First observation and branching fraction and decay parameter measurements of the weak radiative decay Xi0 --> Lambda e+e-
Abstract
The weak radiative decay Xi0 --> Lambda e+e- has been detected for the first time. We find 412 candidates in the signal region, with an estimated background of 15 +/- 5 events. We determine the branching fraction B(Xi0 --> Lambda e+e-) = [7.6 +/- 0.4(stat) +/- 0.4(syst) +/- 0.2(norm)] x 10-6, consistent with an internal bremsstrahlung process, and the decay asymmetry parameter alphaXiLambdaee = -0.8 +/- 0.2, consistent with that of Xi0 --> Lambda gamma. The charge conjugate reaction Xi0bar --> Lambdabar e+e- has also been observed.
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