Heidelberg 2022 – wissenschaftliches Programm

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T: Fachverband Teilchenphysik

T 33: Top Quarks: Production (Exp.) 2

T 33.3: Vortrag

Dienstag, 22. März 2022, 16:45–17:00, T-H18

Studying prospects of a measurement of the cross section of top-quark pair production with additional charm quarks in the lepton+jets channel at ATLAS at √s=13 TeV — •Lukas Ehrke, Tobias Golling, Manuel Guth, Johnny Raine, and Knut Zoch — Université de Genève, Geneva, Switzerland

The goal of this analysis is to measure the inclusive cross section of tt production with additional charm quarks in the ATLAS collaboration. This talk focuses on the semileptonic tt decay channel for which it would be the first measurement of this cross section. The measurement will benefit several analyses where this process is a non negligible background, most notably in the search for a tt pair in association with a Higgs boson where the Higgs boson decays into two b-quarks.

To reduce background processes not containing a tt pair b-tagging is needed, whereas to identify the events with additional c-quarks c-tagging is needed. A further complication in the lepton+jets channel are c-quarks originating from the hadronically decaying W boson. Therefore, the existing flavour tagging methods are extended to allow for simultaneous b- and c-tagging. New working points are derived on a 2D plane, and based on the b- and c-multiplicity, multiple regions are defined with different contributions of the different tt+jets components. Initial studies show promising sensitivity to the cross section. The measurement in the lepton+jets channel benefits from larger statistics compared to the dilepton channel. However, the charm quarks from the hadronic W decays pose a greater modelling challenge.