Universal geometrical scaling of the elliptic flow

TL;DR

This paper demonstrates a universal geometrical scaling law for elliptic flow across different collision energies and centralities, supporting the idea of underlying universal dynamics in high-energy nuclear collisions.

Contribution

It extends the concept of geometric scaling to elliptic flow data, showing a universal behavior from RHIC to LHC energies, including photons.

Findings

Excellent scaling observed across all energies and centralities

Photons also follow the scaling curve, challenging existing models

Supports the universality of initial or final state effects in collision dynamics

Abstract

The presence of scaling variables in experimental observables provide very valuable indications of the dynamics underlying a given physical process. In the last years, the search for geometric scaling, that is the presence of a scaling variable which encodes all geometrical information of the collision as well as other external quantities as the total energy, has been very active. This is motivated, in part, for being one of the genuine predictions of the Color Glass Condensate formalism for saturation of partonic densities. Here we extend these previous findings to the case of experimental data on elliptic flow. We find an excellent scaling for all centralities and energies, from RHIC to LHC, with a simple generalization of the scaling previously found for other observables and systems. Interestingly the case of the photons, difficult to reconcile in most formalisms, nicely fit the scaling curve. We discuss the possible interpretations of this finding in terms of initial or final state effects.