Deriving a parton shower for jet thermalization in QCD plasmas
Ismail Soudi, Adam Takacs
TL;DR
This paper tackles jet quenching and jet thermalization in the quark-gluon plasma by deriving a first-principles parton-shower algorithm from the linearized QCD effective kinetic theory (EKT). By recasting the linearized Boltzmann equation for perturbations $\delta f_a$ on an equilibrium background into a shower formalism with a no-collision Sudakov factor, it incorporates real/virtual collisions, recoils, holes, quantum statistics, and $2\to 1$ merging, thereby enabling a particle-level description of jet energy loss and equilibration. The authors demonstrate consistency with the linearized EKT, analyze the high-energy limit where the cascade reduces to a DGLAP-like energy-loss evolution, and implement the full inelastic EKT dynamics to recover thermalization and access multi-particle correlations beyond molecular chaos. This framework opens the door to event-by-event jet-medium simulations with interfaces to vacuum showers and hadronization, and to systematic studies of fluctuations, correlations, and space-time inhomogeneities in heavy-ion collisions.
Abstract
Jet quenching - the modification of high-energy jets in the quark-gluon plasma - has been extensively studied through weakly coupled scattering amplitudes embedded in parton-shower frameworks. These models, often combined with bulk hydrodynamic evolution, successfully describe a wide range of observables, though they typically rely on assumptions of rapid thermalization and simplified treatments of medium response. Parallel to these developments, jet thermalization has been investigated within the finite-temperature QCD effective kinetic theory, which provides our best microscopic understanding of equilibration in heavy-ion collisions. Early studies of linearized perturbations have highlighted both the promise and the limitations of current approaches, as existing MC implementations face challenges - particularly in the treatment of recoils and particle merging. Building on this foundation, we introduce a new parton-shower algorithm that exactly reproduces the dynamics of the linearized EKT, enabling a first-principles description of jet thermalization with proper inclusion of recoils, holes, quantum statistics, and merging processes.