Modelling of Longitudinal-Longitudinal polarisation of the ZZ final state in the four-lepton decay channel at the ATLAS experiment

This note summarises the state-of-the-art modelling of the polarised ZZ production used in the ATLAS Run2 ZZ polarisation measurement. Monte Carlo samples for the main production modes, quark-induced q¯q→ZZ process, the electroweak (EW) production of ZZ in association with two jets, qq→ZZjj, and the loop-induced gg→ZZ were simulated for either the polarised or unpolarised ZZ final state in the four-charged-lepton decay channel. The simulated polarisation fractions of q¯q→ZZ events were reweighted to account for the next-to-leading order QCD and EW corrections, calculated at fixed-order with the MoCaNLO program. For the loop-induced gg→ZZ process, the simulated unpolarised events were reweighted to obtain polarisation templates by taking the predicted polarisation fraction calculated by MoCaNLO. No reweighting is applied to the EW qq→ZZjj process and the original MC simulation of polarisation templates is used. Kinematic distributions at the truth level are presented, allowing comparisons with current and future theoretical predictions.