the N∗(1535) resonance. The threshold laboratory photon energy for this reaction (at the peak of the S11 resonance) is View the MathML source. We will discuss it somewhat above threshold, at View the MathML source, in order to reach lower (absolute) values of the squared 4-momentum transfer from the initial photon to the final ϕ-meson. In these conditions, we expect the t-channel π0- and η-meson exchanges to drive the dynamics underlying the γp→ϕηp process. The initial photon dissociates into the final ϕ-meson and a virtual pseudoscalar meson (π0 or η). The virtual pseudoscalar meson scatters from the proton target to produce the final ηp state. The π0p→ηp and ηp→ηp amplitudes are derived in the framework of a coupled-channel effective field theory of meson-baryon scattering. We found the η-meson exchange to be largely dominant. The η–π0 interference is of the order of 20–30%. The sign of this term is not known and has a significant influence on the results. The πN→ηN amplitude being largely determined by data on the π−p→ηn reaction, we found that the γp→ϕηp reaction cross section is rather directly related to the η-nucleon scattering amplitude in the N∗(1535) resonance region. Accurate data on the γp→ϕηp process would therefore put additional constraints on this still poorly known amplitude.