Pressure evolution and flux tubes formation in the Glasma produced in high energy nuclear collisions

M. Ruggieri, L. Oliva. G. X. Peng, V. Greco

Published 2017-07-25Version 1

We consider the SU(2) Glasma with gaussian fluctuations and study its evolution by means of classical Yang-Mills equations solved numerically on a lattice. Neglecting in this first study the longitudinal expansion we follow the evolution of the pressures of the system and compute the effect of the fluctuations in the early stage up to $t\approx 2$ fm/c, that is the time range in which the Glasma is relevant for high energy collisions. We measure the ratio of the longitudinal over the transverse pressure, $P_L/P_T$, and we find that unless the fluctuations carry a substantial amount of the energy density at the initial time, they do not change significantly the evolution of $P_L/P_T$ in the early stage, and that the system remains quite anisotropic; in addition to this, we find that changing the spectrum of the initial fluctuations leaving at the same time the energy density unchanged, does not affect $P_L/P_T$ in a substantial way. We also measure the longitudinal fields correlators, which are important to understand the flux tube formation from the initial Glasma color strings: while at initial time fields appear to be anticorrelated, this anticorrelation disappears in the very early stage and the increase of the correlation length in the transverse plane signals the transition from color strings to color flux tubes. Moreover the gaussian fluctuations do not alter in a significant way the correlation functions.