Search for lepton number violating decays B +→π -μ +μ + and B +→K -μ +μ +

A search is performed for the lepton number violating decay B +→h -μ +μ +, where h - represents a K - or a π -, using an integrated luminosity of 36pb -1 of data collected with the LHCb detector. The decay is forbidden in the standard model but allowed in models with a Majorana neutrino. No signal is observed in either channel and limits of B(B +→K -μ +μ +)<5. 4×10 -8 and B(B +→π -μ +μ +)<5.8×10 -8 are set at the 95% confidence level. These improve the previous best limits by factors of 40 and 30, respectively.