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Measurement of $\sigma(b \bar{b})$ with inclusive final states

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Abstract

A measurement of the cross section for the production of $b\bar{b}$ pairs based on $b$ inclusive final states is presented using LHCb data collected from $pp$ collisions at $\sqrt s$= 7 TeV in 2010, corresponding to an integrated luminosity of $\sim$18 pb$^{-1}$. The inclusive $b\bar{b}$ sample is selected on the basis of decay vertices displaced from the primary interaction. The measurement has been performed in a region of pseudorapidity 2.5 $<\eta<$ 4.0 and transverse momentum $p_{\rm T}$ $> 5$ GeV of the $b$ hadron candidate. The selected sample is a mixture of $b\bar{b}$ and $c\bar{c}$ events with a negligible contamination of light quarks, a measurement of the cross section for the production of $c\bar{c}$ can therefore be performed simultaneously. The results are $\sigma^{b\bar{b}} = 7.7\pm0.12 \rm{(stat)}\pm0.84 \rm{(syst)} \mu$b and $\sigma^{c\bar{c}} = 104.6\pm2.7 \rm{(stat)}\pm11.4 \rm{(syst)} \mu$b, inside the kinematic range defined above.

Figures and captions

$\Delta\phi$ between the $b\bar{b}$ quark pairs: distributions are shown at the very first {\sc Pythia} production step (continuous red line) and at the last step before hadronization (dotted black line). The distribution for the $b$ hadron pairs is shown in the yellow filled histogram.

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Difference in azimuthal angles of the two $b$ hadrons for {\sc Pythia} at the LO approximation (black line) and {\sc Powheg} at the NLO approximation (blue filled histogram) in the $b\bar{b}$-inclusive events.

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Resolution in (a) $\phi$ and (b) $\theta$ for the seed measured as described in the text for events with one $b$ hadron and one reconstructed seed.

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Distribution of $\Delta \phi$ of a seed pair before (black line) and after (red histogram) the merging procedure.

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(a) Correlations in $\eta$ between the $B^{0} \rightarrow D^{-} \pi^{+}$ decay, and the seed reconstructed with the particles originating from the signal $B^{0}$. (b) Correlations in $\eta$ between the $B^{0} \rightarrow D^{-} \pi^{+}$ decay and the seed reconstructed without the particles originating from the signal $B^{0}$.

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Comparison of the transverse momentum of the seed before and after calibration (red histogram and black points respectively), and with true $b$ hadrons (yellow filled histogram), in the fiducial region of the measurement. Distributions are normalized to unity.

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Distributions of (a) $\Delta\phi$ and (b) $p_{\rm T}$ of the seeds. Data (black dots), $b\bar{b}$ (yellow light histogram), $c\bar{c}$ (blue dark histogram). Expected contributions of $b\bar{b}$ and $c\bar{c}$ are subsequently added.

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Response of the BDTG (defined in the text) for data (black dots) fitted with shapes evaluated from simulated $b\bar{b}$ (red dotted line) and $c\bar{c}$ (green dashed line) events. The fit result is indicated by the solid blue line.

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Animated gif made out of all figures.

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Tables and captions

Requirements on the tracks to form two- or three-track seeds.

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Requirements on the reconstructed secondary vertices of two or three tracks. The seed $p_{\rm T}$ is defined as the sum of the four-momenta of constituent tracks. DOCA indicates the distance of closest approach between two tracks.

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Sources of systematic uncertainties.

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