Aachen 2019 – scientific programme
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T: Fachverband Teilchenphysik
T 58: Top-Physik II
T 58.6: Talk
Wednesday, March 27, 2019, 17:15–17:30, S10
Studies on the measurement of the ttZ production cross section in the multilepton channel — Otmar Biebel1, •Florian Fischer1, Thomas McCarthy2, and Jeannine Wagner-Kuhr1 — 1Ludwig-Maximilians-Universität, München — 2Max-Planck-Institut für Physik, München
The measurement of the production cross section of top-antitop quark pairs in association with a Z boson is sensitive to the coupling between top quarks and Z bosons. In the Standard Model, this coupling is precisely predicted via the weak interaction and therefore any deviation from the Standard Model value is an indicator for new physics. Although, with four leptons in the final state, the tetralepton decay channel is the most rare leptonic decay channel of ttZ, it has the highest signal purity of all.
In this talk, studies for an analysis with the full Run-2 dataset taken by the ATLAS experiment in the years 2015 to 2018, corresponding to an integrated luminosity of 140 fb−1, are performed. In order to increase the signal efficiency and to reconstruct not only the Z boson but also tt and thus the whole ttZ system with four leptons in the final state, a neutrino weighting method has been applied. For the differential cross section measurement kinematic variables of the ttZ system and its decay products are tested for differences between several Monte Carlo generators. In addition, the benefits of jets reconstructed with a particle-flow algorithm will be studied in the context of this analysis.