4.2.1. Measurements at <sup>√</sup>*<sup>s</sup>* <sup>=</sup> 7 TeV

The initial LHC measurement of *A*<sup>C</sup> was performed by CMS using 1.09 fb−<sup>1</sup> of luminosity [69]. The *At*¯*<sup>t</sup>* <sup>C</sup> was measured using distribution <sup>Δ</sup>|*η*<sup>|</sup> <sup>=</sup> <sup>|</sup>*ηt*|−|*η*¯*t*<sup>|</sup> and <sup>Δ</sup>*y*<sup>2</sup> = (*yt* <sup>−</sup>*y*¯*t*)(*yt* <sup>+</sup>*y*¯*t*) shown in Figure 27. Using 12,757 data events with the expected background of 2520 ± 246 events, the inclusive asymmetry is measured to be *<sup>A</sup>t*¯*t*,*<sup>η</sup>* <sup>C</sup> = (−1.7 ± 3.2(stat.) +2.5 <sup>−</sup>3.6(syst.))%, and *<sup>A</sup>t*¯*t*,*<sup>y</sup>* <sup>C</sup> = (−1.3 ± 2.8(stat.) +2.9 <sup>−</sup>3.1(syst.))%, consistent with the QCD NLO + EW predictions of (1.36 ± 0.08)% and (1.15 ± 0.06)% [21], respectively.

**Figure 27.** Reconstructed <sup>Δ</sup>|*η*<sup>|</sup> (**left**) and <sup>Δ</sup>*y*<sup>2</sup> (**right**) distributions for the -+jets channel. The outermost bins include the overflows [69].

Similarly, the initial ATLAS measurement of the charge asymmetry was performed using 1.04 fb−<sup>1</sup> of luminosity [65]. The measured inclusive asymmetry is *At*¯*<sup>t</sup>* <sup>C</sup> = (−1.9 ± 2.8(stat.) ± 2.4(syst.))% which is consistent with the NLO QCD + NLO EW prediction *A*<sup>C</sup> = (1.23 ± 0.05)% [24]. The differential measurement of the asymmetry as a function of *mt*¯*<sup>t</sup>* was measured only in two bins and had large uncertainties.

The measurements at <sup>√</sup>*<sup>s</sup>* <sup>=</sup> 7 TeV using full statistics were performed by both ATLAS and CMS in both -+jets and dilepton channels. In the -+jets channel, both ATLAS using 4.7 fb−<sup>1</sup> [105] and CMS using 5.0 fb−<sup>1</sup> [107] measure the asymmetry inclusively and and also differentially as a function of *mt*¯*t*, *yt*¯*t*, *<sup>p</sup>*T,t¯t. The inclusive results are *<sup>A</sup>t*¯*<sup>t</sup>* <sup>C</sup> = (0.6 ± 1.0(stat. + syst.))% for ATLAS and *At*¯*<sup>t</sup>* <sup>C</sup> = (0.4 ± 1.0(stat.) ± 1.1(syst.))% for CMS. The differential asymmetries are shown in Figures 28 and 29.

**Figure 28.** Distributions of *A*<sup>C</sup> as a function of *mt*¯*<sup>t</sup>* in (**a**), *p*T,t¯t in (**b**), and *yt*¯*<sup>t</sup>* in (**c**). The measured *A*<sup>C</sup> values are compared with the NLO QCD + EW predictions (SM) [24] and the predictions for a color-octet axigluon [105].

**Figure 29.** The unfolded Δ|*y*| distribution in (**a**), the charge asymmetry as a function of *yt*¯*<sup>t</sup>* in (**b**), *p*T,t¯t in (**c**), and *mt*¯*<sup>t</sup>* in (**c**). The measured values are compared to NLO QCD + EW calculations of Ref. [21], and to the predictions of a model featuring an effective axial-vector coupling of the gluon (EAG) [117]. The error bars on the differential asymmetry values indicate the statistical and total uncertainties [107].

In the dilepton channel, both ATLAS using 4.6 fb−<sup>1</sup> [106] and CMS using 5.0 fb−<sup>1</sup> [108] measure the *t*¯*t* and dileptonic asymmetry inclusively: *At*¯*<sup>t</sup>* <sup>C</sup> = (2.1 ± 2.5(stat.) ± 1.7(syst.))%, *A*-- <sup>C</sup> = (2.4 <sup>±</sup> 1.5(stat.) <sup>±</sup> 0.9(syst.))% in ATLAS while *<sup>A</sup>t*¯*<sup>t</sup>* <sup>C</sup> = (−1.0 ± 1.7(stat.) ± 0.8(syst.))%, *A*-- <sup>C</sup> <sup>=</sup> 0.9 <sup>±</sup> 1.0(stat.) <sup>±</sup> 0.6(syst.))% in CMS. The comparison of the inclusive ATLAS *<sup>A</sup>t*¯*<sup>t</sup>* <sup>C</sup> and *<sup>A</sup>*-- C measurements to the theory prediction is shown in Figure 30. CMS also measured the dileptonic asymmetry as a function of *t*¯*t* mass, rapidity, and transverse momentum, see Figure 31.

**Figure 30.** The comparison of correlated inclusive *A*-- <sup>C</sup> and *<sup>A</sup>t*¯*<sup>t</sup>* <sup>C</sup> measurements to the NLO QCD+EW prediction [24] and the prediction of the POWHEG+ PYTHIA generator [106].

**Figure 31.** The dependence of *A*-- <sup>C</sup> on *mt*¯*<sup>t</sup>* in (**a**), *yt*¯*<sup>t</sup>* in (**b**), and *p*T,t¯t in (**c**). The inner and outer error bars represent the statistical and total uncertainty, respectively [108].

To summarize the measurements at <sup>√</sup>*<sup>s</sup>* <sup>=</sup> 7 TeV: both ATLAS and CMS measurements are in agreement with predictions. The most precise measurement of the *t*¯*t* charge asymmetry has a total uncertainty of 1.0%. The initial measurements with partial statistics had large (≈3%) and about the same statistical and systematic uncertainties. This is a bit different to the Tevatron measurements where statistical uncertainty was dominant in most of the measurements. This is mostly due to the large *t*¯*t* sample already available for initial measurements and the fact these were measurements at the very early of the LHC running, so the detectors were not well understood yet. The full statistics measurements improved both statistical and systematic precision considerably. They are now mostly limited by the statistical uncertainty, especially dilepton measurements. The differential measurements are also in agreement with the predictions, they are mostly statistically limited and not really even able to disfavor BSM models.
