Study of $a_1(1260)$ in the $γp \to π^+π^+π^- n$ reaction

Abstract

We investigate the discovery potential of the $a_1(1260)$ photoproduction in the $γp \to a_1(1260)^+ n$ and $γp \to π^+π^+π^- n$ reactions via the $π$-exchange mechanism. For the $γp \to π^+π^+π^- n$ reaction, we perform a calculation for the differential and total cross sections by including the contributions from the $a_1(1260)$ intermediate resonance decaying into $ρπ$ then into $π^+π^+π^-$. Besides, the non-resonance process is also considered. With a lower mass of $a_1(1260)$, we get a fairly good description of the experimental data for the invariant $π^+π^+π^-$ mass distributions. For the $γp \to a_1(1260)^+ n$ reaction, with our model parameters, the total cross section is of the order of 10 $μ$b at photon beam energy $E_γ \sim$ 2.5 GeV. It is expected that our model calculations could be tested by future experiments.