A search for top-antitop quark resonances with the ATLAS detector at the LHC

[摘要] Various extensions to the Standard Model postulate the existence of heavy particles that decay to a top-antitop quark pair. If one of these particles exists with a mass of a few TeV then it may be produced during proton-proton collisions at the Large Hadron Collider (LHC). The analysis presented in this thesis searches 36 fb−1 of √s = 13 TeV proton- proton collision data collected by the ATLAS detector for evidence of a top-antitop quark resonance, and sets upper limits on the production cross section of new heavy particles in a set of benchmark models. The observed top-antitop quark invariant mass spectrum agrees well with the spectrum expected under the Standard Model and no evidence of a top-antitop quark resonance is found. A 1% width Z′ boson in a topcolour-assisted technicolour model is observed to be excluded at masses below 3.0 TeV, a 30% (15%) width Kaluza-Klein gluon in a Randall-Sundrum model is observed to be excluded at masses below 3.7 TeV (3.8 TeV), and a 3-6% width Kaluza-Klein graviton in a Randall-Sundrum model is observed to be excluded in the mass interval 0.45 < mGKK < 0.65 TeV. Some techniques developed to improve the sensitivity of the analysis are described: a new method of electron-in-jet overlap removal and a reconstruction of semi-boosted and very boosted top-antitop quark decay topologies. A study evaluating the prospects of this search at the High Luminostiy LHC is also presented. It estimates that a search of 3000 fb−1 of proton-proton collision data collected using an upgraded ATLAS detector will be able to exclude a Z′ boson at masses below 4 TeV.

[发布机构] University:University of Glasgow;Department:School of Physics and Astronomy

[关键词] LHC ATLAS.