Statistical hadronization of supercooled QGP

Two-particle interferometry has become a powerful tool for studying the size and duration of particle production from elementary collisions to heavy ions like Au+Au at RHIC or Pb+Pb at SPS. For the case of nuclear collisions, the interest mainly focuses on the possible transient formation of a deconfined state of matter. This could affect the size of the region from where the hadrons (mostly pions) are emitted as well as the time for particle production. Comparing recent data from RHIC with SPS data one finds a ``puzzle'': all the HBT radii are pretty similar although the center of mass energy is changed by an order of magnitude. Also already at CERN energies it was seen that Rout/Rside ratio close to 1, contrary to expectations of some models. Discussions at "Quark Matter 2002" lead to the conclusion that the duration of particle emission, as well as the lifetime of the system before freeze out, appear to be shorter than the predictions of most of the model at the physics market. Although there is a set of models based on very fast 3D Bjorken hydrodynamical expansion and hadronization from supercooled QGP phase [see T. Csorgo, A. Ster, nucl-th/0207016 and references therein], which are in much better agreement with experimental data than all the others.

It was demonstrated that a strong first-order QCD phase transition within continuous hydrodynamical expansion would lead to long lifetimes of the particle source, which would manifest itself as a large Rout/Rside ratio [D. Rischke, M. Gyulassy, Nucl. Phys. A 608 (1996) 479]. Now this type of hadronization is excluded by experimental data.

An alternative possibility, proposed in Refs. [T. Csorgo, L.P. Csernai, Phys. Lett. B 333 (1994) 494], is the hadronization from the supercooled QGP. This is expected to be a very fast shock-like process. If the hadronization from supercooled QGP (in order to avoid the entropy decrease) coincides with freeze out then this could explain the flash-like particle emission (Rout/Rside~1).

In the Refs. [20,p14 (see CV)] we study the fast hadronization and chemical freeze-out (CFO) of locally thermalized supercooled quark gluon plasma (QGP) described by hydrodynamical evolution. This process is idealized by sudden hadronization and FO over a 3D hypersurface. The matter crossing the hypersurface is controlled by conservation of energy, momentum and relevant current conservation laws, nondecreasing entropy condition and additionally, by assumption of apparent thermal and chemical equilibrium distribution of the resulting hadron gas (HG). By apparent equilibrium distribution we mean that although there is clearly no room for kinetic equilibration in elementary collisions - or in fast, simultaneous phase transition and CFO in nuclear collisions - the final hadron spectra are dictated by maximum entropy bound by conservation of energy and charge densities. Although the simultaneous phase transition and CFO are assumed to be a non-equilibrium process, we can still exploit the apparent equilibrium parametrization - the consequence of statistical nature of hadronization.

This project is still in progress - there are more questions to be answered [21,p19-p21 (see CV)] before we will understand the HBT results.