Search for the lepton number violating decays $B^{+}\to \pi^- \mu^+   \mu^+$ and $B^{+}\to K^- \mu^+ \mu^+$
  A search is performed for the lepton number violating decay $B^{+}\to h^- \mu^+ \mu^+$, 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 $B(B^{+} \to K^- \mu^+ \mu^+) < 5.4\times 10^{-8}$ and $B(B^{+} \to \pi^- \mu^+ \mu^+) < 5.8\times 10^{-8}$ are set at the 95% confidence level. These improve the previous best limits by factors of 40 and 30, respectively. 
The LHCb Collaboration: R. Aaij, C. Abellan Beteta, B. Adeva, M.   Adinolfi, C. Adrover, A. Affolder, Z. Ajaltouni, J. Albre...
hep-ex