Anatomy of the differential gluon structure function of the proton from the experimental data on F2p(x,Q2)

The differential gluon structure function of the proton F(x,Q²) introduced by Fadin, Kuraev, and Lipatov in 1975 is used in many applications of small-x QCD. We report here ready-to-use parametrizations of F(x,Q²) from the κ-factorization phenomenology of the experimental data on the small-x proton structure function F_2p(x,Q²). These parametrizations are based partly on the available Dokshitzer-Gribov-Lipatov-Altarelli-Parisi (DGLAP) evolution fits [Glück-Reya-Vogt, Coordinated Theoretical/Experimental Project on QCD Phenomenology (CTEQ), and Martin-Roberts-Stirling] to parton distribution functions and on realistic extrapolations into a soft region. We discuss the impact of soft gluons on various observables. The x dependence of the F(x,Q²) so determined varies strongly with Q² 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,Q²) by the soft and hard Regge components with intercepts Δ_soft=0 and Δ_hard~0.4.