Dortmund 2021 – scientific programme
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T: Fachverband Teilchenphysik
T 29: Top quark decay and top properties I
T 29.6: Talk
Tuesday, March 16, 2021, 17:20–17:35, Td
Measurement of top quark charge asymmetry in ttγ production in the ATLAS experiment — Ivor Fleck, Carmen Diez Pardos, and •Amartya Rej — Center for Particle Physics Siegen, Experimentelle Teilchenphysik, Universität Siegen
The top quarks and anti-top quarks produced via initial quarks at the LHC are emitted in slightly different directions depending on their charge, referred to as charge asymmetry (Ac). The asymmetry is due to QCD interference contributions at next-to-leading order accuracy and it is 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 associated with a photon (ttγ), the fraction of top quark pairs produced via qq annihilation increases compared 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 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.