Saturation and BFKL dynamics in the HERA data at small-x

Abstract

Abstract We show that the HERA data for the inclusive structure function F2(x,Q2) for x⩽10−2 and 0.045⩽Q2⩽45 GeV2 can be well described within the color dipole picture, with a simple analytic expression for the dipole–proton scattering amplitude, which is an approximate solution to the non-linear evolution equations in QCD. For dipole sizes less than the inverse saturation momentum 1/Qs(x), the scattering amplitude is the solution to the BFKL equation in the vicinity of the saturation line. It exhibits geometric scaling and scaling violations by the diffusion term. For dipole sizes larger than 1/Qs(x), the scattering amplitude saturates to one. The fit involves three parameters: the proton radius R, the value x0 of x at which the saturation scale Qs equals 1 GeV, and the logarithmic derivative of the saturation momentum λ. The value of λ extracted from the fit turns out to be consistent with a recent calculation using the next-to-leading order BFKL formalism.