137 research outputs found
Multistrange baryon production in relativistic heavy ion collisions
Using a multiphase transport model, we study the production of multistrange
baryons from the hadronic matter formed in relativistic heavy ion collisions.
The mechanism we introduce is the strangeness-exchange reactions between
antikaons and hyperons. We find that these reactions contribute significantly
to the production of multistrange baryons in heavy ion collisions at SPS
energies, which has been found to be appreciably enhanced. We have also made
predictions for multistrange baryon production in heavy ion collisions at RHIC
and found a similar enhancement.Comment: 6 pages, RevTex, 8 figs include
Transverse flow and hadro-chemistry in Au+Au collisions at \sqrt{s_{NN}}=200 GeV
We present a hydrodynamic assessment of preliminary particle spectra observed
in Au+Au collisions at \sqrt{s_{NN}}=200 GeV. The hadronic part of the
underlying equation of state is based on explicit conservation of (measured)
particle ratios throughout the resonance gas stage after chemical freezeout by
employing chemical potentials for stable mesons, nucleons and anti-nucleons. We
find that under these conditions the data (in particular the proton spectra)
favor a low freeze-out temperature of around 100 MeV. Furthermore we show that
through inclusion of a moderate pre-hydrodynamic transverse flow field the
shape of the spectra improves with respect to the data. The effect of the
initial transverse boost on elliptic flow and the freeze-out geometry of the
system is also elucidated.Comment: as published: more data included in Fig. 1, discussions throughout
the text improved, 6 pages, 4 figure
Effect of tensor couplings in a relativistic Hartree approach for finite nuclei
The relativistic Hartree approach describing the bound states of both
nucleons and anti-nucleons in finite nuclei has been extended to include tensor
couplings for the - and -meson. After readjusting the parameters
of the model to the properties of spherical nuclei, the effect of
tensor-coupling terms rises the spin-orbit force by a factor of 2, while a
large effective nucleon mass sustains. The overall
nucleon spectra of shell-model states are improved evidently. The predicted
anti-nucleon spectra in the vacuum are deepened about 20 -- 30 MeV.Comment: 31 pages, 4 postscript figures include
Open charm and charmonium production at relativistic energies
We calculate open charm and charmonium production in reactions at
= 200 GeV within the hadron-string dynamics (HSD) transport approach
employing open charm cross sections from and reactions that are
fitted to results from PYTHIA and scaled in magnitude to the available
experimental data. Charmonium dissociation with nucleons and formed mesons to
open charm ( pairs) is included dynamically. The 'comover'
dissociation cross sections are described by a simple phase-space model
including a single free parameter, i.e. an interaction strength , that
is fitted to the suppression data for collisions at SPS
energies. As a novel feature we implement the backward channels for charmonium
reproduction by channels employing detailed balance. From our
dynamical calculations we find that the charmonium recreation is comparable to
the dissociation by 'comoving' mesons. This leads to the final result that the
total suppression at = 200 GeV as a function of centrality
is slightly less than the suppression seen at SPS energies by the NA50
Collaboration, where the 'comover' dissociation is substantial and the backward
channels play no role. Furthermore, even in case that all directly produced
mesons dissociate immediately (or are not formed as a mesonic state),
a sizeable amount of charmonia is found asymptotically due to the + meson channels in central collisions of at =
200 GeV which, however, is lower than the yield expected from binary
scaling of collisions.Comment: 42 pages, including 14 eps figures, discussions extended and
references added, to be published in Phys. Rev.
Comparison of space-time evolutions of hot/dense matter in =17 and 130 GeV relativistic heavy ion collisions based on a hydrodynamical model
Based on a hydrodynamical model, we compare 130 GeV/ Au+Au collisions at
RHIC and 17 GeV/ Pb+Pb collisions at SPS. The model well reproduces the
single-particle distributions of both RHIC and SPS.
