Observation of the electromagnetic Dalitz decay $D^{\ast 0}\to D^{0}e^{+}e^{-}$

TL;DR

This paper reports the first observation of the electromagnetic Dalitz decay $D^{*0} o D^{0} e^{+} e^{-}$, measuring its branching fraction and ratio to the radiative decay using data from the BESIII detector.

Contribution

The study provides the first experimental evidence of the decay $D^{*0} o D^{0} e^{+} e^{-}$ and measures its branching fraction, expanding understanding of charm meson electromagnetic decays.

Findings

First observation of $D^{*0} o D^{0} e^{+} e^{-}$ decay

Branching fraction ratio $(11.08 extpm0.76 extpm0.49) imes 10^{-3}$

Branching fraction $(3.91 extpm0.27 extpm0.17 extpm0.10) imes 10^{-3}$

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 $D^{\ast 0}\to D^{0}e^{+}e^{-}$ is observed for the first time with a statistical significance of $13.2\sigma$. The ratio of the branching fraction of $D^{\ast 0}\to D^{0}e^{+}e^{-}$ to that of $D^{\ast 0}\to D^{0} \gamma$ is measured to be $(11.08\pm0.76\pm0.49)\times 10^{-3}$. By using the world average value of the branching fraction of $D^{\ast 0}\to D^{0} \gamma$, the branching fraction of $D^{\ast 0}\to D^{0}e^{+}e^{-}$ is determined to be $(3.91\pm0.27\pm0.17\pm0.10)\times 10^{-3}$, where the first uncertainty is statistical, the second systematic and the third external branching fractions.