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M. Ablikim, М. Н. Ачасов, P. Adlarson, R. Aliberti, A. Amoroso, M. R. An, Q. An, Y. Bai, O. Bakina, I. Balossino, Y. Ban, V. Batozskaya, K. Begzsuren, N. Berger, M. Bertani, D. Bettoni, F. Bianchi, E. Bianco, J. Bloms, A. Bortone, I. Boyko, R. A. Briere, A. Brueggemann, H. Cai, X. Cai, A. Calcaterra, G. F. Cao, N. Cao, S. A. Çetin, J. F. Chang, T. T. Chang, W. L. Chang, G. R., G. Chelkov, C. Chen, Chao Chen, G. Chen, Haifeng Chen, M. L. Chen, S. J. Chen, S. M. Chen, T. Chen, Xiaoyan Chen, X. T. Chen, Y. B. Chen, Y. Q. Chen, Z. J. Chen, W. S. Cheng, S. K. Choi, X. Chu, G. Cibinetto, S. C. Coen, F. Cossio, J. J. Cui, H. L. Dai, J. P. Dai, A. Dbeyssi, R. E. de Boer, D. Dedovich, Z. Y. Deng, A. Denig, I. Denysenko, M. Destefanis, F. De Mori, B. Ding, X. X. Ding, Y. Ding, Y. Ding, J. Dong, L. Y. Dong, M. Y. Dong, X. Dong, S. X. Du, Z. H. Duan, P. Egorov, Y. L. Fan, J. Fang, S. S. Fang, Wenxing Fang, Y. Fang, R. Farinelli, L. Fava, F. Feldbauer, G. Felici, C. Q. Feng, J. H. Feng, K. Fischer, M. Fritsch, C. Fritzsch, C. D. Fu, Y. W. Fu, He Gao, Yang Gao, Yang Gao, S. Garbolino, I. Garzia, P. Ge, Z. W. Ge, C. Geng, E. Gersabeck
Abstract
Using $(10\text{ }087\ifmmode\pm\else\textpm\fi{}44)\ifmmode\times\else\texttimes\fi{}{10}^{6}$ $J/\ensuremath{\psi}$ events collected with the BESIII detector, the radiative hyperon decay ${\mathrm{\ensuremath{\Sigma}}}^{+}\ensuremath{\rightarrow}p\ensuremath{\gamma}$ is studied at an electron-positron collider experiment for the first time. The absolute branching fraction is measured to be $(0.996\ifmmode\pm\else\textpm\fi{}0.02{1}_{\mathrm{stat}}\ifmmode\pm\else\textpm\fi{}0.01{8}_{\mathrm{syst}})\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$, which is lower than its world average value by 4.2 standard deviations. Its decay asymmetry parameter is determined to be $\ensuremath{-}0.652\ifmmode\pm\else\textpm\fi{}0.05{6}_{\mathrm{stat}}\ifmmode\pm\else\textpm\fi{}0.02{0}_{\mathrm{syst}}$. The branching fraction and decay asymmetry parameter are the most precise to date, and the accuracies are improved by 78% and 34%, respectively.