Discovery of Jet Quenching at RHIC and the Opacity of the Produced Gluon Plasma

The predicted quenching of jets in A+A at RHIC energies has been discovered by STAR and PHENIX in preliminary data reported at this conference. We apply the GLV theory of QCD radiative energy loss to estimate the opacity, L/λ_g, of the gluon plasma produced in Au+Au collisions at 130 AGeV. We show that (in contrast to the factor of two Cronin enhancement of π^0 found at the SPS by WA98) the factor of 5-8 suppression of p_T \sim 2-4 GeV π^0 reported by PHENIX can be accounted for with an effective static plasma opacity L/λ_g \approx 3-4.