Measurements of t t-bar charge asymmetry using dilepton final states in pp collisions at sqrt(s) = 8 TeV

The CMS collaboration
Khachatryan, Vardan , Sirunyan, Albert M , Tumasyan, Armen , Adam, Wolfgang , Aşılar, Ece , Bergauer, Thomas , Brandstetter, Johannes , Brondolin, Erica , Dragicevic, Marko , Erö, Janos
Phys.Lett.B 760 (2016) 365-386, 2016.

Abstract (data abstract)
The charge asymmetry in $\mathrm{t\bar{t}}$ events is measured using dilepton final states produced in pp collisions at the LHC at $\sqrt{s}=8\:$TeV. The data sample, collected with the CMS detector, corresponds to an integrated luminosity of 19.5 inverse femtobarns. The measurements are performed using events with two oppositely charged leptons (electrons or muons) and two or more jets, where at least one of the jets is identified as originating from a bottom quark. The charge asymmetry is measured from differences in kinematic distributions, unfolded to the parton level, of positively and negatively charged top quarks and leptons. The $\mathrm{t\bar{t}}$ and leptonic charge asymmetries are found to be 0.011 +/- 0.011 (stat) +/- 0.007 (syst) and 0.003 +/- 0.006 (stat) +/- 0.003 (syst), respectively. These results, as well as charge asymmetry measurements made as a function of $\mathrm{t\bar{t}}$ system kinematic properties, are in agreement with predictions of the standard model. For the normalized differential cross sections as a function of $\Delta|y_\mathrm{t}|$ and $\Delta|\eta_{\ell}|$ the distributions are normalized to unit area, i.e. the bin values (and their associated covariances) should be multiplied by the bin widths to give the fraction of events in that bin. For the normalized double-differential cross sections as a function of the $\mathrm{t\bar{t}}$ system variables and $\Delta|y_\mathrm{t}|$ or $\Delta|\eta_{\ell}|$, the quoted bin values (and their associated covariances) are for the fraction of events in that bin, such that the sum of all bin contents is equal to one. The lower and upper $\Delta|y_\mathrm{t}|$ and $\Delta|\eta_{\ell}|$ bins (starting and ending at -2 and +2, respectively) contain underflow and overflow events, i.e. the complete distribution from -infinity to +infinity is covered. Bin values are reported to four decimal places, and covariances to four significant figures. Any missing figures are zeros.

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