Precision Measurement of the Decay Σ^{+}→pγ in the Process J/ψ→Σ^{+}Σ[over ¯]^{-}

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doi:10.1103/PhysRevLett.130.211901

Using (10 087 +/- 44) x 10(6) J/psi events collected with the BESIII detector, the radiative hyperon decay Sigma(+) -> p gamma is studied at an electron-positron collider experiment for the first time. The absolute branching fraction is measured to be (0.996 +/- 0.021(stat) +/- 0.018(syst)) x 10(-3), which is lower than its world average value by 4.2 standard deviations. Its decay asymmetry parameter is determined to be -0.652 +/- 0.056(stat) +/- 0.020(syst). The branching fraction and decay asymmetry parameter are the most precise to date, and the accuracies are improved by 78% and 34%, respectively.