1,271 research outputs found
The STAR Photon Multiplicity Detector
Details concerning the design, fabrication and performance of STAR Photon
Multiplicity Detector (PMD) are presented. The PMD will cover the forward
region, within the pseudorapidity range 2.3--3.5, behind the forward time
projection chamber. It will measure the spatial distribution of photons in
order to study collective flow, fluctuation and chiral symmetry restoration.Comment: 15 pages, including 11 figures; to appear in a special NIM volume
dedicated to the accelerator and detectors at RHI
Nuclear expansion with excitation
The expansion of an isolated hot spherical nucleus with excitation energy and
its caloric curve are studied in a thermodynamic model with the SkM* force as
the nuclear effective two-body interaction. The calculated results are shown to
compare well with the recent experimental data from energetic nuclear
collisions. The fluctuations in temperature and density are also studied. They
are seen to build up very rapidly beyond an excitation energy of 9 MeV/u.
Volume-conserving quadrupole deformation in addition to expansion indicates,
however, nuclear disassembly above an excitation energy of 4 MeV/uComment: 17 pages, 5 figures, revtex4; calculations with deformation adde
Hot Nuclear Matter in Asymmetry Chiral Sigma Model
In the frame work of SU(2) chiral sigma model, the nuclear matter properties
at zero and finite temperature have been investigated. We have analyzed the
nuclear matter equation of state by varying different parameters, which agrees
well with the one derived from the heavy-ion collision experiment at extreme
densities and reliable realistic(DBHF) model at low density region. We have
then calculated the temperature dependent asymmetric nuclear matter, also
investigated the critical temperature of liquid gas phase transition and
compared with the experimental data. We found that the critical temperature in
our model is in the range of 14-20 MeV.Comment: 21 pages, 10 figures, to be published in Nuclear Physics
Glassy Phase Transition and Stability in Black Holes
Black hole thermodynamics, confined to the semi-classical regime, cannot
address the thermodynamic stability of a black hole in flat space. Here we show
that inclusion of correction beyond the semi-classical approximation makes a
black hole thermodynamically stable. This stability is reached through a phase
transition. By using Ehrenfest's scheme we further prove that this is a glassy
phase transition with a Prigogine-Defay ratio close to 3. This value is well
placed within the desired bound (2 to 5) for a glassy phase transition. Thus
our analysis indicates a very close connection between the phase transition
phenomena of a black hole and glass forming systems. Finally, we discuss the
robustness of our results by considering different normalisations for the
correction term.Comment: v3, minor changes over v2, references added, LaTeX-2e, 18 pages, 3 ps
figures, to appear in Eour. Phys. Jour.
Isospin influences on particle emission and critical phenomenon in nuclear dissociation
Features of particle emission and critical point behavior are investigated as
functions of the isospin of disassembling sources and temperature at a moderate
freeze-out density for medium-size Xe isotopes in the framework of isospin
dependent lattice gas model. Multiplicities of emitted light particles,
isotopic and isobaric ratios of light particles show the strong dependence on
the isospin of the dissociation source, but double ratios of light isotope
pairs and the critical temperature determined by the extreme values of some
critical observables are insensitive to the isospin of the systems. Values of
the power law parameter of cluster mass distribution, mean multiplicity of
intermediate mass fragments (), information entropy () and Campi's
second moment () also show a minor dependence on the isospin of Xe
isotopes at the critical point. In addition, the slopes of the average
multiplicites of the neutrons (), protons (), charged particles
(), and IMFs (), slopes of the largest fragment mass number
(), and the excitation energy per nucleon of the disassembling source
() to temperature are investigated as well as variances of the
distributions of , , , , and . It
is found that they can be taken as additional judgements to the critical
phenomena.Comment: 9 Pages, 8 figure
Search for DCC in 158A GeV Pb+Pb Collisions
A detailed analysis of the phase space distributions of charged particles and
photons have been carried out using two independent methods. The results
indicate the presence of nonstatistical fluctuations in localized regions of
phase space.Comment: Talk at the PANIC99 Conference, June 9-16, 199
Present Status and Future of DCC Analysis
Disoriented Chiral Condensates (DCC) have been predicted to form in high
energy heavy ion collisions where the approximate chiral symmetry of QCD has
been restored. This leads to large imbalances in the production of charged to
neutral pions. Sophisticated analysis methods are being developed to
disentangle DCC events out of the large background of events with
conventionally produced particles. We present a short review of current
analysis methods and future prospects.Comment: 12 pages, 5 figures. Invited talk presented at the 13th International
Conference on Ultrarelativistic Nucleus-Nucleus Collisions (Quark Matter 97),
Tsukuba, Japan, 1-5 Dec 199
Central Pb+Pb Collisions at 158 A GeV/c Studied by Pion-Pion Interferometry
Two-particle correlations have been measured for identified negative pions
from central 158 AGeV Pb+Pb collisions and fitted radii of about 7 fm in all
dimensions have been obtained. A multi-dimensional study of the radii as a
function of kT is presented, including a full correction for the resolution
effects of the apparatus. The cross term Rout-long of the standard fit in the
Longitudinally CoMoving System (LCMS) and the vl parameter of the generalised
Yano-Koonin fit are compatible with 0, suggesting that the source undergoes a
boost invariant expansion. The shapes of the correlation functions in Qinv and
Qspace have been analyzed in detail. They are not Gaussian but better
represented by exponentials. As a consequence, fitting Gaussians to these
correlation functions may produce different radii depending on the acceptance
of the experimental setup used for the measurement.Comment: 13 pages including 10 figure
Search for Disoriented Chiral Condensates in 158 AGeV Pb+Pb Collisions
The restoration of chiral symmetry and its subsequent breaking through a
phase transition has been predicted to create regions of Disoriented Chiral
Condensates (DCC). This phenomenon has been predicted to cause anomalous
fluctuations in the relative production of charged and neutral pions in
high-energy hadronic and nuclear collisions. The WA98 experiment has been used
to measure charged and photon multiplicities in the central region of 158 AGeV
Pb+Pb collisions at the CERN SPS. In a sample of 212646 events, no clear DCC
signal can be distinguished. Using a simple DCC model, we have set a 90% C.L.
upper limit on the maximum DCC production allowed by the data.Comment: 20 Pages, LaTeX, uses elsart.cls, 8 eps figures included, submitted
to Physics Letters
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