212 Appendix E: Standard pQCD Results A useful relation comes from eikonality: In order to motivate the work of Appendix F we will derive the 0 th order bremsstrahlung radiation loss for massive quarks and gluons using two meth- ods and find that the results are inconsistent. We will find that the usual pQCD approach of calculating the radiation spectrum from a monojet only is consistent with a dijet calculation in the massless limit only. For massive gluons the longitudinal polarization must be considered, and its contribution to the spectrum from the away-side jet will be O (1) in an expansion in powers of 1 /E $^{+}$. We will find the following relations useful in evaluating Feynman diagrams related to bremsstrahlung, which we will refer to as Peskin’s Trick: k + ≫ k − ⇒ xE + ≫ k 2 xE + ⇒ ( xE $^{+}$)2 ≫ k 2 ⇒ xE + ≫ | k | . (E.10) ¯ u ( p $^{′}$) γ $^{µ}$ϵ ∗ $_{µ}$( / p ′ + m ) = ¯ u ( p $^{′}$)2 p ′ $^{µ}$ϵ ∗ $_{µ}$; ( / P + m ) γ $^{µ}$ϵ ∗ $_{µ}$u ( P ) = 2 P $^{µ}$ϵ ∗ $_{µ}$u ( P ) . (E.11) E.2 Monojet vs. Dijet 0 th Order Radiation E.2.1 Peskin’s Trick