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T: Fachverband Teilchenphysik

T 65: Top quarks: differential cross sections

T 65.8: Vortrag

Mittwoch, 1. April 2020, 18:15–18:30, H-HS VIII

Differential Measurement of the Associated Production of a Single Top Quark and a Z Boson at the CMS Experiment — •David Walter — DESY, Hamburg, Germany

The top quark is the heaviest particle of the standard model (SM) and can be produced through strong interactions in top quark-antiquark pairs, or polarised as a single top quark (or antiquark) via the electroweak interaction. The associated production of a single top quark and a Z boson (pp → tZq) includes the tZ coupling as well as the coupling of three vector bosons (WWZ) and is therefore a unique process to study the couplings of heavy particles in the SM. As early as 2018, the CMS Collaboration observed the SM production of tZq in its final state with three leptons. It was found to be in agreement with the SM prediction. In an ongoing analysis, a differential cross section measurement is being pursued. This can give more detailed insight into the modeling of the process in the SM while some of the distributions are also sensitive to beyond SM effects.

In this presentation, the analysis strategy is outlined. This includes the reconstruction of the leptons and jets as well as of the composite objects from the Z boson and the top quark. Furthermore, a multiclass neural network to isolate the signal from various background processes is shown. Based on this, first results of the signal extraction are presented. A maximum likelihood unfolding procedure is discussed to obtain results that are corrected for detector effects and effects of the hadronization process.