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ISSN - 03702693, Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics, 2017, p. -

Observation of ψ(3686)→η<sup>′</sup>e<sup>+</sup>e<sup>−</sup>

Ablikim M., Achasov M. N., Ahmed S., Albrecht M., Alekseev M., Amoroso A., An F. F., An Q., Bai J. Z., Bai Y., Bakina O., Baldini Ferroli R., Ban Y., Begzsuren K., Bennett D. W., Bennett J. V., Berger N., Bertani M., Bettoni D., Bianchi F., Boger E., Boyko I., Briere R. A., Cai H., Cai X., Cakir O., Calcaterra A., Cao G. F., Cetin S. A., Chai J., Chang J. F., Chelkov G., Chen G., Chen H. S., Chen J. C., Chen M. L., Chen P. L., Chen S. J., Chen X. R., Chen Y. B., Cheng W., Chu X. K., Cibinetto G., Cossio F., 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., Fang J., Fang S. S., Fang Y., Farinelli R., Fava L., Fegan S., Feldbauer F., Felici G., Feng C. Q., Fioravanti E., Fritsch M., Fu C. D.

© 2018 The Author Using a data sample of 448.1×106ψ(3686) events collected with the BESIII detector at the BEPCII collider, we report the first observation of the electromagnetic Dalitz decay ψ(3686)→η′e+e−, with significances of 7.0σ and 6.3σ when reconstructing the η′meson via its decay modes η′→γπ+π−and η′→π+π−η (η→γγ), respectively. The weighted average branching fraction is determined to be B(ψ(3686)→η′e+e−)=(1.90±0.25±0.11)×10−6, where the first uncertainty is statistical and the second systematic.