Reactionp+p→π++p+nat 405 MeV

The azimuthal asymmetry of pion production in the reaction $p+p\to {\pi }^{+}+p+n$ was measured using the 53% polarized 405-MeV proton beam from the Carnegie Institute of Technology's synchrocyclotron. Pions produced in a liquid hydrogen target were successively detected on the left and on the right by means of their stopping and subsequent $\pi \mu e$ decay in a 6-in. propane bubble chamber. Elastically scattered protons were used to monitor the incident beam intensity. The pions which stopped in the chamber had an average c.m. momentum of 0.52 μc and c.m. production angles between 80 and 105°. The observed pion asymmetry is $\left|\epsilon \right|=(20\mathrm{}\pm 6.5)\%$, in the same direction as the previously observed asymmetry for the ($\mathrm{pp}$, ${\pi }^{+}d$) reaction. The similarity between the observed pion asymmetry and that for the ($\mathrm{pp}$, ${\pi }^{+}d$) reaction suggests that their reaction amplitudes are similar, and thus that ${}_{}{}^3{}_{}{}^{}S$ rather than $P$ states are predominant for the final-state nucleons in the ($\mathrm{pp}$, ${\pi }^{+}\mathrm{pn}$) reaction at this energy. The estimated total cross section (0.63±0.06 mb) is in good agreement with the calculation of Mandelstam.