A new interpretation of the QCD phase transition and of strangeness as QGP signature

Abstract

We address the question of how to identify the QCD phase transition using measured light (u,d,s-structured) hadrons, without invoking comparison to the QCD ${ϵ}_c$ predictions, and extract ${ϵ}_c$ from the data. We analyse several particle and nuclear collisions and extract their chemical freeze-out temperature $T$ at zero baryochemical potential (${\mu }_B$). We find at ${\mu }_B=0$ a universal rise and saturation of both the $T$ and of the strangeness suppression factor ${\lambda }_s$ (=$\frac{2\bar{s}}{\bar{u}+\bar{d}}$) with increasing initial energy density (${ϵ}_i$). The onset of saturation of both $T$ and ${\lambda }_s$, is interpreted as due to the event of the QCD phase transition. The critical energy density is estimated to be ${ϵ}_c$ $\sim$ 1 +0.3 -0.5 GeV/fm${}^3$, corresponding approximately to a $\sqrt{s}$ of $\sim$ 8.8 GeV for central Pb+Pb collisions. Concerning the role of strangeness, we identify trivial and non-trivial sources of strangeness enhancement: The peak of ${\lambda }_s$ in Pb+Pb collisions at $\sqrt{s}$=8.8 GeV and other phenomena of 'strangeness enhancement' defined with respect to p+p data, are trivially traced back to the different baryochemical potentials and ${ϵ}_i$ of the compared systems. A non trivial redefined '${\lambda }_s$ enhancement' is however also present. The netbaryonfree ${\lambda }_s$ limit is estimated to be approximately reached in Au+Au collisions at the LHC.

Comments: 5 pages, 3 figures in eps, talk given at XXXI International Symposium on Multiparticle Dynamics, Sept 1-7, 2001, Datong China. URL http://ismd31.ccnu.edu.cn/ This paper is the "University of Bern preprint BUHE-01-03"