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Institute of High Energy Physics, Beijing 100049, People's Republic of China.
G.I. Budker Institute of Nuclear Physics SB RAS (BINP), Novosibirsk 630090, Russia.
Phys Rev Lett. 2015 Nov 27;115(22):221805. doi: 10.1103/PhysRevLett.115.221805. Epub 2015 Nov 25.
We report the first measurement of the absolute branching fraction for Λ_{c}^{+}→Λe^{+}ν_{e}. This measurement is based on 567 pb^{-1} of e^{+}e^{-} annihilation data produced at sqrt[s]=4.599 GeV, which is just above the Λ_{c}^{+}Λ[over ¯]{c}^{-} threshold. The data were collected with the BESIII detector at the BEPCII storage rings. The branching fraction is determined to be B(Λ{c}^{+}→Λe^{+}ν_{e})=[3.63±0.38(stat)±0.20(syst)]%, representing a significant improvement in precision over the current indirect determination. As the branching fraction for Λ_{c}^{+}→Λe^{+}ν_{e} is the benchmark for those of other Λ_{c}^{+} semileptonic channels, our result provides a unique test of different theoretical models, which is the most stringent to date.
我们报告了对Λc+→Λe+νe绝对分支比的首次测量。该测量基于在质心能量√s = 4.599 GeV下产生的567 pb−1的e+e−湮灭数据，此能量刚好高于Λc+Λc−阈值。数据是利用北京谱仪III（BESIII）探测器在BEPCII储存环上收集的。确定分支比为B(Λc+→Λe+νe)=[3.63±0.38(统计)±0.20(系统)]%，与当前的间接测定相比，精度有显著提高。由于Λc+→Λe+νe的分支比是其他Λc+半轻子衰变道分支比的基准，我们的结果为不同理论模型提供了独特的检验，这是迄今为止最严格的检验。
