First Direct Measurement of the Absolute Branching Fraction of ${\Sigma }^{+}\to \Lambda e^{+}{\nu }_e$

BESIII Collaboration, M. Ablikim, M. N. Achasov +591

The first direct measurement of the absolute branching fraction of ${\Sigma }^{+}\to \Lambda e^{+}{\nu }_e$ is reported based on an $e^{+}{e}^{-}$ annihilation sample of $(10087\pm 44)\times 10^6$ $J/\psi$ eve…