Search for hyperon $\Delta S=\Delta Q$ violating decay $\Xi^{0}\to\Sigma^{-}e^{+}\nu_{e}$

TL;DR

This study searches for a rare hyperon decay that violates a fundamental rule, using a large dataset, but finds no signal and sets a new, more stringent upper limit on its occurrence.

Contribution

First experimental search for the $ o o$ decay with improved upper limit, constraining new physics beyond the Standard Model.

Findings

No significant signal observed.

Upper limit on branching fraction set at 1.6×10⁻⁴.

Result improves previous limit by about ten times.

Abstract

Using a data sample of $(1.0087\pm0.0044)\times10^{10}$ $J/\psi$ decay events collected with the BESIII detector at the center-of-mass energy of $\sqrt{s}=3.097$ GeV, we present a search for the hyperon semileptonic decay $\Xi^{0}\to\Sigma^{-}e^{+}\nu_{e}$ which violates the $\Delta S=\Delta Q$ rule. No significant signal is observed, and the upper limit on the branching fraction $\mathcal{B}(\Xi^{0}\to\Sigma^{-}e^{+}\nu_{e})$ is determined to be $1.6\times10^{-4}$ at the 90% confidence level. This result improves the previous upper limit result by about one order of magnitude.