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ISSN - 00319007, EISSN - 10797114, Physical Review Letters, 2015, vol. 115, 22, p. -

Measurement of the Absolute Branching Fraction for Λc+ → Λe+νe

Ablikim M., Achasov M. N., Ai X. C., Albayrak O., Albrecht M., Ambrose D. J., Amoroso A., An F. F., An Q., Bai J. Z., Baldini Ferroli R., Ban Y., Bennett D. W., Bennett J. V., Bertani M., Bettoni D., Bian J. M., Bianchi F., Boger E., Boyko I., Briere R. A., Cai H., Cai X., Cakir O., Calcaterra A., Cao G. F., Cetin S. A., Chang J. F., Chelkov G., Chen G., Chen H. S., Chen H. Y., Chen J. C., Chen M. L., Chen S. J., Chen X., Chen X. R., Chen Y. B., Cheng H. P., Chu X. K., Cibinetto G., Dai H. L., Dai J. P., Dbeyssi A., Dedovich D., Deng Z. Y., Denig A., Denysenko I., Destefanis M., De Mori F., Ding Y., Dong C., Dong J., Dong L. Y., Dong M. Y., Dou Z. L., Du S. X., Duan P. F., Fan J. Z., Fang J., Fang S. S., Fang X., Fang Y., Fava L., Fedorov O., Feldbauer F., Felici G., Feng C. Q.

© 2015 American Physical Society. We report the first measurement of the absolute branching fraction for Λc+→Λe+νe. This measurement is based on 567 pb-1 of e+e- annihilation data produced at s=4.599 GeV, which is just above the Λc+Λ¯c- threshold. The data were collected with the BESIII detector at the BEPCII storage rings. The branching fraction is determined to be B(Λc+→Λe+νe)=[3.63±0.38(stat)±0.20(syst)]%, representing a significant improvement in precision over the current indirect determination. As the branching fraction for Λc+→Λe+νe is the benchmark for those of other Λc+ semileptonic channels, our result provides a unique test of different theoretical models, which is the most stringent to date.