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

A systemical analysis of the initial fluctuation effect on the collective flows for $\text{Au}+\text{Au}$ at $1A$ GeV is 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 reconstructed by 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 the squeeze-out effect, and some discrepancies between the flows extracted by these different plane methods appear, which indicate that the flows are affected by the evolution of dynamics. In addition, we find that the squeeze-out flow is also proportional to initial eccentricity. Our calculations also qualitatively give a trend for the excitation function of the elliptic flow similar to that of the FOPI Collaboration experimental data. Finally, we address the nucleon number scaling of the flows for light particles. Even though the initial fluctuation significantly decreases the ratio ${v}_{4}/{v}_{2}^{2}$ and ${v}_{3}/({v}_{1}{v}_{2})$, all fragments to mass number 4 keep the same curve and show independence from transverse momentum.