First measurement of the charge asymmetry in beauty-quark pair production at a hadron collider

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.