Abstract
The parton-level top quark (t) forward-backward asymmetry and the anomalous chromoelectric left({hat{d}}_{mathrm{t}}right) and chromomagnetic left({hat{mu}}_{mathrm{t}}right) moments have been measured using LHC pp collisions at a center-of-mass energy of 13 TeV, collected in the CMS detector in a data sample corresponding to an integrated luminosity of 35.9 fb−1. The linearized variable {A}_{mathrm{FB}}^{(1)} is used to approximate the asymmetry. Candidate mathrm{t}overline{mathrm{t}} events decaying to a muon or electron and jets in final states with low and high Lorentz boosts are selected and reconstructed using a fit of the kinematic distributions of the decay products to those expected for mathrm{t}overline{mathrm{t}} final states. The values found for the parameters are {A}_{mathrm{FB}}^{(1)}={0.048}_{-0.087}^{+0.095}{left(mathrm{stat}right)}_{-0.029}^{+0.020}left(mathrm{syst}right),{hat{mu}}_{mathrm{t}}=-{0.024}_{-0.009}^{+0.013}{left(mathrm{stat}right)}_{-0.011}^{+0.016}left(mathrm{syst}right), and a limit is placed on the magnitude of left|{hat{d}}_{mathrm{t}}right| < 0.03 at 95% confidence level.
Highlights
We describe here a search for anomalies in the angular distribution of produced tt pairs
Candidate tt events decaying to a muon or electron and jets in final states with low and high Lorentz boosts are selected and reconstructed using a fit of the kinematic distributions of the decay products to those expected for tt final states
Previous LHC measurements sensitive to the top quark angular production asymmetry performed by the ATLAS [24, 25] and CMS [26–29] Collaborations focused on the top quark charge asymmetry AC, which does not separate the qq initial states from the gg and qg initial states, and uses only part of the available information
Summary
Measuring the top quark forward-backward asymmetry at the LHC is considerably more challenging than at the Tevatron, where the tt cross section is dominated by the qq subprocess and the incident quark and antiquark directions are well defined by the proton and antiproton beams. Where K is an NLO normalization factor, αS = gs2/4π is the strong coupling constant, β = 1 − 4m2t /m2tt is the velocity of the top quark in the center-of-mass frame, and α(β) is the longitudinal polarization of the exchanged gluon This parameterization describes the process to NLO precision, using a linear approximation for the NLO forward-backward. Linear combinations of normalized three-dimensional distributions (templates) in mtt , xF, and c∗ reconstructed from simulated SM tt events generated at NLO are used in a simultaneous likelihood fit to the observed differential cross section in 12 total channels defined by the decay topology, lepton charge, and lepton flavor. A total general linear combination of these templates is fitted to data to independently extract the three values of A(F1B) , dt, and μt
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