Optimal sensitivity of anomalous charged triple gauge couplings through $W$ boson helicity at the $e^+e^-$ colliders

TL;DR

This paper investigates how to optimally measure anomalous charged triple gauge couplings at future $e^+e^-$ colliders using $W$ boson helicity states, employing the optimal observable technique to achieve tighter constraints than traditional methods.

Contribution

It introduces a model-independent SMEFT approach combined with the optimal observable technique to enhance sensitivity to anomalous couplings in $WW$ production at $e^+e^-$ colliders.

Findings

Optimal observable technique yields significantly tighter limits than $ ext{chi}^2$ analysis.

Different $W$ helicity states impact the sensitivity to anomalous couplings.

Constraints on CP-violating operators are discussed in relation to electron EDM.

Abstract

We study the estimation of anomalous charged triple gauge couplings (cTGCs) parameterized in a model-independent Standard Model effective field theory (SMEFT) framework via $WW$ production followed by semi-leptonic decay at the $e^+e^-$ colliders. The anomalous $(WWV~(V=\gamma,Z))$ couplings are given in terms of Wilson coefficients of three CP-conserving and two CP-violating dimension-6 operators in the HISZ basis. We adopt the optimal observable technique (OOT) to extract the sensitivity of these anomalous couplings and compare it with the latest experimental limits on anomalous couplings studied at the LHC. The limits on the anomalous couplings obtained via OOT are significantly tighter than the ones obtained using standard $\chi^2$ analysis. The impact of different helicity combinations of the $W$ boson pair in determining optimal sensitivity is analyzed. The constraints on CP-violating operators from the electron electric dipole moment (EDM) are also discussed.