The Jet Quenching in High Energy Nuclear Collisions and Quark-gluon Plasma

We investigate the energy loss of quark and gluon jets in quark-gluon plasma produced in central Au+Au collisions at RHIC energy. We use the physical characteristic of initial and mixed phases, which were found in effective quasiparticle model for SPS and RHIC energy [5]. At investigation of energy loss we take into account also the production of hot glue at first stage. The energy loss in expanding plasma is calculated in dominant first order of radiation intensity [3, 4] with accounting of finite kinematic bounds. We calculate the suppression of π 0-spectra with moderate high p ⊥ , which is caused by energy loss of quark and gluon jets. The comparison with suppression of π 0 reported by PHENIX show, that correct quantitative description of suppression we have only in model of phase transition with decrease of thermal gluon mass and effective coupling G(T) in region of phase transition plasma into hadrons (at T ≃ T c). However quasiparticle model with increase of these values at T → T c in accordance with perturbative QCD lead to too great energy loss of gluon and quark jets, which disagrees with data on suppression of π 0. Thus it is possible with help of hard processes to investigate the structure of phase transition. We show also, that energy losses at SPS energy are too small in order to be observable. This is caused in fact by sufficiently short plasma phase at this energy.