1,620 research outputs found
Hubble-like flows in relativistic heavy-ion collisions
We study the dynamical appearance of scaling solutions in relativistic
hydrodynamics. The phase transition effects are included through the
temperature dependent sound velocity. If a pre-equilibrium transverse flow is
included in the initial conditions, then it may reach the form of the
asymptotic Hubble flow, r/t, in short evolution times, 7-15 fm. The numerical
solutions are found to support to the freeze-out models (Blast-Wave, Buda-Lund,
Cracow).Comment: 4 pages, 6 Postscript figures, uses hiph-preprint.sty, contribution
to the Quark Matter 2005 poster proceedings. Minor stylistic correction
Initial condition for hydrodynamics, partonic free streaming, and the uniform description of soft observables at RHIC
We investigate the role of the initial condition used for the hydrodynamic
evolution of the system formed in ultra-relativistic heavy-ion collisions and
find that an appropriate choice motivated by the models of early-stage
dynamics, specifically a simple two-dimensional Gaussian profile, leads to a
uniform description of soft observables measured in the Relativistic Heavy-Ion
Collider (RHIC). In particular, the transverse-momentum spectra, the
elliptic-flow, and the Hanbury-Brown--Twiss correlation radii, including the
ratio R_out/R_side as well as the dependence of the radii on the azimuthal
angle (azHBT), are properly described. We use the perfect-fluid hydrodynamics
with a realistic equation of state based on lattice calculations and the
hadronic gas at high and low temperatures, respectively. We also show that the
inclusion of the partonic free-streaming in the early stage allows to delay the
start of the hydrodynamical description to comfortable times of the order of 1
fm/c. Free streaming broadens the initial energy-density profile, but generates
the initial transverse and elliptic flow. The data may be described equally
well when the hydrodynamics is started early, or with a delay due to partonic
free-streaming.Comment: 4 pages, 4 figure
Particle Identification in the ALICE Experiment
The particle identification capabilities of the ALICE experiment are unique
among the four major LHC experiments. The working principles and excellent
performance of the central barrel detectors in a high-multiplicity environment
are presented as well as two physics examples: the extraction of transverse
momentum spectra of charged pions, kaons, protons, and the observation of the
anti-4He-nucleus.Comment: Quark Matter 2011 Proceeding
Describing transverse dynamics and space-time evolution at RHIC in a hydrodynamic model with statistical hadronization
A hydrodynamic model coupled to the statistical hadronization code
Therminator is used to study a set of observables in the soft sector at RHIC. A
satisfactory description of the pT-spectra and elliptic flow is obtained,
similarly to other hydrodynamic models. With the Gaussian initial conditions
the transverse femtoscopic radii are also reproduced, providing a possible
solution of the RHIC HBT puzzle.Comment: to appear in the conference proceedings for Quark Matter 2009, March
30 - April 4, Knoxville, Tennesse
Early dynamics of transversally thermalized matter
We argue that the idea that the parton system created in relativistic
heavy-ion collisions is formed in a state with transverse momenta close to
thermodynamic equilibrium and its subsequent dynamics at early times is
dominated by pure transverse hydrodynamics of the perfect fluid is compatible
with the data collected at RHIC. This scenario of early parton dynamics may
help to solve the problem of early equilibration.Comment: 4 pages, 2 figures, Talk given by M. Chojnacki at Quark Matter 2008,
Jaipur, Indi
Measurement of , K, p transverse momentum spectra with ALICE in proton-proton collisions at 0.9 and 7 TeV
Results of the measurement of the , K, p transverse momentum
() spectra at mid-rapidity in proton-proton collisions at
TeV are presented. Particle identification was performed using
the energy loss signal in the Inner Tracking System (ITS) and the Time
Projection Chamber (TPC), while information from the Time-of-Flight (TOF)
detector was used to identify particles at higher transverse momentum. From the
spectra at TeV the mean transverse momentum ()
and particle ratios were extracted and compared to results obtained for
collisions at TeV and lower energies.Comment: Quark Matter 2011 proceeding
Hydrodynamics and perfect fluids: uniform description of soft observables in Au+Au collisions at RHIC
It is argued that the use of the initial Gaussian energy density profile for
hydrodynamics leads to much better uniform description of the RHIC heavy-ion
data than the use of the standard initial condition obtained from the Glauber
model. With the modified Gaussian initial conditions we successfully reproduce
the transverse-momentum spectra, v2, and the pionic HBT radii (including their
azimuthal dependence). The emerging consistent picture of hadron production
hints that a solution of the long standing RHIC HBT puzzle has been found.Comment: Talk presented by WF at the XXXVIII International Symposium on
Multiparticle Physic
Instability of Boost-invariant hydrodynamics with a QCD inspired bulk viscosity
We solve the relativistic Navier-Stokes equations with homogeneous
boost-invariant boundary conditions, and perform a stability analysis of the
solution. We show that, if the bulk viscosity has a peak around as
inferred from QCD-based arguments, the background solution "freezes" at
to a nearly constant temperature state. This state is however highly unstable
with respect to certain inhomogeneous modes. Calculations show that these modes
have enough time to blow up and tear the system into droplets. We conjecture
that this is how freeze-out occurs in the QGP created in heavy ion collisions,
and perhaps similar transitions in the early universe.Comment: Accepted for publication, Rapid Communication in Physical Review C
Discussion extended, derivation and conclusions not change
Early anisotropic hydrodynamics and the RHIC early-thermalization and HBT puzzles
We address the problem if the early thermalization and HBT puzzles in
relativistic heavy-ion collisions may be solved by the assumption that the
early dynamics of the produced matter is locally anisotropic. The hybrid model
describing the purely transverse hydrodynamic evolution followed by the
perfect-fluid hydrodynamic stage is constructed. The transition from the
transverse to perfect-fluid hydrodynamics is described by the Landau matching
conditions applied at a fixed proper time. The global fit to the RHIC data
reproduces the soft hadronic observables (the pion, kaon, and the proton
spectra, the pion and kaon elliptic flow, and the pion HBT radii) with the
accuracy of about 20%. These results indicate that the assumption of the very
fast thermalization may be relaxed. In addition, the presented model suggests
that a large part of the inconsistencies between the theoretical and
experimental HBT results may be removed.Comment: replaced with the version published in Phys.Rev.C 8
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