Deep-inelastic scattering in k factorization and the anatomy of the differential gluon structure function of the proton

The differential gluon structure function of the proton, F(x, Q(2)), introduced by Fadin, Kuraev, and Lipatov in 1975 is extensively used in small-x QCD. We report here the first determination of F(x, Q(2)) from experimental data on the small-x proton structure function F-2p(x, q(2)). We give convenient parametrizations for F(x, Q(2)) based partly on the available DGLAP evolution fits (GRV, CTEQ, and MRS) to parton distribution functions and on realistic extrapolations into the soft region. We discuss the impact of soft gluons on various observables. The x dependence of the so-determined F(x, Q(2)) varies strongly with Q(2) and does not exhibit simple Regge properties. Nonetheless, the hard-to-soft diffusion is found to give rise to a viable approximation of the proton structure function F-2p(x, Q(2)) by the soft and hard Reege components with intercepts Delta (soft) = 0 and Delta (hard) similar to 0.4. (C) 2001 MAIK "Nauka/Interperiodica".