Branching ratio and asymmetry for. Xi. sup 0 r arrow. Lambda. gamma

We have measured the branching ratio {Gamma}({Xi}{sup 0}{r arrow}{Lambda}{gamma})/{Gamma}({Xi}{sup 0}{r arrow}{Lambda}{pi}{sup 0}) to be (1.06{plus minus}0.12(stat){plus minus}0.11(syst)){times}10{sup {minus}3}. In 670 000 {Lambda}{gamma} candidates we found 116{plus minus}13 {Xi}{sup 0}{r arrow}{Lambda}{gamma} decays (background subtracted). These compare with 29 510 {Xi}{sup 0}{r arrow}{Lambda}{pi}{sup 0} events reconstructed from the {Lambda}{gamma}{gamma} sample. Monte Carlo studies gave the relative acceptances for the two processes. The helicity of the {Lambda} yielded the product of asymmetry parameters {alpha}({Lambda}{r arrow}{ital p}{pi}{sup {minus}}){alpha}({Xi}{sup 0}{r arrow}{Lambda}{gamma})=0.27{plus minus}0.28, which implies {alpha}({Xi}{sup 0}{r arrow}{Lambda}{gamma})=0.43{plus minus}0.44, where the uncertainty is all statistical.