ar X iv : h ep - p h / 98 01 32 1 v 2 1 1 A ug 1 99 8 Dilepton emission from an equilibrating non - abelian plasma

We study dilepton production from a thermally equilibrating quark-gluon plasma expected to be formed in ultra relativistic heavy-ion collisions. The pre-equilibrium dynamics of quark-gluon plasma is studied within the color flux-tube model by solving non-abelian relativistic transport equations. This dilepton rate crucially depends on the collision time of the plasma. The results are compared with the Drell-Yan productions. We suggest that a measurement of this rate at RHIC and LHC will determine the initial field energy density. One of the primary aims of the ultra relativistic heavy-ion collision experiment is to detect a new phase of matter, viz quark-gluon-plasma(QGP). It is known from lattice quantum chromodynamics that hadronic matter undergoes a transition to this quark-gluon plasma phase at very high temperatures (∼ 200MeV) and densities (∼ 2GeV /f m 3) [1]. While such a phase did exist in the early universe, after ∼ 10 −4 seconds of the big bang, it is interesting if we can recreate the early universe and experimentally verify this QCD phase transition in the laboratory i.e. in high energy heavy-ion collisions. In the near future, the relativistic heavy ion collider(RHIC) at BNL (Au-Au collisions at √ s = 200GeV) and large Hadron Collider(LHC) at CERN (Pb-Pb collisions at √ s ≃ 6.4T eV) [2,3] will provide the best oppurtunity to study such a phase transition. As this plasma exist for a very short time (∼ 10f m) and formed over a very small volume (∼ 100f m 3), the direct detection of this phase is not possible in these experiments. The proposed signatures for its detection are therefore indirect, and the prominent ones are : 1) J/ψ supression [4], 2) electromagnetic probes such as dilepton and direct photon production [5,6], and 3) strangeness enhancement [7]. It has been suggested by Matsui and Satz that J/ψ suppression is a good probe [4] for the detection of an equilibrated quark-gluon plasma. Their calculation is based on lattice QCD which assumes equilibration of the plasma. However, in heavy-ion collisions such as at RHIC and LHC the assumption of such an equilibration of quark-gluon plasma is only suggestive. One does not know exactly when the plasma equilibrates and there is no concrete calculation on this aspects. This sets an uncertainty in the calculation of J/ψ survival probability which is determined from screening. In this regard, there are calculations of J/ψ suppressions in the equilibrating quark-gluon plasma [8,9] using short-distance …