Ξ Resonances in Ξ− Be interactions II. Properties of Ξ(1820) and Ξ(1960) in the\(\Lambda \bar K^0 \) and\(\Sigma ^0 \bar K^0 \) channels

In an experiment at the CERN-SPS charged hyperon beam, we have investigated the inclusive\(\Lambda \bar K^0 \) and\(\Sigma ^0 \bar K^0 \) final states formed in Ξ− Be interactions. In the\(\Lambda \bar K^0 \) channel, we observe a signal at 1826 MeV/c2 which can be identified with the known Ξ(1820) resonance. We determine its mass and width to be:M=1826±4 MeV/c2, Г=12±14 MeV/c2. A moment analysis is consistent with a spin of 3/2 and indicates a negative parity for this spin assignment. Also in the\(\Lambda \bar K^0 \) channel, we observe a 3.6σ signal with the following parameters:M=1963±5 MeV/c2, Г=25±15 MeV/c2. This state, which we call Ξ(1960), is not observed in the\(\Sigma ^0 \bar K^0 \) channel, leading to an upper limit on the ratio of partial widths\(\Sigma \bar K/\Lambda \bar K\) of 2.3 (90% confidence level). A moment analysis of the\(\Lambda \bar K^0 \) final state indicates a spin of 5/2 or greater in the natural spin-parity series 5/2+, 7/2−, etc.