Threshold $π^-$ Photoproduction on the Neutron

Abstract: Recent data from the PIONS$@$MAX-lab Collaboration, measuring the total cross section of the pion incoherent photoproduction $\gamma d\to\pi^-pp$ near threshold, have been used to extract the E${0+}$ multipole and total cross section of the reaction $\gamma n!\to!\pi^-p$, also near threshold. These are the first measurements of the reaction $\gamma d\to\pi^-pp$ in the threshold region. The value of E${0+}$ is extracted through a fit to the deuteron data in a photoproduction model accounting for final-state interactions. The model takes an $S$-wave approximation for the elementary reaction $\gamma n!\to!\pi^-p$ with E${0+}! = $ const in the threshold region. The obtained value E${0+} = -31.86\pm 0.8$ (in $10^{-3}/m_{\pi^+}$ units) is in agreement with other existing results. Model predictions for the total cross section $\sigma(\gamma n!\to!\pi^-p)$ are also given.