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T: Fachverband Teilchenphysik
T 88: Top quarks: associated production
T 88.3: Vortrag
Donnerstag, 2. April 2020, 17:00–17:15, L-4.001
Studies on the measurement of the ttZ production cross section in the dilepton channel — Otmar Biebel1, •Florian Fischer1, and Thomas McCarthy2 — 1Ludwig-Maximilians-Universität München — 2Max-Planck-Institut für Physik, München
In the Standard Model of Particle Physics, the coupling of the Z boson to top quarks is precisely predicted via the weak interaction. As its value is experimentally not yet well constrained, several possible extensions of the Standard Model predicting modifications to this coupling could not be ruled out nor confirmed so far. Therefore a more accurate understanding of electroweak processes could significantly benefit from a precise measurement of this coupling at the LHC.
A process that is particularly sensitive to this coupling is the associated production of top-antitop quark pairs with a Z boson. Analyses targeting final states with three or four leptons offer the benefit of a very high signal purity. However, they suffer from low branching ratios. In contrast, the dileptonic channel currently being considered targets events in which the Z boson decays leptonically but the tt system decays to a fully hadronic final state.
Multivariate techniques are employed to improve the discrimination between signal events and the two dominant backgrounds: the production of top-antitop quark pairs, and the associated production of Z bosons with jets. For the studies presented in this talk, LHC Run 2 data collected by the ATLAS detector between 2015 and 2018 at a centre-of-mass energy of 13 TeV, as well as simulated data normalised to an integrated luminosity of 139 fb−1, have been used.