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

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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.