# Disentangle contributions to small-system collectivity via scans of light nucleus-nucleus collisions

## TL;DR

This paper proposes a systematic scan of small symmetric nucleus-nucleus collisions at RHIC to differentiate between initial-state and final-state origins of observed collective effects in small systems.

## Contribution

It introduces a new experimental approach using symmetric small systems and transport models to disentangle initial-state and final-state contributions to collectivity.

## Key findings

- Different elliptic flow trends observed between symmetric and asymmetric systems.
- Triangular flow shows similar behavior across systems.
- Comparison of O+O collisions at different energies aids in understanding geometry effects.

## Abstract

The observation of multi-particle azimuthal correlations in high-energy small-system collisions has led to intense debate on its origin and the possible coexistence from two competing theoretical scenarios: one based on initial-state intrinsic momentum anisotropy (ISM), and the other based on final-state collective response to the collision geometry (FSM). To complement the previous scan of asymmetric collision systems ($p$+Au, $d$+Au and He+Au), we propose a scan of small symmetric collision systems at RHIC, such as C+C, O+O, Al+Al and Ar+Ar $\sqrt{s_{\mathrm{NN}}}=0.2$ TeV, to provide further insights in disentangling contributions from these two scenarios. These symmetric small systems have the advantage of providing a better controlled initial geometry dominated by the average shape of the overlap region, as opposed to fluctuation-driven geometries in asymmetric systems. A transport model is employed to investigate the expected geometry response in the FSM scenario. Different trends of elliptic flow with increasing charge particle multiplicity are observed between symmetric and asymmetric systems, while triangular flow appears to show a similar behavior. Furthermore, a comparison of O+O collisions at $\sqrt{s_{\mathrm{NN}}}=0.2$ TeV and at $\sqrt{s_{\mathrm{NN}}}=2.76-7$ TeV, as proposed at the LHC, provides a unique opportunity to disentangle the collision geometry effects at nucleon level from those arising from subnucleon fluctuations.