Theses and Dissertations from UMD
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Item DIRECTED AND ELLIPTIC FLOW MEASUREMENTS: A COMPARISON BETWEEN THE PARTICIPANT AND SPECTATOR PLANES IN Pb+Pb COLLISIONS AT √sNN = 5.02 TeV WITH CMS AT THE LHC(2024) Lascio, Samuel Andrew; Mignerey, Alice C.; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Directed and elliptic flow of unidentified charged hadrons at mid-rapidity are measured as a function of transverse momentum (pT) and pseudorapidity (η) in ultra-relativistic PbPb collisions at √sNN = 5.02 TeV with the Large Hadron Collider (LHC) at CERN. The reaction plane (RP) angle is approximated using participants and spectator neutrons measured with the Compact Muon Solenoid (CMS) detector and the newly installed Spectator Reaction Plane Detector (SRPD), respectively. The SRPD is the latest addition to the existing Zero Degree Calorimeter (ZDC) designed to measure spectator neutrons +/- 140 m from the interaction point at CMS. The Event Plane (EP) Method is used to calculate the v1odd, v1even, and v2 harmonic flow parameters as functions of η and pT. The directed flow measurements using participants and spectators with CMS are compared and contrasted. Overall results are in good agreement between participants and spectators, however v1even(pT) measurements using spectators begin to show the opposite trend to those using participants at pT > 2 GeV/c. Results are compared to those obtained by A Large Ion Collider Experiment (ALICE), which is another experiment at the CERN LHC. Directed flow results do not agree with those obtained by ALICE. Additionally, the first elliptic flow measurements using the EP Method and mixed harmonics with the SRPD are reported. A slight asymmetry in v2(η) is observed using spectators. The elliptic flow results do agree with ALICE. Tracking efficiency as determined by the CMS collaboration is applied to the data and potential corruption as a result is discussed. Results strongly support continued use of the SRPD as a spectator neutron detector for reaction plane determination within the CMS ZDC.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.