Statistical Ensembles with Fluctuating Extensive Quantities

We suggest an extension of the standard concept of statistical ensembles. Namely, we introduce a class of ensembles with extensive quantities fluctuating according to an externally given distribution. As an example the influence of energy fluctuations on multiplicity fluctuations in limited segments of momentum space for a classical ultra-relativistic gas is considered.Comment: 4 pages, 2 figure

Quark-Gluon Plasma Signatures in Nucleus--Nucleus Collisions at CERN SPS

Two signatures of the quark-gluon plasma -- strangeness `enhancement' and $J/\psi$ `suppression' -- in nucleus--nucleus collisions at the SPS energies are critically discussed.Comment: Invited Talk at Symposium on Fundamental Issues in Elementary Matter, In Honor and Memory of Michael Danos, Bad Honnef, Germany, 25-29 September 2000 (to be published in Heavy Ion Physics) Ref. [6] is correcte

Thermodynamical Consistency of Excluded Volume Hadron Gas Models

The new excluded volume hadron gas model by Singh et al. [1-7] is critically discussed. We demonstrate that in this model the results obtained from relations between thermodynamical quantities disagree with the corresponding results obtained by statistical ensemble averaging. Thus, the model does not satisfy the requirements of thermodynamical consistency

Critical line of the deconfinement phase transition

Phase diagram of strongly interacting matter is discussed within the exactly solvable statistical model of the quark-gluon bags. The model predicts two phases of matter: the hadron gas at a low temperature T and baryonic chemical potential muB, and the quark-gluon gas at a high T and/or muB. The nature of the phase transition depends on a form of the bag mass-volume spectrum (its pre-exponential factor), which is expected to change with the muB/T ratio. It is therefore likely that the line of the 1st} order transition at a high muB/T ratio is followed by the line of the 2nd order phase transition at an intermediate muB/T, and then by the lines of "higher order transitions" at a low muB/T.Comment: 13 pages, 6 figure