Measurement of the Decay $\Xi^{0}\to\Lambda\gamma$ with Entangled $\Xi^{0}\bar{\Xi}^{0}$ Pairs

TL;DR

This study measures the first absolute branching fraction and decay asymmetry of the hyperon decay $ ext{Xi}^0 o ext{Lambda} ext{gamma}$ using entangled pairs at an electron-positron collider, providing new insights into weak radiative hyperon decays.

Contribution

It presents the first measurement of the absolute branching fraction and decay asymmetry parameter for $ ext{Xi}^0 o ext{Lambda} ext{gamma}$ decay using entangled $ ext{Xi}^0 ar{ ext{Xi}}^0$ pairs.

Findings

Branching fraction measured as (1.347 ± 0.066 ± 0.054)×10⁻³.

Decay asymmetry parameter found to be -0.741 ± 0.062 ± 0.019.

No significant CP violation observed in the decay.

Abstract

In this Letter, a systematic study of the weak radiative hyperon decay $\Xi^{0}\to\Lambda\gamma$ at an electron-positron collider using entangled $\Xi^{0}\bar{\Xi}^{0}$ pair events is presented. The absolute branching fraction for this decay has been measured for the first time, and is $\left(1.347 \pm 0.066_{\mathrm stat.}\pm0.054_{\mathrm syst.}\right)\times 10^{-3}$. The decay asymmetry parameter, which characterizes the effect of parity violation in the decay, is determined to be $-0.741 \pm 0.062_{\mathrm stat.}\pm 0.019_{\mathrm syst.}$. The obtained results are consistent with the world average values within the uncertainties, offering valuable insights into the underlying mechanism governing the weak radiative hyperon decays. The charge conjugation parity ($CP$) symmetries of branching fraction and decay asymmetry parameter in the decay are also studied. No statistically significant violation of charge conjugation parity symmetry is observed.