ar X iv : n uc l - th / 9 90 70 35 v 1 8 J ul 1 99 9 1 The QGP - Stall or Not ?

1] proposed to use the time-delay signal in Bose-Einstein correlations (BEC) as a signature for the possible formation of a quark-gluon plasma (QGP) in relativistic heavy-ion collisions. In particular, they suggested to measure the ratio of the transversal interferometry radii, R out /R side , which can be obtained by fitting experimental BEC data with a parametrization introduced by G. Bertsch [2] et al. in 1988. The transverse radius parameter R out has compared to the transverse radius parameter R side an additional temporal dependence which should be sensitive to a prolonged lifetime of a fireball, in case a QGP was formed in a relativistic heavy-ion collision. This latter phenomenon is known under the term " QGP stall ". In the following, I shall explain why I believe that the time-delay signal in Bose-Einstein correlations is not a good signature for the possible formation of a QGP. Let us consider two quite different equations of state (EOS) of nuclear matter within a true relativistic hydrodynamic framework (i.e., HYLANDER-C) [3]. The first one, EOS-I, has a phase-transition to a QGP at T C = 200 MeV (ǫ C = 1.35 GeV /f m 3) [4]. The second EOS, EOS-II, is a purely hadronic EOS, which has been extracted from the transport code RQMD (cf., Ref. [5]) under the assumption of fully acchieved thermalization. If one assumes for each EOS different initial conditions before the hydrodynamical expansions, one can fit simultaneously hadronic single inclusive momentum spectra and BEC, which have been measured recently by the CERN/NA44 and CERN/NA49 Collaborations (cf., [4,5]), respectively. In particular, for the acceptance of the NA44 experiment a ratio R out /R side ≈ 1.15 was found [4] while using both EOS, EOS-I and EOS-II. Little difference was seen in the BEC of identical pion pairs while considering the two different EOS. In the following, we shall assume for central Au+Au collisions at BNL/RHIC beam energies a set of fireball initial conditions, IC-I, which are similar to those as described in Ref. [7]. From these fireball initial conditions, IC-I, single inclusive momentum spectra have been calculated while using EOS-I and EOS-II in the hydrodynamic expansions. We note, that the rapidity spectra of both calculations differ in width and nomalization