Coherent photon bremsstrahlung and dynamics of heavy-ion collisions: comparison of different models

TL;DR

This paper compares different schematic models for coherent photon bremsstrahlung in relativistic heavy-ion collisions, analyzing their predictions and agreement with microscopic transport models, especially at AGS energies.

Contribution

It introduces and compares various schematic models for photon bremsstrahlung, highlighting their agreement and differences with microscopic transport model predictions.

Findings

Models agree in the soft photon limit

At AGS energies, bremsstrahlung exceeds $b50$ MeV photon yield from $c0^0$ decays

Coherent photon bremsstrahlung is sensitive to final velocity distribution

Abstract

Differential spectra of coherent photon bremsstrahlung in relativistic heavy ion collisions are calculated within various schematic models of the projectile-target stopping. Two versions of the degradation length model, based on a phenomenological deceleration law, are considered. The simple shock wave model is studied analytically. The predictions of these models agree in the soft photon limit, where the spectrum is determined only by the final velocity distribution of charged particles. The results of these models in the case of central Au+Au collisions at various bombarding energies are compared with the predictions of the microscopic transport model UrQMD. It is shown that at the AGS energy the coherent photon bremsstrahlung exceeds the photon yield from $\pi^0$-decays at photon energies $\omega\loo 50$ MeV.