Canonical aspects of strangeness enhancement

Abstract

Strangeness enhancement (SE) in heavy ion collisions can be understood in the statistical model on the basis of canonical suppression. In this formulation,SE is a consequence of the transition from canonical to the asymptotic grand canonical limit and is predicted to be a decreasing function of collision energy. This model predictions are consistent with the recent NA49 data on $\Lambda$ enhancement at $p_{lab}=40, 80, 158$ GeV.Comment: 4 pages, 4 figures. To appear in the proceedings of Quark Matter 2002 (Nantes, France

Strangeness report

“…For the most central bin, the enhancement is larger at 40 GeV than at 160 GeV. Qualitatively, an increase of the enhancement at low energy is actually predicted by the canonical suppression model, the magnitude of the observed effect, however, is very small compared with the predicted increase by a factor 4 to 5 [33]. The centrality dependence of the enhancement at low energy is steeper than at the top SPS energy.…”

Hadron yields and the phase diagram of strongly interacting matter

“…The relative abundances of light flavor hadrons are determined by a few thermal parameters and, in the simplest case, approximately proportional to the Boltzmann factors. This is true with the only exception of strange particles, which deviate from the expected equilibrium abundance by a factor which depends on the strangeness content of the particle [5,6]. In central heavy ion collisions [3], strange particles were however found to follow the expected equilibrium distribution 1 .…”

“…Another approach consist in the implementation of the "canonical suppression" mechanism (i.e. strangeness has to be conserved exactly and not on average) [6] on a smaller volume than the overall size of the system, determined by a "canonical radius" parameter, R C . The parameter γ c is introduced because charm can only be created in the initial phases of the collisions (it is too heavy to be created thermally) [15] and it is thus expected to be significantly out of equilibrium.…”

System and Energy Dependence of Strangeness Production with STAR

“…Strange yields in heavy ion collisions, when compared to lighter systems, seem to universally scale with dN ch /dη for SPS and RHIC energies. It is also predicted that the greater the number of strange quarks in the particle, the greater the effect of phase space suppression when modeled with respect to the number of participants, N part [ 10]. Even though the expected ordering of the suppression is observed at RHIC, theΛ andΞ measurements normalized to their pp values do not …”