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arXiv · 2107.06704

First Measurement of the Absolute Branching Fraction of $Λ\to p μ^- \barν_μ$

M. Ablikim·M. N. Achasov·P. Adlarson·S. Ahmed·M. Albrecht·R. Aliberti·A. Amoroso·M. R. An·Q. An·X. H. Bai·Y. Bai·O. Bakina·R. Baldini Ferroli·I. Balossino·Y. Ban·K. Begzsuren·N. Berger·M. Bertani·D. Bettoni·F. Bianchi·J. Bloms·A. Bortone·I. Boyko·R. A. Briere·H. Cai·X. Cai·A. Calcaterra·G. F. Cao·N. Cao·S. A. Cetin·J. F. Chang·W. L. Chang·G. Chelkov·D. Y. Chen·G. Chen·H. S. Chen·M. L. Chen·S. J. Chen·X. R. Chen·Y. B. Chen·Z. J Chen·W. S. Cheng·G. Cibinetto·F. Cossio·X. F. Cui·H. L. Dai·X. C. Dai·A. Dbeyssi·R. E. de Boer·D. Dedovich·Z. Y. Deng·A. Denig·I. Denysenko·M. Destefanis·F. De Mori·Y. Ding·C. Dong·J. Dong·L. Y. Dong·M. Y. Dong·X. Dong·S. X. Du·Y. L. Fan·J. Fang·S. S. Fang·Y. Fang·R. Farinelli·L. Fava·F. Feldbauer·G. Felici·C. Q. Feng·J. H. Feng·M. Fritsch·C. D. Fu·Y. Gao·Y. G. Gao·I. Garzia·P. T. Ge·C. Geng·E. M. Gersabeck·A Gilman·K. Goetzen·L. Gong·W. X. Gong·W. Gradl·M. Greco·L. M. Gu·M. H. Gu·Y. T. Gu·C. Y Guan·A. Q. Guo·L. B. Guo·R. P. Guo·Y. P. Guo·A. Guskov·T. T. Han·W. Y. Han·X. Q. Hao·F. A. Harris·K. L. He
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Abstract

The absolute branching fraction of $Λ\to p μ^- \barν_μ$ is reported for the first time based on an $e^+e^-$ annihilation sample of ten billion $J/ψ$ events collected with the BESIII detector at $\sqrt{s}=3.097$ GeV. The branching fraction is determined to be ${\mathcal B}(Λ\to pμ^- \barν_μ) = [1.48\pm0.21(\rm stat) \pm 0.08(\rm syst)]\times 10^{-4}$, which is a significant improvement in precision over the previous indirect measurements. Combining this result with the world average of ${\mathcal B}(Λ\to p e^- \barν_{e})$, we obtain the ratio, $\frac{Γ(Λ\to p μ^- \barν_μ)}{Γ(Λ\to p e^- \barν_{e})}$, to be $0.178 \pm 0.028$, which agrees with the standard model prediction assuming lepton flavor universality. The asymmetry of the branching fractions of $Λ\to p μ^- \barν_μ$ and $\barΛ \to \bar{p} μ^+ ν_μ$ is also determined, and no evidence for $CP$ violation is found.

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M. Ablikim, M. N. Achasov, P. Adlarson, S. Ahmed, M. Albrecht, R. Aliberti, A. Amoroso, M. R. An, Q. An, X. H. Bai, Y. Bai, O. Bakina, R. Baldini Ferroli, I. Balossino, Y. Ban, K. Begzsuren, N. Berger, M. Bertani, D. Bettoni, F. Bianchi, J. Bloms, A. Bortone, I. Boyko, R. A. Briere, H. Cai, X. Cai, A. Calcaterra, G. F. Cao, N. Cao, S. A. Cetin, J. F. Chang, W. L. Chang, G. Chelkov, D. Y. Chen, G. Chen, H. S. Chen, M. L. Chen, S. J. Chen, X. R. Chen, Y. B. Chen, Z. J Chen, W. S. Cheng, G. Cibinetto, F. Cossio, X. F. Cui, H. L. Dai, X. C. Dai, A. Dbeyssi, R. E. de Boer, D. Dedovich, Z. Y. Deng, A. Denig, I. Denysenko, M. Destefanis, F. De Mori, Y. Ding, C. Dong, J. Dong, L. Y. Dong, M. Y. Dong, X. Dong, S. X. Du, Y. L. Fan, J. Fang, S. S. Fang, Y. Fang, R. Farinelli, L. Fava, F. Feldbauer, G. Felici, C. Q. Feng, J. H. Feng, M. Fritsch, C. D. Fu, Y. Gao, Y. G. Gao, I. Garzia, P. T. Ge, C. Geng, E. M. Gersabeck, A Gilman, K. Goetzen, L. Gong, W. X. Gong, W. Gradl, M. Greco, L. M. Gu, M. H. Gu, Y. T. Gu, C. Y Guan, A. Q. Guo, L. B. Guo, R. P. Guo, Y. P. Guo, A. Guskov, T. T. Han, W. Y. Han, X. Q. Hao, F. A. Harris, K. L. He. 2021-07-14. First Measurement of the Absolute Branching Fraction of $Λ\to p μ^- \barν_μ$. https://doi.org/10.1103/physrevlett.127.121802

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