Mapping Nuclear Deformation with Differential Radial Flow in Heavy-Ion Collisions

TL;DR

This study uses advanced hydrodynamic simulations to explore how nuclear deformation influences radial flow patterns in heavy-ion collisions, revealing correlations and decorrelation effects that can inform nuclear structure understanding.

Contribution

It is the first to systematically analyze the impact of nuclear deformation on differential radial flow, including transverse and longitudinal fluctuations, using realistic 3D hydrodynamic models.

Findings

Quadrupole deformation $eta_2$ enhances radial flow in central collisions.

Universal step-like behavior of Pearson coefficient $ ho(n(p_T), [p_T])$ across systems.

Large $eta_2$ suppresses, while $eta_4$ enhances longitudinal flow decorrelation.

Abstract

In relativistic heavy-ion collisions, the radial flow of the fireball, usually characterized by transverse momentum spectra of final-state particles, encodes essential information about the hot and dense nuclear matter created in the collisions. However, the response of radial flow, including its $p_T$-differential structure $v_0(p_T)$ and longitudinal fluctuations $v_0(\eta)$, to intrinsic nuclear deformation remains unexplored. Using realistic $(3+1)$-dimensional viscous hydrodynamic calculations with Trento-3D initial conditions, we investigate how nuclear deformation affects the differential radial flow. We observe a clear, positive correlation between quadrupole deformation $\beta_2$ and radial flow: both magnitudes of $v_0$ and $v_0(p_T)$ are enhanced in central collisions when $\beta_2$ is increased. In contrast, the Pearson coefficient $\rho(n(p_T), [p_T])$ exhibits a universal step-like behavior across all collision systems and centralities. Further analysis of longitudinal decorrelation of radial flow reveals a rich structure: in central collisions, large $\beta_2$ tends to suppress the decorrelation, whereas hexadecapole deformation $\beta_4$ tends to enhance it. Such decorrelation effect increases toward peripheral collisions. Our results demonstrate that precise measurements of radial flow, spanning transverse momentum and longitudinal dependences, can provide powerful, complementary constraints on nuclear deformation in high-energy nucleus-nucleus collisions.