Observation of a resonance in the KSp decay channel at a mass of 1765 MeV/c2

We report on the observation of a KSp resonance signal at a mass of 1765 ± 5 MeV/c2, with intrinsic width Γ = 108 ± 22 MeV/c2, produced inclusively in Σ--nucleus interactions at 340 GeV/c in the hyperon beam experiment WA89 at CERN. The signal was observed in the kinematic region xF>0.7, in this region its production cross section rises approximately linearly with (1-xF), reaching BR(X→KSp)dσ/dxF=(5.2±2.3)μb per nucleon at xF=0.8. The hard xF spectrum suggests the presence of a strong leading particle effect in the production and hence the identification as a Σ*+ state. No corresponding peaks were observed in the K-p and Λπ± mass spectra.