Four-Charged-Particle Final States from the Interaction of 2.7-GeV/cπ+on Deuterium

Abstract

Reactions leading to four nonstrange, charged particles from the interaction of 2.7-GeV/c ${\pi }^{+}$ on deuterium have been studied. Only events containing at least one visible stopping proton track were included. The spectator model of the ${\pi }^{+}d$ interaction has been examined and found to be a good approximation. This model not only gives a good description of the final state of the spectator nucleon, but is also supported by the similarity of such reacitons as ${\pi }^{+}d\to \mathrm{pp}{\rho }^0$ and ${\pi }^{-}p\to n{\rho }^0$. Meson ($M$) resonance production in the reaction ${\pi }^{+}d\to \mathrm{ppM}$ is prominent, including $\eta (0.21\mathrm{}\pm 0.04 \mathrm{mb})$, $\omega (0.80\mathrm{}\pm 0.08 \mathrm{mb})$, $\rho (2.20\mathrm{}\pm 0.25 \mathrm{mb})$, $f(0.51\mathrm{}\pm 0.20 \mathrm{mb})$, $A_1(0.17\mathrm{}\pm 0.10 \mathrm{mb})$, $A_2(0.14\mathrm{}\pm 0.08 \mathrm{mb})$, and ${\eta }^{\prime }(0.05\mathrm{}\pm 0.02 \mathrm{mb})$ (errors are statistical). The baryon resonance $\Delta \mathrm{}\left(1238\right)\mathrm{}$ is also observed to be produced in a variety of reactions. The $\rho$ and $\omega$ production processes have been examined in some detail, including a determination of the spin density matrix elements. Also, the $3\pi$ system in the $\mathrm{pp}{\pi }^{+}{\pi }^{-}{\pi }^0$ final state has been studied at energies near the $A_1$ and $A_2$ masses in an attempt to separate these particles from the several other processes contributing to this final state. The results of a spin-parity analysis of the $A$ mesons are presented.