Pion absorption in 4He above the delta resonance.

The reaction $^{4}\mathrm{He}$ (${\mathrm{\ensuremath{\pi}}}^{+}$,pp)pn was measured at ${\mathit{T}}_{\mathrm{\ensuremath{\pi}}}$=500 MeV. The angular distribution of quasifree two-body absorption which was obtained agrees in detail with the free \ensuremath{\pi}d\ensuremath{\rightarrow}pp reaction and scales according to the number of T=0 pn pairs in $^{4}\mathrm{He}$. Possible evidence for pd final-state interactions is discussed. The extrapolated total cross section for four-body absorption is 2.5\ifmmode\pm\else\textpm\fi{}0.6 mb, which is substantially less than predicted from a model based on \ensuremath{\Delta}\ensuremath{\Delta} excitation.