# Observation of the suppressed decay $\Lambda^{0}_{b}\rightarrow p\pi^{-}\mu^{+}\mu^{-}$

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## Abstract

The suppressed decay $\Lambda^{0}_{b}\rightarrow p\pi^{-}\mu^{+}\mu^{-}$, excluding the $J/\psi$ and $\psi(2S)\rightarrow \mu^{+}\mu^{-}$ resonances, is observed for the first time with a significance of 5.5 standard deviations. The analysis is performed with proton-proton collision data corresponding to an integrated luminosity of $3\mathrm{fb}^{-1}$ collected with the LHCb experiment. The $\Lambda^{0}_{b}\rightarrow p\pi^{-}\mu^{+}\mu^{-}$ branching fraction is measured relative to the $\Lambda^{0}_{b}\rightarrow J/\psi(\rightarrow \mu^{+}\mu^{-})p\pi^{-}$ branching fraction giving \begin{align} \nonumber \frac{\mathcal{B}(\Lambda^{0}_{b}\rightarrow p\pi^{-}\mu^{+}\mu^{-})}{\mathcal{B}({\Lambda^{0}_{b}\rightarrow J/\psi(\rightarrow \mu^{+}\mu^{-})p\pi^{-}})} &= 0.044\pm0.012\pm0.007, \end{align} where the first uncertainty is statistical and the second is systematic. This is the first observation of a $b\rightarrow d$ transition in a baryonic decay.

## Figures and captions

 One of the lowest-order diagrams for the decay $\Lambda ^0_ b \rightarrow p \pi ^- \mu ^+\mu ^-$ . Fig1.pdf [9 KiB] HiDef png [106 KiB] Thumbnail [49 KiB] *.C file Mass distribution of $\Lambda ^0_ b \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} p \pi ^-$ candidates compared to the result of the fit. The fit parameterisation is described in the text. Fig2.pdf [164 KiB] HiDef png [289 KiB] Thumbnail [229 KiB] *.C file Mass distribution of $\Lambda ^0_ b \rightarrow p \pi ^- \mu ^+\mu ^-$ candidates compared to the result of the fit. The fit parameterisation is described in the text. Fig3.pdf [18 KiB] HiDef png [282 KiB] Thumbnail [202 KiB] *.C file Animated gif made out of all figures. PAPER-2016-049.gif Thumbnail

## Tables and captions

 Summary of the systematic uncertainties on the $\Lambda ^0_ b \rightarrow p \pi ^- \mu ^+\mu ^-$ branching fraction. Table_1.pdf [58 KiB] HiDef png [99 KiB] Thumbnail [47 KiB] tex code

## Supplementary Material [file]

 This ZIP file contains supplementary material for the publication LHCb-PAPER-2016-049. The files are: Fig1-S.pdf Fig2-S.pdf Fig1-S.pdf [14 KiB] HiDef png [108 KiB] Thumbnail [92 KiB] *C file Fig2-S.pdf [14 KiB] HiDef png [115 KiB] Thumbnail [101 KiB] *C file

Created on 21 October 2019.