# Search for the lepton number violating decays $B^{+}\rightarrow \pi^- \mu^+ \mu^+$ and $B^{+}\rightarrow K^- \mu^+ \mu^+$

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## Abstract

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.

## Figures and captions

 s-channel diagram for $B ^+ \!\rightarrow K ^- \mu ^+ \mu ^+$ ( $B ^+ \!\rightarrow \pi ^- \mu ^+ \mu ^+$ ) where the decay is mediated by an on-shell Majorana neutrino. figure1.pdf [8 KiB] HiDef png [59 KiB] Thumbnail [13 KiB] *.C file Invariant mass distribution of $K ^+ \mu ^+ \mu ^-$ events after the application of the selection criteria. In (a) requiring the muon pair to be compatible with coming from a ${ J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ decay and in (b) excluding invariant mass windows around the ${ J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ and $\psi {(2S)}$ for the muon pair. The curve is the fit to data as described in the text. figure2.pdf [20 KiB] HiDef png [236 KiB] Thumbnail [74 KiB] *.C file Relative efficiency between the $B ^+ \!\rightarrow K ^- \mu ^+ \mu ^+$ signal and the $B ^+ \!\rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K ^+$ normalisation channel. The plot has been symmetrised over the diagonal. figure3.pdf [127 KiB] HiDef png [715 KiB] Thumbnail [131 KiB] *.C file The 95 % CL branching fraction limits for $B ^+ \!\rightarrow K ^- \mu ^+ \mu ^+$ (light-coloured line) and $B ^+ \!\rightarrow \pi ^- \mu ^+ \mu ^+$ (dark-coloured line) as a function of the Majorana neutrino mass $m_\nu=m_{h\mu}$. figure4.pdf [13 KiB] HiDef png [71 KiB] Thumbnail [31 KiB] *.C file Animated gif made out of all figures. PAPER-2011-009.gif Thumbnail

## Tables and captions

 Sources of systematic error and their fractional uncertainty on the relative efficiency. Table_1.pdf [47 KiB] HiDef png [91 KiB] Thumbnail [15 KiB] tex code

Created on 20 April 2019.Citation count from INSPIRE on 20 April 2019.