Improved measurements of the Dalitz decays η/η'→γ
e^+e^-
BESIII Collaboration,M. Ablikim,M. N. Achasov,P. Adlarson,O. Afedulidis,X. C. Ai,R. Aliberti,A. Amoroso,Q. An,Y. Bai,O. Bakina,I. Balossino,Y. Ban,H. -R. Bao,V. Batozskaya,K. Begzsuren,N. Berger,M. Berlowski,M. Bertani,D. Bettoni,F. Bianchi,E. Bianco,A. Bortone,I. Boyko,R. A. Briere,A. Brueggemann,H. Cai,X. Cai,A. Calcaterra,G. F. Cao,N. Cao,S. A. Cetin,J. F. Chang,W. L. Chang,G. R. Che,G. Chelkov,C. Chen,C. H. Chen,Chao Chen,G. Chen,H. S. Chen,M. L. Chen,S. J. Chen,S. L. Chen,S. M. Chen,T. Chen,X. R. Chen,X. T. Chen,Y. B. Chen,Y. Q. Chen,Z. J. Chen,Z. Y. Chen,S. K. Choi,X. Chu,G. Cibinetto,F. Cossio,J. J. Cui,H. L. Dai,J. P. Dai,A. Dbeyssi,R. E. de Boer,D. Dedovich,C. Q. Deng,Z. Y. Deng,A. Denig,I. Denysenko,M. Destefanis,F. De Mori,B. Ding,X. X. Ding,Y. Ding,Y. Ding,J. Dong,L. Y. Dong,M. Y. Dong,X. Dong,M. C. Du,S. X. Du,Z. H. Duan,P. Egorov,Y. H. Fan,J. Fang,J. Fang,S. S. Fang,W. X. Fang,Y. Fang,Y. Q. Fang,R. Farinelli,L. Fava,F. Feldbauer,G. Felici,C. Q. Feng,J. H. Feng,Y. T. Feng,K. Fischer,M. Fritsch,C. D. Fu,J. L. Fu,Y. W. Fu,H. Gao,Y. N. Gao,Yang Gao,S. Garbolino,I. Garzia,P. T. Ge,Z. W. Ge,C. Geng,E. M. Gersabeck,A. Gilman,K. Goetzen,L. Gong,W. X. Gong,W. Gradl,S. Gramigna,M. Greco,M. H. Gu,Y. T. Gu,C. Y. Guan,Z. L. Guan,A. Q. Guo,L. B. Guo,M. J. Guo,R. P. Guo,Y. P. Guo,A. Guskov,J. Gutierrez,K. L. Han,T. T. Han,X. Q. Hao,F. A. Harris,K. K. He,K. L. He,F. H. Heinsius,C. H. Heinz,Y. K. Heng,C. Herold,T. Holtmann,P. C. Hong,G. Y. Hou,X. T. Hou,Y. R. Hou,Z. L. Hou,B. Y. Hu,H. M. Hu,J. F. Hu,T. Hu,Y. Hu,G. S. Huang,K. X. Huang,L. Q. Huang,X. T. Huang,Y. P. Huang,T. Hussain,F. Hölzken,N Hüsken,N. in der Wiesche,M. Irshad,J. Jackson,S. Janchiv,J. H. Jeong,Q. Ji,Q. P. Ji,W. Ji,X. B. Ji,X. L. Ji,Y. Y. Ji,X. Q. Jia,Z. K. Jia,D. Jiang,H. B. Jiang,P. C. Jiang,S. S. Jiang,T. J. Jiang,X. S. Jiang,Y. Jiang,J. B. Jiao,J. K. Jiao,Z. Jiao,S. Jin,Y. Jin,M. Q. Jing,X. M. Jing,T. Johansson,S. Kabana,N. Kalantar-Nayestanaki,X. L. Kang,X. S. Kang,M. Kavatsyuk,B. C. Ke,V. Khachatryan,A. Khoukaz,R. Kiuchi,O. B. Kolcu,B. Kopf,M. Kuessner,X. Kui,A. Kupsc,W. Kühn,J. J. Lane,P. Larin,L. Lavezzi,T. T. Lei,Z. H. Lei,H. Leithoff,M. Lellmann,T. Lenz,C. Li,C. Li,C. H. Li,Cheng Li,D. M. Li,F. Li,G. Li,H. Li,H. B. Li,H. J. Li,H. N. Li,Hui Li,J. R. Li,J. S. Li,Ke Li,L. J Li,L. K. Li,Lei Li,M. H. Li,P. R. Li,Q. M. Li,Q. X. Li,R. Li,S. X. Li,T. Li,W. D. Li,W. G. Li,X. Li,X. H. Li,X. L. Li,Xiaoyu Li,Y. G. Li,Z. J. Li,Z. X. Li,C. Liang,H. Liang,H. Liang,Y. F. Liang,Y. T. Liang,G. R. Liao,L. Z. Liao,Y. P. Liao,J. Libby,A. Limphirat,D. X. Lin,T. Lin,B. J. Liu,B. X. Liu,C. Liu,C. X. Liu,F. H. Liu,Fang