Measurement of the charge asymmetry in highly boosted top-quark pair production in $\sqrt{s}=$ 8 TeV $pp$ collision data collected by the ATLAS experiment

Abstract

In the $pp\to t\bar{t}$ 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.

19 pages, plus author list - 36 pages total, 3 figures, 2 tables. Published in Physics Letters B. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/TOPQ-2015-10/