First observation and branching fraction and decay parameter measurements of the weak radiative decay Xi0 --> Lambda e+e-

TL;DR

This paper reports the first observation of the weak radiative decay Xi0 --> Lambda e+e-, measuring its branching fraction and decay asymmetry parameter, confirming theoretical predictions and expanding understanding of hyperon decays.

Contribution

The first detection and measurement of the Xi0 --> Lambda e+e- decay, including its branching fraction and decay asymmetry parameter, providing new experimental data.

Findings

Branching fraction B(Xi0 --> Lambda e+e-) = (7.6 +/- 0.4(stat) +/- 0.4(syst) +/- 0.2(norm)) x 10^{-6}

Decay asymmetry parameter alpha_{XiLambdaee} = -0.8 +/- 0.2

Charge conjugate decay also observed

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 alpha_{XiLambdaee} = -0.8 +/- 0.2, consistent with that of Xi0 --> Lambda gamma. The charge conjugate reaction Xi0_bar --> Lambda_bar e+e- has also been observed.