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Determination of top couplings in associated top pair events using ATLAS data (TopCoup)
Start date: Jan 1, 2014, End date: Dec 31, 2018 PROJECT  FINISHED 

The discovery of a new particle, compatible with the Higgs boson, at the Large Hadron Collider, marked a major triumph of the Standard Model of particle physics. However, many fundamental questions remain and direct or indirect evidence of new physics can be probed with the large number of proton-proton collision data, collected in 2011 and 2012 at 7 and 8 TeV centre-of-mass energy.With this proposal we plan to exploit the large sample of top-quark pair events that is already recorded, and the sample that will be collected from 2015 onwards, at the ultimate energy of 14 TeV. In particular we plan to study the coupling of top quarks to neutral bosons, by measuring the production of associated tt̄γ, tt̄Z and tt̄H. Anomalous electromagnetic or weak couplings could be uncovered by studying kinematic properties of the resulting photon or Z-boson, once the signal is established. By studying the tt̄H production in detail the mechanism of Yukawa coupling of the Higgs boson to fermions will be tested, possibly providing important confidence in the characterisation of the new boson.In all measurements we plan to include the tt̄ dilepton channel, that, despite the smaller branching fraction has typically superior signal-to-noise ratios. An essential part of the programme will be the calibration of the b-tagging algorithms, where we plan to use tt̄ events. For associated Higgs production we will explore the decays H→ bb̄ and H→ γγ.
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