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

Using a data sample of $(1.0087\pm 0.0044)\times {10}^{10}J/\psi$ decay events collected with the BESIII detector at the center-of-mass energy of $\sqrt{s}=3.097\mathrm{GeV}$, we present a search for the hyperon semileptonic decay ${\mathrm{\Xi }}^0\to {\mathrm{\Sigma }}^{-}{e}^{+}{\nu }_e$ which violates the $\mathrm{\Delta }S=\mathrm{\Delta }Q$ rule. No significant signal is observed, and the upper limit on the branching fraction $\mathcal{B}({\mathrm{\Xi }}^0\to {\mathrm{\Sigma }}^{-}{e}^{+}{\nu }_e)$ is determined to be $1.6\times {10}^{-4}$ at the 90% confidence level. This result improves the previous upper limit result by about one order of magnitude.

Figure 1

The Feynman diagram of the $\mathrm{\Delta }S=\mathrm{\Delta }Q$ violating decay ${\mathrm{\Xi }}^0\to {\mathrm{\Sigma }}^{-}{e}^{+}{\nu }_e$.

Figure 2

$M_{\mathrm{BC}}$ distribution of ST ${\overline{\mathrm{\Xi }}}^0$ candidates with fit results overlaid. The black dots with error bar represent data, the blue curve represents the fit result, the red dashed curve represents the signal component and the green dashed curve represents the background component. The red arrows indicate the ST signal region.

Figure 3

The $M_{\mathrm{BC}}$ distribution of the ST side for DT ${\mathrm{\Xi }}^0$ candidates with fit results overlaid. The black dots with error bar represent data, the blue curve represents the fit result, the black dashed curve represents the peaking background component and the green dashed curve represents the other background component. The red dotted curve shows the signal shape normalized to the branching fraction $\mathcal{B}({\mathrm{\Xi }}^0\to {\mathrm{\Sigma }}^{-}{e}^{+}{\nu }_e)=1.6\times {10}^{-4}$. The red arrows indicate the DT signal region.

Figure 4

The normalized-likelihood distributions before and after incorporating systematic uncertainties. The blue dashed curve represents the raw-likelihood distribution. The red solid curve represents the updated likelihood distribution after incorporating the systematic uncertainties. The top $x$ axis is for the number of signal events and the bottom $x$ axis is for the corresponding branching fraction. The shadowed area represents the integration region and the red arrow indicates the upper limits at the 90% confidence level.