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$_s18pm$5 MeV/c$^2$, with intrinsic width $_s18Gamma = 108_s18pm 22$ MeV/c$^2$, produced inclusively in $_s18Sigma^-$-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_s18to K_S p)_s18cdot d_s18sigma /dx_F = (5.2_s18pm 2.3) _s18mu b $ per nucleon at $x_F=0.8$. The hard _s18xf spectrum suggests the presence of a strong leading particle effect in the production and hence the identification as a $_s18Sigma^{*_s16}$ state. No corresponding peaks were observed in the $K^- p$ and $_s18Lambda _s18pi^{_s18pm}$ mass spectra.