Threshold ${\pi }^{-}$ 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.

Comments: 7 pages, 4 figures, 2 tables