202 Appendix D: Formation Time and Brick Estimates For large- x Bethe-Heitler radiation one sees from Eq. (D.6) that Eq. (D.10) then gives τ$_{f}$ ∼ E M 2 ∼ γ M . (D.13) γ$_{c}$ ∼ M αT . (D.14) D.2 AdS/CFT Brick Estimate We wish to more rigorously derive Eq. (5.5). Recall that Eq. (5.5) justifies Eq. (5.6), the back-of-the-envelope explanation for the momentum independences and normalization for R $^{cb}$( p$_{T}$ ) = R c $_{AA}$( p$_{T}$ ) /R b $_{AA}$( p$_{T}$ ) for AdS/CFT Drag-type heavy quark energy loss. From the simple trailing string model of [342, 343] we have by Eq. (5.1) where dp$_{T}$ dt = − µp, (D.15) µ = π √ λT 2 2 M , (D.16) p ( t ) = p (0) e − ∫ dt $^{′}$µ ( t $^{$^{′}$)}$. (D.17) with T the temperature of the SYM plasma and M the heavy quark mass. Solving Eq. (D.15) one finds that