The first measurement of the semileptonic decay Ξ⁻ → Λ e⁻ νbare
The BESIII Collaboration has reported the first measurement of the semileptonic decay Ξ⁻ → Λ e⁻ νbare at an electron-positron collider, providing the first determination of its absolute branching fraction, as well as the first update of the Ξ⁻ axial charge in more than four decades. The result has been published in Physical Review Letters [Phys. Rev. Lett. 137, 091801 (2026)].