Measurement of the D0 → K− π+ e+ e− branching fraction and search for D0 → π+ π− e+ e− and D0 → K+ K− e+ e− decays at Belle

We present a study of the rare charm meson decays D0 → KþK−eþe−, πþπ−eþe−, and K−πþeþe− using a 942 fb−1 dataset collected by the Belle detector at the KEKB asymmetric-energy eþe− collider. We identify D0 candidates via the charge of the pion from D*þ → D0πþ decays and normalize the branching fractions to D0 → K−πþπ−πþ decays. The branching fraction for decay D0 → K−πþeþe− is measured to be ð39.6 ± 4.5 ðstatÞ ± 2.9 ðsystÞÞ × 10−7, with the dielectron mass in the ρ=ω mass region 675 < mee < 875 MeV=c2. We also search for D0 → h−hð0Þþeþe− (hð0Þ ¼ K, π) decays with the dielectron mass near the η and ϕ resonances, and away from these resonances for the KþK−eþe− and πþπ−eþe− modes. For these modes, we find no significant signals and set 90% confidence level upper limits on their branching fractions at the Oð10−7Þ level.