Ablikim, M.Achasov, M. N.Adlarson, P.Ahmed, S.Albrecht, M.Aliberti, R.Zou, J. H.2026-04-042026-04-0420242470-00102470-0029https://doi.org/10.1103/PhysRevD.110.L111101https://hdl.handle.net/11411/10567Using (27.12 +/- 0.14) x 10(8) psi(3686) decays and data samples of e(+)e(-) collisions with root s from 4.130 to 4.780 GeV collected with the BESIII detector, we report the first observation of the electromagnetic Dalitz transition h(c) -> e(+)e(-)eta(c) with a statistical significance of 5.4 sigma. We measure the ratio of the branching fractions B(h(c) -> e(+)e(-)eta(c))/B(h(c) -> gamma eta(c)) separately for the h(c) samples produced via psi(3686) -> pi(0)h(c) and e(+)e(-) -> pi(+)pi(-)h(c). The average ratio is determined to be (0.59 +/- 0.10(stat) +/- 0.04(syst))%, where the uncertainty includes both statistical and systematic components.eninfo:eu-repo/semantics/openAccessDecaysArticle2-s2.0-8521267748810.1103/PhysRevD.110.L11110110.1103/PhysRevD.110.L11110111Q1110Q1WOS:001381819100002