Quantum chromodynamics (QCD) is the theory that concerns how the strong force interacts with subatomic particles. Topological configurations that interpolate between vacuum states have been shown to play an important role in the quark-gluon plasma (QGP), believed to be created in heavy ion collisions. The possible existence of [special characters omitted]-odd domains in the QGP combined with an external magnetic field that is produced in mid-central collisions may be the ingredients necessary for the so-called chiral magnetic effect (CME). The CME is the consequence of topological features called sphalerons (that are created in the hot QCD matter) in the presence of a strong magnetic field, and it induces a separation of negatively and positively charged particles along the direction of the field. This separation varies its orientation from event to event, resulting in the expectation value of any [special characters omitted]-odd observable to vanish, making it necessary to measure the variation in fluctuations. Any indication of a real charge dipole moment could be evidence for local parity violation (LPV), which would have profound implications on our understanding of the natural world.
In this dissertation, charge dependent azimuthal correlations are used to measure the charge separation fluctuations in gold ion collisions at STAR. There are three primary analyses: measuring charge distributions as a function of beam energy, by selecting specific hadron species to filter background effects, and for uranium ion collisions. The beam energy analysis shows that a small charge separation shrinks with diminishing beam energy, eventually vanishing at the lowest energies. The kaon-pion correlations are performed to eliminate specific background effects unrelated to the CME, and behave consistently with results using all types of hadrons. The uranium analysis attempts to distinguish how much of the azimuthal correlations are influenced by elliptic anisotropy, suggesting the signal is coming from a mixture of CME and strong interaction backgrounds. From the evidence gathered from these analyses, we conclude that there are signs of small charge separations congruous to predictions from the CME, however, much of the signal is obscured by other strong interaction backgrounds. The effective contribution strengths are calculated and suggestions for improvements are made in the conclusion.
|School Location:||United States -- Connecticut|
|Source:||DAI-B 75/05(E), Dissertation Abstracts International|
|Subjects:||Physics, Particle physics|
|Keywords:||Azimuthal correlations, Chiral magnetic effect, Heavy ion collisions, Local perity violation, QCD QGP, STAR|
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