Measurement of the Ξ0→Λγ decay asymmetry and branching fraction

Abstract In data taken with the NA48 experiment at the CERN SPS in 1999, 730 candidates of the weak radiative hyperon decay Ξ 0 → Λγ have been found with an estimated background of 58±8 events. From these events the Ξ 0 → Λγ decay asymmetry has been determined to α ( Ξ 0 → Λγ )=−0.78±0.18 stat ±0.06 syst , which is the first evidence of a decay asymmetry in Ξ 0 → Λγ . The branching fraction of the decay has been measured to be Br( Ξ 0 → Λγ )=(1.16±0.05 stat ±0.06 syst )×10 −3 .