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

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 $Gamma = 108pm 22$ 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(Xto K_S p)cdot dsigma /dx_F = (5.2pm 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 $Sigma^{*+}$ state. No corresponding peaks were observed in the $K^- p$ and $Lambda pi^{pm}$ mass spectra.