Percolation of color sources and the equation of state of QGP in central Au–Au collisions at $\sqrt{s_{\mathit{NN}}}=200$ GeV

Abstract

The Color String Percolation Model (CSPM) is used to determine the equation of state (EOS) of the QGP produced in central Au-Au collisions at $\sqrt{s_{NN}}$ = 200 A GeV using STAR data at RHIC. When the initial density of interacting colored strings exceeds the 2D percolation threshold a cluster is formed, which defines the onset of color deconfinement. These interactions also produce fluctuations in the string tension which transforms the Schwinger particle (gluon) production mechanism into a maximum entropy thermal distribution. The single string tension is determined by identifying the known value of the universal hadron limiting temperature $T_{c}$ = 167.7 $\pm$ 2.6 MeV with the CSPM percolation temperature at the critical threshold $\xi_{c}$ =1.2. At mid-rapidity the initial Bjorken energy density and the initial temperature determine the number of degrees of freedom consistent with the formation of a $\sim$ 2+1 flavor QGP. An analytic expression for the equation of state, the sound velocity $C_{s}^{2}(\xi)$ is obtained in CSPM. The CSPM $C_{s}^{2}(\xi)$ and the bulk thermodynamic values $\varepsilon /T^{4}$ and $s /T^{3}$ are in excellent agreement in the phase transition region with recent lattice QCD simulations (LQCD) by the HotQCD Collaboration.