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) -> 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*(0) -> D(0)e(+)e(-) to that of D*(0) -> D-0 gamma is measured to be (11.08 +/- 0.76 +/- 0.49) x 10(-3). By using the world average value of the branching fraction of D*(0) -> D-0 gamma, the branching fraction of D*(0) -> D(0)e(+)e(-) is determined to be (3.91 +/- 0.27 +/- 0.17 +/- 0.10) x 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) -> D-0 gamma.