Resummation of small x contributions to hard-scattering amplitudes

The summation of the small x corrections to hard scattering QCD amplitudes by collinear factorisation method is reconsidered and the K-factor is derived in leading log x approximation. The corresponding expression by Catani and Hautmann (1994) has to be corrected. The significance of the correction is demonstrated in the examples of structure function F_L and of exclusive electroproduction.