Todd Kempel, a graduate student in the Experimental Nuclear Physics group, has been awarded one of two 2011 Brookhaven National Laboratory RHIC & AGS Thesis Awards, for his thesis titled "Understanding the J/Psi Production Mechanism at PHENIX". The purpose of the award is to recognize the most outstanding thesrs work related to research conducted at the Relativistic Heavy Ion Collider, AGS, NSRL, Tandem or ATF facilities at BNL.
The J/Psi meson, a bound state of a charm and an anti-charm quark, was discovered in 1974, yet the mechanism for the binding of the two quarks is still largely unknown. Several models have been proposed for the so-called production mechanism, but none of them satisfactorily describe all available data. Because the J/Psi is composed of two heavy quarks, the production of the quarks should have a dierent energy scale from their relative motion, and production may be understood by separating the two scales using non-relativistic QCD (quantum chromodynamics). Such an understanding would shed light on one of the basic components of QCD: hadronization. Todd's thesis work presented two novel measurements sensitive to the J/Psi production mechanism using the PHENIX detector.
The first measurement utilized polarized proton beams at RHIC for a transverse single spin asymmetry of J/Psi mesons, sensitive to both the internal structure of the colliding protons and to the production mechanism of the J/Psi . This is the first time such a measurement has been made, and the resulting asymmetry is inconsistent with zero, a fact which has strong implications for understanding of both the proton and the J/Psi .
The second measurement was a determination of the angular distribution of decay leptons in the J/Psi rest frame. Measurements of such distributions have been made in the past, but very few have determined all relevant coefficients or considered the coordinate system used in the J/Psi rest frame. Using various coordinate systems and measuring all relevant coefficients will provide a much richer understanding of the J/Psi at a phenomenological level and should provide guidance to theorists in pursuit of the production mechanism.