Effects of initial flow velocity fluctuation in event-by-event (3+1)D hydrodynamics

TL;DR

This study investigates how initial flow velocity fluctuations in event-by-event (3+1)D hydrodynamics affect hadron spectra and elliptic flow in high-energy heavy-ion collisions, highlighting the impact of initial conditions on final observables.

Contribution

It introduces a detailed modeling of initial flow velocity fluctuations from semi-hard scatterings and their effects on final particle spectra and flow in hydrodynamic simulations.

Findings

Initial flow velocity fluctuations lead to harder transverse momentum spectra.

Fluctuations cause a reduction in elliptic flow at high transverse momentum.

Semi-hard scatterings significantly influence initial flow conditions.

Abstract

Hadron spectra and elliptic flow in high-energy heavy-ion collisions are studied within a (3+1)D ideal hydrodynamic model with fluctuating initial conditions given by the AMPT Monte Carlo model. Results from event-by-event simulations are compared with experimental data at both RHIC and LHC energies. Fluctuations in the initial energy density come from not only the number of coherent soft interactions of overlapping nucleons but also incoherent semi-hard parton scatterings in each binary nucleon collision. Mini-jets from semi-hard parton scatterings are assumed to be locally thermalized through a Gaussian smearing and give rise to non-vanishing initial local flow velocities. Fluctuations in the initial flow velocities lead to harder transverse momentum spectra of final hadrons due to non-vanishing initial radial flow velocities. Initial fluctuations in rapidity distributions lead to expanding hot spots in the longitudinal direction and are shown to cause a sizable reduction of final hadron elliptic flow at large transverse momenta.