Clustering of Color sources and the Equation of State in Heavy Ion Collisions at RHIC and LHC Energies

Abstract

The initial temperature $T_{i}$, energy density $\varepsilon_{i}$, and formation time $\tau_{i}$ of the initial state of the QGP formed in the heavy ion collisions at RHIC and LHC energies are determined using the data driven Color String Percolation Model (CSPM). Multiparticle production by interacting strings stretched between projectile and target form a spanning cluster at the percolation threshold. The relativistic kinetic theory relation for $\eta/s$ is evaluated as a function of $\it T$ and the mean free path ($\lambda_{mfp}$) using data and CSPM. $\eta/s$($T_{i}$, $\lambda_{mfp}$) describes the transition from a strongly interacting QGP at $T/T_{c} \sim 1$ to a weakly coupled QGP at $T/T_{c} \ge 6$. We find that the reciprocal of $\eta/s$ is equal to the trace anomaly $\Delta = \varepsilon-3P/T^{4}$ which also describes the transition. We couple this initial state of the QGP to a 1D Bjorken expansion to determine the sound velocity $c_{s}^{2}$ of the QGP for 0.85 $\le T/T_{c} \leq 3$. The bulk thermodynamic quantities and the equation of state are in excellent agreement with LQCD results.