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Probing momentum dependence of hydrodynamization in heavy-ion collisions

Akihiko Monnai

TL;DR

The paper addresses momentum-dependent hydrodynamization in heavy-ion collisions by extending relativistic hydrodynamics to non-thermal momentum distributions. It develops two non-thermal schemes: (i) Tsallis-based hydrodynamics that embeds a high-$p_T$ tail via the Tsallis parameter $q$ in the distribution with a modified equation of state, and (ii) a momentum-cutoff approach that excludes medium-high momentum from the bulk while ensuring a smooth hadron–QGP transition. A key finding is that $q>1$ elevates $P/T^4$ at the critical temperature $T_c$, extending the hydrodynamic description to higher $p_T$ for charged hadrons, while the cutoff scenario can non-trivially affect direct-photon elliptic flow through the modified photon emission rates and source mix. The work provides momentum-differentiated insights into flow observables and photon anisotropies in heavy-ion collisions, offering new handles on QGP dynamics and outlining future directions including viscosity and event-by-event analyses.

Abstract

The fluidity of the hot and dense QCD matter is a key characteristic of the medium created in high-energy heavy-ion collisions. We extend the framework of the relativistic hydrodynamic model to incorporate non-thermal momentum distributions that may emerge during the dynamical evolution of the collision system. Numerical simulations are performed to elucidate the phenomenological implications of these modifications on charged hadrons and direct photons measured in collider experiments.

Probing momentum dependence of hydrodynamization in heavy-ion collisions

TL;DR

The paper addresses momentum-dependent hydrodynamization in heavy-ion collisions by extending relativistic hydrodynamics to non-thermal momentum distributions. It develops two non-thermal schemes: (i) Tsallis-based hydrodynamics that embeds a high- tail via the Tsallis parameter in the distribution with a modified equation of state, and (ii) a momentum-cutoff approach that excludes medium-high momentum from the bulk while ensuring a smooth hadron–QGP transition. A key finding is that elevates at the critical temperature , extending the hydrodynamic description to higher for charged hadrons, while the cutoff scenario can non-trivially affect direct-photon elliptic flow through the modified photon emission rates and source mix. The work provides momentum-differentiated insights into flow observables and photon anisotropies in heavy-ion collisions, offering new handles on QGP dynamics and outlining future directions including viscosity and event-by-event analyses.

Abstract

The fluidity of the hot and dense QCD matter is a key characteristic of the medium created in high-energy heavy-ion collisions. We extend the framework of the relativistic hydrodynamic model to incorporate non-thermal momentum distributions that may emerge during the dynamical evolution of the collision system. Numerical simulations are performed to elucidate the phenomenological implications of these modifications on charged hadrons and direct photons measured in collider experiments.
Paper Structure (6 sections, 6 equations, 4 figures)

This paper contains 6 sections, 6 equations, 4 figures.

Table of Contents

  1. Introduction
  2. The model
  3. Hydrodynamic model with high-momentum components
  4. Hydrodynamic model with low-momentum components
  5. Numerical results
  6. Summary and conclusion

Figures (4)

  • Figure 1: Schematic of transverse momentum spectra in nuclear collisions and momentum regions covered by the hydrodynamic model with (a) conventional thermal distribution, (b) Tsallis distribution, and (c) thermal distribution with a momentum cutoff.
  • Figure 2: The equation-of-state models (a) with Tsallis statistics and (b) with momentum cutoffs.
  • Figure 3: Charged particle $p_T$ spectra for (a) 0-5% and (b) 20-30% centrality classes and (c) $v_2$ for the 20-30% centrality class with thermal ($q=1$) and Tsallis ($q=1.07$) distributions.
  • Figure 4: Elliptic flow of (a) thermal photons, (b) thermal and prompt photons, and (c) direct photons with different momentum cutoffs.