Disappearance of partonic collectivity in $\sqrt{s_{NN}}$ = 3 GeV Au+Au collisions at RHIC

TL;DR

This study measures flow patterns in gold-gold collisions at 3 GeV, revealing the disappearance of partonic collectivity and dominance of baryonic interactions, contrasting with higher energy results.

Contribution

It provides the first detailed flow measurements at 3 GeV, showing the breakdown of NCQ scaling and highlighting baryonic interactions in the medium.

Findings

Negative $v_2$ for all hadrons at 3 GeV

Positive $v_1$ slopes indicating repulsive baryonic interactions

Transport models reproduce observed flow features

Abstract

We report on the measurements of directed flow $v_1$ and elliptic flow $v_2$ for hadrons ($\pi^{\pm}$, $K^{\pm}$, $K_{S}^0$, $p$, $\phi$, $\Lambda$ and $\Xi^{-}$) from Au+Au collisions at $\sqrt{s_{NN}}$ = 3\,GeV and $v_{2}$ for ($\pi^{\pm}$, $K^{\pm}$, $p$ and $\overline{p}$) at 27 and 54.4\,GeV with the STAR experiment. While at the two higher energy midcentral collisions the number-of-constituent-quark (NCQ) scaling holds, at 3\,GeV the $v_{2}$ at midrapidity is negative for all hadrons and the NCQ scaling is absent. In addition, the $v_1$ slopes at midrapidity for almost all observed hadrons are found to be positive, implying dominant repulsive baryonic interactions. The features of negative $v_2$ and positive $v_1$ slope at 3\,GeV can be reproduced with a baryonic mean-field in transport model calculations. These results imply that the medium in such collisions is likely characterized by baryonic interactions.