In the beginning, there was quark gluon plasma (QGP). QGP persisted for only on the order of microseconds after the Big Bang. This exotic state of matter consists of deconfined quarks and gluons under extreme conditions. It is believed that the QGP state can be recreated in the laboratory through heavy-ion collisions at ultra-high energies. The Relativistic Heavy-Ion Collider (RHIC) at Brookhaven National Laboratory appears to produce sufficiently high energy to exceed the threshold for creating the QGP phase. There are four experiments at RHIC, and one of the largest is the Solenoidal Tracker at RHIC (STAR). The STAR detector utilizes a Time Projection Chamber with full azimuthal acceptance to track as many as thousands of produced particles from a single nucleus-nucleus collision. The QGP state of matter has many proposed signatures. This project explores the anisotropic elliptic flow properties of gold (Au) on gold collisions. Elliptic flow corresponds to the second harmonic coefficient (v2) of a Fourier decomposition of the transverse momentum distribution of emitted particles. Elliptic flow is the dominant term in the quantitative description of the collective motion among the particles produced in this type of heavy-ion collision.
The focus of this dissertation is on a single type of particle, the charged kaon (K±). Charged kaons are the least massive particles that contain strange quarks. Using conventional techniques based on rate of energy loss, identification of charged kaons becomes difficult above a momentum of ~ 600 MeV/c. This project uses a topological method to identify decaying charged kaons up to transverse momenta ~ 4 GeV/c. Our topological method has the drawback of relatively low efficiency, which decreases with increasing momentum.
The data set studied in this dissertation corresponds to gold on gold interactions at the maximum energy of the RHIC machine, and collisions across the full range of impact parameters are analyzed. Possible charged kaons are tagged from a list of candidates. The viable charged kaons are chosen using a series of stringent identification criteria. The reaction plane is determined for each event, and elliptic flow is calculated, correcting for the systematic effects caused by the finite reaction plane resolution.
The dependence of elliptic flow on transverse momentum is highly significant when different particle types can be compared. The data for charged kaons falls into a pattern where there is a universal curve for the amount of flow per constituent quark as a function of the quark's transverse momentum. This universal curve can account for the flow observed for all known particle types. It suggests that the collective motion must have been imparted during the early phase of the collision when a QGP state existed. A different pattern would be expected if the collective motion had been imparted after the quarks had coalesced into hadrons, or if the QGP state had not been formed at all. The dissertation discusses the significance of the new evidence, and the caveats and possible alternative explanations.
|Advisor:||Keane, Declan, Margetis, Spiros|
|Commitee:||Aron, Richard, Fai, George, Keane, Declan, Margetis, Spiros, Selinger, Robin|
|School:||Kent State University|
|Department:||College of Arts and Sciences / Department of Physics|
|School Location:||United States -- Ohio|
|Source:||DAI-B 78/11(E), Dissertation Abstracts International|
|Subjects:||Physics, Nuclear physics|
|Keywords:||Elliptic, Elliptic flow, GeV/c, Kaons, Particle, Quarks|
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