A search for the decay $B^0\to\phi\mu^+\mu^-$ is performed using proton-proton collisions at centre-of-mass energies of 7, 8, and 13 TeV collected by the LHCb experiment and corresponding to an integrated luminosity of 9 fb$^{-1}$. No evidence for the $B^0\to \phi \mu^+ \mu^-$ decay is found and an upper limit on the branching fraction, excluding the $\phi$ and charmonium regions in the dimuon spectrum, of $4.4 \times 10^{-3}$ at a 90$\%$ credibility level, relative to that of the $B^0_s \to \phi \mu^+ \mu^-$ decay, is established. Using the measured $B^0_s\to\phi\mu^+\mu^-$ branching fraction and assuming a phase-space model, the absolute branching fraction of the decay $B^0\to \phi \mu^+ \mu^-$ in the full $q^2$ range is determined to be less than $3.2 \times 10^{-9}$ at a 90$\%$ credibility level.
Standard Model Feynman diagrams for the decay $ B ^0 \rightarrow \phi\mu^+\mu^-$. (a), (b), (c) represent the weak annihilation contributions, while (d) represents the contribution from $\omega-\phi$ mixing. |
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The $ K ^+ K ^- \mu^+\mu^-$ mass distributions of selected $B_s^0 \rightarrow J/\psi\phi$ candidates in (left) Run 1 and (right) Run 2 data, with the fit projections overlaid. The red solid line is $ B ^0_ s \rightarrow { J \mskip -3mu/\mskip -2mu\psi } \phi$ signal, the red dashed line is $ B ^0 \rightarrow { J \mskip -3mu/\mskip -2mu\psi } K ^+ K ^- $ signal, the green dashed line is the partially reconstructed background component, the violet dotted line is the combinatorial background component, and the blue dash-dot line is the $\Lambda ^0_ b \rightarrow { J \mskip -3mu/\mskip -2mu\psi } {p}K^-$ background component. |
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The $ K ^+ K ^- \mu^+\mu^-$ mass distributions of selected nonresonant $ B _{( s )}^0 \rightarrow \phi\mu^+\mu^-$ candidates in (left) Run 1 and (right) Run 2 data. The red solid line is $ B ^0_ s \rightarrow \phi\mu^+\mu^-$ signal, the red dashed line is $ B ^0 \rightarrow \phi\mu^+\mu^-$ signal, the green dashed line is the partially reconstructed background component, the violet dotted line is the combinatorial background component, the blue dash-dot line is the $\Lambda ^0_ b \rightarrow pK^-\mu^+\mu^-$ background component, the violet dash-dot line is the $B^0\rightarrow K^{*0}(\rightarrow K^+\pi^-)\mu^+\mu^-$ background component, and the orange dash-dot line is the $ B ^0_ s \rightarrow D_s^-(\rightarrow \phi\mu^-\bar{\nu})\mu^+\nu$ background component. |
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Smeared profile likelihood ratio curve from the simultaneous fit to the Run 1 and Run 2 data samples. The red shaded area indicates the $90\%$ crediblity interval of $\mathcal{R}$. |
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Animated gif made out of all figures. |
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Efficiencies of background decay processes relative to that of the decay $B_s^0 \rightarrow \phi \mu^+ \mu^-$ evaluated using simulated samples. The uncertainties are due to limited sizes of these samples. |
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Systematic uncertainties on the measurement of $\mathcal{R}$ for additive and multiplicative sources. |
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Created on 27 April 2024.