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Achasov, M. N.; Ahmed, S.; Amoroso, A.; Bai, J. Z.; Bennett, D. W.; Calcaterra, A.; Chai, J.; Chen, P. L.; Cibinetto, G.; Dai, H. L.; Dbeyssi, A.; Ding, Y.; Dou, Z. L.; Fang, Y.; Farinelli, R.; Felici, G.; Greco, M.; Gu, M. H.; Harris, F. A.; He, X. Q.; Heng, Y. K.; Hou, Z. L.; Huang, G. S.; Huang, X. T.; Huang, X. Z.; Ji, Q. P.; Ke, B. C.; Kopf, B.; Kuemmel, M.; Kurth, M.; Li, J. W.; Li, X. L.; Li, X. Q.; Liang, Y. F.; Lin, C. X.; Liu, Fang; Liu, H. B.; Liu, J. B.; Liu, K.; Liu, Q.; Liu, Zhiqing; Lou, X. C.; Lu, H. J.; Lyu, X. R.; Ma, F. C.; Ma, L. L.; Mitchell, R. E.; Mo, Y. J.; Muramatsu, H.; Mustafa, A.; Nefedov, Y.; Nerling, F.; Nikolaev, I. B.; Ning, Z.; Olsen, S. L.; Pacetti, S.; Papenbrock, M.; Peters, K.; Pitka, A.; Qi, M.; Qi, T. Y.; Qian, S.; Qin, N.; Rashid, K. H.; Rosner, Ch; Sarantsev, A.; Sheng, H. Y.; Sosio, S.; Sun, L.; Tang, X.; Tsednee, B.; Wang, B.; Wang, M.; Wang, M. Z.; Wang, Y. F.; Wang, Z. Y.; Wei, D. H.; Wiedner, U.; Wolke, M.; Wu, L. H.; Xie, Y. G.; Xiu, Q. L.; Xu, J. J.; Yan, W. C.; Yan, Y. H.; Yuncu, A.; Zhang, B. X.; Zhang, B. Y.; Zhang, H. Y.; Zhang, J. Q.; Zhang, X. Y.; Zhang, Y. T.; Zhao, G.; Zhao, J. W.; Zhao, S. J.; Zhao, Y. B.; Zheng, Y. H.; Zhu, K.; Zhu, K. J.; Zou, J. H.
Physical review. D, 2019, Letnik: 99, Številka: 1Journal Article
Using a data sample of (1310.6 ± 7.0) × 106 J / ψ decay events collected with the BESIII detector at BEPCII, we study the electromagnetic Dalitz decay J / ψ → η′e+e− with two dominant η′ decay modes, η′ → γπ+π− and η′ → π+π−η. The branching fraction is determined to be B(J / ψ → η′e+e−) = (6.59 ± 0.07 ± 0.17) × 10−5, which improves in precision by a factor of 2 over the previous BESIII measurement. A search for the dark photon (γ′) is performed via J / ψ → η′γ′, γ′ → e+e−. Excluding the ω and ϕ mass regions, no significant signal is observed in the mass range from 0.1 to 2.1 GeV / c2. We set upper limits at the 90% confidence level on B(J / ψ → η′γ′) × B(γ′ → e+e−), B(J / ψ → η′γ′) and the mixing strength as a function of dark photon mass. This is among the first searches for dark photons in charmonium decays.
