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Observation of $B^0_{(s)} \to J/\psi p \overline{p}$ decays and precision measurements of the $B^0_{(s)}$ masses

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Abstract

The first observation of the decays $B^0_{(s)} \to J/\psi p \overline{p}$ is reported, using proton-proton collision data corresponding to an integrated luminosity of $5.2{\text{ fb}}^{-1}$, collected with the LHCb detector. These decays are suppressed due to limited available phase space, as well as due to Okubo-Zweig-Iizuka or Cabibbo suppression. The measured branching fractions are \begin{align*} \mathcal{B}(B^0 \to J/\psi p \overline{p}) &= (4.51\pm 0.40\; \text{(stat)} \pm 0.44\; \text{(syst)}) \times 10^{-7}, \\ \mathcal{B}(B^0_s \to J/\psi p \overline{p}) &= (3.58\pm 0.19\; \text{(stat)} \pm 0.39\; \text{(syst)}) \times 10^{-6}. \end{align*} For the $B^0_s$ meson, the result is much higher than the expected value of $ {\cal O} (10^{-9})$. The small available phase space in these decays also allows for the most precise single measurement of both the $B^0$ mass as ${5279.74 \pm 0.30\; ({\rm stat})\pm 0.10\; ({\rm syst})}$ MeV, and the $B^0_s$ mass as ${5366.85 \pm 0.19\; ({\rm stat})\pm 0.13\; ({\rm syst})}$ MeV.

Figures and captions

Leading Feynman diagrams for (a) $ B ^0 \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} p \overline{ p }{} $ and (b) $ B ^0_ s \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} p \overline{ p }{} $ decays.

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Fit to the $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} p \overline{ p }{} $ invariant-mass distribution of the $ B ^0_{\scaleto{(}{6.6pt}s\scaleto{)}{6.6pt}}$ signal modes.

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The three angular variables $\{\theta_\ell,\theta_h,\chi\}$ for the decay $B\rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} (\rightarrow \mu ^+ \mu ^- ) h^+ h^-$, where $h\in \{p,K\}$. The dihadron (in red) and dilepton (in blue) coordinate systems lie back-to-back with a common vertical $\hat{y}$ axis. The angle between the decay planes is $\chi\in (-\pi,\pi]$, while the two helicity angles, $\theta_h$ and $\theta_\ell$, are defined in the dihadron and dilepton rest frames, respectively.

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Animated gif made out of all figures.

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Tables and captions

Signal yields and masses for $ B ^0$ and $ B ^0_ s $ mesons.

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Systematic uncertainties on the branching fraction measurements for Run 1 and Run 2. The total uncertainties on the branching fraction ratios (${\rm BFR}$) are the sum of the systematic uncertainties, added in quadrature. The total uncertainties on the absolute branching fractions ($\mathcal{B}$) include the normalization and the uncertainties on the ratio $f_s/f_d$ from external measurments as well.

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Systematic uncertainties of $ B ^0$ and $ B ^0_ s $ mass measurements.

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Supplementary Material [file]

Supplementary material full pdf

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This ZIP file contains supplemetary material for the publication LHCb-PAPER-2018-046. The files are: LHCb-PAPER-2018-046_supplementary.pdf : An overview of the extra figures *.pdf, *.png, *.eps : The figures in variuous formats to compile, just do ``pdflatex main``

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Created on 18 October 2019.