391 research outputs found
Transverse hydrodynamics with sudden hadronization -- production of strangeness
We consider a physical scenario for ultra-relativistic heavy-ion collisions
where, at the early stage, only transverse degrees of freedom of partons are
thermalized, while the longitudinal motion is described by free streaming. When
the energy density of the partonic system drops to a certain critical value,
the partons hadronize and the newly formed hadronic system freezes out. This
sudden change is described with the help of the Landau matching conditions
followed by the simulations done with THERMINATOR. The proposed scenario
reproduces well the transverse-momentum spectra, the elliptic flow coefficient
v2, and the HBT radii of pions and kaons studied at RHIC (Au+Au collisions at
the top beam energy). It also reproduces quite well the transverse-momentum
spectra of hyperons.Comment: talk presented by WF at the Strangeness in Quark Matter Conference,
Buzios, Brazil, Sept. 27 - oct. 2, 200
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
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
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
Transient dynamics of nonlinear magneto-optical rotation
We analyze nonlinear magneto-optical rotation (NMOR) in rubidium vapor
subjected to continuously-scanned magnetic field. By varying magnetic-field
sweep rate, a transition from traditionally-observed dispersive-like NMOR
signals (low sweep rate) to oscillating signals (higher sweep rates) is
demonstrated. The transient oscillatory behavior is studied versus light and
magnetic-field parameters, revealing a strong dependence of the signals on
magnetic-sweep rate and light intensity. The experimental results are supported
with density-matrix calculations, which enable quantitative analysis of the
effect. Fitting of the signals simulated versus different parameters with a
theoretically-motivated curve reveals presence of oscillatory and static
components in the signals. The components depend differently on the system
parameters, which suggests their distinct nature. The investigations provide
insight into dynamics of ground-state coherence generation and enable
application of NMOR in detection of transient spin couplings.Comment: 9 pages, 7 figures, Submitted to Physical Review
Energy and system size dependence of chemical freeze-out in relativistic nuclear collisions
We present a detailed study of chemical freeze-out in p-p, C-C, Si-Si and
Pb-Pb collisions at beam momenta of 158A GeV as well as Pb-Pb collisions at
beam momenta of 20A, 30A, 40A and 80A GeV. By analyzing hadronic multiplicities
within the statistical hadronization model, we have studied the parameters of
the source as a function of the number of the participating nucleons and the
beam energy. We observe a nice smooth behaviour of temperature, baryon chemical
potential and strangeness under-saturation parameter as a function of energy
and nucleus size. Interpolating formulas are provided which allow to predict
the chemical freeze-out parameters in central collisions at centre-of-mass
energies > 4.5 GeV and for any colliding ions. Specific discrepancies between
data and model emerge in particle ratios in Pb-Pb collisions at SPS between 20A
and 40A GeV of beam energy which cannot be accounted for in the considered
model schemes.Comment: 22 pages, 10 figures. References added and updated. Table correcte
Free-streaming approximation in early dynamics of relativistic heavy-ion collisions
We investigate an approximation to early dynamics in relativistic heavy-ion
collisions, where after formation the partons are free streaming and around the
proper time of 1 fm/c undergo a sudden equilibration described in terms of the
Landau matching condition. We discuss physical and formal aspects of this
approach. In particular, we show that initial azimuthally asymmetric transverse
flow develops for non-central collisions as a consequence of the sudden
equilibration. Moreover, the energy-momentum tensor from the free-streaming
stage matches very smoothly to the form used in the transverse hydrodynamics,
whereas matching to isotropic hydrodynamics requires a more pronounced change
in the energy-momentum tensor. After the hydrodynamic phase statistical
hadronization is carried out with the help of THERMINATOR. The physical results
for 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 within our approach. The agreement is equally good for a
purely hydrodynamic evolution started at an early proper time of 0.25 fm/c, or
for the free streaming started at that time, followed by the sudden
equilibration at tau ~1 fm/c and then by perfect hydrodynamics. Thus, the
inclusion of free streaming allows us to delay the start of hydrodynamics to
more realistic times of the order of 1 fm/c.Comment: 10 pages, 12 figure
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