Study of a new method for high energy top tagging at the ATLAS experiment

Vittori, Camilla (2014) Study of a new method for high energy top tagging at the ATLAS experiment. [Laurea magistrale], Università di Bologna, Corso di Studio in Fisica [LM-DM270]
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Since its discovery, top quark has represented one of the most investigated field in particle physics. The aim of this thesis is the reconstruction of hadronic top with high transverse momentum (boosted) with the Template Overlap Method (TOM). Because of the high energy, the decay products of boosted tops are partially or totally overlapped and thus they are contained in a single large radius jet (fat-jet). TOM compares the internal energy distributions of the candidate fat-jet to a sample of tops obtained by a MC simulation (template). The algorithm is based on the definition of an overlap function, which quantifies the level of agreement between the fat-jet and the template, allowing an efficient discrimination of signal from the background contributions. A working point has been decided in order to obtain a signal efficiency close to 90% and a corresponding background rejection at 70%. TOM performances have been tested on MC samples in the muon channel and compared with the previous methods present in literature. All the methods will be merged in a multivariate analysis to give a global top tagging which will be included in ttbar production differential cross section performed on the data acquired in 2012 at sqrt(s)=8 TeV in high phase space region, where new physics processes could be possible. Due to its peculiarity to increase the pT, the Template Overlap Method will play a crucial role in the next data taking at sqrt(s)=13 TeV, where the almost totality of the tops will be produced at high energy, making the standard reconstruction methods inefficient.

Tipologia del documento
Tesi di laurea (Laurea magistrale)
Autore della tesi
Vittori, Camilla
Relatore della tesi
Corso di studio
Curriculum B: Fisica nucleare e subnucleare
Ordinamento Cds
Parole chiave
Top quark, ATLAS, top tagging, Template Overlap Method, hadronic top
Data di discussione della Tesi
24 Ottobre 2014

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