703 research outputs found
Anisotropic flow of strange particles at RHIC
Space-time picture of the anisotropic flow evolution in Au+Au collisions at
BNL RHIC is studied for strange hadrons within the microscopic quark-gluon
string model. The directed flow of both mesons and hyperons demonstrates wiggle
structure with the universal antiflow slope at |y| < 2 for minimum bias events.
This effect increases as the reaction becomes more peripheral. The development
of both components of the anisotropic flow is closely related to particle
freeze-out. Hadrons are emitted continuously, and different hadronic species
are decoupled from the system at different times. These hadrons contribute
differently to the formation and evolution of the elliptic flow, which can be
decomposed onto three components: (i) flow created by hadrons emitted from the
surface at the onset of the collision; (ii) flow produced by jets; (iii)
hydrodynamic flow. Due to these features, the general trend in elliptic flow
formation is that the earlier mesons are frozen, the weaker their elliptic
flow. In contrast, baryons frozen at the end of the system evolution have
stronger v2.Comment: proceedings of the conference SQM2004 (September 2004, Cape Town,
South Africa
Directed flow in heavy-ion collisions at NICA: what is interesting to measure?
We study the formation of the directed flow of hadrons in nuclear collisions
at energies between AGS and SPS in Monte Carlo cascade model. The slope of the
proton flow at midrapidity tends to zero (softening) with increasing impact
parameter of the collision. For very peripheral topologies this slope becomes
negative (antiflow). The effect is caused by rescattering of hadrons in
remnants of the colliding nuclei. Since the softening of the proton flow can be
misinterpreted as indication of the presence of quark-gluon plasma, we propose
several measurements at NICA facility which can help one to distinguish between
the cases with and without the plasma formation.Comment: 5 pages, 3 figures, Contribution to the NICA White Paper (EPJA,
topical issue
Violation of energy-per-hadron scaling in a resonance matter
Yields of hadrons, their average masses and energies per hadron at the stage
of chemical freeze-out in (ultra)relativistic heavy-ion collisions are analyzed
within the statistical model. The violation of the scaling / = 1 GeV
observed in Au+Au collisions at = 130 AGeV is linked to the
formation of resonance-rich matter with a considerable fraction of baryons and
antibaryons. The rise of the energy-per-hadron ratio in baryon-dominated matter
is discussed. A violation of the scaling condition is predicted for a very
central zone of heavy-ion collisions at energies around 40 AGeV.Comment: 5 pages incl. 3 figures and 2 tables, to be published in Phys. Rev.
Microscopic description of anisotropic flow in relativistic heavy ion collisions
Anisotropic flow of hadrons is studied in heavy ion collisions at SPS and
RHIC energies within the microscopic quark-gluon string model. The model was
found to reproduce correctly many of the flow features, e.g., the wiggle
structure of direct flow of nucleons at midrapidity, or centrality, rapidity,
and transverse momentum dependences of elliptic flow. Further predictions are
made. The differences in the development of the anisotropic flow components are
linked to the freeze-out conditions, which are quite different for baryons and
mesons.Comment: Proceedings of the Erice School on Nuclear Physics (Erice, Italy,
September 16-24, 2003
Transition to resonance-rich matter in heavy ion collisions at RHIC energies
The equilibration of hot and dense nuclear matter produced in the central
region in central Au+Au collisions at AGeV is studied within the
microscopic transport model UrQMD. The pressure here becomes isotropic at fm/c. Within the next 15 fm/c the expansion of the matter proceeds
almost isentropically with the entropy per baryon ratio .
During this period the equation of state in the -plane has a very
simple form, . Comparison with the statistical model (SM) of
an ideal hadron gas reveals that the time of fm/ may be too
short to attain the fully equilibrated state. Particularly, the fractions of
resonances are overpopulated in contrast to the SM values. The creation of such
a long-lived resonance-rich state slows down the relaxation to chemical
equilibrium and can be detected experimentally.Comment: Talk at the conference Strangeness'2000, to be published in J. of
Phys.
Gluon shadowing in the Glauber-Gribov model at HERA
We calculate shadowing using new data on the gluon density of the Pomeron
recently measured with high precision at HERA. The calculations are made in a
Glauber-Gribov framework and Pomeron tree-diagrams are summed up within a
unitarity-conserving procedure. The total cross section of \vphot A
interaction is then found in a parameter-free description, employing gluon
diffractive and inclusive distribution functions as input. A strong shadowing
effect is obtained, in good agreement with several other models. Impact
parameter dependence of gluon shadowing is also presented.Comment: 18 pages, 6 figures; references added, discussion of model enlarged,
calculation of low-x contribution corrected; to appear in Phys. Let
Supercooling of rapidly expanding quark-gluon plasma
We reexamine the scenario of homogeneous nucleation of the quark-gluon plasma
produced in ultra-relativistic heavy ion collisions. A generalization of the
standard nucleation theory to rapidly expanding system is proposed. The
nucleation rate is derived via the new scaling parameter . It is
shown that the size distribution of hadronic clusters plays an important role
in the dynamics of the phase transition. The longitudinally expanding system is
supercooled to about 3-6%, then it is reheated, and the hadronization is
completed within 6-10 fm/c, i.e. 5-10 times faster than it was estimated
earlier, in a strongly nonequilibrium way.Comment: 12 pages, LaTeX, 3 eps figure
Strangeness production in heavy ion collisions at SPS and RHIC within two-source statistical model
The experimental data on hadron yields and ratios in central Pb+Pb and Au+Au
collisions at SPS and RHIC energies, respectively, are analysed within a
two-source statistical model of an ideal hadron gas. These two sources
represent the expanding system of colliding heavy ions, where the hot central
fireball is embedded in a larger but cooler fireball. The volume of the central
source increases with rising bombarding energy. Results of the two-source model
fit to RHIC experimental data at midrapidity coincide with the results of the
one-source thermal model fit, indicating the formation of an extended fireball,
which is three times larger than the corresponding core at SPS.Comment: Talk at "Strange Quarks in Matter" Conference (Strangeness'2001),
September 2001, Frankfurt a.M., German
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