137 Chapter 6 Heavy Quark Photon Production Radiation 6.1 Introduction The confidence in the application of perturbative QCD methods to jet energy loss in heavy ion collisions gained from the early quantitative understanding of π and η suppression with null direct- γ control [238, 277] has recently come into serious doubt [438]. Evidence from measurements such as high- p$_{T}$ correlations [417, 439] and nonphotonic electrons [423, 424] demonstrates clear disagree- ment with perturbative models [152, 357, 374, 435, 440]. Several papers postu- late alternative nonperturbative energy loss mechanisms [250, 342, 343, 436], and a new measurement, the double ratio of charm to bottom nuclear mod- ification factors, has been suggested as a robust observable for testing some of these novel ideas [441]. Electromagnetic radiation from quark jets, as it is transparent to the partonic medium, holds enormous promise as a new tool for investigating jet energy loss mechanisms; naively one expects the spectrum of