235 research outputs found
Indications of early thermalization in relativistic heavy-ion collisions
The directed flow of particles emitted from the fireball created in a
heavy-ion collision is shown to be a very sensitive measure of the pressure
equilibration in the first 1 fm/c of the evolution. Performing a 3+1
dimensional relativistic hydrodynamic calculation with nonequilibrated
longitudinal and transverse pressures, we show that the directed flow is
strongly reduced if the pressure imbalance survives for even a short time.
Transverse momentum spectra, elliptic flow and interferometry correlation radii
are not very sensitive to this early pressure anisotropy. Comparison with the
data points toward a short equilibration time of the order of fm/c or
less
Directed flow in ultrarelativistic heavy-ion collisions
We study the generation of directed flow in the hydrodynamic expansion of the
hot matter formed in ultrarelativistic heavy-ion collisions at 200GeV. The
experimentally observed negative directed flow in a wide range of central
pseudorapidities isreproduced assuming that the fireball is tilted away from
the collision axis. The tilt of the source is consistent with a preferential
emission in the forward/backward hemisphere from forward/backward participating
nucleons. The model reproduces the experimentally observed scaling of the
directed flow when going from Au-Au to Cu-Cu systems.Comment: figure adde
A comparison of different methods in the study of dynamical fluctuations in high energy e+e- collisions
Different methods in the study of anomalous scaling of factorial moments in
high energy e+e- collisions are examined in some detail. It is shown that the
horizontal and vertical factorial moments are equivalent only when they are
used in combination with the cummulant variables. The influence of different
reference frames and that of phase space restrictions is also discussed.Comment: 5 pages, 6 figure
Intermittency in Branching Processes
We study the intermittency properties of two branching processes, one with a
uniform and another with a singular splitting kernel. The asymptotic
intermittency indices, as well as the leading corrections to the asymptotic
linear regime are explicitly computed in an analytic framework. Both models are
found to possess a monofractal spectrum with . Relations with
previous results are discussed.Comment: 20 pages, UCLA93/TEP/2
Asymmetry and the Neutron Skin in Heavy Nuclei
In heavy nuclei the spatial distribution of protons and neutrons is
different. At CERN SPS energies production of and differs for
, , and scattering. These two facts lead to an impact
parameter dependence of the to ratio in
collisions. A recent experiment at CERN seems to confirm qualitatively these
predictions. It may open a possibility for determination of neutron density
distribution in nuclei.Comment: 6 pages and 2 figures, a talk by A.Szczurek at the international
conference MESON2004, June 4-8, Cracow, Polan
On the possible space-time fractality of the emitting source
Using simple space-time implementation of the random cascade model we
investigate numerically a conjecture made some time ago which was joining the
intermittent behaviour of spectra of emitted particles with the possible
fractal structure of the emitting source. We demonstrate that such details are
seen, as expected, in the Bose-Einstein correlations between identical
particles. \\Comment: Thoroughly rewritten and modify version, to be published in Phys.
Rev.
Search for Scaling Dimensions for Random Surfaces with c=1
We study numerically the fractal structure of the intrinsic geometry of
random surfaces coupled to matter fields with . Using baby universe
surgery it was possible to simulate randomly triangulated surfaces made of
260.000 triangles. Our results are consistent with the theoretical prediction
for the intrinsic Hausdorff dimension.Comment: 10 pages, (csh will uudecode and uncompress ps-file), NBI-HE-94-3
Multiplicity Distributions and Rapidity Gaps
I examine the phenomenology of particle multiplicity distributions, with
special emphasis on the low multiplicities that are a background in the study
of rapidity gaps. In particular, I analyze the multiplicity distribution in a
rapidity interval between two jets, using the HERWIG QCD simulation with some
necessary modifications. The distribution is not of the negative binomial form,
and displays an anomalous enhancement at zero multiplicity. Some useful
mathematical tools for working with multiplicity distributions are presented.
It is demonstrated that ignoring particles with pt<0.2 has theoretical
advantages, in addition to being convenient experimentally.Comment: 24 pages, LaTeX, MSUHEP/94071
Anomalous radial expansion in central heavy-ion reactions
The expansion velocity profile in central heavy-ion reactions in the Fermi
energy domain is examined. The radial expansion is non-hubblean and in the
surface region it scales proportional to a higher exponent () of
the radius. The anomalous expansion velocity profile is accompanied by a power
law nucleon density profile in the surface region. Both these features of
central heavy-ion reactions disappear at higher energies, and the system
follows a uniform Hubble expansion ()
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