Assocative Photoproduction of Roper Resonance and $\omega$-Meson

Abstract

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

Comments: 20 Pages, Latex, 6 ps figures