Abstract
In the $pp \rightarrow t\bar{t}$ process the angular distributions of top and anti-top quarks are expected to present a subtle difference, which could be enhanced by processes not included in the Standard Model. This Letter presents a measurement of the charge asymmetry in events where the top-quark pair is produced with a large invariant mass. The analysis is performed on 20.3 fb$^{-1}$ of $pp$ collision data at $\sqrt{s} =$ 8 TeV collected by the ATLAS experiment at the LHC, using reconstruction techniques specifically designed for the decay topology of highly boosted top quarks. The charge asymmetry in a fiducial region with large invariant mass of the top-quark pair ($m_{t\bar{t}} > $ 0.75 TeV) and an absolute rapidity difference of the top and anti-top quark candidates within $-$2 $ < |y_t| - |y_{\bar{t}}| <$ 2 is measured to be 4.2 $\pm$ 3.2%, in agreement with the Standard Model prediction at next-to-leading order. A differential measurement in three $t\bar{t}$ mass bins is also presented.
Highlights
The charge asymmetry [1,2] in top-quark pair production at hadron colliders constitutes one of the more interesting developments in the last decade of top-quark physics
The results for the charge asymmetry in the four mttintervals are presented in Fig. 2 and Table 3
The charge asymmetry in the rapidity distribution of top-quark pairs produ√ced at large ttinvariant mass has been measured in a sample of s = 8 TeV pp collisions corresponding to an integrated luminosity of 20.3 fb−1, collected with the ATLAS experiment at the Large Hadron Collider (LHC) in 2012
Summary
The charge asymmetry [1,2] in top-quark pair production at hadron colliders constitutes one of the more interesting developments in the last decade of top-quark physics. This Letter presents a measurement of the rapidity-dependent charge asymmetry in top-quark pair production that is based on techniques designed to deal with the collimated decay topology of boosted top quarks. It is based on the techniques described in Refs. It is possible to perform accurate measurements of the charge asymmetry in events with a ttinvariant mass in the TeV range This kinematic regime has a higher sensitivity for the SM asymmetry due to a higher fraction of quark-initiated processes, as well as for BSM models that introduce massive new states.
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