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Study of the rare $B_s^0$ and $B^0$ decays into the $\pi^+\pi^-\mu^+\mu^-$ final state

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Abstract

A search for the rare decays $B_s^0 \to \pi^+\pi^-\mu^+\mu^-$ and $B^0 \to \pi^+\pi^-\mu^+\mu^-$ is performed in a data set corresponding to an integrated luminosity of 3.0 fb$^{-1}$ collected by the LHCb detector in proton-proton collisions at centre-of-mass energies of 7 and 8 TeV. Decay candidates with pion pairs that have invariant mass in the range 0.5-1.3 GeV/$c^2$ and with muon pairs that do not originate from a resonance are considered. The first observation of the decay $B_s^0 \to \pi^+\pi^-\mu^+\mu^-$ and the first evidence of the decay $B^0 \to \pi^+\pi^-\mu^+\mu^-$ are obtained and the branching fractions, restricted to the dipion-mass range considered, are measured to be $\mathcal{B}(B_s^0 \to \pi^+\pi^-\mu^+\mu^-)=(8.6\pm 1.5\,({\rm stat}) \pm 0.7\,({\rm syst})\pm 0.7\,({\rm norm}))\times 10^{-8}$ and $\mathcal{B}(B^0 \to \pi^+\pi^-\mu^+\mu^-)=(2.11\pm 0.51\,({\rm stat}) \pm 0.15\,({\rm syst})\pm 0.16\,({\rm norm}) )\times 10^{-8}$, where the third uncertainty is due to the branching fraction of the decay $B^0\to J/\psi(\to \mu^+\mu^-)K^*(890)^0(\to K^+\pi^-)$, used as a normalisation.

Figures and captions

Mass distribution of $ { B ^0 \!\rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K^{*}(892)^0 }$ candidates with fit projections overlaid. The 2011 and 2012 data sets are combined.

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Mass distributions of (a) the $ { B_{(s)}^0 \!\rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \,\pi^+\pi^- }$ and (b) the $ { B_{(s)}^0 \!\rightarrow \pi^+\pi^-\mu^+\mu^- }$ \ decay candidates in the range 5.19--5.99 $ {\mathrm{\,GeV\!/}c^2}$ with fit projections overlaid. The 2011 and 2012 data sets are combined. In (b), the contribution from ${ B ^0_ s \!\rightarrow \phi \mu^+\mu^- }$ and ${ B ^+ \!\rightarrow K^+ \mu^+\mu^- }$ decays are included in the fit, but they are not visible in the projection, because the corresponding yields are small.

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Background-subtracted distributions of the $\pi^+\pi^-$ invariant mass for (a) $ { B ^0_ s \!\rightarrow \pi^+\pi^-\mu^+\mu^- }$ and (b) $ { B ^0 \!\rightarrow \pi^+\pi^-\mu^+\mu^- }$ candidates (triangular markers). The uncertainties are statistical only. The data are compared with the background-subtracted $\pi^+\pi^-$ mass distributions of (a) $ { B ^0_ s \!\rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \,\pi^+\pi^- }$ and (b) $ { B ^0 \!\rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \,\pi^+\pi^- }$ candidates (histograms).

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Animated gif made out of all figures.

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Tables and captions

Selection efficiencies of the 2011 and 2012 data sets; $\varepsilon_s$ for the $ { B ^0_ s \!\rightarrow \pi^+\pi^-\mu^+\mu^- }$ decay, $\varepsilon_d$ for the $ { B ^0 \!\rightarrow \pi^+\pi^-\mu^+\mu^- }$ decay, and $\varepsilon_n$ for the $ { B ^0 \!\rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K^{*}(892)^0 }$ decay.

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Summary of systematic uncertainties on $\mathcal{R}_{s}$ and $\mathcal{R}_{d}$ .

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Supplementary Material [file]

Supplementary material full pdf

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This ZIP file contains supplementary material for the publication LHCb-PAPER-2014-063. The files are: Supplementary.pdf: An overview of the extra figure *.pdf, *.png, *.eps, *.C: The figures in various formats. The *.C files contain the data on the figures.

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Created on 09 December 2018.Citation count from INSPIRE on 09 December 2018.