Scientists from Brookhaven National Laboratory, Lawrence Berkeley National Laboratory, UC Berkeley and Wayne State University studied the properties of quark-gluon plasma , an aggregate form of matter that exists in the first moments after the Big Bang. The results of the study were published in the journal Physical Review Letters.
Quark-gluon plasma is a liquid of quarks and gluons formed during high-energy collisions of heavy atomic nuclei. In ordinary matter, quarks exist only in a bound state (confinement) due to the powerful nuclear force that produces hadrons. At extremely high temperatures, however, the quarks are in a free state. Just as in an ordinary plasma there is a separation of charges (ionization) of the initially neutral atoms, in a quark-gluon plasma there is a separation of the colored charges of the initially colorless (“white”) hadronic matter.
The quark-gluon plasma has a very low viscosity, which characterizes its resistance to flow. To track changes in viscosity, the scientists developed a new model. It combines the dynamics of viscous fluids in all three spatial dimensions with dynamical models of the initial stage of collisions in the Relativistic Heavy Ion Accelerator (RHIC). Taking into account the evolution of the initial state allowed the researchers to more accurately describe the processes at low beam energies, when the instantaneous collision assumption is invalid. Five million numerically simulated events were used to gather statistics.
The plasma viscosity was found to increase with increasing net baryon density, that is, with increasing relative abundance of baryons (particles consisting of three quarks) compared to antibaryons. This is consistent with some theoretical predictions and allows the models to better fit the experimental data for collisions of gold nuclei at different energies.