Observation of the hindered electromagnetic Dalitz decay ψ(3686) → e+ e-ηc

Authors：Ablikim, M.; Achasov, M. N.; Adlarson, P.; Albrecht, M.; Aliberti, R.; Amoroso, A.; An, M. R.; An, Q.; Bai, X. H.; Bai, Y.; Bakina, O.; Ferroli, R. Baldini; Balossino, I; Ban, Y.; Batozskaya, V; Becker, D.; Begzsuren, K.; Berger, N.; Bertani, M.; Bettoni, D.; Bianchi, F.; Bloms, J.; Bortone, A.; Boyko, I; Briere, R. A.; Brueggemann, A.; Cai, H.; Cai, X.; Calcaterra, A.; Cao, G. F.; Cao, N.; Cetin, S. A.; Chang, J. F.; Chang, W. L.; Chelkov, G.; Chen, C.; Chen, Chao; Chen, G.; Chen, H. S.

Source：Physical Review D, 2022, 106(11): 112002.

DOI：10.1103/PhysRevD.106.112002

• TRANSITION FORM-FACTORS
• VECTOR
• PHI
• MU(+)MU(-)GAMMA
• PRECISION
• PHYSICS
• OMEGA
• ETA

Using a data sample of (448.1 +/- 2.9) x 10(6) psi(3686) decays collected at an e(+)e(& minus;) center-of-mass energy of 3.686 GeV by the BESIII detector at Beijing Electron Positron Collider II, we report an observation of the hindered electromagnetic Dalitz decay psi(3686) -> e(+)e(& minus;)eta(c) with a significance of 7.9 sigma. The branching fraction is determined to be B(psi(3686) -> e(+)e(& minus;)eta(c)) = (3.77 +/- 0.40(stat) +/- 0.18(syst)) x 10(& minus;5), agreeing well with the prediction of the vector meson dominance model. This is the first measurement of the electromagnetic Dalitz transition betwee