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Study of $B_s^0 \to J/\psi \pi^+ \pi^- K^+ K^-$ decays

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Abstract

The decays $B^0_s \rightarrow J/\psi \pi^+\pi^- K^+ K^-$ are studied using a data set corresponding to an integrated luminosity of 9fb$^{-1}$, collected with the LHCb detector in proton-proton collisions at centre-of-mass energies of 7, 8 and 13TeV. The decays $B^0_s \rightarrow J/\psi K^{\ast0} \bar{K}^{\ast0}$ and $B^0_s \rightarrow \chi_{c1}(3872)K^+K^-$, where the $K^+K^-$ pair does not originate from a $\phi$ meson, are observed for the first time. Precise measurements of the ratios of branching fractions between intermediate $\chi_{c1}(3872)\phi$, $J/\psi K^{\ast0}\bar{K}^{\ast0}$, $\psi(2S)\phi$ and $\chi_{c1}(3872)K^+K^-$ states are reported. A structure, denoted as $X(4740)$, is observed in the $J/\psi\phi$ mass spectrum and, assuming a Breit-Wigner parameterisation, its mass and width are determined to be \begin{eqnarray*} m_{X(4740)} & = & 4741 \pm 6 \pm 6 {\mathrm{MeV}}/c^2 , \\ \Gamma_{X(4740)} & = & 53 \pm 15 \pm 11 {\mathrm{MeV}} , \end{eqnarray*} where the first uncertainty is statistical and the second is systematic. In addition, the most precise single measurement of the mass of the $B^0_s$ meson is performed and gives a value of $$ m_{B^0_s} = 5366.98 \pm 0.07 \pm 0.13 {\mathrm{MeV}}/c^2 . $$

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Distribution of the $ { J \mskip -3mu/\mskip -2mu\psi } \pi ^+ \pi ^- K ^+ K ^- $ mass of selected $ B ^0_ s $ candidates shown as points with error bars. A fit, described in the text, is overlaid.

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Distributions of the (top left) $ { J \mskip -3mu/\mskip -2mu\psi } \pi ^+ \pi ^- K ^+ K ^- $, (top right) $ K ^+ K ^- $ and (bottom left) $ { J \mskip -3mu/\mskip -2mu\psi } \pi ^+ \pi ^- $ mass of selected $ B ^0_ s \rightarrow \chi _{ c 1} (3872)\phi $ candidates shown as points with error bars. A fit, described in the text, is overlaid.

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Distributions of the (top left) $ { J \mskip -3mu/\mskip -2mu\psi } \pi ^+ \pi ^- K ^+ K ^- $, (top right) $ K ^+ K ^- $ and (bottom left) $ { J \mskip -3mu/\mskip -2mu\psi } \pi ^+ \pi ^- $ mass of selected $ B ^0_ s \rightarrow \psi {(2 S )} \phi $ candidates shown as points with error bars. A fit, described in the text, is overlaid.

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Distributions of the (left) $ { J \mskip -3mu/\mskip -2mu\psi } \pi ^+ \pi ^- K ^+ K ^- $ and (right) $ { J \mskip -3mu/\mskip -2mu\psi } \pi ^+ \pi ^- $ mass of selected $ B ^0_ s \rightarrow \chi _{ c 1} (3872) K ^+ K ^- $ candidates shown as points with error bars. A fit, described in the text, is overlaid.

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Background-subtracted and efficiency-corrected $ K ^+ K ^- $ mass distribution (points with error bars) of the $ B ^0_ s \rightarrow \chi _{ c 1} (3872) K ^+ K ^- $ decays. For a better visualisation, the highdash-mass region the plot is shown with a reduced vertical scale. A fit, described in the text, is overlaid. The expectation for phasedash-space simulated decays is shown as a green solid line. A distribution with extended vertical scale is shown inset.

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Distributions of the (top left) $ { J \mskip -3mu/\mskip -2mu\psi } \pi ^+ \pi ^- K ^+ K ^- $, (top right) $ K ^+ \pi ^- $ and (bottom left) $ K ^- \pi ^+ $ mass of selected $ B ^0_ s \rightarrow { J \mskip -3mu/\mskip -2mu\psi } K ^{*0} \overline{ K } {}^{*0} $ candidates shown as points with error bars. A fit, described in the text, is overlaid.

