The European Physical Journal C

ISSN: 1434-6044 (printed version)
ISSN: 1434-6052 (electronic version)

Table of Contents

Abstract Volume 5 Issue 1 (1998) pp 143-153
DOI 10.1007/s100529800831

theoretical physics:
On chemical equilibrium in nuclear collisions

F. Becattini (1), M. Gazdzicki (2), J. Sollfrank (3)

(1) INFN Sezione di Firenze, Largo E. Fermi 2, I-50125 Firenze, Italy (e-mail: becattini@fi.infn.it)
(2) Institut für Kernphysik, Universität Frankfurt, August-Euler-Strasse 6, D-60486 Frankfurt, Germany (e-mail: marek@ikf.uni-frankfurt.de)
(3) Fakultät für Physik, Universität Bielefeld, Universitätsstr. 25, D-33615 Bielefeld, Germany (e-mail: sollfran@physik.uni-bielefeld.de)

Received: 31 October 1997 / Published online: 26 February 1998

Abstract. The data on average hadron multiplicities in central A+A collisions measured at CERN SPS are analysed with the ideal hadron gas model. It is shown that the full chemical equilibrium version of the model fails to describe the experimental results. The agreement of the data with the off-equilibrium version allowing for partial strangeness saturation is significantly better. The chemical freeze-out temperature of about 180 MeV seems to be independent of the system size (from S+S to Pb+Pb) and in agreement with that extracted in ${\rm e}^++{\rm e}^-$, $\mathrm{p+p}$ and $\mathrm{p+\bar{p}}\;$ collisions. The strangeness suppression is discussed at both hadron and valence quark level. It is found that the hadronic strangeness saturation factor $\gamma_{\rm S}$ increases from about 0.45 for $\mathrm{p+p}$ interactions to about 0.7 for central A+A collisions with no significant change from S+S to Pb+Pb collisions indicating that the strangeness enhancement in heavy ion collisions cannot be fully attributed to the increased system size. The quark strangeness suppression factor $\lambda_{\rm S}$ is found to be about 0.2 for elementary collisions and about 0.4 for heavy ion collisions independently of collision energy and type of colliding system.

Article in PDF-Format (341 KB)
Article in (gzipped) PS-Format (204 KB)

Online publication: August 4, 1998
LINK Helpdesk
© Springer-Verlag Berlin Heidelberg 1998