We have studied the broad $K\pi \pi$ mass enhancements at 1300 MeV in the reactions $K^{+}p\to p{K}^{+}{\pi }^{-}{\pi }^{+} \mathrm{and} p{K}^0{\pi }^0{\pi }^{+}$ 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/μb). We observe a two-peak substructure in the $K^0{\pi }^0{\pi }^{+}$ mass spectrum at 1260 and 1420 MeV. Our estimated contribution of the $K_N\mathrm{}\left(1420\right)\mathrm{}$ accounts for only about half of the 1420-MeV peak (a discrepancy of about 2.4 standard deviations). The $K^{+}{\pi }^{-}{\pi }^{+}$ mass spectrum has a different shape. Further, assuming the $K\pi \pi$ system to be $S$ wave $1^{+}$ $K_V\mathrm{}\left(890\right)\mathrm{}\pi$ and $\rho \mathrm{}\left(765\right)K$, we have fitted separately the $K^{+}{\pi }^{-}{\pi }^{+}$ and the $K^0{\pi }^0{\pi }^{+}$ Dalitz Plots. We obtain inconsistent fits. This inconsistency and the differences in the $K\pi \pi$ mass spectra could be explained by an additional contribution of an $I=0\mathrm{}$ $S$-wave $\pi \pi$ state in $K^{+}{\pi }^{-}{\pi }^{+}$. The $K\pi \pi$ angular decay distributions imply the dominance of the spin-parity state $1^{+}$ with $M_z=0\mathrm{}$ along the incident beam direction. However, there are other $J^P$ states and states with $M_z\ne 0$. The 1260-MeV $K\pi \pi$ mass region is produced more peripherally than the 1420-MeV region.

• Received 10 December 1971

DOI:https://doi.org/10.1103/PhysRevD.5.2688