Jetology: A precision understanding of jet substructure and the dead-cone effect

  • Jacob Rawling

Student thesis: Phd

Abstract

A measurement of the relative differential cross-section of tt̄ production in proton- proton collisions at sqrt(s) = 13 TeV of a novel observable, A_θ , is presented. The measure- ment was performed in the lepton+jets final state with data recorded by the ATLAS detector. The integrated luminosity of the dataset used was L =138.2 fb^−1 . The effects of the detector were removed using a statistical procedure. The A_θ observable was de- signed to be sensitive to dead-cone effect, a suppression of radiation in the collinear region around a massive radiator. The A_θ observable was found to be sensitive to the radiative properties of the tt̄ system, evaluated by comparison with several NLO pre- dictions. The observed suppression strength of the dead-cone effect was parameterised by the f_DC observable, such that f_DC = 1.0 corresponds to the SM prediction of the dead-cone effect and f_DC ∈ [0, 1]. The dead-cone suppression strength was measured to be f_DC = 0.527 ± 0.041(stat) ± 0.295(syst). The measured f_DC lies 1.77σ from the case where the top quark radiates as if it were massless, f_DC = 0.0. Furthermore, a novel analytic approach top tagging was explored. Two top tagging algorithms were proposed: TopSplitter and Y m splitter. The action of these taggers on top jets and quark-initiated jets were studied using all ordered analytic calculation. The calculation was compared to Monte Carlo prediction, and found that the parton shower used within traditional Monte Carlo captures the all order behaviour of jets after the application top tagging algorithms.
Date of Award1 Aug 2020
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorAndrew Pilkington (Supervisor) & Yvonne Peters (Supervisor)

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