Threshold $π^-$ Photoproduction on the Neutron

Recent data from the PIONS$@$MAX-lab Collaboration, measuring the total cross section of the pion incoherent photoproduction $γd\toπ^-pp$ near threshold, have been used to extract the E$_{0+}$ multipole and total cross section of the reaction $γn\!\to\!π^-p$, also near threshold. These are the first measurements of the reaction $γd\toπ^-pp$ 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 $γn\!\to\!π^-p$ with E$_{0+}\! =$ const in the threshold region. The obtained value E$_{0+} = -31.86\pm 0.8$ (in $10^{-3}/m_{π^+}$ units) is in agreement with other existing results. Model predictions for the total cross section $σ(γn\!\to\!π^-p)$ are also given.

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