[Paper Review] Ab Initio Coupling of Jets to Collective Flow in the Opacity Expansion Approach

Andrey V. Sadofyev|arXiv (Cornell University)|Apr 19, 2021

High-Energy Particle Collisions Research21 references7 citations

TL;DR

This paper computes leading-order corrections to jet momentum broadening and medium-induced branching due to medium velocity and transverse gradients in temperature and density within the opacity expansion. It reveals anisotropic transverse momentum diffusion and directional radiation emission tied to collective flow, enabling direct coupling to hydrodynamic simulations for jet-quenching studies in heavy-ion and electron-ion collisions.

ABSTRACT

We calculate the leading corrections to jet momentum broadening and medium-induced branching that arise from the velocity of the moving medium at first order in opacity. These results advance our knowledge of jet quenching and demonstrate how it couples to collective flow of the quark-gluon plasma in heavy-ion collisions and to the orbital motion of partons in cold nuclear matter in deep inelastic scattering at the electron-ion collider. We also compute the leading corrections to jet momentum broadening due to transverse gradients of temperature and density. We find that these effects lead to both anisotropic transverse momentum diffusion proportional to the medium velocity and anisotropic medium-induced radiation emitted preferentially in the direction of the flow. We isolate the relevant sub-eikonal corrections by working with jets composed of scalar particles with arbitrary color factors interacting with the medium by scalar QCD. Appropriate substitution of the color factors and light-front wave functions allow us to immediately apply the results to a range of processes including $q ightarrow q g$ branching in real QCD. The resulting general expressions can be directly coupled to hydrodynamic simulations on an event-by-event basis to study the correlations between jet quenching and the dynamics of various forms of nuclear matter.

Motivation & Objective

• To understand how jet quenching couples to collective flow in quark-gluon plasma during heavy-ion collisions.
• To identify sub-eikonal corrections from medium velocity and transverse gradients in temperature and density.
• To develop a framework for computing jet momentum broadening and branching corrections in non-uniform media.
• To enable direct coupling of jet dynamics to hydrodynamic simulations for event-by-event analysis.
• To generalize results from scalar QCD to real QCD processes like $q \to qg$ branching via color factor and wave function substitution.

Proposed method

• Employing the opacity expansion approach to compute leading corrections in medium velocity and transverse gradients.
• Using scalar particles with arbitrary color factors to isolate sub-eikonal effects in scalar QCD.
• Deriving corrections to momentum broadening and medium-induced branching from velocity and thermal/density gradients.
• Applying appropriate color factors and light-front wave functions to map results to real QCD processes.
• Formulating general expressions for anisotropic diffusion and radiation that can be fed into hydrodynamic simulations.
• Working in the light-front formalism to ensure compatibility with event-by-event hydrodynamic modeling.

Experimental results

Research questions

• RQ1 How does medium velocity at leading order in opacity affect jet momentum broadening and branching?
• RQ2 What are the leading corrections to jet quenching from transverse gradients in temperature and density?
• RQ3 How does collective flow in the quark-gluon plasma induce anisotropic diffusion and directional radiation in jets?
• RQ4 In what way do sub-eikonal corrections from medium motion modify jet energy loss and radiation patterns?
• RQ5 Can the scalar QCD framework be systematically extended to real QCD processes like $q \to qg$ branching?

Key findings

• Medium velocity induces anisotropic transverse momentum diffusion proportional to the flow velocity.
• Transverse gradients in temperature and density generate additional anisotropic corrections to jet broadening.
• Medium-induced radiation is preferentially emitted in the direction of the medium’s collective flow.
• The framework isolates sub-eikonal corrections that are essential for accurate jet quenching modeling in non-uniform media.
• General expressions derived in scalar QCD can be directly applied to real QCD processes via color factor and wave function substitution.
• The results enable event-by-event coupling of jet quenching to hydrodynamic simulations of nuclear matter.