Polarization of top quark as a probe of its chromomagnetic and chromoelectric couplings in $tW$ production at the Large Hadron Collider

TL;DR

This paper investigates how top quark polarization in $tW$ production at the LHC can be used to probe anomalous chromomagnetic and chromoelectric couplings, providing a novel way to detect new physics effects.

Contribution

It introduces a method to analyze top polarization through decay-lepton angular distributions to constrain anomalous top couplings at the LHC.

Findings

Derived limits on the real part of CMDM $ ho_2$

Set bounds on the imaginary part of CEDM $ ho_3$

Constrained the real part of $Wtb$ coupling $ ef_{2R}$

Abstract

We study the sensitivity of the Large Hadron Collider (LHC) to top quark chromomagnetic (CMDM) and chromoelectric (CEDM) dipole moments and $Wtb$ effective couplings in single-top production in association with a $W^-$ boson, followed by semileptonic decay of the top. The $Wt$ single-top production mode helps to isolate the anomalous $ttg$ and $Wtb$ couplings, in contrast to top-pair production and other single-top production modes, where other new-physics effects can also contribute. We calculate the top polarization and the effects of these anomalous couplings on it at two centre-of-mass (cm) energies, 8 TeV and 14 TeV. As a measure of top polarization, we look at decay-lepton angular distributions in the laboratory frame, without requiring reconstruction of the rest frame of the top, and study the effect of the anomalous couplings on these distributions. We construct certain asymmetries to study the sensitivity of these distributions to top-quark couplings. We determine individual limits on the dominant couplings, viz., the real part of the CMDM $\mathrm{Re}\rho_2$, the imaginary part of the CEDM $\mathrm{Im}\rho_3$, and the real part of the tensor $Wtb$ coupling $\mathrm{Ref_{2R}}$, which may be obtained by utilizing these asymmetries at the LHC. We also obtain simultaneous limits on pairs of these couplings taking two couplings to be non-zero at a time.