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Search for the rare decay $B^0 \to J/\psi\phi$

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Abstract

A search for the rare decay $B^0 \rightarrow J/\psi \phi$ is performed using $pp$ collision data collected with the LHCb detector at centre-of-mass energies of 7, 8 and 13 {Te V}, corresponding to an integrated luminosity of 9 ${\rm fb}^{-1}$. No significant signal of the decay is observed and an upper limit of $1.1 \times 10^{-7}$ at 90% confidence level is set on the branching fraction.

Figures and captions

Feynman diagrams for the decay $ B ^0 \rightarrow { J \mskip -3mu/\mskip -2mu\psi } \phi$ via (a) $\omega-\phi$ mixing and (b) tri-gluon fusion.

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Distributions of the invariant mass $m( K ^+ K ^- )$ in different $m( { J \mskip -3mu/\mskip -2mu\psi } K ^+ K ^- )$ intervals with boundaries at 5220, 5265, 5295, 5330, 5400 and 5550 $\text{ Me V /}c^2$ . They are obtained using simulated $ B ^0_ s \rightarrow { J \mskip -3mu/\mskip -2mu\psi } \phi$ decays and normalised to unity.

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The distributions of $m( { J \mskip -3mu/\mskip -2mu\psi } K ^+ K ^- )$, superimposed by the fit results, for (left) Run 1 and (right) Run 2 data samples, respectively. The top row shows the full $ B ^0_ s $ signals in logarithmic scale while the bottom row is presented in a reduced vertical range to make the $ B ^0 $ peaks visible. The violet (red) solid lines represent the $B^{0}_{(s)}\rightarrow { J \mskip -3mu/\mskip -2mu\psi } K ^+ K ^- $ decays, the orange dotted lines show the $\Lambda ^0_ b $ background and the green dotted lines show the combinatorial background.

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Distribution of $m( K ^+ K ^- )$ in a $\Lambda ^0_ b \rightarrow { J \mskip -3mu/\mskip -2mu\psi } {p} K ^- $ simulation sample superimposed with a fit to a polynomial function.

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$m( K ^+ K ^- )$ distributions of the enhanced combinatorial background in the (left) Run 1 and (right) Run 2 data samples. The $ B ^0_ s \rightarrow { J \mskip -3mu/\mskip -2mu\psi } \phi$ and $\Lambda ^0_ b \rightarrow { J \mskip -3mu/\mskip -2mu\psi } {p} K ^- $ backgrounds are subtracted by injecting simulated events with negative weights.

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Distributions in the (top) $ B ^0_ s $ and (bottom) $ B ^0$ $m( K ^+ K ^- )$ regions, superimposed by the fit results. The left and right columns are shown using the Run 1 and Run 2 data samples, respectively. The violet (red) solid lines are $B^{0}_{(s)}\rightarrow { J \mskip -3mu/\mskip -2mu\psi } \phi$ decays, violet (red) dashed lines are non-$\phi$ $B_{(s)}^{0}\rightarrow { J \mskip -3mu/\mskip -2mu\psi } K ^+ K ^- $ signal, green dotted lines are the combinatorial background component and the orange dotted lines are the $\Lambda ^0_ b $ background component.

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Smeared profile likelihood ratio curve shown as the blue solid line, and the 90% confidence interval indicated by the red area.

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Animated gif made out of all figures.

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Tables and captions

Measured yields of all contributions from the fit to $ { J \mskip -3mu/\mskip -2mu\psi } K ^+ K ^- $ mass distribution, showing the results for the full mass range and for the $ B ^0_ s $ and $ B ^0$ regions.

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Systematic uncertainties on $\mathcal{B}( B ^0 \rightarrow { J \mskip -3mu/\mskip -2mu\psi } \phi)$ for multiplicative and additive sources.

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Supplementary Material [file]

Supplementary material full pdf

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Created on 27 February 2021.