Coherence phenomena between initial and final state radiation in a dense QCD medium

TL;DR

This paper studies how dense QCD media affect the interference between initial and final state radiation, revealing a gradual decoherence and potential modifications to evolution equations with implications for high-energy nuclear collisions.

Contribution

It extends previous opacity-based models to include multiple soft scatterings and introduces a harmonic oscillator approximation for medium effects on radiation interference.

Findings

Gradual decoherence between initial and final state radiation due to multiple scatterings.

Potential large double logarithmic enhancement in gluon multiplicity for dense media.

Implications for modified evolution equations in finite-sized QCD media.

Abstract

In this work we investigate medium modifications to the interference pattern between initial and final state radiation. We compute single gluon production off a highly energetic parton that undergoes a hard scattering and subsequently crosses a dense QCD medium of finite size. We extend our previous studies obtained at first order in opacity by providing general results for multiple soft scatterings and their specific formulation within the harmonic oscillator approximation. We show that there is a gradual onset of decoherence between the initial and final state radiation due to multiple scatterings, that opens the phase space for large angle emissions. By examining the multiplicity of produced gluons, we observe a potentially large double logarithmic enhancement for dense media and small opening angles. This result points to a possible modification of the evolution equations due to a QCD medium of finite size. We briefly comment on the phenomenological consequences of this setup in high-energy nuclear collisions.