39 Chapter 2: Motivation The Ter-Mikayelian (TM) effect [303, 304] is a direct result of radiative quanta gaining mass in a plasma. As in beta decay, production of high mo- mentum charged particles also has radiation associated with the process. For QCD this infrared divergent vacuum radiation is absorbed into fragmenta- tion functions, but in-medium the finite gluon mass regulates and suppresses this radiation. Djordjevic and Gyulassy [305] calculated the QCD analog of the TM effect for single quark pairs. Chapter 6 extends this work to include back-to-back jet production. We find the away-side jet, necessary for charge conservation, fills in the dead cone for heavy quarks, further suppresses the production radiation, and naturally regulates the momentum loss as the jet momentum approaches zero. Previously we argued that by comparing theoretical model results to data jets have the potential to provide information on not just the density of scattering centers but also of the nature of the matter in the medium. The process would be as follows: models qualitatively inconsistent with experimental observations are falsified; models in quantitative agreement with data set limits on medium properties by their input parameter range allowed by data. Clearly the more precise the experimental observable, the more tightly constrained the medium property. Similarly the more sensitive the theoretical results to changes in medium property the stronger the statement about the medium. Of great concern but poorly investigated is the influence of theoretical imprecision— 2.2.5 Fragility