An Investigation of the Neutral Cascade Muon Semileptonic Decay and its Observation at KTeV, Fermilab

The authors report an investigation of the semileptonic decay Ξ0 → Σ+μ-(bar ν)μ. This decay was observed for the first time with nine identified events using the KTeV beam line and detector at Fermilab. The decay is normalized to the Ξ0 beta decay mode and yields a value for the ratio of decay rates Λ(Ξ0 → Σ0 → Σ+μ-(bar ν)μ)/Λ(Ξ0 → Σ+e-(bar ν)e) of (1.8-0.5+0.7(stat.) ± 0.2(syst.)) x 10-2 at the 68,27% confidence level, being the official measurement of KTeV Collaboration. They also used the dominant decay Ξ0 → Λπ0(Λ → pπ-) as normalization mode in an independent analysis which corroborated with the main result. In addition, a new measurement of the Ξ0 → Σ+e-(bar ν)e branching ratio is presented, based on 1139 events and normalized to the Ξ0 → Λπ0(Λ → pπ-) decay mode. The results are in agreement with the SU(3) flavor symmetric quark model