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T: Fachverband Teilchenphysik
T 88: Top quarks: associated production
T 88.6: Vortrag
Donnerstag, 2. April 2020, 17:45–18:00, L-4.001
Measurement of top quark charge asymmetry in ttγ production in the ATLAS experiment — •Amartya Rej, Ivor Fleck, and Carmen Diez Pardos for the ATLAS collaboration — Universitaet Siegen, Germany
Top quarks pairs (tt) produced via initial quarks at the LHC are emitted in slightly different directions depending on its charge, referred to as charge asymmetry (Ac). The asymmetry is due to QCD interference contributions at next-to-leading order accuracy and it is very sensitive to New Physics models. Such asymmetry was observed at the Tevatron experiment, where quark anti-quark (qq) annihilation was the dominant mode of tt production. The asymmetry is diluted at the LHC owing to the very large fraction of gluon fusion initiated tt production. However, recently its evidence has been found by the ATLAS experiment.
In tt production in association with a photon (ttγ), the fraction of top quark pairs produced via qq annihilation increases with respect to tt production and also leading order QED interference contributes to the charge asymmetry. Hence a larger value of charge asymmetry is expected to be found in this process with higher sensitivity to New Physics models. Still, this process has a tiny cross-section compared to tt production, one of the dominant background processes. Thus the background discrimination becomes more challenging. In this presentation, the ongoing effort for the charge asymmetry measurement in ttγ production in the ATLAS experiment will be presented highlighting the analysis methods and related challenges.