Dynamical freeze-out phenomena: The case of $K^\pm, \phi$ transverse momentum spectra in collisions of Au(1.23 A GeV) + Au

TL;DR

This paper investigates the continuous kinetic freeze-out of $K^ ext{±}$ and $ ext{ϕ}$ mesons in gold-gold collisions at 1.23 A GeV, using transport model simulations to analyze transverse momentum spectra and challenge previous late freeze-out interpretations.

Contribution

It demonstrates that a dynamical, continuous freeze-out process explains the spectra, contradicting earlier late freeze-out assumptions based on cross section differences.

Findings

Transverse momentum slope parameters become time independent after 20 fm/c.

The complex reaction network does not support late freeze-out of $K^-$.

Simulations show a continuous freeze-out process rather than a sudden one.

Abstract

We argue on a continuous (dynamical) kinetic freeze-out of $K^\pm, \phi$ observed at midrapidity in collisions Au(1.23 A GeV) + Au. The simulations by means of a transport model of BUU type point to time independent transverse momentum slope parameters after 20 fm/c. The complex interplay of expansion dynamics and strangeness production/exchange/absorption as well as elastic scatterings involved in the reaction network does not support the previous interpretation of a late freeze-out of $K^-$ due to larger cross sections.