# Observation of $B^+_c \rightarrow J/\psi D_s^+$ and $B^+_c \rightarrow J/\psi D_s^{*+}$ decays

[to restricted-access page]

## Abstract

The decays $B^+_c \rightarrow J/\psi D_s^+$ and $B^+_c \rightarrow J/\psi D_s^{*+}$ are observed for the first time using a dataset, corresponding to an integrated luminosity of 3$fb^{-1}$, collected by the LHCb experiment in proton-proton collisions at centre-of-mass energies of $\sqrt{s}$=7 and 8 TeV. The statistical significance for both signals is in excess of 9 standard deviations. The following ratios of branching fractions are measured to be $BR(B^+_c \rightarrow J/\psi D_s^+)/BR(B^+_c \rightarrow J/\psi \pi+) = 2.90 \pm 0.57 \pm 0.24$, $BR(B^+_c \rightarrow J/\psi D_s^{*+}) / BR (B^+_c \rightarrow J/\psi D_s^+) = 2.37 \pm 0.56 \pm 0.10$, where the first uncertainties are statistical and the second systematic. The mass of the \Bc meson is measured to be $m_{B^+_c} = 6276.28 \pm 1.44 (stat) \pm 0.36(syst) MeV/c^2$, using the $B^+_c \rightarrow J/\psi D_s^+$ decay mode.

## Figures and captions

 Feynman diagrams for $B _ c ^+ {}\rightarrow {} { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} {} D ^+_ s$ decays: (a) spectator, (b) colour-suppressed spectator and (c) annihilation topology. Figure1.pdf [106 KiB] HiDef png [43 KiB] Thumbnail [22 KiB] *.C file Mass distributions for selected ${ J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ {} $D ^+_ s$ pairs. The solid curve represents the result of a fit to the model described in the text. The contribution from the $B _ c ^+ \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} D ^{\ast+}_{\mathrm{s}}$ decay is shown with thin green dotted and thin yellow dash-dotted lines for the $\mathcal{A}_{\pm\pm}$ and $\mathcal{A}_{00}$ amplitudes, respectively. The insert shows a zoom of the $B _ c ^+$ mass region. Figure2.pdf [159 KiB] HiDef png [319 KiB] Thumbnail [279 KiB] *.C file Mass distribution for selected $B _ c ^+ {}\rightarrow {} { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} {}\pi ^+$ candidates. The results of a fit to the model described in the text are superimposed (solid line) together with the background component (dotted line). Figure3.pdf [98 KiB] HiDef png [180 KiB] Thumbnail [168 KiB] *.C file Distributions of (a) $\chi^2_{\mathrm{fit}}( B _ c ^+ )$ and (b) $\chi^2_{\mathrm{IP}}( B _ c ^+ )$ for $B _ c ^+ {}\rightarrow {} { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} {}\pi ^+$ events: background subtracted data (red points with error bars), and simulation (blue histogram). Figure4.pdf [112 KiB] HiDef png [197 KiB] Thumbnail [168 KiB] *.C file Animated gif made out of all figures. PAPER-2013-010.gif Thumbnail

## Tables and captions

 Predictions for the ratios of $B _ c ^+$ meson branching fractions. In the case of $\mathcal{R}_{ D {}^{\ast+}_{\mathrm{s}} \mskip -6mu/ D ^+_ s }$ the second uncertainty is related to the unknown relative orbital momentum. Table_1.pdf [64 KiB] HiDef png [41 KiB] Thumbnail [20 KiB] tex code Signal parameters of the unbinned extended maximum likelihood fit to the ${ J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ {} $D ^+_ s$ mass distribution. Table_2.pdf [80 KiB] HiDef png [35 KiB] Thumbnail [17 KiB] tex code Relative systematic uncertainties for the ratio of branching fractions of $B _ c ^+ {}\rightarrow {} { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} {} D ^+_ s$ and $B _ c ^+ {}\rightarrow {} { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} {}\pi ^+$ . Table_3.pdf [63 KiB] HiDef png [80 KiB] Thumbnail [37 KiB] tex code

Created on 10 July 2020.