Search for the hyperon semileptonic decay ${\mathrm{\Xi }}^{-}\to {\mathrm{\Xi }}^0{e}^{-}\overline{{\nu }_e}$

Using $(10.087\pm 0.044)\times {10}^{9}J/\psi$ events collected by the Beijing Spectrum III (BESIII) detector at the Beijing Electron Positron Collider II (BEPCII) collider, we search for the hyperon semileptonic decay ${\mathrm{\Xi }}^{-}\to {\mathrm{\Xi }}^0{e}^{-}{\overline{\nu }}_e$. No significant signal is observed and the upper limit on the branching fraction $\mathcal{B}({\mathrm{\Xi }}^{-}\to {\mathrm{\Xi }}^0{e}^{-}{\overline{\nu }}_e)$ is set to be $2.59\times {10}^{-4}$ at 90% confidence level. This result is one order of magnitude more strict than the previous best limit.

Figure 1

Fit to the invariant mass distribution of the $\overline{\mathrm{\Lambda }}{\pi }^{+}$ candidates, where the black points with error bars are data, and the red dashed line and green dashed line are the signal shape and background shape, respectively. The blue solid line shows the total fit and the pair of red arrows indicates the ST signal region.

Figure 2

Fit to the $q^2$ distribution of the signal candidates, where the black points with error bars are data, and the red dashed line and green dashed line are the signal shape and background shape, respectively. The blue solid line shows the total fit.

Figure 3

The likelihood ratio distribution as a function of $\mathcal{B}({\mathrm{\Xi }}^{-}\to {\mathrm{\Xi }}^0{e}^{-}{\overline{\nu }}_e)$ after (before) smearing with the systematic Gaussian function is the red solid (blue circle-shaped) curve. The red solid (blue dashed) arrow indicates the upper limit on the branching fraction at 90% CL after (before) smearing with the systematic Gaussian function.