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ISSN - 15507998, Physical Review D - Particles, Fields, Gravitation and Cosmology, 2015, vol. 92, 5, p. -

Observation of η′ →ωe+e-

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., Ferroli R. Baldini, 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., Du S. X., Duan P. F., Eren E. E., Fan J. Z., Fang J., Fang S. S., Fang X., Fang Y., Fava L., Feldbauer F., Felici G., Feng C. Q., Fioravanti E., Fritsch M., Fu C. D., Gao Q., Gao X. Y., Gao Y., Gao Z., Garzia I., Goetzen K.

© 2015 American Physical Society.Based on a sample of η′ mesons produced in the radiative decay J/ψ→γη′ in 1.31×109 J/ψ events collected with the BESIII detector, the decay η′→ωe+e- is observed for the first time, with a statistical significance of 8σ. The branching fraction is measured to be B(η′→ωe+e-)=(1.97±0.34(stat)±0.17(syst))×10-4, which is in agreement with theoretical predictions. The branching fraction of η′→ωγ is also measured to be (2.55±0.03(stat)±0.16(syst))×10-2, which is the most precise measurement to date, and the relative branching fraction B(η′→ωe+e-)B(η′→ωγ) is determined to be (7.71±1.34(stat)±0.54(syst))×10-3.