Measurement of the $t\overline{t}Z$ and $t\overline{t}W$ cross sections in proton-proton collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

Abstract

A measurement of the associated production of a top-quark pair ($t\overline{t}$) with a vector boson ($W$, $Z$) in proton-proton collisions at a center-of-mass energy of 13 TeV is presented, using $36.1{\mathrm{fb}}^{-1}$ of integrated luminosity collected by the ATLAS detector at the Large Hadron Collider. Events are selected in channels with two same- or opposite-sign leptons (electrons or muons), three leptons or four leptons, and each channel is further divided into multiple regions to maximize the sensitivity of the measurement. The $t\overline{t}Z$ and $t\overline{t}W$ production cross sections are simultaneously measured using a combined fit to all regions. The best-fit values of the production cross sections are $${\sigma }_{t\overline{t}Z}=0.95\pm 0.08\text{(stat.)}\pm 0.10\text{(syst.)}\mathrm{pb}$$ and $${\sigma }_{t\overline{t}W}=0.87\pm 0.13\text{(stat.)}\pm 0.14\text{(syst.)}\mathrm{pb},$$ in agreement with the Standard Model predictions. The measurement of the $t\overline{t}Z$ cross section is used to set constraints on effective field theory operators which modify the $t\overline{t}Z$ vertex.

Baptiste Ravina

Senior Research Fellow

I’m an experimental particle physicist looking for new physics at the ATLAS experiment with machine learning.