Vector meson production and nuclear effects in FNAL E866

摘要

Fermilab E866/NUSEA is a fixed-target experiment which has made a number of measurements of the production of vector mesons by 800 GeV protons. These include the nuclear dependence of J/psi, (psi)' and phi over very broad ranges in x(sub F) and p(sub T), and the J/psi decay angular distribution at very large x(sub F). Preliminary results from measurements on Be, Fe, and W targets are presented and discussed in the context of nuclear effects such as energy loss and multiple scattering of the partons, absorption of the produced c(anti c) pairs, and shadowing. Production mechanisms involving color-singlet or color-octet states for the c(anti c) pair which eventually forms a J/psi or (psi)' have implications on the strength of absorption in the nucleus and on the angular distribution of the decay muons. Preliminary results on the angular distributions versus x(sub F) and p(sub T) indicate some transverse polarization of the J/psi as predicted by models of production through the color octet state. Measurements of dimuons in the 1 to 3 GeV region explore the nuclear dependence of the phi meson and also the composition of the continuum between the phi and the J/psi. These studies of vector meson production and its nuclear dependence are critical in furthering their understanding of these processes towards future measurements at RHIC and new results from NA50 at CERN, where J/psi suppression is predicted to be an important signature of the creation of quark-gluon plasma in heavy-ion collisions.