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Search for decays of neutral beauty mesons into four muons

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Abstract

A search for the non-resonant decays $B^0_s \rightarrow \mu^{+}\mu^{-}\mu^{+}\mu^{-}$ and $B^0 \rightarrow \mu^{+}\mu^{-}\mu^{+}\mu^{-}$ is presented. The measurement is performed using the full Run 1 data set collected in proton-proton collisions by the LHCb experiment at the LHC. The data correspond to integrated luminosities of $1$ and $2 \mathrm{fb}^{-1}$ collected at centre-of-mass energies of $7$ and $8 \mathrm{TeV}$, respectively. No signal is observed and upper limits on the branching fractions of the non-resonant decays at $95\%$ confidence level are determined to be \mathcal{B}(B^0_s \rightarrow \mu^{+}\mu^{-}\mu^{+}\mu^{-}) & < 2.5 \times 10^{-9} \mathcal{B}(B^0 \rightarrow \mu^{+}\mu^{-}\mu^{+}\mu^{-}) & < 6.9 \times 10^{-10}.

Figures and captions

Feynman diagrams for \subref{subfig:nonResoFMD} the non-resonant $ B ^0_{( s )} \!\rightarrow \mu ^+\mu ^- \mu ^+\mu ^- $ decay, \subref{subfig:NPFMD} a supersymmetric $ B ^0_{( s )} \!\rightarrow S (\rightarrow \mu ^+\mu ^- ) P (\rightarrow \mu ^+\mu ^- )$ decay and \subref{subfig:ResoFMD} the resonant $ B ^0_ s \!\rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} (\rightarrow \mu ^+\mu ^- )\phi (\rightarrow \mu ^+\mu ^- )$ decay (see text).

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Fit to the $ B ^+ \!\rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} (\rightarrow \mu ^+\mu ^- ) K ^+ $ invariant mass distribution. The signal contribution is modelled by a Hypatia2 [26] function (blue dotted line), the combinatorial background by an exponential function (green dash-dotted line). Partially reconstructed decays, such as $ B ^0 \!\rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K ^{*0} $ where one pion is not reconstructed, are modelled by a Gaussian function with an exponential tail towards the lower mass side (red dashed line). Data are shown by black dots.

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Mass distribution of selected $ B ^0_{( s )} \!\rightarrow \mu ^+\mu ^- \mu ^+\mu ^- $ events observed in 3 $\,fb^{-1}$ of data in all considered $ B $ mass regions. Background (red line) is modelled by an exponential function. Signal subregions for $ B ^0$ and $ B ^0_ s $ searches are also shown. The error bars on the individual points with $n$ entries are $\pm\sqrt{n}$.

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Expected and observed 95% CL exclusion in $\mathcal{B}$ ( $ B ^0 \!\rightarrow \mu ^+\mu ^- \mu ^+\mu ^- $ ) vs. $\mathcal{B}$ ( $ B ^0_ s \!\rightarrow \mu ^+\mu ^- \mu ^+\mu ^- $ ) parameters plane.

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Expected and observed 95% CL exclusion in $\mathcal{B}$ ( $ B ^0 \!\rightarrow S (\rightarrow \mu ^+\mu ^- ) P (\rightarrow \mu ^+\mu ^- )$ ) vs. $\mathcal{B}$ ( $ B ^0_ s \!\rightarrow S (\rightarrow \mu ^+\mu ^- ) P (\rightarrow \mu ^+\mu ^- )$ ) parameters plane with scalar and pseudoscalar S and P as described in Sec. 3.

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Animated gif made out of all figures.

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Tables and captions

Definitions of intervals in the $ B ^0$ and $ B ^0_ s $ reconstructed invariant mass distributions.

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Summary of systematic uncertainties affecting the single event sensitivities along with the total systematic uncertainty calculated by adding up the individual components in quadrature. The dominating uncertainty arising from $f_ u / f_ s $ only contributes to $\eta_s$. The uncertainty of the stated selection efficiencies arising from the limited number of simulated events is 0.5% for $ B ^0 \!\rightarrow \mu ^+\mu ^- \mu ^+\mu ^- $ and 0.4% for all other considered decay modes.

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Supplementary Material [file]

Supplementary material full pdf

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This ZIP file contains supplemetary material for the publication LHCB-PAPER-2016-043. The files are: Supplementary.pdf : An overview of the extra figures *.pdf : The figures in variuous formats

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