Quark mass effects in QCD jets
Germán Rodrigo
TL;DR
The thesis addresses how quark masses affect QCD jet observables, particularly in three-jet final states from Z decays at LEP, and proposes extracting the bottom quark mass $m_b$ from LEP data. It develops a framework comparing quark-mass definitions, computes higher-order QCD corrections, and analyzes infrared behavior to show cancellation between real and virtual contributions. The work evaluates jet algorithms (EM, JADE, E, DURHAM) and provides NLO insights and parameterizations that enable a potential high-energy determination of $m_b$ and a test of Renormalization Group running from $b$-quark thresholds to $m_Z$. These results offer a method to probe QCD mass evolution and to improve the precision of strong coupling determinations affected by quark-mass effects.
Abstract
The effects induced by the quark masses in three-jet observables have been studied in this thesis. In particular, we have explored a new method: the study of three-jet observables at LEP, different from QCD Sum Rules and Lattice calculations, for determining the b-quark mass. Among other advantages, it would allow to extract the b quark mass far from threshold, in contrast to the other methods described above and it would provide a test of the QCD Renormalization Group predictions. From our NLO calculation, we have estimated, by exploring the $μ$-dependence of our prediction at m_Z, a theoretical b-quark mass uncertainty of at most 250(MeV) in the DURHAM algorithm, 300(MeV) for JADE and EM and 500(MeV) for the E algorithm. Furthermore, quark mass effects are expected to be quite more important in top production at NLC (Next Linear Collider) and our calculation would be of a great interest.