# Probing the onset of collectivity via scaled particle spectra in ultrarelativistic nuclear collisions

## TL;DR

This paper uncovers a universal scaled particle spectrum in ultrarelativistic nuclear collisions, highlighting collective fluid-like behavior of the quark-gluon plasma and offering a new way to constrain QCD transport properties.

## Contribution

It introduces a novel scaling of particle spectra that reveals universal features across different collision systems and centralities, advancing understanding of QGP collectivity.

## Key findings

- Universal scaled spectrum observed across systems and centralities
- The scaled spectrum constrains QCD transport properties independently
- Current models have limitations revealed by the scaled spectrum analysis

## Abstract

We identify a novel scaling in the transverse momentum spectra of produced particles, obtained by removing the global scales of multiplicity and mean transverse momentum. Hydrodynamic simulations and experimental data reveal an almost universal scaled spectrum across centralities, systems, and even small systems, pointing to its origin in the collective, fluid-like dynamics of the QGP. Comparing this observable with Bayesian a priori distributions shows its independent constraining power on QCD transport properties, while also exposing limitations of current models. A detailed posterior analysis will be pursued in future work, opening a new avenue to refine our understanding of collectivity in heavy-ion collisions.