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Measurement of spin correlations in tt-bar systems in the muon+jets channel using a matrix element method with the CMS detector at the LHC

Beernaert, Kelly

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Título:
Measurement of spin correlations in tt-bar systems in the muon+jets channel using a matrix element method with the CMS detector at the LHC
Autor: Beernaert, Kelly
Assuntos: CERN ; CMS ; matrix element method ; particle physics ; Physics and Astronomy ; top quark physics
Descrição: In this work, the consistency of the spin correlation strength in top quark pair events with the Standard Model (SM) prediction is tested in the muon+jets final state. The events are obtained from pp collisions at a centre-of-mass energy of sqrt(s) = 8 TeV, corresponding to an integrated luminosity of 19.7 fb^(-1). Using a Matrix Element Method, event likelihoods are calculated under two different top quark pair hypotheses: the SM hypothesis and a hypothesis which predicts zero spin correlation. Using the event likelihoods, a variable sensitive to the spin correlation strength is constructed. In a hypothesis testing procedure, the data are found to favour the SM hypothesis. Using a template fit method, the fraction of events that show SM spin correlations is measured to be f = 0.72 +/- 0.08 (stat) +0.15 -0.13 (syst), representing the most precise measurement of this quantity in the lepton+jets channel to date.
Editor: Ghent University. Faculty of Sciences
Data de criação/publicação: 2015
Idioma: Inglês

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