Pion absorption onHe3atTπ=62.5 and 82.8 MeV

Abstract

Pion absorption in ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ was studied at $T_{\pi }$=62.5 and 82.8 MeV using nucleon-nucleon coincidences. For ${\pi }^{+}$ absorption on proton-neutron pairs the differential cross section is the same as that for ${\pi }^{+}$+d→p+p except for an increase by a factor of about 1.5. For ${\pi }^{\mathrm{-}}$ absorption on the proton-proton pair, the differential cross section is asymmetric about 90°, indicating possible isospin mixing. The total cross sections ${\sigma }_{\mathrm{pn}\left({\pi }^{+}\right)}$ are 10.2±0.9 mb and 13.5±1.3 mb at 62.5 and 82.8 MeV and for ${\sigma }_{\mathrm{pp}\left({\pi }^{\mathrm{-}}\right)}$ are 0.70±0.07 mb and 0.92±0.10 mb at 62.5 and 82.8 MeV. The three-body absorption cross sections for ${\pi }^{+}$ and ${\pi }^{\mathrm{-}}$ are found to be comparable to each other and show no strong energy dependence. The three-body absorption cross section ${\sigma }_3$(${\pi }^{+}$) is 6.7±2.5 mb and 5.7±2.3 mb and for ${\pi }^{\mathrm{-}}$, ${\sigma }_3$(${\pi }^{\mathrm{-}}$) is 8.7±1.4 mb and 6.5±2.0 mb at 62.5 and 82.8 MeV, respectively.