668 research outputs found
Van der Waals Excluded Volume Model of Multicomponent Hadron Gas
A generalization of the Van der Waals excluded volume procedure for the
multicomponent hadron gas is proposed. The derivation is based on the grand
canonical partition function for the system of particles of several species
interacting by hard core potentials. The obtained formulae for thermodynamical
quantities are consistent with underlying principles of statistical mechanics
as well as with thermodynamical identities. The model can be applied to the
analysis of experimental data for particle number ratios in relativistic
nucleus-nucleus collisions.Comment: 8 page
Simbol-X Hard X-ray Focusing Mirrors: Results Obtained During the Phase A Study
Simbol-X will push grazing incidence imaging up to 80 keV, providing a strong
improvement both in sensitivity and angular resolution compared to all
instruments that have operated so far above 10 keV. The superb hard X-ray
imaging capability will be guaranteed by a mirror module of 100 electroformed
Nickel shells with a multilayer reflecting coating. Here we will describe the
technogical development and solutions adopted for the fabrication of the mirror
module, that must guarantee an Half Energy Width (HEW) better than 20 arcsec
from 0.5 up to 30 keV and a goal of 40 arcsec at 60 keV. During the phase A,
terminated at the end of 2008, we have developed three engineering models with
two, two and three shells, respectively. The most critical aspects in the
development of the Simbol-X mirrors are i) the production of the 100 mandrels
with very good surface quality within the timeline of the mission; ii) the
replication of shells that must be very thin (a factor of 2 thinner than those
of XMM-Newton) and still have very good image quality up to 80 keV; iii) the
development of an integration process that allows us to integrate these very
thin mirrors maintaining their intrinsic good image quality. The Phase A study
has shown that we can fabricate the mandrels with the needed quality and that
we have developed a valid integration process. The shells that we have produced
so far have a quite good image quality, e.g. HEW <~30 arcsec at 30 keV, and
effective area. However, we still need to make some improvements to reach the
requirements. We will briefly present these results and discuss the possible
improvements that we will investigate during phase B.Comment: 6 pages, 3 figures, invited talk at the conference "2nd International
Simbol-X Symposium", Paris, 2-5 december, 200
Particle Freeze-out and Discontinuities in Relativistic Hydrodynamics
Freeze-out of particles in relativistic hydrodynamics is considered across a
3-dimensional space-time hypersurface. The conservation laws for time-like
parts of the freeze-out hypersurface require different values of temperature,
baryonic chemical potential and flow velocity in the fluid and in the final
particle spectra. We analyze this freeze-out discontinuity and its connection
to the shock-wave phenomena in relativistic hydrodynamics.Comment: 6 figure
Second Cluster Integral and Excluded Volume Effects for the Pion Gas
The quantum mechanical formula for Mayer's second cluster integral for the
gas of relativistic particles with hard-core interaction is derived. The proper
pion volume calculated with quantum mechanical formula is found to be an order
of magnitude larger than its classical evaluation.
The second cluster integral for the pion gas is calculated in quantum
mechanical approach with account for both attractive and hard-core repulsive
interactions. It is shown that, in the second cluster approximation, the
repulsive pion-pion-interactions as well as the finite width of resonances give
important but almost canceling contributions. In contrast, an appreciable
deviation from the ideal gas of pions and pion resonances is observed beyond
the second cluster approximation in the framework of the Van der Waals
excluded-volume model.Comment: 29 pages, Latex, 9 PS-figure
Multiplicity Fluctuations in Hadron-Resonance Gas
The charged hadron multiplicity fluctuations are considered in the canonical
ensemble. The microscopic correlator method is extended to include three
conserved charges: baryon number, electric charge and strangeness. The
analytical formulae are presented that allow to include resonance decay
contributions to correlations and fluctuations. We make the predictions for the
scaled variances of negative, positive and all charged hadrons in the most
central Pb+Pb (Au+Au) collisions for different collision energies from SIS and
AGS to SPS and RHIC.Comment: 19 pages, 4 figure
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
Quark Gluon Bags as Reggeons
The influence of the medium dependent finite width of QGP bags on their
equation of state is analyzed within an exactly solvable model. It is argued
that the large width of the QGP bags not only explains the observed deficit in
the number of hadronic resonances, but also clarifies the reason why the heavy
QGP bags cannot be directly observed as metastable states in a hadronic phase.
The model allows us to estimate the minimal value of the width of QGP bags from
a variety of the lattice QCD data and get that the minimal resonance width at
zero temperature is about 600 MeV, whereas the minimal resonance width at the
Hagedorn temperature is about 2000 MeV. As shown these estimates are almost
insensitive to the number of the elementary degrees of freedom. The recent
lattice QCD data are analyzed and it is found that besides sigma T**4 term the
lattice QCD pressure contains T-linear and T**4 ln T terms in the range of
temperatures between 240 MeV and 420 MeV. The presence of the last term in the
pressure bears almost no effect on the width estimates. Our analysis shows that
at hight temperatures the average mass and width of the QGP bags behave in
accordance with the upper bound of the Regge trajectory asymptotics (the linear
asymptotics), whereas at low temperatures they obey the lower bound of the
Regge trajectory asymptotics (the square root one). Since the model explicitly
contains the Hagedorn mass spectrum, it allows us to remove an existing
contradiction between the finite number of hadronic Regge families and the
Hagedorn idea of the exponentially growing mass spectrum of hadronic bags.Comment: One section removed, a few references added, the Regge trajectories
of free QGP bags are considere
On the Deconfinement Phase Transition in the Resonance Gas
We obtain the constraints on the ruling parameters of the dense hadronic gas
model at the critical temperature and propose the quasiuniversal ratios of the
thermodynamic quantities. The possible appearence of thermodynamical
instability in such a model is discussed.Comment: 7 pages, plain LaTeX, BI-TP 94/4
The High E_T Drop of J/psi to Drell-Yan Ratio from the Statistical c anti-c Coalescence Model
The dependence of the J/psi yield on the transverse energy E_T in heavy ion
collisions is considered within the statistical c anti-c coalescence model. The
model fits the NA50 data for Pb+Pb collisions at the CERN SPS even in the
high-E_T region (E_T > 100 GeV). Here E_T-fluctuations and E_T-losses in the
dimuon event sample naturally create the celebrated drop in the J/psi to
Drell-Yan ratio.Comment: 14 pages, REVTeX, 1 PS-figure. v2: References are corrected and
update
Local Thermal and Chemical Equilibration and the Equation of State in Relativistic Heavy Ion Collisions
Thermodynamical variables and their time evolution are studied for central
relativistic heavy ion collisions from 10.7 to 160 AGeV in the microscopic
Ultrarelativistic Quantum Molecular Dynamics model (UrQMD). The UrQMD model
exhibits drastic deviations from equilibrium during the early high density
phase of the collision. Local thermal and chemical equilibration of the
hadronic matter seems to be established only at later stages of the quasi-
isentropic expansion in the central reaction cell with volume 125 fm.
distributions at all collision energies for with a unique
Baryon energy spectra in this cell are approximately reproduced by Boltzmann
rapidly dropping temperature. At these times the equation of state has a simple
form: . At 160 AGeV the strong deviation from
chemical equilibrium is found for mesons, especially for pions, even at the
late stage of the reaction. The final enhancement of pions is supported by
experimental data.Comment: 17 Pages, LaTex, 8 eps figures. Talk given at SQM'98 conference,
20-24 July 1998, Padova, Italy, submitted to J. Phys.
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