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Precision measurement of the $B_{c}^{+}$ meson mass

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Abstract

A precision measurement of the $B_{c}^{+}$ meson mass is performed using proton-proton collision data collected with the LHCb experiment at centre-of-mass energies of $7, 8$ and $13$ TeV, corresponding to a total integrated luminosity of $9.0 {\rm fb}^{-1}$. The $B_{c}^{+}$ mesons are reconstructed via the decays $B_{c}^{+} \rightarrow J\mskip -3mu/\mskip -2mu\psi\mskip 2mu \pi^+$, $B_{c}^{+} \rightarrow J\mskip -3mu/\mskip -2mu\psi\mskip 2mu \pi^+ \pi^- \pi^+$, $B_{c}^{+} \rightarrow J\mskip -3mu/\mskip -2mu\psi\mskip 2mu p \bar{p} \pi^+$, $B_{c}^{+} \rightarrow J\mskip -3mu/\mskip -2mu\psi\mskip 2mu D_{s}^{+}$, $B_{c}^{+} \rightarrow J\mskip -3mu/\mskip -2mu\psi\mskip 2mu D^{0} K^{+}$ and $B_{c}^{+} \rightarrow B_{s}^{0} \pi^{+}$. Combining the results of the individual decay channels, the $B_{c}^{+}$ mass is measured to be $6274.47 \pm 0.27 ({\rm stat}) \pm 0.17 ({\rm syst}) \mathrm{ Me V}/c^{2}$. This is the most precise measurement of the $B_{c}^{+}$ mass to date. The difference between the $B_{c}^{+}$ and $B_{s}^{0}$ meson masses is measured to be $907.75 \pm 0.37 ({\rm stat}) \pm 0.27 ({\rm syst}) \mathrm{ Me V}/c^{2}$.

Figures and captions

Distributions of invariant-mass $m$ for $B_{c}^{+}$ candidates selected in the studied decay channels, where data are shown as the points with error bars; the total fits are shown as solid blue curves; the signal component are red dotted curves; the background components purple dotted curves.

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Distributions of mass difference $\Delta m$ for the $B_{c}^{+} \rightarrow B_{s}^{0} (D_{s}^{-} \pi^{+}) \pi^{+}$ and $B_{c}^{+} \rightarrow B_{s}^{0} (J\mskip -3mu/\mskip -2mu\psi\mskip 2mu \phi) \pi^{+}$ decay modes, where data are shown as the points with error bars; the total fits are shown as solid blue curves; the signal component are red dotted curves; the background components purple dotted curves.

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Individual $B_{c}^{+}$ mass measurements and their combination. The red (inner) cross-bars show the statistical uncertainties, and the blue (outer) cross-bars show the total uncertainties.

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Individual mass difference measurements and their combination. The red (inner) cross-bars show the statistical uncertainties, and the blue (outer) cross-bars show the total uncertainties on the measurement.

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Tables and captions

Signal yields, mass values and mass resolutions as obtained from fits shown in Fig. 1, together with the mass corrected for the effects of final-state radiation and selection as described in the text. The uncertainties are statistical only.

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Signal yields, mass difference $(\Delta M)$ and resolution as obtained from fits shown in Fig. 2, together with the values corrected for the effects of final-state radiation and selection as described in the text. The uncertainties are statistical only.

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Summary of systematic uncertainties (in $\mathrm{ Me V}/c^{2}$) on the $B_{c}^{+}$ mass.

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Summary of systematic uncertainties on the mass difference $\Delta M$ (in $\mathrm{ Me V}/c^{2}$) for the $B_{s}^{0} (D_s^- \pi^+) \pi^+$ and $B_{s}^{0} (J\mskip -3mu/\mskip -2mu\psi\mskip 2mu \phi) \pi^{+}$ decays.

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Breakdown of systematic uncertainties (in $\mathrm{ Me V}/c^{2}$) in the combination of the $B_{c}^{+}$ mass and the mass difference $\Delta M$. The total uncertainty is the sum in quadrature of the uncertainty of different sources.

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Weights of the decay modes in the combination of the $B_{c}^{+}$ mass and the mass difference $\Delta M$.

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Created on 05 March 2021.