π++pInteractions at 646 MeV

Abstract

A 14-in. liquid-hydrogen-filled bubble chamber in a 17.5-kG magnetic field was exposed to a beam of negative pions produced by the Cosmotron at Brookhaven National Laboratory. About 26 000 pictures were taken and examined for the following final states: (1) elastic scattering (${\ensuremath{\pi}}^{\ensuremath{-}}p$); (2) ${\ensuremath{\pi}}^{+}$ production (${\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{+}n$); (3) ${\ensuremath{\pi}}^{0}$ production (${\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{0}p$); (4) neutrals. Values for the cross sections for these processes are $\ensuremath{\sigma}(\mathrm{elastic})=17.56\ifmmode\pm\else\textpm\fi{}0.43$ mb, $\ensuremath{\sigma}({\ensuremath{\pi}}^{+})=7.14\ifmmode\pm\else\textpm\fi{}0.23$ mb, $\ensuremath{\sigma}({\ensuremath{\pi}}^{0})=4.65\ifmmode\pm\else\textpm\fi{}0.17$ mb. The elastic-scattering angular dependence in the c.m. system is fitted by a power-series expansion in $cos\ensuremath{\theta}$ and gives the following coefficients: ${a}_{0}=0.27\ifmmode\pm\else\textpm\fi{}0.02$, ${a}_{1}=1.48\ifmmode\pm\else\textpm\fi{}0.11$, ${a}_{2}=3.86\ifmmode\pm\else\textpm\fi{}0.22$, ${a}_{3}=\ensuremath{-}0.29\ifmmode\pm\else\textpm\fi{}0.53$, ${a}_{4}=\ensuremath{-}0.65\ifmmode\pm\else\textpm\fi{}0.28$, ${a}_{5}=1.69\ifmmode\pm\else\textpm\fi{}0.52$ (units: mb/sr). Cross sections for multiple-pion production were also measured: $\ensuremath{\sigma}({\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{0}n)=0.33\ifmmode\pm\else\textpm\fi{}0.04$ mb, $\ensuremath{\sigma}({\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}p)=0.08\ifmmode\pm\else\textpm\fi{}0.02$ mb. The total neutral cross section was $\ensuremath{\sigma}(\mathrm{neutrals})=11.78\ifmmode\pm\else\textpm\fi{}0.43$ mb; the total charged events cross section was $\ensuremath{\sigma}(\mathrm{charged})=29.76\ifmmode\pm\else\textpm\fi{}0.69$ mb; and the total cross section was $\ensuremath{\sigma}(\mathrm{total})=41.54\ifmmode\pm\else\textpm\fi{}0.82$ mb. For single-pion production events, two-body mass distributions and angular distributions were compared with the predictions of the Olsson-Yodh isobar model.