Diboson production in the SMEFT at dimension-8

TL;DR

This paper analyzes the impact of dimension-8 and dimension-6 operators in diboson production at the LHC within SMEFT, highlighting the significance of dimension-8 effects at scales below 3 TeV and their implications for current and future data analysis.

Contribution

It provides a comprehensive differential analysis of dimension-8 effects in diboson production and assesses their interplay with dimension-6 contributions using existing LHC data.

Findings

Dimension-8 effects are significant below 3 TeV scales.

Current LHC data can constrain dimension-8 operators.

Dimension-6 analysis remains robust when marginalizing over dimension-8 effects.

Abstract

We present a comprehensive analysis of dimension-8 and dimension-6 effects in fully leptonic $WZ$ and $WW$ production at the Large Hadron Collider (LHC) within the Standard Model (SM) Effective Field Theory (SMEFT). We focus on dimension-8 operators with maximal energy growth in the quark-(anti)quark-initiated production channel and assess their impact differentially through a variety of observables, including polarisation-sensitive ones. Leveraging existing data from measurements at the LHC, we perform fits to quantify the sensitivity of current and future data to dimension-8 effects and evaluate their interplay with squared dimension-6 contributions. By marginalising over the dimension-8 operators we examine the robustness of a dimension-6 SMEFT analysis in diboson production. We find that dimension-8 effects become subdominant only for new-physics scales above 3 TeV.