Ablikim, M.Achasov, M.N.Adlarson, P.Afedulidis, O.Ai, X.C.Aliberti, R.Çetin, Serkant Ali2024-05-192024-05-1920242470-0010https://doi.org/10.1103/PhysRevD.109.072001https://hdl.handle.net/20.500.12713/4519Based on a data sample of 10 billion J/? events collected with the BESIII detector, improved measurements of the Dalitz decays ?/????e+e- are performed, where the ? and ?? are produced through the radiative decays J/????/??. The branching fractions of ???e+e- and ????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 ???e+e- is determined to be ??=(0.749±0.027±0.007) GeV/c2. Within the multipole model, we extract the electromagnetic transition form factors for ????e+e- to be ???=(0.802±0.007±0.008) GeV/c2 and ???=(0.113±0.010±0.002) GeV/c2. The results are consistent with both theoretical predictions and previous measurements. The characteristic sizes of the interaction regions for the ? and ?? 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 ?/????e+e-, and the upper limits of the branching fractions as a function of the dark photon are given at 90% confidence level. © 2024 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the "https://creativecommons.org/licenses/by/4.0/"Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by SCOAP3.eninfo:eu-repo/semantics/openAccessArticle10972-s2.0-8519063944210.1103/PhysRevD.109.072001Q1