Abstract
This paper reports inclusive and differential measurements of the tbar{t} charge asymmetry A_{text {C}} in 20.3~{mathrm{fb}^{-1}} of sqrt{s} = 8~mathrm TeV{} pp collisions recorded by the ATLAS experiment at the Large Hadron Collider at CERN. Three differential measurements are performed as a function of the invariant mass, transverse momentum and longitudinal boost of the tbar{t} system. The tbar{t} pairs are selected in the single-lepton channels (e or mu ) with at least four jets, and a likelihood fit is used to reconstruct the tbar{t} event kinematics. A Bayesian unfolding procedure is performed to infer the asymmetry at parton level from the observed data distribution. The inclusive tbar{t} charge asymmetry is measured to be A_{text {C}}{} = 0.009 pm 0.005 (stat. + syst.). The inclusive and differential measurements are compatible with the values predicted by the Standard Model.
Highlights
Background modellingW+jets: The predictions of normalisation and flavour composition of the W +jets background are affected by large uncertainties, but the in situ data-driven technique described in Sect. 5.2 reduces these to a negligible level
The ATLAS detector [33] consists of the following main subsystems: an inner tracking system immersed in a 2 T magnetic field provided by a superconducting solenoid, electromagnetic (EM) and hadronic calorimeters, and a muon spectrometer incorporating three large superconducting toroid magnets composed of eight coils each
Z+jets: Uncertainties affecting the modelling of the Z +jets background include a 5 % normalisation uncertainty from the theoretical next-to-next-toleading order (NNLO) cross section [74], as well as an additional 24 % normalisation uncertainty added in quadrature for each additional inclusive jet-multiplicity bin, based on a comparison among different algorithms for merging LO matrix elements and parton showers [89]
Summary
The interest in precisely measuring charge asymmetries in top-quark pair production at the LHC has grown after the CDF and D0 collaborations reported measurements of AFB that were significantly larger than the SM predictions, in both the inclusive and differential case as a function of mttand of the rapidity of the ttsystem, ytt [10,11,27,28,29,30]. For specific simple models [20], tension still exists between the LHC and Tevatron results This motivates the interest in a more precise measurement of the ttproduction charge asymmetry at the LHC.
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