Jet transport and photon bremsstrahlung via longitudinal and transverse scattering

TL;DR

This paper investigates how both longitudinal and transverse scatterings affect photon bremsstrahlung from hard partons in dense nuclear matter, revealing the importance of momentum exchanges in both directions on emission spectra.

Contribution

It introduces a comprehensive framework including longitudinal and transverse momentum exchanges to derive photon emission spectra in dense media, extending previous models.

Findings

Photon bremsstrahlung is affected by both transverse diffusion and longitudinal drag.

Longitudinal drag reduces stimulated photon emission.

The derived spectrum accounts for second-order momentum gradients.

Abstract

We study the effect of multiple scatterings on the propagation of hard partons and the production of jet-bremsstrahlung photons inside a dense medium in the framework of deep-inelastic scattering off a large nucleus. We include the momentum exchanges in both longitudinal and transverse directions between the hard partons and the constituents of the medium. Keeping up to the second order in a momentum gradient expansion, we derive the spectrum for the photon emission from a hard quark jet when traversing dense nuclear matter. Our calculation demonstrates that the photon bremsstrahlung process is influenced not only by the transverse momentum diffusion of the propagating hard parton, but also by the longitudinal drag and diffusion of the parton momentum. A notable outcome is that the longitudinal drag tends to reduce the amount of stimulated emission from the hard parton.