1,282 research outputs found
Quark-Gluon Plasma Fireball
Lattice-QCD results provide an opportunity to model, and extrapolate to
finite baryon density, the properties of the quark-gluon plasma (QGP). Upon
fixing the scale of the thermal coupling constant and vacuum energy to the
lattice data, the properties of resulting QGP equations of state (EoS) are
developed. We show that the physical properties of the dense matter fireball
formed in heavy ion collision experiments at CERN-SPS are well described by the
QGP-EoS we presented. We also estimate the properties of the fireball formed in
early stages of nuclear collision, and argue that QGP formation must be
expected down to 40A GeV in central Pb--Pb interactions.Comment: 10 pages, 9 postscript figures, 1 table, uses revtex, V3: introduced
difference between n_f and n_s; fireball restframe energy corrected,
references added. Publisched version in press Phys. Rev.
A model for the time uncertainty measurements in the Auger surface detector array
The precise determination of the arrival direction of cosmic rays is a
fundamental prerequisite for the search for sources or the study of their
anisotropies on the sky. One of the most important aspects to achieve an
optimal measurement of these directions is to properly take into account the
measurement uncertainties in the estimation procedure. In this article we
present a model for the uncertainties associated with the time measurements in
the Auger surface detector array. We show that this model represents well the
measurement uncertainties and therefore provides the basis for an optimal
determination of the arrival direction. With this model and a description of
the shower front geometry it is possible to estimate, on an event by event
basis, the uncertainty associated with the determination of the arrival
directions of the cosmic rays
Gluon production, cooling and entropy in nuclear collisions
We study the cooling (heating) of a glue-parton gas due to production
(destruction) of particles and determine the associated production of entropy.
We incorporate sharing of the system energy among a changing number of
particles. We find that the entropy of an evolving glue-parton gas changes in
an insignificant range once the initial high temperature state has been formed,
despite a great change in particle number and temperature.Comment: Replaced for bad printing on US paper. 7 pages, LaTeX, 4 postscript
figure
Theoretical and Experimental Topics on Ultra High Energy Cosmic Rays
Since their first observation in 1962, the existence of Ultra High Energy
Cosmic Rays (UHECR) remains a mystery in modern astrophysics. Those cosmic
rays, with energies well above 50 EeV (eV), can hardly be
accelerated, even in the most active parts of our universe such as FR-II radio
galaxies or AGNs, nor can they travel on distances larger than 100 Mpc. In the
following some of the production and acceleration models for UHECR are reviewed
and some of the transport issues are exposed. Finally the detection and
identification on Earth of those ``cosmic bullets'' are presented.Comment: 46 pages, 16 figures. Lecture given at the XXVIII International
Meeting on Fundamental Physics, Sanlucar de Barameda, Cadiz Spain, 14-18
February 200
Strangeness and Particle Freeze-out in Nuclear Collisions at 14.6 Gev a
We study the chemical conditions at freeze-out associated with the production
of strange-particles in Si-Au collisions at 14.6 GeV A. We obtain freeze-out
chemical potentials and temperature, and determine the entropy as well as the
final particle abundance. We also consider in detail the alternative evolution
scenarios involving the hadronic gas and the deconfined phase.Comment: 12 pages, LaTeX, 3 postscript figure
Observing Quark-Gluon Plasma with Strange Hadrons
We review the methods and results obtained in an analysis of the experimental
heavy ion collision research program at nuclear beam energy of 160-200A GeV. We
study strange, and more generally, hadronic particle production experimental
data. We discuss present expectations concerning how these observables will
perform at other collision energies. We also present the dynamical theory of
strangeness production and apply it to show that it agrees with available
experimental results. We describe strange hadron production from the
baryon-poor quark-gluon phase formed at much higher reaction energies, where
the abundance of strange baryons and antibaryons exceeds that of nonstrange
baryons and antibaryons.Comment: 39 journal pages (155kb text), 8 postscript figures, 8 table
An Estimate of the Spectral Intensity Expected from the Molecular Bremsstrahlung Radiation in Extensive Air Showers
A detection technique of ultra-high energy cosmic rays, complementary to the
fluorescence technique, would be the use of the molecular Bremsstrahlung
radiation emitted by low-energy electrons left after the passage of the showers
in the atmosphere. The emission mechanism is expected from quasi-elastic
collisions of electrons produced in the shower by the ionisation of the
molecules in the atmosphere. In this article, a detailed calculation of the
spectral intensity of photons at ground level originating from the transitions
between unquantised energy states of free ionisation electrons is presented. In
the absence of absorption of the emitted photons in the plasma, the obtained
spectral intensity is shown to be 5 10^{-26} W m^{-2}Hz^{-1} at 10 km from the
shower core for a vertical shower induced by a proton of 10^{17.5} eV.Comment: 16 pages, 6 figures, accepted in Astroparticle Physics. Compared to
v1 version: 1. Inclusion of ro-vibrational processes. 2. Use of more accurate
ionization potential values and energy distribution of the secondary
electron
Heavy Flavor Hadrons in Statistical Hadronization of Strangeness-rich QGP
We study b, c quark hadronization from QGP. We obtain the yields of charm and
bottom flavored hadrons within the statistical hadronization model. The
important novel feature of this study is that we take into account the high
strangeness and entropy content of QGP, conserving strangeness and entropy
yields at hadronization.Comment: v2 expended: 20 pages, 23 figures, 5 tables, in press EPJ-
- …