Photoproduction $\gamma p \to f_0(980) p$ in an effective Lagrangian approach

The most recent data on differential cross sections and photon beam asymmetries $\Sigma$ from the LEPS2/BGOegg Collaboration for the $\gamma p \to f_0(980) p$ reaction are analyzed within a tree-level effective Lagrangian approach. The $t$-channel $\rho$ and $\omega$ exchanges, the $u$- and $s$-channel $N$ exchanges, the interaction current, and the possible $s$-channel $N^*$ exchanges are taken into account in constructing the reaction amplitudes to reproduce the data. The results show that the contributions from either the $N(2040)3/2^+$ or the $N(2100)1/2^+$ resonance exchange in the $s$ channel are necessarily required to describe the LEPS2/BGOegg data and they dominate the differential cross sections of $\gamma p \to f_0(980) p$. Further analysis shows that the contributions from the $t$-channel $\rho$ and $\omega$ exchanges and the interaction current are rather small to both differential cross sections and photo beam asymmetries, and the contributions from $u$-channel $N$ exchange are considerable in the case of including $N(2040)3/2^+$ in the model while negligible in the case of including $N(2100)1/2^+$ in the model. Predictions of target asymmetries $T$ for $\gamma p \to f_0(980) p$ are given, which can be examined by future experiments.