On the Early Stage of Nucleus--Nucleus Collisions

TL;DR

This paper develops a statistical model for the early stages of nucleus-nucleus collisions, suggesting the formation of Quark Gluon Plasma at SPS energies, supported by data on particle production and fluctuations.

Contribution

It introduces a combined model using fitted parameters and Bag model equations to describe the transition from confined to deconfined states in nuclear collisions.

Findings

Evidence for Quark Gluon Plasma formation at SPS energies.

Model explains scaling of pion and strangeness production.

Predicts energy dependence of particle multiplicities and fluctuations.

Abstract

A statistical model of the early stage of central nucleus--nucleus (A+A) collisions is developed. We suggest a description of the confined state with several free parameters fitted to a compilation of A+A data at the AGS. For the deconfined state a simple Bag model equation of state is assumed. The model leads to the conclusion that a Quark Gluon Plasma is created in central nucleus--nucleus collisions at the SPS. This result is in quantitative agreement with existing SPS data on pion and strangeness production and gives a natural explanation for their scaling behaviour. The localization and the properties of the transition region are discussed. It is shown that the deconfinement transition can be detected by observation of the characteristic energy dependence of pion and strangeness multiplicities, and by an increase of the event--by--event fluctuations. An attempt to understand the data on J/psi production in Pb+Pb collisions at the SPS within the same approach is presented.