Observation of the electromagnetic Dalitz decay D 0 → D0e + e −

Abstract

Based on 3.19 fb-1 of e+e- collision data accumulated at the center-of-mass energy 4.178 GeV with the BESIII detector operating at the BEPCII collider, the electromagnetic Dalitz decay D∗0→D0e+e- is observed for the first time with a statistical significance of 13.2σ. The ratio of the branching fraction of D∗0→D0e+e- to that of D∗0→D0γ is measured to be (11.08±0.76±0.49)×10-3. By using the world average value of the branching fraction of D∗0→D0γ, the branching fraction of D∗0→D0e+e- is determined to be (3.91±0.27±0.17±0.10)×10-3, where the first uncertainty is statistical, the second is systematic and the third is from external input of the branching fraction for D∗0→D0γ. © 2021 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.