459 research outputs found
Resolving the plasma profile via differential single inclusive suppression
The ability of experimental signatures to resolve the spatio-temporal profile
of an expanding quark gluon plasma is studied. In particular, the single
inclusive suppression of high momentum hadrons versus the centrality of a
heavy-ion collision and with respect to the reaction plane in non-central
collisions is critically examined. Calculations are performed in the higher
twist formalism for the modification of the fragmentation functions. Radically
different nuclear geometries are used. The influence of different initial gluon
distributions as well as different temporal evolution scenarios on the single
inclusive suppression of high momentum pions are outlined. It is demonstrated
that the modification versus the reaction plane is quite sensitive to the
initial spatial density. Such sensitivity remains even in the presence of a
strong elliptic flow.Comment: 5 pages, 4 figures, RevTex
Chemical freeze-out temperature in hydrodynamical description of Au+Au collisions at sqrt(s_NN) = 200 GeV
We study the effect of separate chemical and kinetic freeze-outs to the ideal
hydrodynamical flow in Au+Au collisions at RHIC (sqrt(s_NN) = 200 GeV energy).
Unlike in earlier studies we explore how these effects can be counteracted by
changes in the initial state of the hydrodynamical evolution. We conclude that
the reproduction of pion, proton and antiproton yields necessitates a chemical
freeze-out temperature of T = 150 MeV instead of T = 160 - 170 MeV motivated by
thermal models. Unlike previously reported, this lower temperature makes it
possible to reproduce the p_T-spectra of hadrons if one assumes very small
initial time, tau_0 = 0.2 fm/c. However, the p_T-differential elliptic flow,
v_2(p_T) remains badly reproduced. This points to the need to include
dissipative effects (viscosity) or some other refinement to the model.Comment: 8 pages, 7 figures; Accepted for publication in European Physical
Journal A; Added discussion about the effect of weak decays to chemical
freeze-out temperature and a figure showing isentropic curves in T-mu plan
Baryonic Strangeness and Related Susceptibilities in QCD
The ratios of off-diagonal to diagonal conserved charge susceptibilities
e.g., chi_{BS}/chi_{S}, chi_{QS}/chi_{S}, related to the quark flavor
susceptibilities, have proven to be discerning probes of the flavor carrying
degrees of freedom in hot strongly interacting matter. Various constraining
relations between the different susceptibilities are derived based on the
Gell-Mann-Nishijima formula and the assumption of isospin symmetry. Using
generic models of deconfined matter and results form lattice QCD, it is
demonstrated that the flavor carrying degrees of freedom at a temperature above
1.5T_c are quark-like quasiparticles. A new observable related by isospin
symmetry to C_{BS} = -3chi_{BS}/chi_{S} and equal to it in the baryon free
regime is identified. This new observable, which is blind to neutral and
non-strange particles, carries the potential of being measured in relativistic
heavy-ion collisions.Comment: 12 pages, 5 figures, RevTex
Single-freeze-out model for ultra relativistic heavy-ion collisions at TeV and the LHC proton puzzle
The single-freeze-out model with parametrized hypersurface and flow geometry
is employed to analyze the transverse-momentum spectra of hadrons produced in
the Pb+Pb collisions at the collision energy of { TeV}
at the CERN Large Hadron Collider (LHC). With the notable exception for protons
and antiprotons, we find a very good agreement between the model results and
the data for the measured hadron species. The additional analysis of the HBT
radii of pions helps us to select, from several different types of freeze-out
studied in this work, the most realistic form of the freeze-out hypersurface.
