2,550 research outputs found
Strangeness production within Parton-Hadron-String Dynamics (PHSD)
The Parton-Hadron-String Dynamics (PHSD) transport approach consistently
simulates the full evolution of a relativistic heavy-ion collision from the
initial hard scatterings string formation through the dynamical deconfinement
phase transition to the quark gluon plasma (QGP), to the hadronization and to
subsequent interactions in the hadronic phase. The transport theoretical
description of quarks and gluons is based on a dynamical quasiparticle model
for partons matched to reproduce recent lattice QCD results in thermodynamic
equilibrium. The transition from partonic to hadronic degrees of freedom is
described by covariant transition rates for the fusion of quark-antiquark pairs
or three quarks (antiquarks). Studying Pb+Pb reactions from 40 to 158 A GeV, we
find that at most 40% of the collision energy is stored in the dynamics of the
partons. This implies that a large fraction of non-partonic, i.e. hadronic or
string-like matter, which can be viewed as a hadronic corona, is present in
these reactions, thus neither hadronic nor purely partonic models can be
employed to extract physical conclusions in comparing model results with data.
On the other hand, comparing the PHSD results to those of the Hadron-String
Dynamics (HSD) approach without the phase transition to QGP, we observe that
the existence of the partonic phase has a sizeable influence on the transverse
mass distribution of final kaons due to the repulsive partonic mean fields and
initial partonic scattering. Furthermore, we find a significant effect of the
QGP on the production of multi-strange antibaryons due to a slightly enhanced
s+sbar pair production in the partonic phase from massive time-like gluon decay
and to a more abundant formation of strange antibaryons in the hadronization
process.Comment: Talk given at the International Conference Strangeness in Quark
Matter 2009 (SQM 09
Is soft physics entropy driven?
The soft physics, pT < 2 GeV/c, observables at both RHIC and the SPS have now
been mapped out in quite specific detail. From these results there is mounting
evidence that this regime is primarily driven by the multiplicity per unit
rapidity, dNch/deta. This suggests that the entropy of the system alone is the
underlying driving force for many of the global observables measured in
heavy-ion collisions. That this is the case and there is an apparent
independence on collision energy is surprising. I present the evidence for this
multiplicity scaling and use it to make some extremely naive predictions for
the soft sector results at the LHC.Comment: Proceedings of Hot Quarks 2006. 8 figures, 6 page
Probing hadronic formation times with antiprotons in p+A reactions at AGS energies
The production of antiprotons in reactions is calculated in a
microscopic transport approach employing hadronic and string degrees of freedom
(HSD). It is found that the abundancies of antiprotons as observed by the E910
Collaboration in reactions at 12.3 GeV/c as well as 17.5 GeV/c can
approximately be described on the basis of primary proton-nucleon and secondary
meson-baryon production channels for all targets. The transport calculations
demonstrate that the antiproton rapidity distributions for heavy targets are
sensitive to the (or hadron) formation time in the nuclear medium.
Within our analysis the data from the E910 Collaboration are reasonably
described with a formation time of fm/c in the hadron rest frame.Comment: 18 pages, LaTeX, 8 postscript figures; submitted to Nucl. Phys.
