The Cabibbosuppressed semileptonic decay $B^{+}\to p\overline{p}\mu^{+}\nu_{\mu}$ is observed for the first time using a sample of $pp$ collisions corresponding to an integrated luminosity of 1.0, 2.0 and 1.7fb$^{1}$ at centreofmass energies of 7, 8 and 13TeV, respectively. The differential branching fraction is measured as a function of the $p\overline{p}$ invariant mass using the decay mode $B^{+}\to J/\psi K^{+}$ for normalisation. The total branching fraction is measured to be \begin{align*} \mathcal{B}(B^{+}\to p\overline{p}\mu^{+}\nu_{\mu}) = (5.27 ^{+0.23}_{0.24} \pm 0.21 \pm 0.15)\times 10^{6}, \end{align*} where the first uncertainty is statistical, the second systematic and the third is from the uncertainty on the branching fraction of the normalisation channel.
Result of training (a) the chargedisolation BDT and (b) the partreco BDT. The chosen selection on the classifier outputs are indicated by the dashed red line. For some candidates there are no additional tracks near the $B$decay vertex; these candidates are accepted and do not appear in the chargedisolation BDT output. The background samples shown here have the $\overline{ \Lambda} {}^_ c $ and $\overline{ D } {}^0 $ hadrons decaying via $\overline{ \Lambda} {}^_ c \rightarrow \overline p K ^+ \pi ^ $ and $\overline{ D } {}^0 \rightarrow \mu ^+ X$. The partreco BDT is trained on a mixture of background modes with only one shown here for illustration. 
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Distribution of $m( { J \mskip 3mu/\mskip 2mu\psi \mskip 2mu} K ^+ )$ with the fit result shown for the 2016 data set. 
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Distributions of $ m_{\mathrm{corr}}$ {} in each $ m( p \overline p )$ {} bin with the fit results shown. 
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Differential branching fraction as a function of the $ p \overline p $ {} invariant mass. The $\eta _ c \rightarrow p \overline p $, $ { J \mskip 3mu/\mskip 2mu\psi \mskip 2mu} \rightarrow p \overline p $ and $\psi {(2S)} \rightarrow p \overline p $ vetoes are indicated by the (left) red, (middle) blue and (right) pink bands, respectively. The red dashed line represents the prediction of the pQCD model normalised to the observed branching fraction [8]. 
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Animated gif made out of all figures. 
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Relative efficiencies for Run 1 and 2016 and the weighted combination of both. 
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Summary of the systematic uncertainties on the differential branching fractions. The contributions pertaining to the efficiency estimate are first, those for the yield extraction are below. The particle identification and tracking efficiency uncertainties are assumed to be 100% correlated between Run 1 and 2016. The total correlations of the uncertainties between the bins are shown in Table 4. 
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Number of observed $ B ^+ \rightarrow p \overline p \mu ^+ \nu _\mu $ {} candidates and differential branching fraction in each bin of $ m( p \overline p )$ {} . The uncertainties on the signal yields are statistical only. For the differential branching fractions the first uncertainties are statistical, the second systematic and the third from the uncertainties on the branching fractions of the normalisation channel. 
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Correlations in the uncertainties between bins of $ m( p \overline p )$ {} . 
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Covariance matrix for bins of $ m( p \overline p )$ {} . 
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Supplementary material full pdf 
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This ZIP file contains supplemetary material for the publication LHCbPAPER2019034. The files are: supplementary.tex : The latex source of the supplementary material supplementary.pdf : An overview of the extra figures *.pdf, *.C, *.png, *.eps : The figures in variuous formats 
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Created on 27 February 2021.