Isospin Dependence of Pion Absorption on Nucleon Pairs atTπ=65MeV

Abstract

Angular distributions of differential cross sections were measured for the first time for pion absorption on a $T=1\mathrm{}$, $S=0\mathrm{}$ nucleon pair and for absorption on a $T=0\mathrm{}$, $S=1\mathrm{}$ pair in the ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ nucleus. A large isospin dependence is observed in the differential cross sections. The ratio of cross sections $\frac{\sigma \left({}_{}{}^3{}_{}{}^{}\mathrm{He}\right({\pi }^{+},2p\left)\right)}{\sigma \left({}_{}{}^3{}_{}{}^{}\mathrm{He}\right({\pi }^{-},pn\left)\right)}$ is 15.2±1.2. The results show evidence of an isoscalar component of the final state in the reaction ${}_{}{}^3{}_{}{}^{}\mathrm{He}({\pi }^{-},pn)n$, which cannot be mediated by $\Delta$ resonance formation.