We find that discrepancy ratio between the model and experiment for the
proton/antiproton spectra depends on , dropping from 2 in the soft region
to 1 around GeV.Comment: 9 pages, 10 figure
Space-time evolution of bulk QCD matter
We introduce a combined fully three-dimensional macroscopic/microscopic
transport approach employing relativistic 3D-hydrodynamics for the early,
dense, deconfined stage of the reaction and a microscopic non-equilibrium model
for the later hadronic stage where the equilibrium assumptions are not valid
anymore. Within this approach we study the dynamics of hot, bulk QCD matter,
which is being created in ultra-relativistic heavy ion collisions at RHIC. Our
approach is capable of self-consistently calculating the freezeout of the
hadronic system, while accounting for the collective flow on the hadronization
hypersurface generated by the QGP expansion. In particular, we perform a
detailed analysis of the reaction dynamics, hadronic freezeout, and transverse
flow.Comment: 24 pages, 27 figure
Anisotropic flow of charged and identified hadrons in the quark-gluon string model for Au+Au collisions at sqrt(s) = 200 GeV
The pseudorapidity behaviour of the azimuthal anisotropy parameters v_1 and
v_2 of inclusive charged hadrons and their dependence on the centrality has
been studied in Au+Au collisions at full RHIC energy of sqrt(s) = 200 GeV
within the microscopic quark-gluon string model. The QGSM simulation results
for the directed flow v_1 show antiflow alignment within the pseudorapidity
range |eta| < 2 in a fair agreement with the experimental v_1(eta) data, but
cannot reproduce the further development of the antiflow up to |eta| around
3.5. The eta dependence of the elliptic flow v_2 extracted from the simulations
agrees well with the experimental data in the whole pseudorapidity range for
different centrality classes. The centrality dependence of the integrated
elliptic flow of charged hadrons in the QGSM almost coincides with the PHOBOS
experimental distribution. The transverse momentum dependence of the elliptic
flow of identified and inclusive charged hadrons is studied also. The model
reproduces quantitatively the low p_T part of the distributions rather good,
but underestimates the measured elliptic flow for transverse momenta p_T > 1
GeV/c. Qualitatively, however, the model is able to reproduce the saturation of
the v_2(p_T) spectra with rising p_T as well as the crossing of the elliptic
flow for mesons and baryons.Comment: REVTeX, 10 pages, 10 figures, v2: extended discussion of the model
results, accepted for publication in Phys. Rev.
Heavy Ion Physics at the LHC with the ATLAS Detector
The ATLAS detector at CERN will provide a high-resolution
longitudinally-segmented calorimeter and precision tracking for the upcoming
study of heavy ion collisions at the LHC (sqrt(s_NN)=5520 GeV). The calorimeter
covers |eta|<5 with both electromagnetic and hadronic sections, while the inner
detector spectrometer covers |eta|<2.5. ATLAS will study a full range of
observables necessary to characterize the hot and dense matter formed at the
LHC. Global measurements (particle multiplicities, collective flow) will
provide access into its thermodynamic and hydrodynamic properties. Measuring
complete jets out to 100's of GeV will allow detailed studies of energy loss
and its effect on jets. Quarkonia will provide a handle on deconfinement
mechanisms. ATLAS will also study the structure of the nucleon and nucleus
using forward physics probes and ultraperipheral collisions, both enabled by
segmented Zero Degree Calorimeters.Comment: 9 pages, 8 figures, submitted to the Proceedings of Quark Matter
2006, Shanghai, China, November 14-20, 200
Investigation of shock waves in the relativistic Riemann problem: A comparison of viscous fluid dynamics to kinetic theory
We solve the relativistic Riemann problem in viscous matter using the
relativistic Boltzmann equation and the relativistic causal dissipative
fluid-dynamical approach of Israel and Stewart. Comparisons between these two
approaches clarify and point out the regime of validity of second-order fluid
dynamics in relativistic shock phenomena. The transition from ideal to viscous
shocks is demonstrated by varying the shear viscosity to entropy density ratio
. We also find that a good agreement between these two approaches
requires a Knudsen number .Comment: Version as published in PRC 82, 024910 (2010); 16 pages, 16 figures,
typos correcte
meson production and partonic collectivity at RHIC
New results on -meson production and elliptic flow measurements
from RHIC 2004 run (Run-IV) have been reviewed. In addition, the di-hadron
correlation function between the trigged and and the associated
soft particles was simulated. Knowledge about these results are discussed.Comment: 8 pages, 7 figures; Invited talk in International Conference on
Strangess in Quark Matter (SQM2006), UCLA, California, USA, March 26-31,
2006; to be publsihed in the Proceeding isuue of J. Phys.
Is there still any Tc mystery in lattice QCD? Results with physical masses in the continuum limit III
The present paper concludes our investigations on the QCD cross-over
transition temperatures with 2+1 staggered flavours and one-link stout
improvement. We extend our previous two studies [Phys. Lett. B643 (2006) 46,
JHEP 0906:088 (2009)] by choosing even finer lattices (=16) and we work
again with physical quark masses. The new results on this broad cross-over are
in complete agreement with our earlier ones. We compare our findings with the
published results of the hotQCD collaboration. All these results are confronted
with the predictions of the Hadron Resonance Gas model and Chiral Perturbation
Theory for temperatures below the transition region. Our results can be
reproduced by using the physical spectrum in these analytic calculations. The
findings of the hotQCD collaboration can be recovered by using a distorted
spectrum which takes into account lattice discretization artifacts and heavier
than physical quark masses. This analysis provides a simple explanation for the
observed discrepancy in the transition temperatures between our and the hotQCD
collaborations.Comment: 25 pages, 10 figures and 3 table
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