Effect of initial fluctuations on the collective flow in intermediate-energy heavy ion collisions

TL;DR

This study investigates how initial fluctuations influence collective flow patterns in intermediate-energy heavy ion collisions, revealing that fluctuations weaken squeeze-out effects and affect flow measurements, with implications for understanding collision dynamics.

Contribution

It provides a systematic analysis of initial fluctuation effects on collective flows using the IQMD model, highlighting their impact on flow observables and scaling behaviors.

Findings

Initial fluctuations weaken the squeeze-out effect.

Flow measurements are affected by the evolution of dynamics.

Flow ratios show nucleon number scaling despite fluctuations.

Abstract

A systemical analysis of the initial fluctuation effect on the collective flows for Au+Au at 1$A$ GeV has been presented in the framework of Isospin-dependent Quantum Molecular Dynamics model (IQMD), and a special focus on the initial fluctuation effect on the squeeze-out is emphasized. The flows calculated by the participant plane reconstructedby the initial geometry in coordinate space are compared with those calculated by both the ideal reaction plane and event plane methods. It is found that initial fluctuation weakens squeeze-out effect, and somediscrepancies between the flows extracted by the above different plane methods appearwhich indicate that the flows are affected by the evolution of dynamics. In addition, we found that the squeeze-out flow is also proportional to initial eccentricity. Our calculations also qualitatively give the similar trend for the excitation function of the elliptic flow of the FOPI experimental data. Finally we address the nucleon number scaling of the flows for light particles. Even though initial fluctuation decreases the ratio of $v_4/v_2^2$ as well as $v_3/(v_1v_2$) a lot, all fragments to mass number 4 keep the same curve and shows independent of transverse momentum.