Strangeness production in hadronic models and recombination models

TL;DR

This paper compares hadronic and recombination models for strange particle production in heavy ion collisions, highlighting the effects of local equilibration and flow on particle yields and spectra.

Contribution

It introduces a hybrid UrQMD-hydrodynamic model to study strangeness production and analyzes the origins of Phi-mesons and baryon-to-meson ratios.

Findings

Hybrid approach shows enhanced strange particle yields.

Energy-independent scaling of baryon/meson ratios suggests flow effects.

Maximum in p_T spectra may not indicate quark coalescence.

Abstract

We present recent results on the production, spectra and elliptic flow of strange particles in dynamic simulations employing hadronic degrees of freedom and from recombination models. The main focus will be on the Ultra-relativistic Molecular Dynamics (UrQMD) Boltzmann approach to relativistic heavy ion collisions and a hybrid approach with intermediate hydrodynamic evolution based on UrQMD (available for download as UrQMD v3.3). Compared to the standard binary collision approach, an enhancement of the strange particle particle yields is found in the hybrid approach due to the assumption of local equilibration. The production origins of the Phi-meson in the hybrid approach are studied in further detail. We also present results on the transverse momentum spectra of baryon to meson ratios of strange particles. Due to the approximate energy independent scaling of this ratio as a function of p_T we argue, that a maximum in these spectra may not be a unique sign for quark coalescence but can be understood in terms of flow and fragmentation.