Measurements of the Absolute Branching Fraction of the Semileptonic Decay $\mathbf{\Xi^{-}\rightarrow \Lambda e^- \bar\nu_{e}}$ and the Axial Charge of the $\mathbf\Xi^{-}$

Abstract

Using $(10087\pm44)\times10^6$ $J/\psi$ events collected with the BESIII detector, we study the semileptonic decay $\Xi^{-}\rightarrow \Lambda e^- \bar\nu_{e}$ for the first time at an electron-positron collider. The absolute branching fraction is determined for the first time to be $(3.60\pm0.40_{\mathrm{stat}}\pm0.10_{\mathrm{syst}})\times10^{-4}$, which is 3.9 standard deviations below the world average. In addition, using an 11-dimensional angular analysis, the axial-vector to vector coupling $g_{av}$ is determined to be $0.18\pm0.07_{\mathrm{stat}}\pm0.02_{\mathrm{syst}}$. These results are used to test various SU(3)-flavour effective models. Under the SU(3)-flavour symmetry limit, the axial charge is found to be $g_A^H = 0.22\pm0.08_{\mathrm{stat}}\pm0.02_{\mathrm{syst}}$. Despite using only 5\% of the statistics of previous experiments, this analysis achieves a comparable precision for the axial charge.