Observation of a resonance in the K${}_s$p decay channel at a mass of 1765 MeV/c${}^2$

Abstract

We report on the observation of a K${}_s$p resonance signal at a mass of 1765$\pm$5 MeV/c${}^2$, with intrinsic width $\Gamma =108\pm 22$ MeV/c${}^2$, produced inclusively in ${\Sigma }^{-}$-nucleus interactions at 340 GeV/c in the hyperon beam experiment WA89 at CERN. The signal was observed in the kinematic region $x_F>0.7$, in this region its production cross section rises approximately linearly with $(1-x_F)$, reaching $BR(X\to K_{S}p)\cdot d\sigma /d{x}_F=(5.2\pm 2.3)\mu b$ per nucleon at $x_F=0.8$. The hard \xf spectrum suggests the presence of a strong leading particle effect in the production and hence the identification as a ${\Sigma }^{\ast +}$ state. No corresponding peaks were observed in the $K^{-}p$ and $\Lambda {\pi }^{\pm }$ mass spectra.

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