Early-Time Dynamics of Heavy-Ion Collisions through Energy Correlators: celestial blocks and the spacetime structure of out-of-equilibrium QCD matter

TL;DR

This paper introduces a novel approach using energy correlators and celestial block decomposition to probe the early, anisotropic, out-of-equilibrium phase of QCD matter in heavy-ion collisions, revealing spacetime structure insights.

Contribution

It develops a new method combining classical Yang-Mills simulations, effective kinetic theory, and celestial block analysis to study early-time QCD dynamics through jet substructure.

Findings

Identified an observable sensitive to spatial anisotropies in out-of-equilibrium QCD matter.

Demonstrated qualitative agreement between analytical models and Monte Carlo simulations.

Proposed higher-point correlators to further probe microscopic QCD structures.

Abstract

Ultrarelativistic heavy-ion collisions provide a unique window into far-from-equilibrium states of QCD matter. The initial stages of these events are characterized by highly anisotropic, nonthermal dynamics that precede hydrodynamization, yet they remain largely inaccessible through conventional soft observables. In this work, we show that the substructure of mid-rapidity jets provides direct sensitivity to the spacetime structure of this early, anisotropic phase. Using classical Yang-Mills simulations and effective kinetic theory to model the early-time evolution of the jet quenching parameter, we compute the azimuthally differential energy-energy correlator within the BDMPS-Z framework. By decomposing the result into celestial blocks, we isolate the coefficients that encode the anisotropic geometry and dynamics of the underlying medium. We identify an observable that couples directly to spatial anisotropies in the out-of-equilibrium QCD matter and also discuss the impact of medium response on its behavior. We further extend our study to mid-rapidity jets generated with the JEWEL Monte-Carlo, adjusted to incorporate an anisotropic medium background, and find qualitative agreement with the analytical expectations. Finally, we discuss how higher-point energy correlators and generalized energy-flow operators can enhance the sensitivity to the microscopic structure of far-from-equilibrium QCD matter.