Meson and Isobar Resonance Production inπ−pInteractions at 3.63BeVc

Abstract

${\ensuremath{\pi}}^{\ensuremath{-}}p$ interactions at 3.63 $\frac{\mathrm{BeV}}{c}$ have been studied using the BNL 20-in. hydrogen bubble chamber. 1054, 1693, 805, 1025, and 489 events of the reactiont ypes (1) ${\ensuremath{\pi}}^{\ensuremath{-}}+p\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ensuremath{-}}+{\ensuremath{\pi}}^{0}+p$, (2) ${\ensuremath{\pi}}^{\ensuremath{-}}+p\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ensuremath{-}}+{\ensuremath{\pi}}^{+}+n$, (3) ${\ensuremath{\pi}}^{\ensuremath{-}}+p\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ensuremath{-}}+{\ensuremath{\pi}}^{\ensuremath{-}}+{\ensuremath{\pi}}^{+}+p$, (4) ${\ensuremath{\pi}}^{\ensuremath{-}}+p\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ensuremath{-}}+{\ensuremath{\pi}}^{\ensuremath{-}}+{\ensuremath{\pi}}^{+}+p+{\ensuremath{\pi}}^{0}$, and (5) ${\ensuremath{\pi}}^{\ensuremath{-}}+p\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ensuremath{-}}+{\ensuremath{\pi}}^{\ensuremath{-}}+{\ensuremath{\pi}}^{+}+{\ensuremath{\pi}}^{+}+n$, respectively, have been identified. The $\ensuremath{\rho}$ meseon is produced abundantly in reactions (1) and (2), and an analysis of the decay angular distributions of the events in these peaks leads one to believe that they are produced via pion-pion scattering in states of angular-momentum zero and one. A detailed analysis of the energy and momentum-transfer dependence of the phase shifts necessary to describe such scattering is made. Using the Chew-Low method, the results have been extrapolated into the nonphysical region of momentum transfer, and they are found to agree quite well quantitatively with predicted values. Reaction (3) is found to be dominated by ${\ensuremath{\rho}}^{0}$ and ${N}^{*}$ (1238) production. ${\ensuremath{\rho}}^{\ensuremath{-}}$ and ${\ensuremath{\omega}}^{0}$ production are the dominant features of reaction (4). Both of these mesons seem to be produced along with nucleon isobars. The ${\ensuremath{\rho}}^{\ensuremath{-}}$ channel furnishes examples of these isobars decaying into a pion and into the 1238-MeV ${N}^{*}$, which in turn breaks up into a ${\ensuremath{\pi}}^{+}$ and a $p$. A peak is also found in the (${\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\omega}}^{0}$) mass spectrum at 1250 MeV. Cross sections for the reactions and the various resonance channels are also presented.