What Does the CMS Measurement of W-polarization Tell Us about the Underlying Theory of the Coupling of W-Bosons to Matter?

TL;DR

This paper analyzes CMS measurements of W-boson polarization at the LHC, emphasizing the importance of interference effects and proposing the $L_P$ variable as a tool to probe W-fermion couplings and potential deviations from the Standard Model.

Contribution

It demonstrates the significance of interference effects in W polarization measurements and advocates for the $L_P$ variable as a sensitive probe of W-fermion couplings and new physics.

Findings

Interference between W polarizations affects differential cross-sections.

The $L_P$ variable effectively probes W-fermion couplings.

Sensitivity to W polarization exceeds that to coupling parameters.

Abstract

We discuss results of the CMS collaboration on the sensitivity of the LHC to $W$ boson polarisation in the process $pp\to W^\pm + jet \to e^\pm jet+\not\!\!P_T$ using the $L_P$ variable directly connected to $\theta^*$ angle of the outgoing lepton in the rest frame of the decaying $W$. We have shown that for a given $L_P$, interference between different polarizations of the $W$-boson is not negligible, and needs to be taken into account when considering the differential cross-section with respect to $L_P$. The $L_P$ variable suggested by CMS collaboration is highly suitable variable to study LHC sensitivity to $g_V,g_A$ couplings of $W$-boson to fermions. We note that the experimental sensitivity to W-boson polarization which is much higher than that to ($g_V,g_A$) parameter space can be turned around and used to identify deviations from the Standard Model as a signal for new physics at the LHC.