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Evidence for the decay $B^0 \to J/\psi \omega$ and measurement of the relative branching fractions of $B^0_s$ meson decays to $J/\psi \eta$ and $J/\psi \eta'$

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Abstract

First evidence of the $B^0\to J/\psi\omega$ decay is found and the $B_{s}^0\to J/\psi\eta$ and $B_{s}^0\to J/\psi\eta^{\prime}$ decays are studied using a dataset corresponding to an integrated luminosity of 1.0 $\mathrm{fb}^{-1}$ collected by the LHCb experiment in proton-proton collisions at a centre-of-mass energy of $\sqrt{s} = 7$ TeV. The branching fractions of these decays are measured relative to that of the $\mathrm{B}^0\to J/\psi\rho^0$ decay: $$\frac{Br(B^0\to J/\psi\omega)}{Br(B^0\to J/\psi\rho^0)} = 0.89 \pm0.19(stat)^{+0.07}_{-0.13}(syst)$$ $$\frac{Br(B^0_s\to J/\psi\eta)}{Br(B^0\to J/\psi\rho^0)} = 14.0 \pm 1.2(stat)^{+1.1}_{-1.5}(syst)^{+1.1}_{-1.0}(\frac{f_d}{f_s}),$$ $$\frac{Br(B^0_s\to J/\psi\eta^{\prime})}{Br(B^0\to J/\psi\rho^0)} = 12.7\pm1.1(stat)^{+0.5}_{-1.3}(syst)^{+1.0}_{-0.9}(\frac{f_d}{f_s}),$$ where the last uncertainty is due to the knowledge of $f_d/f_s$, the ratio of b-quark hadronization factors that accounts for the different production rate of $B^0$ and $B^0_s$ mesons. The ratio of the branching fractions of $B^0_s\to J/\psi\eta^{\prime}$ and $B^0_s\to J/\psi\eta$ decays is measured to be $$ \frac{Br(B^0_s\to J/\psi\eta^{\prime})}{Br(B^0_s\to J/\psi\eta)} = 0.90\pm0.09(stat)^{+0.06}_{-0.02}(syst).$$

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Examples of the dominant diagrams for the $\mathrm{B}^0_{\mathrm{(s)}}\rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \mathrm{X}^0$ decays (where $\mathrm{X}^0=\eta ,\,\eta ^{\prime},\,\omega $ or $\rho ^0$).

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Invariant mass distribution for selected $ B ^0 \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \omega $ candidates. The black dots correspond to the data distribution, the thick solid blue line is the total fit function, the blue dashed line shows the background contribution and the orange thin line is the signal component of the fit function.

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Background-subtracted (a) $\gamma {}\gamma $ and (b) $\pi ^+\pi ^- {}\pi ^0 $ invariant mass distributions for $ B ^0 \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \pi ^+\pi ^- \gamma\gamma$ decays. In both distributions the line is the result of the fit described in the text.

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Invariant mass distributions for selected $ B ^0_ s \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \eta ^{\left(\prime\right)}$ candidates: (a) $ B ^0_ s \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \eta \left(\eta \rightarrow \gamma {}\gamma \right)$, (b) $ B ^0_ s \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \eta \left(\eta \rightarrow \pi ^+\pi ^- {}\pi ^0 \right)$, (c) $ B ^0_ s \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \eta ^{\prime}\left(\eta ^{\prime}\rightarrow \rho ^0\gamma \right)$ and (d) $ B ^0_ s \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \eta ^{\prime}\left(\eta ^{\prime}\rightarrow \pi ^+\pi ^- {}\eta \right)$. In all distributions the black dots show the data. The thin solid orange lines show the signal $ B ^0_ s $ contributions and the orange dot-dashed lines correspond to the $ B ^0 $ contributions. The blue dashed lines show the combinatorial background contributions and the dotted blue lines show the partially reconstructed background components. The total fit functions are drawn as solid blue lines. The results of the fit are described in the text.

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Background-subtracted invariant mass distributions for (a) $\gamma {}\gamma $ from $ B ^0_ s \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \eta (\eta \rightarrow \gamma {}\gamma )$; (b) $\pi ^+\pi ^- {}\pi ^0 $ from $ B ^0_ s \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \eta (\eta \rightarrow \pi ^+\pi ^- {}\pi ^0 )$; (c) and (d) $\pi ^+\pi ^- \gamma $ and $\pi ^+\pi ^- $ from $ B ^0_ s \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \eta ^{\prime}(\eta ^{\prime}\rightarrow \rho ^0\gamma ,\,\rho \rightarrow \pi ^+\pi ^- )$; (e) and (f) $\eta \pi ^+\pi ^- $ and $\gamma {}\gamma $ from $ B ^0_ s \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \eta ^{\prime}(\eta ^{\prime}\rightarrow \eta \pi ^+\pi ^- )$. The purple line is the result of the fit described in the text.

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Invariant mass distribution for selected $\mathrm{B}^0_{\mathrm{(s)}}\rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \pi ^+\pi ^- $ candidates. The black dots show the data. The dot-dashed thin orange line shows the signal $ B ^0 $ contribution and the orange solid line shows the signal $ B ^0_ s $ contribution, a reflection from misidentified $ B ^0 \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} (\mathrm{K^*}\rightarrow \mathrm{K}\pi )$ is shown by a blue dotted line. The blue dashed line shows the background contribution. The total fit function is shown as a solid blue line.

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Background-subtracted $\pi ^+\pi ^-$ invariant mass distribution from $ B ^0 \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \pi ^+\pi ^- $ decays. The black dots show the data. A violet solid line denotes the total fit function, the solid orange line shows the $\rho ^0$ signal contribution and the blue dashed line shows the $\mathrm{f}_2(1270)$ contribution. The blue dot-dashed line shows the contribution from the $\mathrm{f}_0(500)$. The region $\pm40 \mathrm{MeV/c}^2$ around the $\mathrm{K}^0_{\mathrm{S}}$ mass is excluded from the fit.

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Animated gif made out of all figures.

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Tables and captions

Signal yields, $\mathcal{Y}_{ B ^0_ s }$, the fitted $ B ^0_ s $ mass, $\mathrm{m}_{ B ^0_ s }$ and mass resolutions, $\sigma_{ B ^0_ s }$ for the $ B ^0_ s \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} {}\eta ^{\left(\prime\right)}$ decays.

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Fitted yields of the $\rho ^0$ resonance, the relative yields of the $\mathrm{f}_2(1270)$ and $\mathrm{f}_0(500)$ components and probabilities, $\mathcal{P}$, of the fits to the uncorrected and efficiency-corrected $\pi ^+\pi ^-$ invariant mass distributions.

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Branching fractions of the intermediate resonances, total efficiencies (excluding the branching fractions of the intermediate resonances), $\varepsilon^{\mathrm{tot}}$, and the photon and $\pi ^0$ efficiency correction factors $\eta^{\mathrm{corr}}$ for various channels. For the $ B ^0 \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \rho ^0$ decay the total efficiency includes only the detector acceptance and trigger efficiencies, as the reconstruction and selection efficiency for this channel has been discussed in Sect. ???.

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Relative systematic uncertainties for ratios of the branching fractions ($\mathcal{R}$) for the $ B ^0_ s \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \eta ^{(\prime)}$ channels $\left[\%\right]$.

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Systematic uncertainties for ratios of the branching fractions ($\mathcal{R}$) relative to $ B ^0 \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \rho ^0$ $\left[\%\right]$.

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