Simulation of symmetric cumulants in heavy-ion collisions

Abstract

The quark-gluon plasma (QGP) is a fluid of free quarks and gluons that exists under the extreme conditions of high temperature and/or high pressure. This plasma can be investigated by performing high energy heavy-ion collisions. These collisions can also be simulated by computer models, which will be done at a centre of mass energy of sqrt(s_NN) = 5.02 TeV in this research. These models contain parameters that one would like to know, e.g. parameters for the shear viscosity eta/s of the QGP. After the collision, there are different stages that have to be described. One of these stages is the QGP, which can be described by hydrodynamics. We will see how the physics of the different stages works and how it can be implemented in a computer program, from the initial collision to the final particles that hit the detectors. We will then describe how relevant physical information can be extracted from these detections. It will turn out that the momentum distribution transverse to the collision axis will not be isotropic, which can be characterised by the flow coefficients v_n, of which the elliptic flow v_2 will be the most important one. We will also introduce the Symmetric Cumulants, an observable that is not yet implemented in the currently used program. They measure the correlation between the different flow coefficients. We will look at different system sizes to get a complete view of this observable.

The information about different observables can be compared to experimental data. By using Bayesian analysis, one can obtain a good guess for the values of the different parameters. In this way, we can investigate the quark-gluon plasma and the other important physics of a heavy-ion collision. The hope is that the simulated Symmetric Cumulants are sensitive for the chosen set of parameters, so that this additional observable will constrain the parameters further.