Liu,Feng Liu,G. M. Liu,H. Liu,H. B. Liu,H. M. Liu,Huanhuan Liu,Huihui Liu,J. B. Liu,J. Y. Liu,K. Liu,K. Y. Liu,Ke Liu,L. Liu,L. C. Liu,Lu Liu,M. H. Liu,P. L. Liu,Q. Liu,S. B. Liu,T. Liu,W. K. Liu,W. M. Liu,X. Liu,X. Liu,Y. Liu,Y. Liu,Y. B. Liu,Z. A. Liu,Z. D. Liu,Z. Q. Liu,X. C. Lou,F. X. Lu,H. J. Lu,J. G. Lu,X. L. Lu,Y. Lu,Y. P. Lu,Z. H. Lu,C. L. Luo,M. X. Luo,T. Luo,X. L. Luo,X. R. Lyu,Y. F. Lyu,F. C. Ma,H. Ma,H. L. Ma,J. L. Ma,L. L. Ma,M. M. Ma,Q. M. Ma,R. Q. Ma,X. T. Ma,X. Y. Ma,Y. Ma,Y. M. Ma,F. E. Maas,M. Maggiora,S. Malde,A. Mangoni,Y. J. Mao,Z. P. Mao,S. Marcello,Z. X. Meng,J. G. Messchendorp,G. Mezzadri,H. Miao,T. J. Min,R. E. Mitchell,X. H. Mo,B. Moses,N. Yu. Muchnoi,J. Muskalla,Y. Nefedov,F. Nerling,I. B. Nikolaev,Z. Ning,S. Nisar,Q. L. Niu,W. D. Niu,Y. Niu,S. L. Olsen,Q. Ouyang,S. Pacetti,X. Pan,Y. Pan,A. Pathak,P. Patteri,Y. P. Pei,M. Pelizaeus,H. P. Peng,Y. Y. Peng,K. Peters,J. L. Ping,R. G. Ping,S. Plura,V. Prasad,F. Z. Qi,H. Qi,H. R. Qi,M. Qi,T. Y. Qi,S. Qian,W. B. Qian,C. F. Qiao,J. J. Qin,L. Q. Qin,X. S. Qin,Z. H. Qin,J. F. Qiu,S. Q. Qu,Z. H. Qu,C. F. Redmer,K. J. Ren,A. Rivetti,M. Rolo,G. Rong,Ch. Rosner,S. N. Ruan,N. Salone,A. Sarantsev,Y. Schelhaas,K. Schoenning,M. Scodeggio,K. Y. Shan,W. Shan,X. Y. Shan,J. F. Shangguan,L. G. Shao,M. Shao,C. P. Shen,H. F. Shen,W. H. Shen,X. Y. Shen,B. A. Shi,H. C. Shi,J. L. Shi,J. Y. Shi,Q. Q. Shi,R. 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arxiv（2024）
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摘要
Based on a data sample of 10 billion J/ψ events collected with the
BESIII detector, improved measurements of the Dalitz decays
η/η'→γ e^+e^- are performed, where the η and
η' are produced through the radiative decays J/ψ→γη/η'. The branching fractions of η→γ e^+e^- and
η'→γ e^+e^- are measured to be (7.07 ± 0.05 ±
0.23)×10^-3 and (4.83±0.07±0.14)×10^-4, respectively.
Within the single pole model, the parameter of electromagnetic transition form
factor for η→γ e^+e^- is determined to be
Λ_η=(0.749 ± 0.027 ± 0.007) GeV/c^2. Within the
multi-pole model, we extract the electromagnetic transition form factors for
η'→γ e^+e^- to be Λ_η' = (0.802 ± 0.007±
0.008) GeV/c^2 and γ_η' = (0.113±0.010±0.002)
GeV/c^2. The results are consistent with both theoretical predictions and
previous measurements. The characteristic sizes of the interaction regions for
the η and η' are calculated to be (0.645 ± 0.023 ± 0.007 )
fm and (0.596 ± 0.005 ± 0.006) fm, respectively. In addition, we
search for the dark photon in η/η^'→γ e^+e^-,
and the upper limits of the branching fractions as a function of the dark
photon are given at 90% confidence level.
