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Abstract
Ultra-relativistic heavy ion collisions are believed to produce a state of deconfined quark-gluon plasma that is similar to the universe just after the Big Bang. To investigate the properties of this matter, a Beam Energy Scan was performed at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Lab. Information about the phase diagram describing the matter produced in these collisions can be gained by studying the beam energy dependence of various observables. One such analysis is Hanbury Brown Twiss (HBT) interferometry which is used to measure the size and shape of the regions emitting particles which are in turn related to dynamical processes that drive the evolution of the collisions.
In this thesis analyses using two-pion HBT interferometry are presented for Au+Au collisions at sqrt(sNN) = 7.7, 11.5, 19.6, 27, 39, 62.4, and 200 GeV measured in the STAR detector during the Beam Energy Scan program. The dependence of extracted correlation lengths (radii) are studied as a function of beam energy, azimuthal angle relative to the reaction plane, centrality and transverse mass, mT. The eccentricity of the entire fireball at kinetic freeze-out can be extracted from the azimuthally-differential analysis. This freeze-out shape is believed to be sensitive to changes in the equation of state when measured as a function of beam energy. A new global fit method is studied as an alternate method to directly measure the parameters in the azimuthal analysis. The freeze-out eccentricity is observed to decrease monotonically with beam energy which is qualitatively consistent with the trends from all model predictions and quantitatively most consistent with a hadronic transport model.
