Measurement of Branching Fraction and Transition Magnetic Moment of the Hyperon Dalitz Decay ${\Sigma }^0\to \Lambda e^{+}{e}^{-}$

Abstract

Based on a data sample of 10 billion $J/\psi$ events collected with the BESIII detector operating at the BEPCII collider, the Dalitz decay ${\Sigma }^0\to \Lambda e^{+}{e}^{-}$ is studied experimentally for the first time. The ${\Sigma }^0$ hyperons are produced through the process $J/\psi \to {\Sigma }^0{\bar{\Sigma }}^0$ and analyzed using a double-tag method. The absolute branching fraction is measured to be $\mathcal{B}({\Sigma }^0\to \Lambda e^{+}{e}^{-})=(6.34\pm 0.25_{stat.}\pm 0.23_{syst.})\times 10^{-3}$. This result shows a $2\sigma$ discrepancy from the theoretical calculation quoted in the PDG, where the uncertainties are statistical and systematic, respectively. In addition to the branching fraction, the transition magnetic moment $\mu$ is determined to be $(1.74\pm 0.03_{stat.}\pm 0.09_{syst.}){\mu }_N$, where ${\mu }_N=e/(2m_p)$ represents the nucleon magnetic moment, providing valuable insight into the intrinsic structure of the ${\Sigma }^0$ hyperon.

10 pages, 3 figures; supplemental material included