99 research outputs found
Matching Stages of Heavy Ion Collision Models
Heavy ion reactions and other collective dynamical processes are frequently
described by different theoretical approaches for the different stages of the
process, like initial equilibration stage, intermediate locally equilibrated
fluid dynamical stage and final freeze-out stage. For the last stage the best
known is the Cooper-Frye description used to generate the phase space
distribution of emitted, non-interacting, particles from a fluid dynamical
expansion/explosion, assuming a final ideal gas distribution, or (less
frequently) an out of equilibrium distribution. In this work we do not want to
replace the Cooper-Frye description, rather clarify the ways how to use it and
how to choose the parameters of the distribution, eventually how to choose the
form of the phase space distribution used in the Cooper-Frye formula. Moreover,
the Cooper-Frye formula is used in connection with the freeze-out problem,
while the discussion of transition between different stages of the collision is
applicable to other transitions also. More recently hadronization and molecular
dynamics models are matched to the end of a fluid dynamical stage to describe
hadronization and freeze-out. The stages of the model description can be
matched to each other on spacetime hypersurfaces (just like through the
frequently used freeze-out hypersurface). This work presents a generalized
description of how to match the stages of the description of a reaction to each
other, extending the methodology used at freeze-out, in simple covariant form
which is easily applicable in its simplest version for most applications.Comment: 9 pages, 2 figure
Explicit Model Realizing Parton-Hadron Duality
We present a model that realizes both resonance-Regge (Veneziano) and
parton-hadron (Bloom-Gilman) duality. We first review the features of the
Veneziano model and we discuss how parton-hadron duality appears in the
Bloom-Gilman model. Then we review limitations of the Veneziano model, namely
that the zero-width resonances in the Veneziano model violate unitarity and
Mandelstam analyticity. We discuss how such problems are alleviated in models
that construct dual amplitudes with Mandelstam analyticity (so-called DAMA
models). We then introduce a modified DAMA model, and we discuss its
properties. We present a pedagogical model for dual amplitudes and we construct
the nucleon structure function F2(x,Q2). We explicitly show that the resulting
structure function realizes both Veneziano and Bloom-Gilman duality.Comment: 11 pages, 8 figure
QGP flow fluctuations and the characteristics of higher moments
The dynamical development of expanding Quark-gluon Plasma (QGP) flow is
studied in a 3+1D fluid dynamical model with a globally symmetric, initial
condition. We minimize fluctuations arising from complex dynamical processes at
finite impact parameters and from fluctuating random initial conditions to have
a conservative fluid dynamical background estimate for the statistical
distributions of the thermodynamical parameters. We also avoid a phase
transition in the equation of state, and we let the matter supercool during the
expansion.
Then central Pb+Pb collisions at TeV are studied in an
almost perfect fluid dynamical model, with azimuthally symmetric initial state
generated in a dynamical flux-tube model. The general development of
thermodynamical extensives are also shown for lower energies.
We observe considerable deviations from a thermal equilibrium source as a
consequence of the fluid dynamical expansion arising from a least fluctuating
initial state
NeXSPheRIO results on azimuthal anisotropy in Au-Au collisions at 200A GeV
In this work, we present the results obtained by the hydrodynamic code
NeXSPheRIO on anisotropic flows. In our calculation, we made use of
event-by-event fluctuating initial conditions, and chemical freeze-out was
explicitly implemented. We studied directed flow, elliptic flow and forth
harmonic coefficient for various hadrons at different centrality windows for
Au+Au collisions at 200 AGeV. The results are discussed and compared with
experimental data from RHIC.Comment: 6 pages and 6 figures, sqm2008 contributio
Collective Deceleration of Ultrarelativistic Nuclei and Creation of Quark-Gluon Plasma
We propose a unified space-time picture of baryon stopping and quark-gluon
plasma creation in ultrarelativistic heavy-ion collisions. It is assumed that
the highly Lorentz contracted nuclei are decelerated by the coherent color
field which is formed between them after they pass through each other. This
process continues until the field is neutralized by the Schwinger mechanism.
Conservation of energy and momentum allow us to calculate the energy losses of
the nuclear slabs and the initial energy density of the quark-gluon plasma.Comment: 11 pages in revtex, 2 eps figure
Separable potential model for interactions at low energies
The effective separable meson-baryon potentials are constructed to match the
equivalent chiral amplitudes up to the second order in external meson momenta.
We fit the model parameters (low energy constants) to the threshold and low
energy data. In the process, the -proton bound state problem is
solved exactly in the momentum space and the 1s level characteristics of the
kaonic hydrogen are computed simultaneously with the available low energy
cross sections. The model is also used to describe the
mass spectrum and the energy dependence of the amplitude.Comment: 31 pages, v2 - added corrections to make it compatible with the
published versio
- âŚ