Search for Lepton Number Violating DecaysB+→π−μ+μ+andB+→K−μ+μ+

A search is performed for the lepton number violating decay $B^{+}\rightarrow h^- \mu^+ \mu^+$, where $h^-$ represents a $K^-$ or a $\pi^-$, using data from the LHCb detector corresponding to an integrated luminosity of $36pb^{-1}$. 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 $B(B^{+} \rightarrow K^- \mu^+ \mu^+) < 5.4\times 10^{-8}$ and $B(B^{+} \rightarrow \pi^- \mu^+ \mu^+) < 5.8\times 10^{-8}$ are set at the 95% confidence level. These improve the previous best limits by factors of 40 and 30, respectively.