# Search for the rare decay $B^{+} \rightarrow \mu^{+}\mu^{-}\mu^{+}\nu_{\mu}$

[to restricted-access page]

## Abstract

A search for the rare leptonic decay $B^{+} \rightarrow {\mu}^{+}{\mu}^{-}{\mu}^{+}{\nu}_{{\mu}}$ is performed using proton-proton collision data corresponding to an integrated luminosity of $4.7$ fb$^{-1}$ collected by the LHCb experiment. The search is carried out in the region where the lowest of the two ${\mu}^{+}{\mu}^{-}$ mass combinations is below $980$MeV/c$^{2}$. The data are consistent with the background-only hypothesis and an upper limit of $1.6 \times 10^{-8}$ at 95% confidence level is set on the branching fraction in the stated kinematic region.

## Figures and captions

 Feynman diagrams of the contributions (top left) $B ^+ \rightarrow \mu ^+ \nu _\mu \gamma^{*}$ with $\gamma^{*}\rightarrow \mu ^+\mu ^-$, (top right) $B ^+ \rightarrow \mu ^+ \nu _\mu V$ and (bottom) bremsstrahlung to the $B ^+ \rightarrow \mu ^+ \mu ^- \mu ^+ \nu _\mu$ decay. Figure_1A.eps [168 KiB] HiDef png [160 KiB] Thumbnail [88 KiB] *.C file Figure_1B.eps [169 KiB] HiDef png [159 KiB] Thumbnail [89 KiB] *.C file Figure_1C.eps [152 KiB] HiDef png [218 KiB] Thumbnail [136 KiB] *.C file Fit to the mass distribution of the selected $B ^+ \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K ^+$ candidates. The combinatorial background (purple) and misidentified $B ^+ \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \pi ^+$ decays (orange) are stacked up while the $B ^+ \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K ^+$ signal is shown as a dashed line. The data points are shown as black points with the total fit overlaid as a red solid line. Figure_2.eps [34 KiB] HiDef png [248 KiB] Thumbnail [187 KiB] *.C file Template distributions for signal and misidentified background shapes for high and low fractional corrected mass uncertainty. A low uncertainty on the corrected mass corresponds to data with better mass resolution. The shape of the misidentification template is obtained from a control sample while the signal template is obtained from simulation. A systematic uncertainty on the signal shape due to the choice of the signal model is not shown, as it is too small to be visible. Figure_3.pdf [91 KiB] HiDef png [268 KiB] Thumbnail [186 KiB] *.C file Corrected mass distribution of the selected $B ^+ \rightarrow \mu ^+ \mu ^- \mu ^+ \nu _\mu$ candidates with the fit overlaid. Samples with low and high corrected mass uncertainty are fitted as individual samples but are merged in the figure. The fit has components for (green) combinatorial background, (blue) misidentified candidates and (orange) partially reconstructed candidates. The signal component is not visible as the fitted signal yield is negative. The best fit is the solid red line while the dashed line shows how the total would have looked like if the signal had the branching fraction predicted in Ref. [11]. Figure_4.pdf [22 KiB] HiDef png [309 KiB] Thumbnail [244 KiB] *.C file Animated gif made out of all figures. PAPER-2018-037.gif Thumbnail

## Tables and captions

 Summary of systematic uncertainties. Numbers are on the relative uncertainty of the normalisation for the branching fraction of the signal. Table_1.pdf [28 KiB] HiDef png [72 KiB] Thumbnail [33 KiB] tex code

Created on 02 November 2019.