Search for D0 meson decays to π+π−e+e− and K+K−e+e− final states

A search for D0 meson decays to the πþπ−eþe− and KþK−eþe− final states is reported using a sample of proton-proton collisions collected by the LHCb experiment at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 6 fb−1. The decay D0 → πþπ−eþe− is observed for the first time when requiring that the two electrons are consistent with coming from the decay of a ϕ or ρ0=ω meson. The corresponding branching fractions are measured relative to the D0 → K−π−½eþe−ρ0=ω decay, where the two electrons are consistent with coming from the decay of a ρ0 or ω meson. No evidence is found for the D0 → KþK−eþe− decay and world-best limits are set on its branching fraction. The results are compared to, and found to be consistent with, the branching fractions of the D0 → πþπ−μþμ− and D0 → KþK−μþμ− decays recently measured by LHCb and confirm lepton universality at the current precision.