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

We show that the HERA data for the inclusive structure function F-2(x, Q(2)) for x less than or equal to 10(-2) and 0.045 less than or equal to Q(2) less than or equal to 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/Q(s) (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/Q(s) (x), the scattering amplitude saturates to one. The fit involves three parameters: the proton radius R, the value x(0) of x at which the saturation scale Q(s) equals 1 GeV, and the logarithmic derivative of the saturation momentum lambda. The value of lambda extracted from the fit turns out to be consistent with a recent calculation using the next-to-leading order BFKL formalism. (C) 2004 Elsevier B.V. All rights reserved.