Onset of Constituent Quark Number Scaling in Heavy-Ion Collisions at RHIC

Le résumé fourni par la source

Partonic collectivity is one of the necessary signatures for the formation of quark-gluon plasma in high-energy nuclear collisions. Number of constituent quarks (NCQ) scaling has been observed for hadron elliptic flow ${v}_{2}$ in top energy nuclear collisions at the Relativistic Heavy Ion Collider and the LHC, and this has been theoretically suggested as strong evidence for partonic collectivity. In this Letter, a systematic analysis of ${v}_{2}$ of ${\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}$, ${K}^{\ifmmode\pm\else\textpm\fi{}}$, ${K}_{S}^{0}$, $p$, and $\mathrm{\ensuremath{\Lambda}}$ in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{{s}_{\mathrm{NN}}}=3.2$, 3.5, 3.9, and 4.5 GeV, with the STAR experiment at the Relativistic Heavy Ion Collider, is presented. NCQ scaling is markedly violated at 3.2 GeV, consistent with a hadronic-interaction dominated equation of state. However, as the collision energy increases, a gradual evolution to NCQ scaling is observed. This beam-energy dependence of ${v}_{2}$ for all hadrons studied provides evidence for the onset of dominant partonic interactions by $\sqrt{{s}_{\mathrm{NN}}}=4.5\text{ }\text{ }\mathrm{GeV}$.

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