Multipion Final States fromπ−pInteractions at 3.2 and 4.2GeVc

Abstract

We have analyzed approximately 30 000 four-prong events at ${\pi }^{-}$ beam momenta of 3.2 and 4.2 $\frac{\mathrm{GeV}}{c}$, obtained with the 72-in. hydrogen bubble chamber at the Lawrence Radiation Laboratory. We present all the effective-mass distributions obtainable from the final states $p{\pi }^{+}{\pi }^{-}{\pi }^{-}$, $p{\pi }^{+}{\pi }^0{\pi }^{-}{\pi }^{-}$, and $n{\pi }^{+}{\pi }^{+}{\pi }^{-}{\pi }^{-}$, as well as the cross sections of the these final states. In addition, we present the results of our study of the quasi-three-body final states $N^{*++}\mathrm{}\left(1238\right)\mathrm{}{\pi }^{-}{\pi }^{-}$, $p{\pi }^{-}{\rho }^0$, $p{\pi }^{-}\omega$, and $p{\pi }^{-}\eta$. We have given particular emphasis to the production and decay of the $A_1$, $A_2$, and $B$ enhancements; the $A_1$ and $B$ enhancements observed in our data are consistent with the interpretations as kinematic enhancements, although the possibility exists that what we observe at our energies is an admixture of resonant states and kinematic enhancements. On the other hand, the $A_2$ enhancement can be interpreted only as a genuine resonant state. From the study of the decay angular correlations in the $A_2$ region as well as the control regions, we have determined that the lowest possible quantum numbers of the $A_2$ are $J^P=2^{+}$.