Measurements of the Absolute Branching Fraction of the Semileptonic Decay $\hat{\mathbf{I}}{ž}^{-}\to \hat{\mathbf{I}}›{\mathbf{e}}^{-}\overline{\hat{\mathbf{I}}}{½}_{\mathbf{e}}$ and the Axial Charge of the $\hat{\mathbf{I}}{ž}^{-}$

Abstract

Using $(10087\pm 44)\times 10^6$ $J/\ddot{I}ˆ$ events collected with the BESIII detector, we study the semileptonic decay $\hat{I}{ž}^{-}\to \hat{I}›e^{-}\bar{\hat{I}}{½}_e$ for the first time at an electron-positron collider. The absolute branching fraction is determined for the first time to be $(3.60\pm 0.40_{\mathrm{stat}}\pm 0.10_{\mathrm{syst}})\times 10^{-4}$, 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 $0.18\pm 0.07_{\mathrm{stat}}\pm 0.02_{\mathrm{syst}}$. 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 $g_A^H=0.22\pm 0.08_{\mathrm{stat}}\pm 0.02_{\mathrm{syst}}$. Despite using only 5\% of the statistics of previous experiments, this analysis achieves a comparable precision for the axial charge.

10 pages, 4 figures