Measurement of the branching ratio of the decay Ξ0→Σ+μ−ν¯μ

From the 2002 data taking with a neutral kaon beam extracted from the CERN-SPS, the NA48/1 experiment observed 97 Ξ0→Σ+μ−ν¯μ candidates with a background contamination of 30.8±4.2 events. From this sample, the BR(Ξ0→Σ+μ−ν¯μ) is measured to be (2.17±0.32stat±0.17syst)×10−6.