Elliptic flow in Au+Au collisions at 200 GeV per nucleon pair

Abstract

The Relativistic Heavy Ion Collider (RHIC) has provided its experiments with the most energetic nucleus-nucleus collisions ever achieved in a laboratory. These collisions allow for the study of the properties of nuclear matter at very high temperature and energy density, and may uncover new forms of matter created under such conditions. This thesis presents measurements of the elliptic flow amplitude, v₂, in Au+Au collisions at RHIC's top center of mass energy of 200 GeV per nucleon pair. Elliptic flow is interesting as a probe of the dynamical evolution of the system formed in the collision. The elliptic flow dependences on transverse momentum, centrality, and pseudorapidity were measured using data collected by the PHOBOS detector during the 2001 RHIC run. The reaction plane of the collision was determined using the multiplicity detector, and the azimuthal angles of tracks reconstructed in the spectrometer were then correlated with the found reaction plane. The v₂ values grow almost linearly with transverse momentum, up to P[sub]T of approximately 1.5 GeV, saturating at about 14%. As a function of centrality, v₂ is minimum for central events, as expected from geometry, and increases up to near 7% (for 0 < [eta] < 1) at (N[sub]part) = 83. The v2 dependence on pseudorapidity was measured over the range 0 < [eta] < 1.8 for three centrality rangess: 3-15%, 15-25% and 25-50%. For all but the most central of the three centrality ranges, v₂ is seen to decrease with increasing starting already near mid-rapidity. The results, their comparison to models and interpretation are discussed.