# Measurement of the lifetime of the $B_c^+$ meson using the $B_c^+ \rightarrow J/\psi\pi^+$ decay mode

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## Abstract

The difference in total widths between the $B_c^+$ and $B^+$ mesons is measured using 3.0fb$^{-1}$ of data collected by the LHCb experiment in 7 and 8 TeV centre-of-mass energy proton-proton collisions at the LHC. Through the study of the time evolution of $B_c^+ \rightarrow J/\psi \pi^+$ and $B^+\rightarrow J/\psi K^+$ decays, the width difference is measured to be $$\Delta\Gamma \equiv \Gamma_{B_c^+} - \Gamma_{B^+} = 4.46 \pm 0.14 \pm 0.07mm^{-1}c,$$ where the first uncertainty is statistical and the second systematic. The known lifetime of the $B^+$ meson is used to convert this to a precise measurement of the $B_c^+$ lifetime, $$\tau_{B_c^+} = 513.4 \pm 11.0 \pm 5.7fs,$$ where the first uncertainty is statistical and the second systematic.

## Figures and captions

 Invariant mass distributions for (a) selected $B _ c ^+ \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \pi ^+$ and (b) $B ^+ \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K ^+$ candidates. The fit result with the function described in the text is shown by the red solid line; the signal (background) components are shown with green (blue) dotted (dashed) lines. Fig_1.pdf [143 KiB] HiDef png [207 KiB] Thumbnail [52 KiB] *.C file tex code (a) Decay time distributions for selected $B _ c ^+ \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \pi ^+$ (red solid circles) and $B ^+ \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K ^+$ (blue open squares) decays, with the data points positioned within the $t$ bins according to Eq. (6) in Ref. [63]; (b) ratio of acceptance functions $\mathcal{R}_{\varepsilon}(ct)$. The uncertainties are due to sample size only. For visualization purposes the efficiency ratio is normalized as $\mathcal{R}_{\varepsilon}(0.5\rm \,mm /{\mathit{c}})=1$. Fig_2.pdf [131 KiB] HiDef png [130 KiB] Thumbnail [42 KiB] *.C file tex code Ratio of the efficiency-corrected decay time distributions (points with error bars). The curve shows the result of the fit with an exponential function. The data points are positioned within the $t$ bins according to Eq. (6) in Ref. [63]. Fig_3.pdf [51 KiB] HiDef png [119 KiB] Thumbnail [36 KiB] *.C file tex code Animated gif made out of all figures. PAPER-2014-060.gif Thumbnail

## Tables and captions

 Summary of systematic uncertainties for $\Delta\Gamma$. Table_1.pdf [62 KiB] HiDef png [73 KiB] Thumbnail [11 KiB] tex code

Created on 09 December 2018.Citation count from INSPIRE on 18 December 2018.