A tale of $Z$+jet: SMEFT effects and the Lam-Tung relation

TL;DR

This paper constrains dimension-six operators affecting Z+jet processes using collider data, ruling out explanations for the Lam-Tung relation discrepancy and quantifying potential beyond-Standard Model effects on angular coefficients.

Contribution

It provides new bounds on light-quark dipole operators in SMEFT, excluding their role in the Lam-Tung relation discrepancy and assessing maximum BSM influence on angular observables.

Findings

Constraints exclude BSM explanations for Lam-Tung discrepancy

Limits on SMEFT operators derived from collider data

Maximum BSM impact on angular coefficients quantified

Abstract

We derive constraints on dimension-six light-quark dipole operators within the Standard Model (SM) effective field theory, based on measurements of $Z$ production at SLC and LEP, as well as $Z$+jet production at the LHC. Our new constraints exclude the parameter space that could potentially explain the observed discrepancy between theoretical predictions and experimental data for the Lam-Tung relation. With these updated limits, we model-independently determine the maximum possible influence that beyond-SM contributions could have on the angular coefficients $A_0$ and $A_2$, which enter the Lam-Tung relation.