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Measurement of the $B_c^-$ meson production fraction and asymmetry in 7 and 13 TeV $pp$ collisions

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Abstract

The production fraction of the $B_c^-$ meson with respect to the sum of $B^-$ and $\bar{B}^0$ mesons is measured in both 7 and 13 TeV center-of-mass energy $pp$ collisions produced by the Large Hadron Collider (LHC), using the LHCb detector. The rate, approximately 3.7 per mille, does not change with energy, but shows a transverse momentum dependence. The $B_c^- - B_c^+$ production asymmetry is also measured, and is consistent with zero within the determined statistical and systematic uncertainties of a few percent.

Figures and captions

Distributions of corrected mass $ m_{\mathrm{cor}} $ and $m( { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \mu^-)$ for (top) $7\text{ Te V} $ and (bottom) $13\text{ Te V} $ data, where (a) and (c) are data and (b) and (d) simulated signal. The (red) dashed line indicates the $m( { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \mu^-)>4.5\text{ Ge V} $ requirement.

mcorr-[..].pdf [25 KiB]
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mcorr-2011-data.pdf
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mcorr-2011-mc.pdf
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mcorr-2016-data.pdf
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mcorr-2016-mc.pdf

Fitted $ m_{\mathrm{cor}} $ distributions in (a) $7\text{ Te V} $ and (b) $13\text{ Te V} $ samples. The signal and the backgrounds are shown as the dark (orange) and lighter (gray) areas. The dashed (cyan) curves show the $ B _ c ^- \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \tau ^- \nu _\tau $ components, while the dotted (blue) curves show the $ B _ c ^- \rightarrow \chi_{c0,1,2}\mu ^- \overline{\nu} $ components. The $ B _ c ^- \rightarrow \psi {(2S)} \mu ^- \overline{\nu} $ contribution is also in the fit but is too small to be seen. The total fit is shown by the solid (red) curve.

CorrMa[..].pdf [25 KiB]
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CorrMass_PolScale_Bc2JpsiMuNu_BPT_AllBins_Data_2011.pdf
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CorrMass_PolScale_Bc2JpsiMuNu_BPT_AllBins_Data_2016.pdf

The total efficiency for $ B _ c ^- \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \mu ^- \overline{\nu} $, as a function of $ p_{\mathrm{T}} ( B _ c ^- )$ in different intervals of $\eta$ in (a) 7 TeV and (b) 13 TeV samples.

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Efficiency_Total_Bc2JpsiMuNu_MC2011_BPT.pdf
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Efficiency_Total_Bc2JpsiMuNu_MC2016_BPT.pdf

Invariant-mass distributions of (a) $K^-\pi^+$ and (b) $K^-\pi^+\pi^+$ for 7 $\text{ Te V}$ , and (c) and (d) for 13 $\text{ Te V}$ collisions. The data are shown by solid points. The (red) dashed lines represent the signal components. The combinatorial backgrounds are shown as the dotted (magenta) line, and the solid (blue) line shows the total fit.

b2D0Mu[..].pdf [32 KiB]
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b2D0MuX2011.pdf
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b2DpMuX2011.pdf
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b2D0MuX2016.pdf
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b2DpMuX2016.pdf

Total efficiencies for the (a) $ D ^0 X \mu^-\overline{\nu}$ and (b) $ D ^+ X \mu^-\overline{\nu}$ signals in 7 $\text{ Te V}$ and (c) and (d) in 13 $\text{ Te V}$ samples as functions of $ p_{\mathrm{T}}$ in $\eta$ intervals.

Effici[..].pdf [15 KiB]
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Efficiency_Total_b2D0MuX_MC2011_BPT.pdf
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Efficiency_Total_b2DpMuX_MC2011_BPT.pdf
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Efficiency_Total_b2D0MuX_MC2016_BPT.pdf
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Efficiency_Total_b2DpMuX_MC2016_BPT.pdf

The $k$-factor corrections as a function of invariant mass of (a) $m( { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \mu^-)$, (b) $m( D ^0 \mu^-)$, and (c) $m( D ^+ \mu^-)$ for the 13 $\text{ Te V}$ simulation samples. (The 7 $\text{ Te V}$ results are almost identical.) The points (magenta) are the average $k$-factor corrections, and the (green) dashed line shows a second-order polynomial fit to the average data.

kFacto[..].pdf [26 KiB]
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kFactor_Bc2JpsiMu_MC2016.pdf
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kFactor_b2D0XMu_MC2016.pdf
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kFactor_b2DpXMu_MC2016.pdf

Ratio of production fractions after the $k$-factor correction as a function of (a) $ p_{\mathrm{T}} (H_b)$ and (c) $\eta$ in 7 $\text{ Te V}$ data and (b) and (d) in 13 $\text{ Te V}$ data. The smaller error bars show the statistical uncertainties and the larger ones include the statistical and systematic uncertainties. The horizontal (green) dashed-lines show the average values.

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FINALRESULTS_BcFraction_1D_PT_Data2011_BPT.pdf
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FINALRESULTS_BcFraction_1D_PT_Data2016_BPT.pdf
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FINALRESULTS_BcFraction_1D_ETA_Data2011_BPT.pdf
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FINALRESULTS_BcFraction_1D_ETA_Data2016_BPT.pdf

Ratio of the $ B _ c ^- $ production fractions at 13 TeV to 7 TeV as a function of (a) $ p_{\mathrm{T}} (H_b)$ and (b) $\eta$. The smaller error bars show the statistical uncertainties and the larger ones include the statistical and systematic uncertainties added in quadrature.

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FINALRESULTS_BcFraction_1D_PT_Ratio_2011And2016_BPT.pdf
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FINALRESULTS_BcFraction_1D_ETA_Ratio_2011And2016_BPT.pdf

Animated gif made out of all figures.

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Tables and captions

Charm and charmonium branching fractions for the decay modes used in this analysis.

Table_1.pdf [70 KiB]
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Table_1.pdf

Branching fractions predictions (%). The $ B _ c ^- $ lifetime is taken as 0.507 ps \cite{PDG2018}. The value for the semileptonic decays of the $ B _ c ^-$ meson, ${\cal{B}}^c_{\rm sl}$, is derived by summing the $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \mu^-\overline{\nu}$ and $\eta_c\mu^-\overline{\nu}$ individual predictions with the average predictions of 0.1% for $\psi(2S)\mu^-\overline{\nu}$, the sum of $\chi_{c0,1,2}\mu^-\overline{\nu}$ as 0.6%, and 0.3% for $h_c\mu^-\nu$. In the one case where $\eta_c\mu^-\overline{\nu}$ was not predicted averages from other measurements are used.

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Table_2.pdf

Yields of $B\rightarrow DX\mu^-\overline{\nu}$ decays.

Table_3.pdf [52 KiB]
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Table_3.pdf

Results of the fits to Eq. 5

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Table_4.pdf

The $ B _ c ^- - B _ c ^+ $ production asymmetry ($\times10^{-2}$) as a function of $ p_{\mathrm{T}} (H_b)$ and $\eta$ at 7 TeV and 13 TeV.

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Table_5.pdf

Summary of the relative systematic uncertainties for $f_c/(f_u+f_d)$(%) and the absolute production asymmetries $a_{\rm prod}$(%). For local uncertainties, the ranges correspond to the minimum and maximum uncertainties evaluated in the $ p_{\mathrm{T}} (H_b)$ and $\eta$ ranges.

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Table_6.pdf

Created on 20 February 2021.