J/Ψ Production and Nuclear Effects for d+Au and p+p Collisions in PHENIX at RHIC

The gluon structure function in a nucleon and its nuclear modification may be studied by measuring a particle called J/Ψ that is produced primarily via gluon fusion in high energy collisions between protons or nuclei. The PHENIX Experiment at the Relativistic Heavy Ion Collider (RHIC) has measured the production of J/Ψ particles in d+Au collisions at center-of-mass energies of 200 GeV per nucleon via its lepton decay channels (dielectrons and dimuons). In 2003, approximately 2000 J/Ψ particles from the d+Au data set (and several hundred in p+p) has allowed for measures of its rapidity (between -2.2 and +2.4) and momentum (between 0.5 and 5 GeV/c) distributions. In particular, the ratio of the rapidity distributions of J/Ψ produced in d+Au and p+p collisions is measured as a function of the d+Au impact parameter (centrality dependence of the collision). These preliminary data will ultimately help us understand nuclear effects at this center-of-mass energy (including shadowing) in cold nuclear matter. In addition to comparisons to theoretical models, these data are also compared to the equivalent measurements of J/Ψ produced in lower energy p–A collisions from Fermilab.