Speakers
Description
Measurements of the associated production of a top-quark pair and a $Z$ boson ($t\bar{t}Z$) probe the coupling between the top quark and the $Z$ boson, thereby serving as indirect searches for new physics. Besides, $t\bar{t}Z$ measurements improve background estimation in some of the direct Beyond the Standard Model searches.
The latest ATLAS $t\bar{t}Z$ cross section measurement at $\sqrt{s}=13$ TeV based on the full Run 2 dataset reached unprecedented precision of 6.5% and is consistent with theory prediction at NLO+NNLL.
New $t\bar{t}Z$ analysis from ATLAS uses partial Run 3 dataset at $\sqrt{s}=13.6$ TeV and targets events where top quarks decay into boosted jets. Such boosted topology grants access to the high-energy phase space and thus enhances sensitivity to the Standard Model Effective Field Theory (SMEFT). Besides, it improves background suppression by targeting final state with both leptons and $b$-tagged large-$R$ jets. This ongoing boosted $t\bar{t}Z$ analysis aims to measure inclusive as well as differential cross sections and to interpret the differential measurements in the context of SMEFT. The analysis is divided into two channels based on lepton multiplicity. This talk will focus on the trilepton channel, which targets events with semileptonic decays of the $t\bar{t}$ pair and leptonic decays of the $Z$ boson.