715 research outputs found
Exactly Solvable Models: The Road Towards a Rigorous Treatment of Phase Transitions in Finite Systems
We discuss exact analytical solutions of a variety of statistical models
recently obtained for finite systems by a novel powerful mathematical method,
the Laplace-Fourier transform. Among them are a constrained version of the
statistical multifragmentation model, the Gas of Bags Model and the Hills and
Dales Model of surface partition. Thus, the Laplace-Fourier transform allows
one to study the nuclear matter equation of state, the equation of state of
hadronic and quark gluon matter and surface partitions on the same footing. A
complete analysis of the isobaric partition singularities of these models is
done for finite systems. The developed formalism allows us, for the first time,
to exactly define the finite volume analogs of gaseous, liquid and mixed phases
of these models from the first principles of statistical mechanics and
demonstrate the pitfalls of earlier works. The found solutions may be used for
building up a new theoretical apparatus to rigorously study phase transitions
in finite systems. The strategic directions of future research opened by these
exact results are also discussed.Comment: Contribution to the ``World Consensus Initiative III, Texas A & M
University, College Station, Texas, USA, February 11-17, 2005, 21
Chemical Freeze-out of Strange Particles and Possible Root of Strangeness Suppression
Two approaches to treat the chemical freeze-out of strange particles in
hadron resonance gas model are analyzed. The first one employs their
non-equillibration via the usual \gamma_s factor and such a model describes the
hadron multiplicities measured in nucleus-nucleus collisions at AGS, SPS and
RHIC energies with \chi^2/dof = 1.15. Surprisingly, at low energies we find not
the strangeness suppression, but its enhancement. Also we suggest an
alternative approach to treat the strange particle freeze-out separately, but
with the full chemical equilibration. This approach is based on the
conservation laws which allow us to connect the freeze-outs of strange and
non-strange hadrons. Within the suggested approach the same set of hadron
multiplicities can be described better than within the conventional approach
with \chi^2/dof = 1.06. Remarkably, the fully equilibrated approach describes
the strange hyperons and antihyperons much better than the conventional one.Comment: 6 pages, 5 figure
Prompt muon contribution to the flux underwater
We present high energy spectra and zenith-angle distributions of the
atmospheric muons computed for the depths of the locations of the underwater
neutrino telescopes. We compare the calculations with the data obtained in the
Baikal and the AMANDA muon experiments. The prompt muon contribution to the
muon flux underwater due to recent perturbative QCD-based models of the charm
production is expected to be observable at depths of the large underwater
neutrino telescopes. This appears to be probable even at rather shallow depths
(1-2 km), provided that the energy threshold for muon detection is raised above
TeV.Comment: 7 pages, RevTeX, 7 eps figures, final version to be published in
Phys.Rev.D; a few changes made in the text and the figures, an approximation
formula for muon spectra at the sea level, the muon zenith-angle distribution
table data and references adde
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