The quark form factor in quantum chromodynamics

It is shown how leading logarithmic predictions of certain quark form factor effects in QCD, such as the suppression of the Drell-Yan process at small transverse momenta and of the collinear energy-energy correlation in e⁺e^? annihilation, are invalidated by non-leading logarithms corresponding to the vectorial cancellation of gluon transverse momenta. Simple improved expressions incorporating this phenomenon are presented.