J/Ψ Yield Modification in 200 GeV Per Nucleon Au+Au Collisions with the PHENIX Experiment at RHIC

It has been believed for over 30 years that matter will become a deconfined state of quarks and gluons at sufficiently high energy densities. As the energy density increases, deconfinement occurs due to Debye screening of the color charges, which disrupts the binding of mesons and baryons. The expected deconfinement transition to quark-gluon plasma (QGP) has been observed using collisions of heavy ions to create high energy densities, first at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory, and more recently at the Large Hadron Collider (LHC) at European Organization for Nuclear Research (CERN). The degree to which the binding of a hadron in the plasma is disrupted depends on its radius. Because deconfinement is caused by Debye screening, and the screening length is determined by energy density, small tightly bound heavy quark mesons (referred to as quarkonia) may become deconfined at a higher energy density than the light quark hadrons. Thus, measuring quarkonia production may provide a way to determine the screening length in the QGP, and a program of measurements of modification of charmonium and bottomonium states in heavy ion collisions has been carried out at several accelerators over the last two decades. As part of this effort, measurements of J/psi production in Au+Au collisions have been made by the PHENIX experiment at RHIC, the subject of this thesis. Specifically, J/psi --> e+e- data from Sqrt(sNN) = 200 GeV Au+Au collisions were recorded in 2004, providing the first major quarkonia result from PHENIX. A higher statistics measurement was performed in 2007, but a non-functioning detector subsystem in the PHENIX central arms rendered the data unusable. A still larger data set was recorded 2010, this time with the previously non-functioning detector system working. It is these 2010 data that are the focus of the present analysis. The 2010 dataset contains about 5 times as many measured J/psi as the 2004 dataset. However the increase in signal is accompanied by a large increase in background electrons, which introduces difficulties not present in the 2004 analysis. The goal of this analysis was to improve on the result from the 2004 measurement.