Photon bremsstrahlung and diffusive broadening of a hard jet
Abstract
The photon bremsstrahlung rate from a quark jet produced in deep-inelastic scattering (DIS) off a large nucleus is studied in the collinear limit. The leading medium-enhanced higher twist corrections that describe the multiple scattering of the jet in the nucleus are re-summed to all orders of twist. The propagation of the jet in the absence of further radiative energy loss is shown to be governed by a transverse momentum diffusion equation. We compute the final photon spectrum in the limit of soft photons, taking into account the leading and next-to-leading terms in the photon momentum fraction y. In this limit, the photon spectrum in a physical gauge is shown to arise from two interfering sources: one where the initial hard scattering produces an off-shell quark, which immediately radiates the photon and then undergoes subsequent soft rescattering, and an alternative in which the quark is produced on-shell and propagates through the medium until it is driven off-shell by rescattering and radiates the photon. Our result has a simple formal structure as a product of the photon splitting function, the quark transverse momentum distribution coming from a diffusion equation, and a dimensionless factor that encodes the effect of the interferences encountered by the propagating quark over the length of the medium. The destructive nature of such interferences in the small-y limit is responsible for the origin of the Landau-Pomeranchuck-Migdal (LPM) effect. Along the way we also discuss possible implications for quark jets in hot nuclear matter.
Description
Journals published by the American Physical Society can be found at http://publish.aps.org/Subject
MULTIPLE PARTON SCATTERINGRADIATIVE ENERGY-LOSS
QUARK-GLUON PLASMA
HEAVY-ION COLLISIONS
NUCLEAR ENVIRONMENT
HADRONIC SCATTERING
TRANSVERSE-MOMENTUM
POWER CORRECTIONS
MATTER
QCD
Physics