251 Appendix F: Heavy Quark Production Radiation Derivation Figure F.3: Diagrams contributing to the probability of emitting a photon in a pair production event. F.4.3 Comparison Massive Field, Charge, with Recoil It turns out with the Proca result, Eq. (F.91), is unchanged. p = [ M 2 $_{Q}$/E $^{+}$, E$^{+}$, 0 ] (F.104) p ′ = [(1 − x ) E $^{+}$, k 2 + M 2 Q (1 − x ) E $_{+}$, − k ] (F.105) k = [ xE $^{+}$, k 2 + m 2 γ xE + , k ] , (F.106)