Measurement of polarization observables in gamma and psi production with 800 GeV p+Cu collisions

Despite QCD's success in describing many aspects of the strong interaction, an adequate description of quarkonia production is still missing. While the production of the heavy Q (Q) over bar pair from gluon-gluon fusion or quark-antiquark annihilation can be perturbatively calculated, the long-distance process involving the formation of the bound states is presently not amenable to calculation. Various models of quarkonia production have been proposed, including color singlet and octet components, and these models make predictions for polarization of the quarkonia. FNAL E866 has measured the polarization of quarkonia production in the psi and gamma families. The data show that the gamma(1S) is produced with only slight polarization, and only at large fractional longitudinal momentum (x(F)) or large transverse momenta (P-T), while the Y(2S) and (3S) states are completely polarized. In the psi family, the J/psi is produced with only slight polarization, which changes from transverse to longitudinal as a function of increasing x(F). These results are particularly important to both RHIC and CERN, where charmonium formation plays a critical role in the search for a quark-gluon plasma.