Near-threshold proton-induced neutral pion production from deuterium

Abstract

Total cross sections and angular distributions for the differential cross section and analyzing power of the reaction $^{2}\mathrm{H}$(p\ensuremath{\rightarrow},${\mathrm{\ensuremath{\pi}}}^{0}$${)}^{3}$He have been measured at four energies very near threshold (0.1${\mathit{T}}_{\mathrm{\ensuremath{\pi}}}^{\mathrm{c}.\mathrm{m}.}$2.7 MeV). The large asymmetries observed in the angular distributions of the differential cross section indicate strong constructive interference between the amplitudes for s-wave pion emission and the amplitudes for p-wave emission. A measure of the s-wave strength at zero energy is obtained and found to be consistent with the results from pionic atoms. The new data indicate that the excitation function for this reaction differs significantly from that of p+n\ensuremath{\rightarrow}d+${\mathrm{\ensuremath{\pi}}}^{0}$.