Phi meson production in In-In collisions at $E_{\rm lab}$=158$A$ GeV: evidence for relics of a thermal phase

TL;DR

This paper uses a hybrid Boltzmann+hydrodynamics model to analyze phi meson production in In-In collisions at 158A GeV, providing evidence for relics of a thermal phase in heavy-ion collisions.

Contribution

It introduces a hybrid model combining hydrodynamics and transport dynamics to better describe phi meson production, highlighting the importance of a thermal phase in the collision evolution.

Findings

Hybrid model matches experimental yield and spectra slope.

Pure transport model fails to reproduce key observables.

Evidence supports the existence of a thermal phase in the collision process.

Abstract

Yields and transverse mass distributions of the $\phi$-mesons reconstructed in the $\phi\to\mu^+\mu^-$ channel in In+In collisions at $E_{\rm lab}$=158$A$ GeV are calculated within an integrated Boltzmann+hydrodynamics hybrid approach based on the Ultrarelativistic Quantum Molecular Dynamics (UrQMD) transport model with an intermediate hydrodynamic stage. The analysis is performed for various centralities and a comparison with the corresponding NA60 data in the muon channel is presented. We find that the hybrid model, that embeds an intermediate locally equilibrated phase subsequently mapped into the transport dynamics according to thermal phase-space distributions, gives a good description of the experimental data, both in yield and slope. On the contrary, the pure transport model calculations tend to fail in catching the general properties of the $\phi$ meson production: not only the yield, but also the slope of the $m_T$ spectra, very poorly compare with the experimental observations.