Anomalous Triple Gauge Couplings in the Effective Field Theory Approach at the LHC

TL;DR

This paper analyzes how to extract anomalous triple gauge couplings from LHC data within the SMEFT framework, highlighting the importance of consistent order calculations and the impact of new physics assumptions.

Contribution

It provides a consistent methodology for extracting aTGC bounds at order Λ^{-2} in SMEFT and discusses the effects of higher-order corrections and process scale cuts.

Findings

Existing bounds are not improved at order Λ^{-2}

Partial Λ^{-4} corrections can lead to overestimated limits

Method to set conservative bounds considering process scale

Abstract

We discuss how to perform consistent extractions of anomalous triple gauge couplings (aTGC) from electroweak boson pair production at the LHC in the Standard Model Effective Field Theory (SMEFT). After recasting recent ATLAS and CMS searches in $pp\to WZ (WW) \to \ell' \nu \ell^+\ell^- (\nu_{\ell})$ channels, we find that: (a) working consistently at order $\Lambda^{-2}$ in the SMEFT expansion the existing aTGC bounds from Higgs and LEP-2 data are not improved, (b) the strong limits quoted by the experimental collaboration are due to the partial $\Lambda^{-4}$ corrections (dimension-6 squared contributions). Using helicity selection rule arguments we are able to explain the suppression in some of the interference terms, and discuss conditions on New Physics (NP) models that can benefit from such LHC analyses. Furthermore, standard analyses assume implicitly a quite large NP scale, an assumption that can be relaxed by imposing cuts on the underlying scale of the process ($\sqrt{\hat{s}}$). In practice, we find almost no correlation between $\sqrt{\hat{s}}$ and the experimentally accessible quantities, which complicates the SMEFT interpretation. Nevertheless, we provide a method to set (conservative) aTGC bounds in this situation, and recast the present searches accordingly. Finally, we introduce a simple NP model for aTGC to compare the bounds obtained directly in the model with those from the SMEFT analysis.