Quantum Chromodynamics and the Precision Phenomenology of Heavy Quarks

TL;DR

This thesis advances the precision phenomenology of QCD at the LHC by providing analytic calculations of multi-parton amplitudes, addressing top quark properties, and exploring heavy quark schemes in Higgs production, crucial for new physics searches.

Contribution

It presents new analytic results for five-parton amplitudes at 1- and 2-loop order, and analyzes heavy quark schemes in Higgs production, improving theoretical predictions for LHC phenomenology.

Findings

NNLO amplitudes for top quark decay and pair production are computed.

Extracted top quark mass and strong coupling constant consistent with world averages.

Demonstrated the validity of different heavy quark schemes with appropriate scale choices.

Abstract

In this thesis we consider the phenomenology of QCD, with particular reference to the ongoing experimental program at the Large Hadron Collider in CERN. The current progress in precision measurement of Standard Model processes at the LHC experiments must be matched with corresponding precision in theoretical predictions. Such calculations are vital if we are to untangle signals of New Physics from LHC data. We consider in particular the amplitudes for five parton interactions at 1- and 2-loop order and present analytic results in terms of rational functions multiplying a basis of master integrals. We address the problem of the solution of a system of integration-by-parts identities for Feynman integrals and demonstrate how some current difficulties may be mitigated. We consider also the properties of the top quark, and present the real-virtual contributions to the calculation of its decay rate. These amplitudes constitute a necessary ingredient in the complete calculation of top quark pair production and decay at NNLO. Turning to phenomenology, we consider the extraction of two important SM parameters, the top mass and the strong coupling constant, from measurements of top pair production at the ATLAS and CMS experiments. We compare with NNLO theory predictions and extract the parameters simultaneously. We find values which are compatible with the current world averages published by the PDG. Finally, we examine the circumstances in which a heavy quark can be considered a constituent of the proton. We look at the production of a Higgs boson in association with b quarks in schemes in which the b may or may not be included in the initial state. We show that predictions in both schemes are well-motivated, and moreover that both are consistent provided a judicious choice of scales is made. We suggest a typical scale choice somewhat lower than the typical hard scale of the process.