Quark form factors and leading double logarithms in quantum chromodynamics

Perturbative quantum-chromodynamic corrections involving the emission of gluons which are both soft and collinear are discussed for both hadronic production of lepton pairs and $e^{+}{e}^{-}$ annihilation. The result is an exponential, double-logarithmic quark "form factor." The differences between previous analyses are clarified and the possible experimental observation of the form factor is discussed and illustrated.