252 Appendix F: Heavy Quark Production Radiation Derivation With Massless Field and Charge with Recoil p = [0 , E $^{+}$, 0 ] (F.107) p ′ = [(1 − x ) E $^{+}$, k 2 (1 − x ) E $_{+}$, − k ] (F.108) k = [ xE $^{+}$, k 2 xE $_{+}$, k ] , (F.109) dE d $^{3}$k = C 4(1 − x ) 2 k 2 , (F.110) the E&M result is where we now find that the limiting form of the massive result is now recov- ered.