The branching fraction of the rare $B^0_s\rightarrow\phi\mu^+\mu^-$ decay is measured using data collected by the LHCb experiment at center-of-mass energies of $7$, $8$ and $13 \rm{TeV}$, corresponding to integrated luminosities of $1$, $2$ and $6 {\rm fb}^{-1}$, respectively. The branching fraction is reported in intervals of $q^2$, the square of the dimuon invariant mass. In the $q^2$ region between $1.1$ and $6.0 {\rm Ge V}^2 /c^4$, the measurement is found to lie $3.6$ standard deviations below a Standard Model prediction based on a combination of Light Cone Sum Rule and Lattice QCD calculations. In addition, the first observation of the rare $B^0_s\rightarrow f_2^\prime(1525)\mu^+\mu^-$ decay is reported with a statistical significance of nine standard deviations and its branching fraction is determined.
Reconstructed invariant mass of the $ K ^+ K ^- \mu ^+ \mu ^- $ system for (left) the $ B ^0_ s \rightarrow { J \mskip -3mu/\mskip -2mu\psi } \phi $ normalization mode and (right) the $ B ^0_ s \rightarrow \phi\mu ^+\mu ^- $ signal candidates, integrated over $ q^2$ and overlaid with the fit projections. |
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Differential branching fraction ${\rm d}{\mathcal B}( B ^0_ s \rightarrow \phi\mu ^+\mu ^- )/{\rm d}q^2$, overlaid with SM predictions using Light Cone Sum Rules [34,36,39] at low $ q^2$ and Lattice calculations [37,38] at high $ q^2$ . The results from the LHCb 3 $\text{ fb} ^{-1}$ analysis [1,31] are shown with gray markers. |
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Reconstructed invariant mass of (left) the $ K ^+ K ^- \mu ^+ \mu ^- $ system and (right) the $ K ^+ K ^- $ system for $ B ^0_ s \rightarrow f_2^\prime\mu ^+\mu ^- $ candidates, overlaid with the fit projections. The $m( K ^+ K ^- )$ distribution is shown in the $ B ^0_ s $ signal region $\pm 50\text{ Me V /}c^2 $ around the known $ B ^0_ s $ mass. |
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Invariant mass of the $ K ^+ K ^- \mu ^+ \mu ^- $ system versus $ q^2$ for selected (top) $ B ^0_ s \rightarrow \phi\mu ^+\mu ^- $ and (bottom) $ B ^0_ s \rightarrow f_2^\prime\mu ^+\mu ^- $ candidates across all data-taking periods. |
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Reconstructed invariant mass of the $ K ^+ K ^- \mu ^+\mu ^- $ system for (left) $ B ^0_ s \rightarrow { J \mskip -3mu/\mskip -2mu\psi } \phi $ and (right) $ B ^0_ s \rightarrow \phi\mu ^+\mu ^- $ candidates, integrated over $ q^2$ , for the (top) 2011--2012, (middle) 2015--2016, and (bottom) 2017--2018 data-taking periods. The data are overlaid with the fit projections. |
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Reconstructed invariant mass of (left) the $ K ^+ K ^- \mu ^+ \mu ^- $ system and (right) the $ K ^+ K ^- $ system for $ B ^0_ s \rightarrow f_2^\prime\mu ^+\mu ^- $ candidates for the (top) 2011--2012, (middle) 2015--2016, and (bottom) 2017--2018 data-taking periods. Distributions are overlaid with the fit projections. The $ K ^+ K ^- $ distribution is shown in the $ B ^0_ s $ signal region $\pm50\text{ Me V} $ around the known $ B ^0_ s $ mass. |
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Animated gif made out of all figures. |
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Differential ${\rm d}{\mathcal B}( B ^0_ s \rightarrow \phi\mu ^+\mu ^- )/{\rm d} q^2 $ branching fraction, both relative to the normalization mode and absolute, in intervals of $ q^2$ . The uncertainties are, in order, statistical, systematic, and due to the uncertainty on the branching fraction of the normalization mode. |
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Systematic uncertainties on the differential branching fraction ${\rm d}{\mathcal B}( B ^0_ s \rightarrow \phi\mu ^+\mu ^- )/{\rm d}q^2$ and on the total branching fraction ${\mathcal B}( B ^0_ s \rightarrow f_2^\prime\mu ^+\mu ^- )$. Ranges indicate the variation across the $ q^2$ intervals. The uncertainty from the branching fraction of the normalization mode, ${\mathcal B}( B ^0_ s \rightarrow { J \mskip -3mu/\mskip -2mu\psi } \phi) $, is quoted separately. |
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Created on 27 April 2024.