Assocative Photoproduction of Roper Resonance and $ω$-Meson

Abstract

Associative photoproduction of $ω$-meson and $N^{*}(1440)$ on nucleons, $γ+N\toω+N^{*}(1440)$, in the near threshold region is investigated in a framework employing effective Lagrangians. Besides $π$-exchange in t-channel, baryon exchanges, i.e. N- and $N^{*}$-exchanges, in the s- and u-channels are also taken into account in calculations of differential cross-section and beam asymmetry. Important inputs of this model are the vector and tensor coupling constants of $ωNN^{*}(1440)$-vertex, which are assumed to be equal to the values of these couplings for $ωNN$ vertex. Using our previous estimation of $ωNN$ coupling constants obtained from a fit to available experimental data on photoproduction of $ω$ meson in the near threshold region, we produce the necessary numerical predictions for different observables in $γ+N\toω+N^{*}(1440)$. Numerical results shows that at low $|$t$|$ dominant contribution comes from t-channel $π$-exchange while effects of nucleon and $N^{*}(1440)$ pole terms can be seen at large $|t|$. Our predictions for the differential cross section and beam asymmetry for the processes $γ+N\toω+N^{*}(1440)$, where N is proton and neutron at $E_γ=2.5$ GeV are presented with zero width approximation and also with the inclusion of width effects of $N^{*}(1440)$.