Precision Collider Physics From Effective Field Theory

Abstract

In this thesis we study the factorization properties in perturbative Quantum Chromodynamics that allow separation of the physics associated with jet formation from that of hard-scattering in high-energy particle collisions. The focus of our work is to understand how factorization theorems can be applied to precision calculations in collider physics, and when they are violated at cross-section level in hardron scattering processes. As an application of strict collinear factorization, we state and proved to all orders a factorization theorem for (soft-drop) groomed jet observables. Our calculation done at two-loop order enabled resummation of cross section matched on to fixed order results producing the first jet substructure predictions at next-to-next-to-next- to-leading-logarithmic accuracy for the LHC. Factorization is known to be violated at amplitude level where incoming particles are collinear to outgoing ones.Through an effective field theory framework with Glauber operators, we computed the perturbative amplitude in space-like collinear limits and obained explicitly two-loop finite terms that breaks factorization. Exploiting scale invariance of two-to-two scattering amplitudes in an essential way, we proved to all orders that for pure Glauber ladder graphs, all amplitude-level factorization violating effects completely cancel at cross section level for any single-scale observable. This narrows down the direction we look into the source factorization-violation in physical cross sections, shedding light on the connection between factorization-violation and the underlying event.