Measurement of the Absolute Branching Fraction and Decay Asymmetry of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi mathvariant="normal">Λ</mml:mi><mml:mo stretchy="false">→</mml:mo><mml:mi>n</mml:mi><mml:mi>γ</mml:mi></mml:mrow></mml:math>
M. Ablikim, M. N. Achasov, P. Adlarson, M. Albrecht, R. Aliberti, A. Amoroso, M. R. An, Q. An, Xiaoshuan Bai, Y. Bai, O. Bakina, R. Baldini Ferroli, I. Balossino, Y. Ban, V. Batozskaya, D. Becker, K. Begzsuren, N. Berger, M. Bertani, D. Bettoni, F. Bianchi, 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, W. L. Chang, G. Chelkov, C. Chen, Chao Chen, G. Chen, H. S. Chen, M. L. Chen, S. J. Chen, S. M. Chen, T. Chen, X. R. Chen, X. T. Chen, Y. B. Chen, Zixin Chen, W. S. Cheng, S. K. Choi, X. Chu, G. Cibinetto, 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, Yayun Ding, J. Dong, L. Y. Dong, M. Y. Dong, X. Dong, S. X. Du, P. Egorov, Y. L. Fan, J. Fang, S. S. Fang, W. X. 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, H. Gao, Y. N. Gao, Yang Gao, S. Garbolino, I. Garzia, P. T. Ge, Z. W. Ge, C. Geng, E. M. Gersabeck, A. Gilman, K. Goetzen, L. Gong, W. X. Gong, W. Gradl, M. Greco
Abstract
The radiative hyperon decay $\mathrm{\ensuremath{\Lambda}}\ensuremath{\rightarrow}n\ensuremath{\gamma}$ is studied using $(10087\ifmmode\pm\else\textpm\fi{}44)\ifmmode\times\else\texttimes\fi{}{10}^{6}\text{ }\text{ }J/\ensuremath{\psi}$ events collected with the BESIII detector operating at BEPCII. The absolute branching fraction of the decay $\mathrm{\ensuremath{\Lambda}}\ensuremath{\rightarrow}n\ensuremath{\gamma}$ is determined to be $(0.832\ifmmode\pm\else\textpm\fi{}0.03{8}_{\mathrm{stat}}\ifmmode\pm\else\textpm\fi{}0.05{4}_{\mathrm{syst}})\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$, which is a factor of 2.1 lower and 5.6 standard deviations different than the previous measurement. By analyzing the joint angular distribution of the decay products, the first determination of the decay asymmetry ${\ensuremath{\alpha}}_{\ensuremath{\gamma}}$ is reported with a value of $\ensuremath{-}0.16\ifmmode\pm\else\textpm\fi{}0.1{0}_{\mathrm{stat}}\ifmmode\pm\else\textpm\fi{}0.0{5}_{\mathrm{syst}}$.