Two-Charged-Particle Final States fromπ−+pInteractions at 2.7GeVc

Abstract

A total of 24 360 events having two charged particles in the final state from ${\pi }^{-}+p$ interactions at an incident ${\pi }^{-}$ momentum of 2.7 $\frac{\mathrm{GeV}}{c}$ have been analyzed. The final states ${\pi }^{-}{\pi }^{+}n$ and ${\pi }^{-}{\pi }^{0}p$ are found to be dominated by rho-meson production, and in addition, significant $N^{*}\mathrm{}\left(1238\right)\mathrm{}$ production is seen. The partial cross sections for the dominant resonant channels are $\sigma =\left(p{\rho }^{-}\right)=(1.3\mathrm{}\pm 0.2)$ mb, $\sigma \left(n{\rho }^0\right)=(2.3\mathrm{}\pm 0.2)$ mb, and $\sigma \left[{\pi }^{-}{N}^{*+}\right(\to p{\pi }^0\left)\right]=(0.5\mathrm{}\pm 0.2)$ mb. The production of the ${\rho }^{-}$ and ${\rho }^0$ and the decay of the ${\rho }^{-}$ agree very well with the predictions of an absorption-modified one-pion-exchange model. The production angular distributions of the ${\rho }^0$ and ${\rho }^{-}$ follow an exponential of the form $A{e}^{+Bt}$. The results from a least-squares fit give $B\left({\rho }^{-}\right)=9.32\mathrm{}\pm 0.08 {\left(\frac{\mathrm{GeV}}{c}\right)}^{-2\mathrm{}}$, $B\left({\rho }^0\right)=10.26\mathrm{}\pm 0.06 {\left(\frac{\mathrm{GeV}}{c}\right)}^{-2\mathrm{}}$. A similar analysis for the elastic-scattering events gave $B\left(\mathrm{el}\right)=7.77\mathrm{}\pm 0.05 {\left(\frac{\mathrm{GeV}}{c}\right)}^{-2\mathrm{}}$. The ${\rho }^0$ decay distributions are asymmetric and they have been analyzed using a simple model which includes $S-P$-wave interference. No clear evidence is seen for a $T=0\mathrm{}$, $J=0\mathrm{}$ resonance at a mass near that of the $\rho$. The $N^{*}\mathrm{}\left(1238\right)\mathrm{}$ resonance production...