Measurements and interpretations of $W^{\pm}Z$ production cross-sections in $pp$ collisions at $\sqrt{s} =$ 13 TeV with the ATLAS detector

TL;DR

This paper reports precise measurements of $W^{\u00b1}Z$ production cross-sections at 13 TeV with the ATLAS detector, compares them with Standard Model predictions, and explores potential new physics via effective field theory.

Contribution

It provides the first detailed differential and integrated cross-section measurements of $W^{b1}Z$ production at 13 TeV, including CP-violation sensitive observables and EFT interpretation.

Findings

Measured integrated cross-section with 4% precision.

No significant deviation from Standard Model predictions.

Set limits on CP-conserving and CP-violating operators.

Abstract

Measurements of integrated and differential cross-sections for $W^{\pm}Z$ production in proton-proton collisions are presented. The data collected by the ATLAS detector at the Large Hadron Collider from 2015 to 2018 at a centre-of-mass energy of $\sqrt{s} =$ 13 TeV are used, corresponding to an integrated luminosity of 140 fb$^{-1}$. The $W^{\pm}Z$ candidate events are reconstructed using leptonic decay modes of the gauge bosons into electrons or muons. The integrated cross-section per lepton flavour for the production of $W^{\pm}Z$ is measured in the detector fiducial region with a relative precision of 4%. The measured value is compared with the Standard Model prediction at a precision of up to next-to-next-to-leading-order in QCD and next-to-leading-order in electroweak. Cross-sections for $W^+Z$ and $W^-Z$ production and their ratio are presented. The $W^{\pm}Z$ production is also measured differentially as functions of various kinematic variables, including new observables sensitive to CP-violation effects. All measurements are compared with state-of-the-art Standard Model predictions from fixed-order calculations or Monte Carlo generators based on next-to-leading-order matrix elements interfaced with parton showers. An effective field theory interpretation of the measurements is performed, considering both CP-conserving and CP-violating dimension-6 operators modifying the $W^{\pm}Z$ production. In the absence of observed deviations from the Standard Model, limits on CP-conserving Wilson coefficients are extracted using the transverse mass of the $W^{\pm}Z$ system. For CP-violating coefficients a machine learning approach is used to construct an observable with enhanced sensitivity to CP-violation effects.