The numerical solution indicates that huge amount of collision energy in RHIC
is mainly used to produce a large extent of hot fluid rather than to make a
high temperature matter; longitudinal extent of the hot fluid in RHIC is much
larger than that of SPS and initial energy density of the fluid is only 5%
higher than the one in SPS. The solution well describes the HBT radii at SPS
energy but shows some deviations from the ones at RHIC.Comment: 28 pages, 21 figures, REVTeX4, one figure is added and some figures
are replace
Collective flow and two-pion correlations from a relativistic hydrodynamic model with early chemical freeze out
We investigate the effect of early chemical freeze-out on radial flow,
elliptic flow and HBT radii by using a fully three dimensional hydrodynamic
model. When we take account of the early chemical freeze-out, the space-time
evolution of temperature in the hadron phase is considerably different from the
conventional model in which chemical equilibrium is always assumed. As a
result, we find that radial and elliptic flows are suppressed and that the
lifetime and the spatial size of the fluid are reduced. We analyze the p_t
spectrum, the differential elliptic flow, and the HBT radii at the RHIC energy
by using hydrodynamics with chemically non-equilibrium equation of state.Comment: One subsection and two figures adde
Global Observations from PHOBOS
Particle production in Au+Au collisions has been measured in the PHOBOS
experiment at RHIC for a range of collision energies. Three empirical
observations have emerged from this dataset which require theoretical
examination. First, there is clear evidence of limiting fragmentation. Namely,
particle production in central Au+Au collisions, when expressed as
(), becomes energy independent at high energy for a
broad region of around . This energy-independent region grows
with energy, allowing only a limited region (if any) of longitudinal
boost-invariance. Second, there is a striking similarity between particle
production in e+e- and Au+Au collisions (scaled by the number of participating
nucleon pairs). Both the total number of produced particles and the
longitudinal distribution of produced particles are approximately the same in
e+e- and in scaled Au+Au. This observation was not predicted and has not been
explained. Finally, particle production has been found to scale approximately
with the number of participating nucleon pairs for . This scaling
occurs both for the total multiplicity and for high \pT particles (3 <\pT<
4.5 GeV/c).Comment: QM2002 plenary talk, 10 pages, 11 figure
Genuine Correlations of Like-Sign Particles in Hadronic Z0 Decays
Correlations among hadrons with the same electric charge produced in Z0
decays are studied using the high statistics data collected from 1991 through
1995 with the OPAL detector at LEP. Normalized factorial cumulants up to fourth
order are used to measure genuine particle correlations as a function of the
size of phase space domains in rapidity, azimuthal angle and transverse
momentum. Both all-charge and like-sign particle combinations show strong
positive genuine correlations. One-dimensional cumulants initially increase
rapidly with decreasing size of the phase space cells but saturate quickly. In
contrast, cumulants in two- and three-dimensional domains continue to increase.
The strong rise of the cumulants for all-charge multiplets is increasingly
driven by that of like-sign multiplets. This points to the likely influence of
Bose-Einstein correlations. Some of the recently proposed algorithms to
simulate Bose-Einstein effects, implemented in the Monte Carlo model PYTHIA,
are found to reproduce reasonably well the measured second- and higher-order
correlations between particles with the same charge as well as those in
all-charge particle multiplets.Comment: 26 pages, 6 figures, Submitted to Phys. Lett.
Counterpoint. Early intervention for psychosis risk syndromes: Minimizing risk and maximizing benefit
Background: Malhi et al. in this issue critique the clinical high risk (CHR) syndrome for psychosis. Method: Response to points of critique. Results: We agree that inconsistency in CHR nomenclature should be minimized. We respectfully disagree on other points. In our view: a) individuals with CHR and their families need help, using existing interventions, even though we do not yet fully understand disease mechanisms; b) substantial progress has been made in identification of biomarkers; c) symptoms used to identify CHR are specific to psychotic illnesses; d) CHR diagnosis is not “extremely difficult”; e) the pattern of progression, although heterogenous, is discernible; f) “psychosis-like symptoms” are common but are not used to identify CHR; and g) on the point described as ‘the real risk,’ CHR diagnosis does not frequently cause harmful stigma. Discussion: Malhi et al.'s arguments do not fairly characterize progress in the CHR field nor efforts to minimize stigma. That said, much work remains in areas of consistent nomenclature, mechanisms of disease, dissecting heterogeneity, and biomarkers. With regard to what the authors term the “real risk” of stigma associated with a CHR “label,” however, our view is that avoiding words like “risk” and “psychosis” reinforces the stigma that both they and we mean to oppose. Moreover, patients and their families benefit from being given a term that describes what is happening to them
Long-range Angular Correlations On The Near And Away Side In P-pb Collisions At √snn=5.02 Tev
7191/Mar294
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