135 Chapter 5: pQCD vs. AdS/CFT Figure 5.6: The double ratio of R c $_{AA}$( p$_{T}$ ) to R b $_{AA}$( p$_{T}$ ) predictions for Rhic using Eq. (5.1) for AdS/CFT and WHDG [152] for pQCD with a range of input pa- rameters. While the hardening of the production spectrum reduces the dramatic bunching at Rhic as compared to $_{Lhc}$, the lower temperature at Rhic means the AdS/CFT drag formalism is applicable to higher momenta. Note that R cb is plotted to only 50 GeV for $_{Rhic}$. gion of p$_{T}$ for which both approximations are applicable for bottom quarks. The disadvantage of studying the more robust R cb observable is that the AdS momentum reach is limited by the much smaller charm quark mass; an over- lapping momentum region of validity for both coupling limits may not exist for this observable. Further careful study of the “speed limit” and higher order corrections to the AdS/CFT result must be done in order to fruitfully compare R c AA and R cb results to experiment. Or, turning this around, experiment might inform theory as to the correct scales for which these theoretical predictions