Complementary Approach to Anisotropic Flows in Heavy-Ion Collisions

TL;DR

The paper presents a new no-reaction-plane method for extracting flow coefficients in heavy-ion collisions, validated with simulations, which simplifies flow measurement by avoiding event-plane reconstruction.

Contribution

A novel no-reaction-plane approach for flow analysis that accurately captures flow fluctuations without reconstructing the event plane.

Findings

The method yields Pearson correlations of 0.985 for v2 and 0.883 for v1 with true reaction plane calculations.

Both asymmetries for each harmonic contribute equally, enabling simplified flow estimation.

Validation with PHSD simulations confirms the method's effectiveness.

Abstract

We introduce a no-reaction-plane (no-RP) method for extracting directed (\(v_1\)) and elliptic (\(v_2\)) flows in heavy-ion collisions, which eliminates the need for event-plane reconstruction. %by scanning over fixed test angles and using simple count asymmetries. The method is validated with PHSD model simulations of Au+Au collisions at \(\sqrt{s_{NN}} = 9.2\) GeV at freeze-out (impact parameter \(b = 4\) fm). We demonstrate that the two asymmetries for each harmonic contribute equally, i.e., \(\langle A_{\mathrm{ud}}^2\rangle \approx \langle A_{\mathrm{lr}}^2\rangle\) and \(\langle A_1^2\rangle \approx \langle A_2^2\rangle\), so that a single asymmetry measurement suffices for a good flow estimate. Event-by-event comparisons with direct calculations using the true reaction plane yield Pearson correlation coefficients of 0.985 for \(v_2\) and 0.883 for \(v_1\), confirming that the no-RP method captures flow fluctuations well enough.