Theses and Dissertations from UMD
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Item Elliptic flow at forward rapidity in sqrt(s_(NN)) = 200 GeV Au+Au collisions(2012) Richardson, Eric; Mignerey, Alice C.; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Forward rapidity elliptic flow (v2) of both unidentified charged hadrons and decay muons has been measured from √sNN = 200 GeV Au+Au collisions as a function of pseudorapidity (η), transverse momentum, and number of nucleon collision participants. The measurements were performed at Brookhaven National Laboratory's Relativistic Heavy Ion Collider using the PHENIX experiment's Muon Arm spectrometers, located at 1.2 < |η| 2.4. To identify hadrons, which consist mostly of pions, kaons, and protons, a longitudinal momentum cut was applied to tracks stopping in the shallow steel layers of the Muon Arms. Those particles traversing completely through the Muon Arms consist of mostly muons from pion and kaon decays. The standard event plane (EP) method was used to measure v2, whose accuracy was improved ∼20-25% by combining the measured EP angles of several detectors, instead of using the measured EP from a single detector. Additionally, a hit swapping technique was devised to optimize track cuts, estimate background, and apply a background correction. To investigate the ability of the Muon Arms to accurately measure unidentified hadron v2, a GEANT simulation was also undertaken. The forward rapidity v2 results show good agreement with mid-rapidity measurements for central collisions ( 20-30% centrality), indicating a longitudinally extended thermalized medium with similar eccentricity, at least out to the Muon Arm η region. Only when compared to very forward BRAHMS measurements (η ≈ 3) is a v2 suppression seen for central collisions. For increasingly peripheral collisions, a growing suppression in v2 is observed for the Muon Arm measurements compared to mid-rapidity, indicating increased changes in the medium properties of ever smaller systems. For peripheral collisions of the same/similar centralities, an increased suppression is observed toward forward η.Item Elliptic Flow Measured with the PHOBOS Spectrometer at RHIC(2008-07-28) Bindel, Richard Thomas; Mignerey, Alice C; Mignerey, Alice; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory provides experiments with the most energetic nucleus-nucleus collisions ever achieved in a laboratory. These have been used to investigate the phase diagram of nuclear matter at very high temperature and low baryon chemical potential. Under such conditions, quantum chromodynamics predicts a deconfinement of quarks from their hadronic boundaries, and this is believed to result in a phase transition to a quark gluon plasma (QGP). The characterization of the substance in a microscopic collision system is difficult because the matter undergoes significant changes as it rapidly inflates and cools. The collective expansion of the medium perpendicular to the collision axis is a revealing feature that can be related to the early stages of the system evolution. Arising as a consequence of the natural spatial asymmetry in non-head-on collisions, the back-to-back "elliptic flow" is a particularly informative mode of the expansion. The collective movement is characterized in terms of the relaxation of a compressed liquid. The magnitude of the elliptic flow constrains the parameters of various hydrodynamics-based models, and these suggest that the matter behaves as an ultra low-viscosity liquid, achieving local thermal equilibrium very early in the collision evolution. This thesis presents measurements of the elliptic flow anisotropy parameter, v2, for Au+Au and Cu+Cu collisions at center-of-mass energies of 200 GeV and 62 GeV per nucleon pair. The data was taken at the PHOBOS experiment at RHIC using the spectrometer in conjunction with the ring and octagon multiplicity detectors. A Monte Carlo Glauber model is used to establish the eccentricity of the overlap region in non-head-on collisions. When this geometry is taken into account, the elliptic flow is shown to evolve smoothly between collision systems. This behavior is evident, not only in the elliptic flow as a function of reaction centrality, but also as a function of the transverse momentum. The agreement lends support to the prevailing theory of a smooth progression with increasing system size and collision energy towards a hydrodynamic limit.