PoS - Proceedings of Science
Volume 390 - 40th International Conference on High Energy physics (ICHEP2020) - Parallel: Top Quark and Electroweak Physics
Using associated production of top quarks and neutral bosons to probe standard model couplings and search for new physics
K. Zoch* on behalf of the ATLAS collaboration
*corresponding author
Full text: Not available
Abstract
The unprecedentedly large integrated luminosity accumulated by the ATLAS experiment from proton-proton collisions at a centre-of-mass energy of $\sqrt{s} = 13\,\mathrm{TeV}$ at the Large Hadron Collider (LHC) allows the study of rare Standard Model (SM) processes. The associated production of top-quark pairs or single top quarks and neutral bosons is such an example: it directly probes top-quark couplings to photons and $Z$ bosons and tests for deviations from the SM. Three such recent measurements are presented, all of which exploit the full dataset of the most recent Run 2 of the LHC, corresponding to $139\,\mathrm{fb}^{-1}$ of integrated luminosity. The cross-sections for the production of top-quark pairs in association with a photon ($t\bar{t}\gamma$) or with a $Z$ boson ($t\bar{t}Z$) are measured both inclusively and differentially as functions of kinematic observables characterising the $t\bar{t}$+boson system. The measurements are compared to predictions obtained by next-to-leading order (NLO) + parton-shower (PS) Monte Carlo simulations and fixed order NLO calculations, respectively. In a third measurement, the cross-section of single top-quark production in association with a $Z$ boson ($tZq$) probes two SM couplings in the same process, $t$-$Z$ and $W$-$Z$, and it is a background to the rare associated production of a single top quark and a Higgs boson. A neural network is used to improve the background rejection and to extract the signal. The measured cross-section is compared to the NLO SM prediction.
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