446 research outputs found
Hadron Spectra and QGP Hadronization in Au+Au Collisions at RHIC
The transverse mass spectra of Omega hyperons and phi mesons measured
recently by STAR Collaboration in Au+Au collisions at sqrt(s_NN) = 130 GeV are
described within a hydrodynamic model of the quark gluon plasma expansion and
hadronization. The flow parameters at the plasma hadronization extracted by
fitting these data are used to predict the transverse mass spectra of J/psi and
psi' mesons.Comment: 4 pages, 4 figures, Fig. 3 correcte
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
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
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
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
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.
The Legacy of Rolf Hagedorn: Statistical Bootstrap and Ultimate Temperature
In the latter half of the last century, it became evident that there exists
an ever increasing number of different states of the so-called elementary
particles. The usual reductionist approach to this problem was to search for a
simpler infrastructure, culminating in the formulation of the quark model and
quantum chromodynamics. In a complementary, completely novel approach, Hagedorn
suggested that the mass distribution of the produced particles follows a
self-similar composition pattern, predicting an unbounded number of states of
increasing mass. He then concluded that such a growth would lead to a limiting
temperature for strongly interacting matter. We discuss the conceptual basis
for this approach, its relation to critical behavior, and its subsequent
applications in different areas of high energy physics.Comment: 25 pages, 5 figures; to appear in R. Hagedorn and J. Rafelski (Ed.),
"Melting Hadrons, Boiling Quarks", Springer Verlag 201
Strange quark production in a statistical effective model
An effective model with constituent quarks as fundamental degrees of freedom
is used to predict the relative strangeness production pattern in both high
energy elementary and heavy ion collisions. The basic picture is that of the
statistical hadronization model, with hadronizing color-singlet clusters
assumed to be at full chemical equilibrium at constituent quark level. Thus, by
assuming that at least the ratio between strange and non-strange constituent
quarks survives in the final hadrons, the apparent undersaturation of strange
particle phase space observed in the data can be accounted for. In this
framework, the enhancement of relative strangeness production in heavy ion
collisions in comparison with elementary collisions is mainly owing to the
excess of initial non-strange matter over antimatter and the so-called
canonical suppression, namely the constraint of exact color and flavor
conservation over small volumes.Comment: 22 pages, 9 postscript figures, slightly shortened version published
in Phys. Rev.
A Census Of Highly Symmetric Combinatorial Designs
As a consequence of the classification of the finite simple groups, it has
been possible in recent years to characterize Steiner t-designs, that is
t-(v,k,1) designs, mainly for t = 2, admitting groups of automorphisms with
sufficiently strong symmetry properties. However, despite the finite simple
group classification, for Steiner t-designs with t > 2 most of these
characterizations have remained longstanding challenging problems. Especially,
the determination of all flag-transitive Steiner t-designs with 2 < t < 7 is of
particular interest and has been open for about 40 years (cf. [11, p. 147] and
[12, p. 273], but presumably dating back to 1965). The present paper continues
the author's work [20, 21, 22] of classifying all flag-transitive Steiner
3-designs and 4-designs. We give a complete classification of all
flag-transitive Steiner 5-designs and prove furthermore that there are no
non-trivial flag-transitive Steiner 6-designs. Both results rely on the
classification of the finite 3-homogeneous permutation groups. Moreover, we
survey some of the most general results on highly symmetric Steiner t-designs.Comment: 26 pages; to appear in: "Journal of Algebraic Combinatorics
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The structure of blocks with a Klein four defect group
We prove Erdmann’s conjecture [16] stating that every block with a Klein four defect group has a simple module with trivial source, and deduce from this that Puig’s finiteness conjecture holds for source algebras of blocks with a Klein four defect group. The proof uses the classification of finite simple groups
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