Strangeness Production in AA and pp Collisions

TL;DR

This paper investigates how causality and space-time scales influence strangeness production in high energy collisions, explaining suppression in elementary interactions and its disappearance in heavy ion collisions due to larger hadronization volumes.

Contribution

It provides a theoretical analysis of the space-time dynamics affecting strangeness production and estimates the energies at which suppression effects vanish in different collision types.

Findings

Suppression of strangeness in elementary collisions explained by causality constraints.

Heavy ion collisions achieve full chemical equilibrium due to larger hadronization volumes.

Predicted energy thresholds for the disappearance of strangeness suppression.

Abstract

Boost-invariant hadron production in high energy collisions occurs in causally disconnected regions of finite space-time size. As a result, globally conserved quantum numbers (charge, strangeness, baryon number) are conserved locally in spatially restricted correlation clusters. Their size is determined by two time scales: the equilibration time specifying the formation of a quark-gluon plasma, and the hadronization time, specifying the onset of confinement. The expected values for these scales provide the theoretical basis for the suppression observed for strangeness production in elementary interactions ($pp$, $e^+e^-$) below LHC energies. In contrast, the space-time superposition of individual collisions in high energy heavy ion interactions leads to higher energy densities, resulting in much later hadronization and hence much larger hadronization volumes. This largely removes the causality constraints and results in an ideal hadronic resonance gas in full chemical equilibrium. In the present paper, we determine the collision energies needed for that; we also estimate when $pp$ collisions reach comparable hadronization volumes and thus determine when strangeness suppression should disappear there as well.