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 27 April 2024.