Pionic freeze-out hypersurfaces in relativistic nucleus-nucleus collisions

Anchishkin, D. and Vovchenko, V. and Csernai, László Pál (2013) Pionic freeze-out hypersurfaces in relativistic nucleus-nucleus collisions. PHYSICAL REVIEW C, 87 (1). ISSN 2469-9985

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Abstract

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) = nc. It turns out that for proper value of the critical energy density ǫc equation ǫ(t, r) = ǫc gives the same freeze- out hypersurface. It is shown that for big enough collision energies Ekin ≥ 40A GeV/c (√s ≥ 8A GeV/c) the multipion system at a time moment τ ceases to be one connected unit but splits up into two separate spatial parts (drops), which move in opposite direc- tions from one another with velocities which approach the speed of light with increase of collision energy. This time τ is approximately invariant of the collision energy, and the corresponding τ =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.

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