Evidence of pair production of longitudinally polarised vector bosons and study of CP properties in $ZZ \to 4\ell$ events with the ATLAS detector at $\sqrt{s} = 13$ TeV

TL;DR

This paper reports on the measurement of longitudinally polarised Z boson pair production and CP properties in $ZZ o 4\ell$ events at 13 TeV, using ATLAS data, providing insights into Standard Model predictions and potential new physics.

Contribution

First measurement of longitudinally polarised $ZZ$ production significance and cross-section at 13 TeV, and analysis of CP-sensitive observables to constrain anomalous couplings.

Findings

Longitudinal $ZZ$ production observed with 4.3 sigma significance.

Measured cross-section of $2.45 \pm 0.60$ fb aligns with Standard Model.

Constraints placed on anomalous CP-odd neutral triple gauge couplings.

Abstract

A study of the polarisation and CP properties in $ZZ$ production is presented. The used data set corresponds to an integrated luminosity of 140 fb$^{-1}$ of proton-proton collisions at a centre-of-mass energy of $13$ TeV recorded by the ATLAS detector at the Large Hadron Collider. The $ZZ$ candidate events are reconstructed using two same-flavour opposite-charge electron or muon pairs. The production of two longitudinally polarised $Z$ bosons is measured with a significance of 4.3 standard deviations, and its cross-section is measured in a fiducial phase space to be $2.45 \pm 0.60$ fb, consistent with the next-to-leading-order Standard Model prediction. The inclusive differential cross-section as a function of a CP-sensitive angular observable is also measured. The results are used to constrain anomalous CP-odd neutral triple gauge couplings.