Measurement of the top quark forward-backward production asymmetry and the anomalous chromoelectric and chromomagnetic moments in pp collisions at $\sqrt{s} =$ 13 TeV

TL;DR

This paper measures the top quark forward-backward asymmetry and anomalous chromoelectric and chromomagnetic moments in proton-proton collisions at 13 TeV, providing new constraints on these parameters using CMS data.

Contribution

It introduces a novel measurement of top quark asymmetry and moments at 13 TeV, with improved analysis techniques and tighter limits compared to previous studies.

Findings

Measured asymmetry $A_ ext{FB}^{(1)}$ = 0.048 with uncertainties.

Set a limit on the chromoelectric moment $| ext{d}_t| < 0.03$ at 95% CL.

Provided the first constraints on these moments at 13 TeV.

Abstract

The parton-level top quark (t) forward-backward asymmetry and the anomalous chromoelectric ($\hat{d}_\mathrm{t}$) and chromomagnetic ($\hat{\mu}_\mathrm{t}$) 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 $\mathrm{t\bar{t}}$ 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 $\mathrm{t\bar{t}}$ final states. The values found for the parameters are $A_\mathrm{FB}^{(1)} =$ 0.048 $^{+0.095}_{-0.087}$ (stat) $^{+0.020}_{-0.029}$ (syst), $\hat{\mu}_\mathrm{t} =-$ 0.024 $^{+0.013}_{-0.009}$ (stat) $^{+0.016}_{-0.011}$ (syst), and a limit is placed on the magnitude of $|\hat{d}_\mathrm{t}|$ $<$ 0.03 at 95% confidence level.