Investigation of Low-MassKππSystems in 12-GeV/cK+pInteractions

Abstract

We have studied the broad $K\ensuremath{\pi}\ensuremath{\pi}$ mass enhancements at 1300 MeV in the reactions ${K}^{+}p\ensuremath{\rightarrow}p{K}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{+} \mathrm{and} p{K}^{0}{\ensuremath{\pi}}^{0}{\ensuremath{\pi}}^{+}$ at 12 GeV/c. Our data were obtained from a 600 000-picture exposure of the SLAC 82-in. hydrogen bubble chamber (which corresponds to a path length of 35 events/\ensuremath{\mu}b). We observe a two-peak substructure in the ${K}^{0}{\ensuremath{\pi}}^{0}{\ensuremath{\pi}}^{+}$ mass spectrum at 1260 and 1420 MeV. Our estimated contribution of the ${K}_{N}(1420)$ accounts for only about half of the 1420-MeV peak (a discrepancy of about 2.4 standard deviations). The ${K}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{+}$ mass spectrum has a different shape. Further, assuming the $K\ensuremath{\pi}\ensuremath{\pi}$ system to be $S$ wave ${1}^{+}$ ${K}_{V}(890)\ensuremath{\pi}$ and $\ensuremath{\rho}(765)K$, we have fitted separately the ${K}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{+}$ and the ${K}^{0}{\ensuremath{\pi}}^{0}{\ensuremath{\pi}}^{+}$ Dalitz Plots. We obtain inconsistent fits. This inconsistency and the differences in the $K\ensuremath{\pi}\ensuremath{\pi}$ mass spectra could be explained by an additional contribution of an $I=0$ $S$-wave $\ensuremath{\pi}\ensuremath{\pi}$ state in ${K}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{+}$. The $K\ensuremath{\pi}\ensuremath{\pi}$ angular decay distributions imply the dominance of the spin-parity state ${1}^{+}$ with ${M}_{z}=0$ along the incident beam direction. However, there are other ${J}^{P}$ states and states with ${M}_{z}\ensuremath{\ne}0$. The 1260-MeV $K\ensuremath{\pi}\ensuremath{\pi}$ mass region is produced more peripherally than the 1420-MeV region.