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Measurement of the ratio of $B_c^+$ branching fractions to $J/\psi\pi^+$ and $J/\psi\mu^+\nu_\mu$ final states

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Abstract

The first measurement that relates semileptonic and hadronic decay rates of the $B_c^+$ meson is performed using proton-proton collision data corresponding to 1.0 fb$^{-1}$ of integrated luminosity collected with the LHCb detector. The measured value of the ratio of branching fractions, ${\cal B}(B_c^+ \to J/\psi \pi^+)/{\cal B}(B_c^+\to J/\psi\mu^+\nu_\mu)=0.0469 \pm 0.0028 (stat.) \pm 0.0046 (syst.)$, is at the lower end of available theoretical predictions.

Figures and captions

Invariant-mass distribution of $B_c^+\rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \pi^+$ candidates (black data points). The maximum likelihood fit of the $B_c^+$ signal is superimposed (blue solid line). Individual fit components are also shown: (dashed blue line) the signal, (red long-dashed line) the background and (green dotted line) $B_c^+\rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K^+$ feeddown.

JpsiPi[..].pdf [18 KiB]
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JpsiPiMassFit.pdf

Distribution of $m_{ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \mu}$ for $B_c^+\rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \mu^+\nu_\mu$ candidates selected in simulated event samples of (blue filled points) the signal, (green filled points) the $B_c^+$ feeddown and (red filled squares) the $B_{u,d,s}$ backgrounds. Relative normalization is derived from the fit to the data described later in the text. The part of the spectrum included in the fit is indicated with a vertical dashed black line. The $B_c^+$ feeddown distribution is also shown after magnifying its normalization by a factor of ten (green dashed histogram).

JpsiMu_MC.pdf [21 KiB]
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JpsiMu_MC.pdf

Invariant-mass distribution of $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \mu^+$ pairs from $B_c^+\rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \mu^+\nu_\mu$ candidates (black data points) for (top left) the data, (bottom left) $B_c^+\rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \mu^+\nu_\mu$ signal simulation, (top right) $B_{u,d,s}\rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} X$ background simulation and (bottom right) $B_c^+$ feeddown simulation. The unbinned maximum likelihood fit of the $B_c^+$ signal is superimposed (blue solid line). Individual fit components are also shown: (blue short-dashed line) the signal, (red long-dashed line) the background and (green dotted line) $B_c^+$ feeddown.

JpsiMu[..].pdf [20 KiB]
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JpsiMu_Data.pdf
JpsiMu[..].pdf [18 KiB]
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JpsiMu_BkgMC.pdf
JpsiMu[..].pdf [16 KiB]
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JpsiMu_SignalMC.pdf
JpsiMu[..].pdf [15 KiB]
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JpsiMu_FeedDown.pdf

The measured value of ${\cal R}$ (horizontal solid line) and its $\pm1\sigma$ uncertainty band (dashed lines) compared to the predictions (diamonds). A nonrelativistic reduction of the Bethe-Salpeter equation is used in the predictions of Chang {\slshape et al.\/} [17], El-Hady \eta [20], and Colangelo \eta [21], while the latter also utilizes heavy quark symmetry. A light-front constituent quark model is used by Anisimov \eta [18] and Ke \eta [25]. QCD sum rules are used by Kiselev \eta [22], a relativistic quasipotential Schr\"odinger model is used by Ebert \eta [23], and a relativistic constituent quark model in used by Ivanov \eta [24].

Theory[..].pdf [14 KiB]
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TheoryCompPlot.pdf

Animated gif made out of all figures.

PAPER-2014-025.gif
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Tables and captions

Values of the parameters affecting the estimate of the feeddown fraction in the fit to the $m_{ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \mu}$ distribution. For $B_c^+\rightarrow \chi_{cJ}\mu^+\nu_\mu$, $\sum_{J=0,1,2} R_{{\it f\,J}} \, {\cal B}_{\rm casc\,{\it f\,J}}$ is listed.

Table_1.pdf [54 KiB]
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Table_1.pdf

Summary of systematic uncertainties. The total systematic errors are obtained by adding in quadrature the individual contributions.

Table_2.pdf [54 KiB]
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Table_2.pdf

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