LONGITUDINAL EXPANSION OF MATTER FORMED BY PARTIAL STOPPING IN RELATIVISTIC HEAVY-ION COLLISIONS

We investigate the modification of Landau's solution of hydrodynamic e xpansion of a fireball formed in relativistic heavy ion collisions whe n there is partial transparency. In our model of collision we assume t hat the transparent fraction (of nuclei) creates a color flux tube beh ind it which eventually produces QCD matter (t-fluid) outside the cent ral QCD matter (s-fluid) formed by stopped nuclei. Thus the s-fluid ex pands against the nonzero pressure due to the t-fluid when the transpa rency is small. it makes the boundary condition on the expanding side of the s-fluid different from that of Landau and hence leads to a new solution of the hydrodynamic equations, Using the new solution we calc ulate the particle multiplicity distribution which is different from t hat of Landau, and the modification depends on the fraction of stoppin g.