70 research outputs found
q-Boson approach to multiparticle correlations
An approach is proposed enabling to effectively describe, for relativistic
heavy-ion collisions, the observed deviation from unity of the intercept
\lambda (measured value corresponding to zero relative momentum {\bf p} of two
registered identical pions or kaons) of the two-particle correlation function
C(p,K). The approach uses q-deformed oscillators and the related picture of
ideal gas of q-bosons. In effect, the intercept \lambda is connected with
deformation parameter q. For a fixed value of q, the model predicts specific
dependence of \lambda on pair mean momentum {\bf K} so that, when |{\bf
K}|\gsim 500 - 600 MeV/c for pions or when |{\bf K}|\gsim 700 - 800 MeV/c for
kaons, the intercept \lambda tends to a constant which is less than unity and
determined by q. If q is fixed to be the same for pions and kaons, the
intercepts \lambda_\pi and \lambda_K essentially differ at small mean momenta
{\bf K}, but tend to be equal at {\bf K} large enough (|{\bf K}|\gsim 800MeV/c)
where the effect of resonance decays can be neglected. We argue that it is of
basic interest to check in the experiments on heavy ion collisions: (i) the
exact shape of dependence \lambda = \lambda({\bf K}), and (ii) whether for
|{\bf K}| \gsim 800 MeV/c the resulting \lambda_\pi and \lambda_K indeed
coincide.Comment: 6 pages, revtex, 4 figures, to be published in Mod. Phys. Lett.
Pionic Freeze-out Hypersurfaces in Relativistic Nucleus-Nucleus Collisions
The space-time structure of the multipion system created in central
relativistic heavy-ion collisions is investigated. Using the microscopic
transport model UrQMD we determine the freeze-out hypersurface from equation on
pion density n(t,r)=n_c. It turns out that for proper value of the critical
energy density \epsilon_c equation \epsilon(t,r)=\epsilon_c gives the same
freeze-out hypersurface. It is shown that for big enough collision energies
E_kin > 40A GeV/c (sqrt(s) > 8A GeV/c) the multipion system at a time moment
{\tau} ceases to be one connected unit but splits up into two separate spatial
parts (drops), which move in opposite directions from one another with
velocities which approach the speed of light with increase of collision energy.
This time {\tau} is approximately invariant of the collision energy, and the
corresponding \tau=const. hypersurface can serve as a benchmark for the
freeze-out time or the transition time from the hydrostage in hybrid models.
The properties of this hypersurface are discussed.Comment: 11 pages, 8 EPS figures, references added, minor changes to match
published versio
Time dependence of partition into spectators and participants in relativistic heavy-ion collisions
The process of formation of the participant system in heavy-ion collisions is
investigated in the framework of a simplified analytic Glauber-like model,
which is based on the relativistic Boltzmann transport equation. The key point
lies in the time-dependent partition of the nucleon system into two groups:
nucleons, which did not take part in any interaction before a given time and
nucleons, which already have interacted. In the framework of the proposed model
we introduce a natural energy-dependent temporal scale , which allows us
to remove all dependencies of the model on the collision energy except for the
energy dependence of the nucleon-nucleon cross-section. By investigating the
time dependence of the total number of participants we conclude that the
formation process of the participant system becomes complete at . Time dependencies of participant total angular momentum and vorticity are
also considered and used to describe the emergence of rotation in the reaction
plane.Comment: 24 pages, 10 figures, minor changes to match published versio
The Influence of High Multiplicities at RHIC on the Gamov Factor
The corrections for two-pion correlations due to electromagnetic final-state
interactions at high secondary multiplicities are investigated. The analysis is
performed by solving the Schr\"odinger equation with a potential which is
dictated by the multi-particle environment. Two different post-freeze-out
scenarios are examined. First, for a uniformly spread environment of secondary
particles, a screened Coulomb potential is exploited. It is shown that the
presence of a static and uniform post-freeze-out medium results in a noticeable
deviation from the standard Gamov factor. However, after going to a more
realistic model of an expanding pion system, this conclusion changes
drastically. We argue that the density of the secondary pions n_\pi(t,R), where
R is a distance from the fireball, is bounded from above by n_\pi(t,R)\le
const/R^2 for all times t. Then, a two-particle scalar potential which is found
as a solution of the Maxwell equation for non-uniform medium replaces the
screened one. Even this upper limit does not result in an essential deviation
from the Gamov correction.Comment: 11 pages, 7 figures, minor text corrections are mad
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