Meson Production off the Deuteron

An accurate evaluation of the electromagnetic couplings N$^{\ast}$ ($\Delta^{\ast}) \to \gamma $N from meson photoproduction data remains a paramount task in hadron physics. Here we focus on the single-pion production data and note that a complete solution requires couplings from both charged and neutral resonances, the latter requiring $\pi^{-}$p and $\pi^{\mathrm{0}}$n photoproduction off a neutron target (where the neutron is bound in the deuteron.) Experimental data for neutron-target photoreactions are much less abundant than those utilizing a proton target, constituting only about 15{\%} of the present World database. As a result, our knowledge of the neutral resonance couplings is less precise as compared to the charged values. Extraction of the two-body ($\gamma $n $\to \pi^{-}$p and $\gamma $n $\to $ $\pi^{\mathrm{0}}$n) cross sections requires the use of a model-dependent nuclear correction, which mainly comes from final-state interactions (FSI). We recently applied our FSI corrections to CLAS $\gamma $d $\to \pi ^{-}$pp data to get elementary cross sections for $\gamma $n $\to \pi^{-}$p for a broad energy range, E$_{\gamma}$ \textgreater\ 1 GeV. Then, we did the same for a MAMI-B GDH experiment to get $\gamma $n $\to \pi^{-}$p about the $\Delta $-isobar.