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 (${\pi }^{-}p$); (2) ${\pi }^{+}$ production (${\pi }^{-}{\pi }^{+}n$); (3) ${\pi }^0$ production (${\pi }^{-}{\pi }^{0}p$); (4) neutrals. Values for the cross sections for these processes are $\sigma \left(\mathrm{elastic}\right)=17.56\mathrm{}\pm 0.43$ mb, $\sigma \left({\pi }^{+}\right)=7.14\mathrm{}\pm 0.23$ mb, $\sigma \left({\pi }^0\right)=4.65\mathrm{}\pm 0.17$ mb. The elastic-scattering angular dependence in the c.m. system is fitted by a power-series expansion in $cos\theta$ and gives the following coefficients: $a_0=0.27\mathrm{}\pm 0.02$, $a_1=1.48\mathrm{}\pm 0.11$, $a_2=3.86\mathrm{}\pm 0.22$, $a_3=-0.29\mathrm{}\pm 0.53$, $a_4=-0.65\mathrm{}\pm 0.28$, $a_5=1.69\mathrm{}\pm 0.52$ (units: mb/sr). Cross sections for multiple-pion production were also measured: $\sigma \left({\pi }^{-}{\pi }^{+}{\pi }^{0}n\right)=0.33\mathrm{}\pm 0.04$ mb, $\sigma \left({\pi }^{-}{\pi }^{+}{\pi }^{-}p\right)=0.08\mathrm{}\pm 0.02$ mb. The total neutral cross section was $\sigma \left(\mathrm{neutrals}\right)=11.78\mathrm{}\pm 0.43$ mb; the total charged events cross section was $\sigma \left(\mathrm{charged}\right)=29.76\mathrm{}\pm 0.69$ mb; and the total cross section was $\sigma \left(\mathrm{total}\right)=41.54\mathrm{}\pm 0.82$ mb. For single-pion production events, two-body mass distributions and angular distributions were compared with the predictions of the Olsson-Yodh isobar model.