Evidence for QGP in Pb – Pb 158

The hadronic particle production data from relativistic nuclear Pb–Pb 158 A GeV collisions are successfully described within the chemical non-equilibrium model, provided that the analysis does not include Ω and Ω abundances. We show that there is a subtle influence of the Coulomb potential on strange quarks in quark matter which is also seen in our data analysis, and this Coulomb effect confirms the finding made in the S–Au/W/Pb 200 A GeV collisions that the hadron source is deconfined with respect to strange quark propagation. Physical freeze-out conditions (pressure, specific energy, entropy, and strangeness) are evaluated and considerable universality of hadron freeze-out between the two different collision systems is established. Intense experimental and theoretical work proceeds to explore the mechanisms of quark confinement effect and the properties of the vacuum state of quantum-chromodynamics (QCD), the non-Abelian gauge theory of 'color' charges [1]. Relativistic energy nuclear collisions are the novel experimental tool developed in the past decade to form, study, and explore the 'melted' space-time domain, where we hope to find, beyond the critical Hagedorn temperature T c ≃ 160 MeV [2], freely propagating quarks and gluons in the (color charge) plasma (QGP). There is little doubt that this was in the early Universe the transient state of matter, and that only about 20–40 µsec into evolution did our present confining vacuum freeze-out from the primordial QGP-form. The issue is, if in the attempt to recreate this stage of the evolution of the Universe in laboratory experiments, we can indeed form and study the primordial QGP phase. In some aspects, such as specific entropy and baryon content, notable differences of the laboratory QGP state from the early Universe conditions are expected to arise, not to mention the short laboratory lifespan τ q ≃ 0.5 · 10 −22 sec. There is also the difficult problem of proving the fundamental paradigm beyond a shade of doubt [3]: is there indeed locally deconfined state formed with energy density exceeding by an order of magnitude that of nuclear matter? Much of the current effort is devoted to this challenge. Among several proposed approaches to study of deconfinement, our work relies on the idea of strangeness flavor enhancement, and the associated enhancement of (strange) antibaryon formation [4, 5, 6]. While both these effects have been confirmed experimentally [7], it is here and now that we believe to draw a definitive conclusion, given the advances of experimental …