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Distribution of the $\psi {(2 S )} K ^+ K ^- $ mass for selected $ B ^0_ s \rightarrow { J \mskip -3mu/\mskip -2mu\psi } K ^+ K ^- \pi ^+ \pi ^- $ candidates, enriched in $ B ^0_ s \rightarrow \left(\psi {(2 S )} \rightarrow { J \mskip -3mu/\mskip -2mu\psi } \pi ^+ \pi ^- \right) \left( \phi \rightarrow K ^+ K ^- \right) $ decays (points with error bars). A fit, described in the text, is overlaid.

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Distribution of the (left) $ { J \mskip -3mu/\mskip -2mu\psi } \pi ^+ \pi ^- K ^+ K ^- $ and (right) $ K ^+ K ^- $ mass for selected $ B ^0_ s \rightarrow { J \mskip -3mu/\mskip -2mu\psi } \pi ^+ \pi ^- \phi $ candidates. A fit, described in the text, is overlaid.

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Background-subtracted (left) $ { J \mskip -3mu/\mskip -2mu\psi } \phi $ and (right) $\phi \pi ^+ \pi ^- $ mass distributions from $ B ^0_ s \rightarrow { J \mskip -3mu/\mskip -2mu\psi } \pi ^+ \pi ^- \phi $ decays (points with error bars). The expectation from simulated $ B ^0_ s \rightarrow { J \mskip -3mu/\mskip -2mu\psi } \pi ^+ \pi ^- \phi $ decays is overlaid (green solid line). In the right figure, the background-subtracted $\phi \pi ^+ \pi ^- $ mass distribution in the region $4.68<m_{ { J \mskip -3mu/\mskip -2mu\psi } \phi }<4.78\text{ Ge V /}c^2 $ is shown (red open circles with error bars) together with the corresponding expectation from simulated $ B ^0_ s \rightarrow { J \mskip -3mu/\mskip -2mu\psi } \pi ^+ \pi ^- \phi $ decays (blue dashed line).

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Background-subtracted $ { J \mskip -3mu/\mskip -2mu\psi } \phi $ mass distribution from $ B ^0_ s \rightarrow { J \mskip -3mu/\mskip -2mu\psi } \pi ^+ \pi ^- \phi $ decays (points with error bars). A fit, described in the text, is overlaid.

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Animated gif made out of all figures.

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Tables and captions

Signal yields, $N_{ B ^0_ s \rightarrow X _{ c \overline c }\phi }$, mass of the $ B ^0_ s $ meson, $m_{ B ^0_ s }$, and detector resolution scale factors, $s_{ B ^0_ s }$ and $s_{ X _{ c \overline c }}$, from the fit described in the text. The uncertainties are statistical only.

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Signal yield, $N_{ B ^0_ s \rightarrow { J \mskip -3mu/\mskip -2mu\psi } K ^{*0} \overline{ K } {}^{*0} }$, and mass of the $ B ^0_ s $ meson, $m_{ B ^0_ s }$, from the fit described in the text. The uncertainties are statistical only.

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Signal yield, $N_{ B ^0_ s }$ and mass of the $ B ^0_ s $ meson, $m_{ B ^0_ s }$, from the fit described in the text to the sample enriched in the $ B ^0_ s \rightarrow \psi {(2 S )} \phi $ decays. The uncertainties are statistical only.

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Signal yield $N_{ X (4740)}$, mass $m_{ X (4740)}$ and width $\Gamma_{ X (4740)}$ of the $ X (4740)$ structure, obtained from the fit to the backgrounddash-subtracted $ { J \mskip -3mu/\mskip -2mu\psi } \phi $ mass distribution. The uncertainties are statistical only.

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Relative systematic uncertainties (in %) for the ratios of branching fractions. The sources are described in the text.

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Systematic uncertainties on the $ B ^0_ s $ mass measurement using the sample enriched in the $ B ^0_ s \rightarrow \psi {(2 S )} \phi $ decays. The sources are described in the text.

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Systematic uncertainties for the measurements of the mass and width of the $ X (4740)$ structure. The sources are described in the text.

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Supplementary Material [file]

Supplementary material full pdf

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Created on 06 March 2021.