Search for the Decay D0 → π+ π− μ+ μ−

A search for the D0 → π+ π− μ+ μ− decay, where the muon pair does not originate from a resonance, is performed using proton–proton collision data corresponding to an integrated luminosity of 1.0 fb^−1 recorded by the LHCb experiment at a centre-of-mass energy of 7 TeV. No signal is observed and an upper limit on the relative branching fraction with respect to the resonant decay mode D0 → π+ π− ϕ(→ μ+ μ−), under the assumption of a phase-space model, is found to be B(D0 → π+ π− μ+ μ−) / B(D0 → π+ π− ϕ(→ μ+ μ−))<0.96 at 90% confidence level. The upper limit on the absolute branching fraction is evaluated to be B(D0 → π+ π− μ+ μ−) < 5.5 x 10^−7 at 90% confidence level. This is the most stringent to date.