Measurement of the production cross-section of a single top quark in association with a Z boson in proton–proton collisions at 13 TeV with the ATLAS detector

Abstract

The production of a top quark in association with a Zboson is investigated. The proton–proton collision data collected by the ATLAS experiment at the LHC in 2015 and 2016 at a centre-of-mass energy of √s=13 TeVare used, corresponding to an integrated luminosity of 36.1 fb−1. Events containing three identified leptons (electrons and/or muons) and two jets, one of which is identified as a b-quark jet are selected. The major backgrounds are diboson, t¯tand Z+jetsproduction. A neural network is used to improve the background rejection and extract the signal. The resulting significance is 4.2σin the data and the expected significance is 5.4σ. The measured cross-section for tZqproduction is 600 ±170 (stat.)±140 (syst.)fb.