Pion absorption on 3He at T pi =62.5 and 82.8 MeV.

Abstract

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