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

¹ Instituto de Física, Universidade de São Paulo, R. do Matão, 1371, São Paulo, SP, Brazil
² Instituto de Ciencia e Tecnologia, Universidade Federal de Alfenas, Poços de Caldas, MG, Brazil
³ Stefan Meyer Institute for Subatomic Physics of the Austrian Academy of Sciences, Wiesingerstraße 4 1010 Vienna, Austria
⁴ Instituto de Física, Universidade Federal Fluminense, Av. Milton Tavares de Souza, Niterói, RJ, Brazil
⁵ Faculdade de Ciências Exatas e Tecnologia, Universidade Federal da Grande Dourados, Dourados, MS, Brazil
⁶ Universidade Estadual de Campinas, R. Sérgio Buarque de Holanda, 777, Campinas, SP, Brazil
⁷ Illinois Center for Advanced Studies of the Universe & Department of Physics, University of Illinois at Urbana-Champaign, Urbana, IL, 61801-3003, USA
⁸ Departamento de Física, Centro de Ciências Físicas e Matemáticas, Universidade Federal de Santa Catarina, Campus Universitário Reitor João David Ferreira Lima, Florianópolis, Brazil

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Published online: 17 April 2026

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.