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

Abstract

Using a data sample of (448.1±2.9)×106 ψ(3686) decays collected at an e+e− 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 ψ(3686)→e+e−ηc with a significance of 7.9σ. The branching fraction is determined to be B(ψ(3686)→e+e−ηc)=(3.77±0.40stat±0.18syst)×10−5, agreeing well with the prediction of the vector meson dominance model. This is the first measurement of the electromagnetic Dalitz transition between the ψ(3686) and the ηc, which provides new insight into the electromagnetic properties of this decay, and offers new opportunities to measure the absolute branching fractions of ηc decays.Received 26 August 2022Accepted 9 November 2022DOI:https://doi.org/10.1103/PhysRevD.106.112002Published by the American Physical Society under the terms of the 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.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasBranching fractionElectromagnetic transitionsPhysical SystemsQuarkoniaPropertiesForm factorsTechniquesLepton collidersParticles & Fields