Chiral dynamics in "gamma p --> pi^0 eta p" and related reactions

Abstract

Using a chiral unitary approach for meson-baryon scattering in the strangeness zero sector, where the $N^*(1535)$ and $Δ^*(1700)$ resonances are dynamically generated, we study the reactions $γp \to π^0 ηp$ and $γp \to π^0 K^0 Σ^+$ at photon energies at which the final states are produced close to threshold. Among several reaction mechanisms, we find the most important is the excitation of the $Δ^*(1700)$ state which subsequently decays into a pseudoscalar meson and the $N^*(1535)$. Hence, the reaction provides useful information with which to test current theories of the dynamical generation of the low-lying $1/2^-$ and $3/2^-$ states. Predictions are made for cross sections and invariant mass distributions which can be compared with forthcoming experiments at ELSA.