UCLA

A new form of matter with de-confined quarks and gluons, named the "Quark Gluon Plasma" (QGP), is predicted by Lattice Qutantum Chromodynamics to exist at high temperatures and/or high baryon density regions in the QCD phase diagram. Experimental evidence indicates that the QCD matter created in high energy Au+Au collisions at the Relativistic Heavy Ion Collider (RHIC) in Brookhaven National Lab is a strongly-coupled Quark-Gluon Plasma. One of the central goals of heavy ion physics is to understand the QGP through quantitative comparisons between theoretical calculations and experimental measurements. Heavy flavor quarks are believed to be a unique probe for this task, because they are dominantly produced in the initial hard scatterings, where the production rate can be well calculated by perturbative-QCD(pQCD). When heavy favor quarks traverse the QGP medium, they bear the imprints of the medium via their interactions with the medium. Dynamical models have been developed to calculate the interactions between heavy quarks and the QGP medium to quantitatively extract the medium properties.

This dissertation presents a series of experimental studies with the electrons produced in the semi-leptonic decays of heavy flavor quarks in Au+Au and p+p collisions, which serve as the proxies for heavy flavor quarks. These electrons are referred to as non-photonic electrons (NPE), to be differentiated from the main background of photonic electrons. The production of NPE at high pT is found to be highly suppressed in central and semi-central Au+Au collisions, compared to binary-collision scaled production in p+p collisions. The azimuthal anisotropy of NPE is found to be finite at high pT, and the azimuthal correlation between high pT NPE and low pT hadrons exhibits a broadening in the away-side, both of which strengthen the evidence for a strong coupling between heavy flavor quarks and the QGP medium. In addition, the bottom quark production cross-section in p+p collisions is obtained based on the measured spectrum of NPE and the ratio of bottom/charm decay electrons.