Fast hadron freeze-out generator

We have developed a fast Monte Carlo procedure of hadron generation that allows one to study and analyze various observables for stable hadrons and hadron resonances produced in ultrarelativistic heavy ion collisions. Particle multiplicities are determined based on the concept of chemical freeze-out. Particles can be generated on the chemical or thermal freeze-out hypersurface represented by a parametrization or a numerical solution of relativistic hydrodynamics with given initial conditions and equation of state. Besides standard spacelike sectors associated with the volume decay, the hypersurface may also include nonspacelike sectors related to the emission from the surface of expanding system. For comparison with other models and experimental data, we demonstrate the results based on the standard parametrizations of the hadron freeze-out hypersurface and flow velocity profile under the assumption of a common chemical and thermal freeze-out. The C++ generator code is written under the ROOT framework and is available for public use at http://uhkm.jinr.ru/.

Figure 1

Validation of the MC procedure for ${\rho }_u^{max}=0.65$ (left panel) and 2.0 (right panel): transverse momentum spectra (solid lines) calculated according to Eq. (45) and corresponding MC results (black triangles). Also shown are MC results obtained with a constant residual weight (black points).

Figure 2

${\pi }^{+}$ emission transverse $x$ coordinate (left) and time (right) generated in the Bjorken-like model with the parameters given in Table , ${\eta }_{max}=2$: all ${\pi }^{+}$'s (solid circles), direct ${\pi }^{+}$'s (solid line), decay ${\pi }^{+}$'s from ρ (squares), ω (open circles), $K^{*}(892)$ (up-triangles), and Δ (down-triangles).

Figure 3

Same as Fig. 2, but for the Hubble-like parametrization.

Figure 4

Pseudorapidity [$-\ln \tan (\theta /2),\theta$ is the particle production angle] distributions of charged particles in central Au+Au collisions at $\sqrt{s}{}_{\mathit{NN}}=200$ GeV from the PHOBOS experiment [34] (solid circles) and MC calculations within the Bjorken-like (left panel) and Hubble-like (right panel) models. Model results corresponding to the space-time rapidity range parameter ${\eta }_{max}=5,3$, and 2 are shown by solid, dashed, and dotted lines, respectively.

Figure 5

${\pi }^{+},K^{+}$, and proton transverse momentum spectra at midrapidity $y\approx 0$ in central Au+Au collisions at $\sqrt{s}{}_{\mathit{NN}}=200$ GeV from PHENIX experiment [45] (solid symbols) and MC calculations within the Bjorken-like (dashed lines) and Hubble-like (solid lines) models. Right panel shows the model results obtained with the strangeness suppression parameter ${\gamma }_s=0.8$.

Figure 6

Contributions to the ${\pi }^{+}$ transverse momentum spectrum at midrapidity in central Au+Au collisions at $\sqrt{s}{}_{\mathit{NN}}=200$ GeV calculated within the Bjorken-like model: all ${\pi }^{+}$'s (solid circles), direct ${\pi }^{+}$'s (stars), decay ${\pi }^{+}$'s from ρ (squares), ω (open circles), $K^{*}(892)$ (up-triangles), and Δ (down-triangles).

Figure 7

${\pi }^{\pm }{\pi }^{\pm }$ correlation radii and suppression parameter λ at midrapidity in central Au+Au collisions at $\sqrt{s}{}_{\mathit{NN}}=200$ GeV from the STAR experiment [50] (open circles) and MC calculations within the Bjorken-like model (up-triangles) in different intervals of the pair transverse momentum $k_t$.