Exclusive pion production from few nucleon systems in the region of the Delta 1232 resonance.

Abstract

Angular distributions of the differential cross sections and analyzing powers have been measured for the $^{3}\mathrm{He}$(p\ensuremath{\rightarrow},${\mathrm{\ensuremath{\pi}}}^{+}$) $^{4}\mathrm{He}$ and $^{4}\mathrm{He}$(p\ensuremath{\rightarrow},${\mathrm{\ensuremath{\pi}}}^{+}$${)}^{5}$He reactions at proton bombarding energies between 240 and 507 MeV. These new results provide a comprehensive set of data spanning the region of the ${\mathrm{\ensuremath{\Delta}}}_{1232}$ resonance and are compared with a phenomenological model that incorporates the amplitudes for the pp\ensuremath{\rightarrow}d${\mathrm{\ensuremath{\pi}}}^{+}$ reaction, and with calculations from a microscopic (p,${\mathrm{\ensuremath{\pi}}}^{+}$) model. A $^{5}\mathrm{He}$ final state interaction calculation based upon the low energy n+\ensuremath{\alpha} elastic phase shifts indicates that the $^{4}\mathrm{He}$(p,${\mathrm{\ensuremath{\pi}}}^{+}$${)}^{5}$He spectra are nearly independent of pion angle and proton energy. Comparisons made with the time reversed charge symmetric reaction $^{3}\mathrm{H}$(n,${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$${)}^{4}$He reaction indicate substantial Coulomb effects are still present at 300 MeV.