Top-mass observables: all-orders behaviour, renormalons and NLO + Parton Shower effects

Abstract

In this thesis we focus on the theoretical subtleties of the top-quark mass ($m_t$) determination, issue which persists in being highly controversial. In the first part of the thesis, we investigate the presence of linear renormalons in observables that can be employed to determine the top mass. We considered a simplified toy model to describe $W^{\ast }\to t\bar{b}\to Wb\bar{b}$. The computation is carried out in the limit of a large number of flavours ($n_f$), using a new method that allows to easily evaluate any infrared safe observable at order ${\alpha }_s({\alpha }_s{n}_f{)}^n$ for any $n$. The second part of the thesis is devoted to the comparison of several NLO generators for top-pair production, implemented in the POWHEG BOX framework, that differ by the level of accuracy employed to describe the top decay. The impact of the shower Monte Carlo programs, used to complete the NLO events generated by POWHEG BOX, is also studied. In particular, we discuss the two most widely used shower Monte Carlo programs, i.e. Pythia 8.2 and Herwig 7.1, and we present a method to interface them with processes that contain decayed emitting resonances.

PhD thesis: 152 pages, 50 figures, 34 tables

References in corpus (12)

• Parton distributions for the LHC
• The global electroweak fit at NNLO and prospects for the LHC and ILC
• Measuring the running top-quark mass
• Jets from Massive Unstable Particles: Top-Mass Determination
• Non-perturbative QCD Effects and the Top Mass at the Tevatron
• An NLO+PS generator for $t\bar{t}$ and $Wt$ production and decay including non-resonant and interference effects
• Infrared Renormalization Group Flow for Heavy Quark Masses
• Two-loop Jet-Function and Jet-Mass for Top Quarks
• On the Light Massive Flavor Dependence of the Large Order Asymptotic Behavior and the Ambiguity of the Pole Mass
• The Top Mass: Interpretation and Theoretical Uncertainties
• Recent Top Quark Mass Measurements from CMS
• Top quark mass in ATLAS