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T: Fachverband Teilchenphysik

T 4: Top Quark 1 (Produktion)

T 4.8: Vortrag

Montag, 27. März 2017, 18:30–18:45, JUR 4

Measurement of the ttZ cross section in the 4ℓ-channel with the ATLAS experiment at 13 TeV — Nello Bruscino, Julien Caudron, Markus Cristinziani, Mazuza Ghneimat, Carlo Alberto Gottardo, •Sebastian Heer, Vadim Kostyukhin, Andrea Sciandra, and Kaven Yau Wong — Physikalisches Institut of University of Bonn

The ttZ process is sensitive to the tZ coupling and deviations of the measured cross section from the Standard Model prediction would indicate new physics. The decay channel with 4 leptons in the final state has the smallest branching ratio (0.5% of all ttZ decays) but also the signal with the highest purity. In the Standard Model, the available processes that also have 4 leptons in the final state are few, with the ZZ, the tWZ and the ttH processes being the dominant ones.

This talk will present the latest results, using the full 2015 and 2016 dataset of 36.5 fb⁻¹ taken by the ATLAS detector at a centre-of-mass energy of 13 TeV. The analysis is split into signal regions according to the lepton flavour and number of b-tagged jets and a region, to control the ZZ background. With the increase of the centre-of-mass energy from 8 to 13 TeV the cross sections of all processes are predicted to change differently with respect to each other. Therefore an optimization of the signal regions will also be shown.