The onset of hydrodynamical flow in high energy heavy ion collisions

In this proceedings, we present recent improvements of the Color Glass Condensate effective theory that amounts to taking fully into account the first αs correction to the leading order solution, as well as a subset of higher order corrections. All these corrections are coming from the initial condition, and one can therefore apply the classical-statistical approximation (CSA) that amounts to solve the classical Yang-Mills equation of motion with fluctuating initial condition. On the numerical side, this leads to a fast isotropization of the pressure tensor at already small couplings. In addition, the system seems to experience an anomalously small shear viscosity over entropy ratio.