Harmonic flow correlations in Au+Au reactions at 1.23 AGeV: A new testing ground for the Equation-of-State and expansion geometry

TL;DR

This study investigates harmonic flow correlations in semi-peripheral Au+Au collisions at 1.23 AGeV using UrQMD, revealing strong correlations between flow coefficients and their dependence on rapidity, providing new insights into the Equation-of-State and expansion geometry.

Contribution

It predicts strong correlations between harmonic flow coefficients with respect to the reaction plane at low energies, offering a new testing ground for the Equation-of-State and expansion geometry.

Findings

Sign change of triangular flow with rapidity

Shape of $v_4$ changes from convex to concave

$v_3$ and $v_4$ show specific proportionalities to $v_1v_2$ and $v_2^2$

Abstract

Correlations between the harmonic flow coefficients $v_1$, $v_2$, $v_3$ and $v_4$ of nucleons in semi-peripheral Au+Au collisions at a beam energy of 1.23~AGeV are investigated within the hadronic transport approach Ultra-relativistic Quantum Molecular Dynamics (UrQMD). In contrast to ultra-relativistic collision energies (where the flow coefficients are evaluated with respect to the respective event plane), we predict strong correlations between the flow harmonics with respect to the reaction plane. Based on an event-by-event selection of the midrapidity final state elliptic flow of protons we show that as a function of rapidity, I) the sign of the triangular flow changes, II) that the shape of $v_4$ changes from convex to concave, and III) that $v_3\propto v_1v_2$ and $v_4\propto v_2^2$ for all different event classes, indicating strong correlations between all investigated harmonic flow coefficients.