th / 0 41 20 77 v 1 2 0 D ec 2 00 4 Strange particle production in a single - freeze - out model

The transverse-momentum spectra and elliptic flow of strange particles are calculated in the framework of the single-freeze-out model and compared with the recent RHIC data. An overall very good agreement between the model predictions and the data is obtained. In this paper we use the single-freeze-out model of Refs. [1, 2, 3] to analyze the production of strange particles in relativistic heavy-ion collisions. The model results are compared with the recent RHIC data on the transverse-momentum spectra and elliptic flow of hyperons [4, 5]. In the original formulation [1, 2, 3], the single-freeze-out model is used to describe cylindrically symmetric sytems such as those created in the most central events. A natural extension of the original formulation is obtained by the introduction of the azimuthal asymmetry in both the shape of the freeze-out hypersurface and the transverse-flow field. The asymmetry of the freeze-out hypersurface is taken into account by the following parameterization [6]: t = τ coshα‖ coshα⊥, rz = τ sinhα‖ coshα⊥, rx = τ sinhα⊥ √ 1− ǫ cosφ, ry = τ sinhα⊥ √ 1 + ǫ sinφ. (1) Here the coordinates t and rz are kept as in the symmetric formulation: τ denotes the lifetime of the system, whereas α‖ and α⊥ are the longitudinal and transverse space-time rapidity. The rx-axis lies in the reaction plane, and the ry-axis is perpendicular to the reaction plane. The almond-like shape of the system in the transverse plane is achieved by the introduction of the factors √ 1± ǫ. For positive ǫ the system is elongated out of the reaction plane, as seen in the experiment. The value of ǫ is fitted to reproduce the dependence of the Rside HBT radius on the azimuthal angle [6]. The four-velocity field is defined in the following way: