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.

• Received 5 June 1980

DOI:https://doi.org/10.1103/PhysRevD.23.214