Study of freeze-out dynamics of strange hadrons

Abstract

We study the chemical freeze-out dynamics of strange particles (K, Λ, Σ) from a homogeneous and isotropically expanding hadronic system of π, K, ρ, N, Λ and Σ with zero net baryon density. We use the momentum integrated Boltzmann equation and study their evolution over the bulk hadronic matter, a condition being similar to the one created at top RHIC and LHC energies. The cross-sections, which are input to the equations, are taken either from phenomenological models or parameterized by comparing against experimental data. From this microscopic calculation we find that these strange particles freeze-out near transition temperature ≈ Tc due to large relaxation time. The continuous cease of the inelastic processes due to gradual fall in the temperature and decrease in the number density, thus lead to early freeze out of strange hadrons K, Λ and Σ which happens sequentially near Tc. However, freeze-out of these strange species near Tc appears as a sudden and simultaneous process, which is mostly predicted by thermal model while explaining the yield of identified particles at RHIC and LHC energies.

Understanding the $K^*/K$ ratio in heavy ion collisions

“…These numbers are close to the measured ones. This suggests that a cooling faster than (11), such as the Hubble-like cooling discussed in [30,31], is probably incompatible with data. Another interesting aspect of the figure is that, even with cooling, after some time of evolution the K * /K ratio becomes the same for all initial conditions.…”