Photon bremsstrahlung and diffusive broadening of a hard jet

Understand

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 which 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.