Strangeness enhancements at central rapidity in 40 A GeV/c Pb-Pb collisions
Results are presented on neutral kaon, hyperon and antihyperon production in
Pb-Pb and p-Be interactions at 40 GeV/c per nucleon. The enhancement pattern
follows the same hierarchy as seen in the higher energy data - the enhancement
increases with the strangeness content of the hyperons and with the centrality
of collision. The centrality dependence of the Pb-Pb yields and enhancements is
steeper at 40 than at 158 A GeV/c. The energy dependence of strangeness
enhancements at mid-rapidity is discussed.Comment: 15 pages, 10 figures and 3 tables. Presented at International
Conference on Strangeness in Quark Matter (SQM2009), Buzios, Rio de Janeiro,
Brazil, 27 Sept - 2 Oct 2009. Submitted to J.Phys.G: Nucl.Part.Phys, one
reference adde
Properties of the partonic phase at RHIC within PHSD
The dynamics of partons, hadrons and strings in relativistic nucleus-nucleus
collisions is analyzed within the novel Parton-Hadron-String Dynamics (PHSD)
transport approach, which is based on a dynamical quasiparticle model for
partons (DQPM) matched to reproduce recent lattice-QCD results -- including the
partonic equation of state -- in thermodynamic equilibrium. The transition from
partonic to hadronic degrees of freedom is described by covariant transition
rates for the fusion of quark-antiquark pairs or three quarks (antiquarks),
respectively, obeying flavor current-conservation, color neutrality as well as
energy-momentum conservation. In order to explore the space-time regions of
'partonic matter' the PHSD approach is applied to nucleus-nucleus collisions
from SPS to RHIC energies. Detailed comparisons are presented for hadronic
rapidity spectra and transverse mass distributions. The traces of partonic
interactions are found in particular in the elliptic flow of hadrons as well as
in an approximate quark-number scaling at the top RHIC energy.Comment: Talk presented at the 27th Winter Workshop on Nuclear Dynamics (WWND)
in Colorado, USA on February 6 - 13, 201
Future Experiments in Relativistic Heavy Ion Collisions
The measurements at RHIC have revealed a new state of matter, which needs to
be further characterized in order to better understand its implications for the
early evolution of the universe and QCD. I will show that, in the near future,
complementary key measurements can be performed at RHIC, LHC, and FAIR. I will
focus on results than can be obtained using identified particles, a probe which
has been the basis for this conference over the past three decades. The
sophisticated detectors, built and planned, for all three accelerator
facilities enable us to measure leptons, photons, muons as well as hadrons and
resonances of all flavors almost equally well, which makes these experiments
unprecedented precision tools for the comprehensive understanding of the
physics of the early universe.Comment: 10 pages, 4 figures, Proceedings for Summary Talk at SQM 2007,
Levoca, Slovakia, June 24-29, 200
Rapidity distributions around mid-rapidity of strange particles in Pb-Pb collisions at 158 GeV/c
The production at central rapidity of K0s, Lambda, Xi and Omega particles in
Pb-Pb collisions at 158 A GeV/c has been measured by the NA57 experiment over a
centrality range corresponding to the most central 53% of the inelastic Pb-Pb
cross section. In this paper we present the rapidity distribution of each
particle in the central rapidity unit as a function of the event centrality.
The distributions are analyzed based on hydrodynamical models of the
collisions.Comment: 15 pages, 10 figure
Centrality dependence of the expansion dynamics in Pb-Pb collisions at 158 A GeV/c
Two-particle correlation functions of negatively charged hadrons from Pb-Pb
collisions at 158 GeV/c per nucleon have been measured by the WA97 experiment
at the CERN SPS. A Coulomb correction procedure that assumes an expanding
source has been implemented. Within the framework of an expanding thermalized
source model the size and dynamical state of the collision fireball at
freeze-out have been reconstructed as a function of the centrality of the
collision. Less central collisions exhibit a different dynamics than central
ones: both transverse and longitudinal expansion velocities are slower, the
expansion duration is shorter and the system freezes out showing smaller
dimensions and higher temperature.Comment: 22 pages, 11 figures, Te
Strangeness Report
The paper provides a short report on strangeness production in
ultrarelativistic nucleus-nucleus collision, with the main stress on strange
particle abundances.Comment: Proceedings of Quark Matter 200
Risk factors associated with bacteremia in COVID-19 patients admitted to intensive care unit: a retrospective multicenter cohort study
Purpose: This multicenter observational study was done to evaluate risk factors related to the development of BSI in patients admitted to ICU for COVID-19. Methods: All patients with COVID-19 admitted in two COVID-19 dedicated ICUs in two different hospital between 02–2020 and 02–2021 were recruited. Result: 537 patients were included of whom 265 (49.3%) experienced at least one BSI. Patients who developed bacteremia had a higher SOFA score [10 (8–12) vs 9 (7–10), p < 0.001], had been intubated more frequently [95.8% vs 75%, p < 0.001] and for a median longer time [16 days (9–25) vs 8 days (5–14), p < 0.001]. Patients with BSI had a median longer ICU stay [18 days (12–31.5) vs 9 days (5–15), p < 0.001] and higher mortality [54% vs 42.3%, p < 0.001] than those who did not develop it. Development of BSI resulted in a higher SOFA score [aHR 1.08 (95% CI 1.03–1.12)] and a higher Charlson score [csAHR 1.15 (95% CI 1.05–1.25)]. Conclusion: A high SOFA score and a high Charlson score resulted associated with BSI’s development. Conversely, immunosuppressive therapy like steroids and tocilizumab, has no role in increasing the risk of bacteremia
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