# First measurement of the charge asymmetry in beauty-quark pair production

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## Abstract

The difference in the angular distributions between beauty quarks and antiquarks, referred to as the charge asymmetry, is measured for the first time in $b\bar{b}$ pair production at a hadron collider. The data used correspond to an integrated luminosity of 1.0fb$^{-1}$ collected at 7TeV center-of-mass energy in proton-proton collisions with the LHCb detector. The measurement is performed in three regions of the invariant mass of the $b\bar{b}$ system. The results obtained are: \begin{eqnarray} A_{C}^{b\bar{b}}(40 < M_{b\bar{b}} < 75 \rm{GeV/c^2}) &=& 0.4 \pm 0.4(\rm{stat}) \pm 0.3(\rm{syst})\%\newline A_{C}^{b\bar{b}}(75 < M_{b\bar{b}} < 105 \rm{GeV/c^2}) &=& 2.0 \pm 0.9(\rm{stat}) \pm 0.6(\rm{syst})\%\newline A_{C}^{b\bar{b}}(M_{b\bar{b}} > 105 \rm{GeV/c^2}) &=&1.6 \pm 1.7(\rm{stat}) \pm 0.6(\rm{syst})\% \end{eqnarray} where $A_{C}^{b\bar{b}}$ is defined as the asymmetry in the difference in rapidity between jets formed from the beauty quark and antiquark. The beauty jets are required to satisfy $2<\eta<4$, $E_{\rm T} > 20$GeV, and have an opening angle in the transverse plane $\Delta\phi>2.6$rad. These measurements are consistent with the predictions of the Standard Model.

## Figures and captions

 (top) Corrected mass of TOPO objects associated to bTAG jets in the final event sample. Less than 2% of jets are found to originate from charm. (bottom) Corrected mass of TOPO objects associated to sub-leading { vs} leading jets in the final event sample. A small $c\bar{c}$ contribution is visible near (2,2) ${\mathrm{ Ge V /}c^2}$ . MCOR_BG.pdf [107 KiB] HiDef png [144 KiB] Thumbnail [137 KiB] *.C file MCOR_2D.pdf [23 KiB] HiDef png [296 KiB] Thumbnail [303 KiB] *.C file Reconstructed $\Delta y$ distribution for all selected events after background subtraction and correction for qTAG impurity. The dashed line shows the distribution reflected about the vertical axis. dy_cor.pdf [13 KiB] HiDef png [84 KiB] Thumbnail [53 KiB] *.C file Migration matrix in $\Delta y$ and $M_{b\bar{b}}$ . respon[..].pdf [46 KiB] HiDef png [217 KiB] Thumbnail [187 KiB] *.C file Corrected $\Delta y$ distribution for all selected events. The statistical uncertainties are negligible. The systematic uncertainties are highly correlated from bin to bin and largely cancel in the determination of $A_{\rm C}^{b\bar{b}}$ . The LO SM prediction obtained from Pythia [37,38] is also shown. dsigma_dDy.pdf [13 KiB] HiDef png [87 KiB] Thumbnail [78 KiB] *.C file Animated gif made out of all figures. PAPER-2014-023.gif Thumbnail

## Tables and captions

 Absolute systematic uncertainties (%). Table_1.pdf [46 KiB] HiDef png [78 KiB] Thumbnail [29 KiB] tex code

Created on 20 February 2021.