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

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