171 research outputs found
Renormalization group approach to multiparticle density fluctuations
An iterative procedure is developed with the aim of constructing homogeneity
rules for the distribution P(rho,delta) of the particle density rho at
resolution scale delta. A single iteration step consists of a change in the
normalization point of P(rho,delta) followed by a rescaling. Similar
transformation rule is introduced for density fluctuations contaminated by
Poisson noise. Application of the iterative procedure is given for the
Ginzburg-Landau description of phase-transition from the quark-gluon plasma and
for random cascading models.Comment: 11 pages REVTeX, 1 figure include
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
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
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
Vacuum polarization and plasma oscillations
We evidence the existence of plasma oscillations of electrons-positron pairs
created by the vacuum polarization in an uniform electric field with E < Ec.
Our general treatment, encompassing also the traditional, well studied case of
E > Ec, shows the existence in both cases of a maximum Lorentz factor acquired
by electrons and positrons and allows determination of the a maximal length of
oscillation. We quantitatively estimate how plasma oscillations reduce the rate
of pair creation and increase the time scale of the pair production. These
results are particularly relevant in view of the experimental progress in
approaching the field strengths E < Ec.Comment: to appear in Phys. Lett.
Model independent shape analysis of correlations in 1, 2 or 3 dimensions
A generic, model-independent method for the analysis of the two-particle
short-range correlations is presented, that can be utilized to describe e.g.
Bose-Einstein (HBT or GGLP), statistical, dynamical or other short-range
correlation functions. The method is based on a data-motivated choice for the
zero-th order approximation for the shape of the correlation function, and on a
systematic determination of the correction terms with the help of complete
orthonormal set of functions. The Edgeworth expansion is obtained for
approximately Gaussian, the Laguerre expansion for approximately exponential
correlation functions. Multi-dimensional expansions are also introduced and
discussed.Comment: Latex, 15 pages, uses epsfig.sty elsart.sty, misprints correcte
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
The challenges of urban ageing:Making cities age-friendly in Europe
Urban ageing is an emerging domain that deals with the population of older people living in cities. The ageing of society is a positive yet challenging phenomenon, as population ageing and urbanisation are the culmination of successful human development. One could argue whether the city environment is an ideal place for people to grow old and live at an old age compared to rural areas. This viewpoint article explores and describes the challenges that are encountered when making cities age-friendly in Europe. Such challenges include the creation of inclusive neighbourhoods and the implementation of technology for ageing-in-place. Examples from projects in two age-friendly cities in The Netherlands (The Hague) and Poland (Cracow) are shown to illustrate the potential of making cities more tuned to the needs of older people and identify important challenges for the next couple of years. Overall, the global ageing of urban populations calls for more age-friendly approaches to be implemented in our cities. It is a challenge to prepare for these developments in such a way that both current and future generations of older people can benefit from age-friendly strategies
Fluctuation of Gaps in Hadronization at Phase Transition
Event-by-event fluctuations of hadronic patterns in heavy-ion collisions are
studied in search for signatures of quark-hadron phase transition. Attention is
focused on a narrow strip in the azimuthal angle with small . The
fluctuations in the gaps between particles are quantified by simple measures. A
scaling exponent is shown to exist around . An index is
shown to characterize the critical fluctuation; it is a numerical constant
. All the measures considered in this gap analysis are
experimentally observable. Whether or not the theoretical predictions, based on
simulations using 2-dimensional Ising model, are realistic for heavy-ion
collisions, analysis of the experimental data suggested here should be carried
out, since the existence of a scaling behavior is of interest in its own right.Comment: 10 pages LaTex + 8 eps figure
Cluster Production in Quark-Hadron Phase Transition
The problem of cluster formation and growth in first-order quark-hadron phase
transition in heavy-ion collisions is considered. Behaving as Brownian
particles, the clusters carry out random walks and can encounter one another,
leading to coalescence and breakup. A simulation of the process in cellular
automaton suggests the possibility of a scaling distribution in the cluster
sizes. The experimental determination of the cluster-size distribution is urged
as a means to find a clear signature of phase transition.Comment: 12 pages + 1 figure. Report # OITS-517. To be published in Phys. Rev.
Lett. 71, xxx (1994
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