Measurement of the Xi0 -> Lambda gamma Decay Asymmetry and Branching Fraction

In data taken with the NA48 experiment at the CERN SPS in 1999, 730 candidates of the weak radiative hyperon decay Xi0 -> Lambda gamma have been found with an estimated background of 58+-8 events. From these events the Xi0 -> Lambda gamma decay asymmetry has been determined to alpha(Xi0 -> Lambda gamma) = -0.78 +- 0.18_stat +- 0.06_syst, which is the first evidence of a decay asymmetry in Xi0 -> Lambda gamma. The branching fraction of the decay has been measured to be Br(Xi0 -> Lambda gamma) = (1.16 +- 0.05_stat +- 0.06_syst) x 10^-3.