https://doi.org/10.1140/epjs/s11734-026-02261-7
Regular Article
Physics of collectivity and EOS from the RHIC Beam Energy Scan program
1
Institute of Modern Physics, Chinese Academy of Sciences, 730000, Lanzhou, China
2
School of Nuclear Science and Technology, University of Chinese Academy of Sciences, 100049, Beijing, China
3
Key Laboratory of Quark and Lepton Physics (MOE) and Institute of Particle Physics, Central China Normal University, 430079, Wuhan, China
a
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b
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Received:
28
October
2025
Accepted:
4
March
2026
Published online:
17
March
2026
Abstract
In this article, we will review recent measurements of directed flow 
and elliptic flow 
in Au + Au collisions from the STAR Beam Energy Scan (BES) program. We systematically analyze the distributions for identified hadrons (
, 
, 
) and 
hyperon as functions of rapidity (y), with particular focus on the mid-central collisions. The energy dependence of the slope is extracted across the BES range (
= 3–200 GeV). The atomic mass number (A) dependence of light nuclei and hypernuclei is analyzed to test the validity of the coalescence production mechanism. The constituent quark number (NCQ) scaling is systematically investigated based on measurements of identified particles and strange hadrons. We find that the NCQ scaling approximately holds in Au + Au collisions when 
4.5 GeV, but completely breaks down at = 3.0 and 3.2 GeV. The gradual restoration of NCQ scaling from 3.2 to 4.5 GeV suggests a possible transition in the dominant degrees of freedom from hadrons to partons. The physics of collectivity, the equation of state, and their relevance to the QCD phase diagram will be explored within the framework of both hydrodynamic and hadronic transport model calculations.
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© The Author(s), under exclusive licence to EDP Sciences, Springer-Verlag GmbH Germany, part of Springer Nature 2026
Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.
