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Measurement of the $b$-quark production cross-section in 7 and 13 TeV $pp$ collisions

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Abstract

Measurements of the cross-section for producing \bquark quarks in the reaction $pp\to b\bar{b} X$ are reported in 7 and 13 TeV collisions at the LHC as a function of the pseudorapidity $\eta$ in the range $2<\eta<5$ covered by the acceptance of the LHCb experiment. The measurements are done using semileptonic decays of $b$-flavored hadrons decaying into a ground-state charmed hadron in association with a muon. The cross-sections in the covered $\eta$ range are $72.0\pm 0.3\pm6.8 \mu$b and $144\pm 1\pm 21 \mu$b for 7 and 13 TeV. The ratio is $2.00\pm0.02\pm0.26$, where the quoted uncertainties are statistical and systematic, respectively. The agreement with theoretical expectation is good at 7 TeV, but differs somewhat at 13 TeV. The measured ratio of cross-sections is larger at lower $\eta$ than the model prediction.

Figures and captions

Fits to the $K^+K^-\pi^+$ invariant mass (a) and ln($I\!P$/mm) (b) distributions for data taken at 7 TeV data integrated over $2<\eta<5$. The data are shown as solid circles (black), and the overall fits as solid lines (blue). The dot-dashed (green) curve shows the $D_s^+$ signal from $b$ decay, while the dashed (purple) curve $D_s^+$ from prompt production. The dotted curve (orange) shows the $D^{*+}$ component. The dashed line (red) shows the combinatorial background. The same fits using a logarithmic scale are shown in (c) and (d).

Ds_Mas[..].pdf [31 KiB]
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Ds_Mass_Pt_0_Eta_0.pdf
Ds_IP_[..].pdf [22 KiB]
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Ds_IP_Pt_0_Eta_0.pdf
Ds_Mas[..].pdf [31 KiB]
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Ds_Mass_Pt_0_Eta_0_Log.pdf
Ds_IP_[..].pdf [22 KiB]
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Ds_IP_Pt_0_Eta_0_Log.pdf

The cross-section as a function of $\eta$ for $\sigma(pp\rightarrow H_b X)$, where $H_b$ is a hadron that contains either a $b$ or a $\overline{b}$ quark, but not both, at center-of-mass energies of 7 TeV (a) and 13 TeV (b). The ratio is shown in (c). The smaller error bars (black) show the statistical uncertainties only, and the larger ones (blue) have the systematic uncertainties added in quadrature. The solid line (red) gives the theoretical prediction, while the solid shaded band gives the estimated uncertainty on the predictions at $\pm1 \sigma$, the cross-hatched at $\pm2 \sigma$, and the dashes at $\pm3 \sigma$.

cross_[..].pdf [15 KiB]
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cross_section_7TeV_PtetaProjection.pdf
Ecross[..].pdf [15 KiB]
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Ecross_section_13TeV_PtetaProjection.pdf
Ecross[..].pdf [18 KiB]
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Ecross_section_Ratio_PtetaProjection.pdf

Fits to the invariant masses and ln($I\!P$/mm) distributions integrated over $2<\eta<5$ for 7 TeV running. The data are shown as solid circles (black), and the overall fits as solid lines (blue). The dot-dashed (green) curves show the charm signals from $b$ decay, while the dashed (purple) curves charm background from prompt production. The dashed line (red) shows the combinatorial background. The dotted curve (orange) shows the $D^{*+}$ component only for the $K^+K^-\pi^+$ mass distribution. (a) and (b) show $K^-\pi^+$ combinations, (c) and (d) show $K^-\pi^+\pi^+$ combinations, (e) and (f) show $K^-K^+\pi^+$ combinations, and (g) and (h) show $pK^-\pi^+$ combinations. The fitting procedure is described in the text.

