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 36  pb−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.