Elliptic flow of anti-protons, kaons and pions in Pb-Pb collisions at 2.76 TeV

Abstract

According to the Standard Model of particle physics all matter is made up of fundamental, point-like particles called quarks and leptons. The quarks interact via the strong force, which is mediated by a gauge boson called the gluon. Quantum Chromodynamics (QCD) describes the interactions between quarks and gluons. QCD predicts a phase transition at high temperatures and high densities to a very hot and dense state of matter consisting of new degrees of freedom, called the Quark Gluon Plasma (QGP). It is believed that a QGP existed shortly after the Big Bang and might still exist in heavy neutron stars.

To study the QGP in the laboratory heavy ions are collided using particle accelerators. ALICE is one of the seven LHC experiments at CERN. Its aim is to study the phase transition to the QGP. The data used for this research is the full sample from run 1 of the LHC Pb-Pb runs in 2010, at a center of mass energy of 2.76 TeV per nucleon-pair.

The QGP cannot be observed directly, but as it expands and cools down hadrons are formed that can be detected. The anisotropy of the azimuthal momentum distribution of the formed hadrons is described by a Fourier expansion of which the second coefficient is called the elliptic flow. In this thesis the elliptic flow of anti-protons, kaons and pions is studied using the scalar product method. The elliptic flow is compared qualitatively with a viscous hydrodynamic model to investigate mass ordering of the particle species. In the first chapter some background information is provided.