D0_Mas[..].pdf [31 KiB]
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D0_Mass_Pt_0_Eta_0_Sup.pdf
D0_IP_[..].pdf [22 KiB]
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D0_IP_Pt_0_Eta_0_Sup.pdf
Dp_Mas[..].pdf [79 KiB]
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Dp_Mass_Pt_0_Eta_0_Sup.pdf
Dp_IP_[..].pdf [23 KiB]
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Dp_IP_Pt_0_Eta_0_Sup.pdf
Ds_Mas[..].pdf [31 KiB]
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Ds_Mass_Pt_0_Eta_0_Sup.pdf
Ds_IP_[..].pdf [22 KiB]
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Ds_IP_Pt_0_Eta_0_Sup.pdf
Lc_Mas[..].pdf [31 KiB]
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Lc_Mass_Pt_0_Eta_0_Sup.pdf
Lc_IP_[..].pdf [23 KiB]
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Lc_IP_Pt_0_Eta_0_Sup.pdf

Fits to the invariant masses and ln($I\!P$/mm) distributions integrated over $2<\eta<5$ for 13 TeV running. The data are shown as solid circles (black), and the overall fits as solid lines (blue). The dot-dashed (green) curves show the charm signals from $b$ decay, while the dashed (purple) curves charm background from prompt production. The dashed lines (red) show the combinatorial background. The dotted curve (orange) shows the $D^{*+}$ component only for the $K^+K^-\pi^+$ mass distribution. (a) and (b) show $K^-\pi^+$ combinations, (c) and (d) show $K^-\pi^+\pi^+$ combinations, (e) and (f) show $K^-K^+\pi^+$ combinations, and (g) and (h) show $pK^-\pi^+$ combinations. The fitting procedure is described in the text.

D0_Mas[..].pdf [31 KiB]
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D0_Mass_Pt_0_Eta_0_13TeV_Sup.pdf
D0_IP_[..].pdf [23 KiB]
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D0_IP_Pt_0_Eta_0_13TeV_Sup.pdf
Dp_Mas[..].pdf [30 KiB]
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Dp_Mass_Pt_0_Eta_0_13TeV_Sup.pdf
Dp_IP_[..].pdf [23 KiB]
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Dp_IP_Pt_0_Eta_0_13TeV_Sup.pdf
Ds_Mas[..].pdf [31 KiB]
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Ds_Mass_Pt_0_Eta_0_13TeV_Sup.pdf
Ds_IP_[..].pdf [22 KiB]
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Ds_IP_Pt_0_Eta_0_13TeV_Sup.pdf
Lc_Mas[..].pdf [30 KiB]
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Lc_Mass_Pt_0_Eta_0_13TeV_Sup.pdf
Lc_IP_[..].pdf [22 KiB]
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Lc_IP_Pt_0_Eta_0_13TeV_Sup.pdf

Overall detection efficiencies as a function of $p_{\mathrm{ T}}$ (charm+$\mu$) for the different $\eta$ intervals at 7 TeV. The uncertainties reflect both the statistical and systematic uncertainties added in quadrature.

pt_eff[..].pdf [32 KiB]
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pt_efficienciesFine7TeV.pdf

Animated gif made out of all figures.

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Tables and captions

Measured semileptonic decay branching fractions for $\kern 0.18em\overline{\kern -0.18em B }{} {}^0$ and $ B ^- $ mesons. Yhe correlation of the errors in the underlying measurements in the average is taken into account. The CLEO numbers result from solving Eq. 4.

Table_1.pdf [44 KiB]
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Table_1.pdf

Measured semileptonic decay branching fractions for $B$ mesons and derived branching fractions for $\kern 0.18em\overline{\kern -0.18em B }{} {}^0_ s $ and $\Lambda ^0_ b $ based on the equality of semileptonic widths and the lifetime ratios.

Table_2.pdf [53 KiB]
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Table_2.pdf

$pp\rightarrow H_b X$ cross-sections as a function of $\eta$ for 7 TeV and 13 TeV collisions and their ratio. The first uncertainty is statistical and the second systematic.

Table_3.pdf [31 KiB]
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Table_3.pdf

Systematic uncertainties independent of $\eta$ on the $pp\rightarrow H_bX$ cross-sections at 7 and 13 TeV and their ratio.

Table_4.pdf [34 KiB]
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Table_4.pdf

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

Table_5.pdf [57 KiB]
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Table_5.pdf

Signal yields of charm hadron plus $\mu$ events. Note that the 7 TeV $D^0$ result is prescaled in the trigger by a factor of two with respect to the others.

Table_6.pdf [40 KiB]
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Table_6.pdf

Created on 11 August 2018.Citation count from INSPIRE on 16 August 2018.