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

E. Iancu (1) , K. Itakura (1) , S. Munier (1)

1 SPhT - Service de Physique Théorique

We show that the HERA data for the inclusive structure function $F_2(x,Q^2)$ for $x\le 10^{-2}$ and $0.045\le Q^2 \le 45\,{\rm GeV}^2$ 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 1GeV, 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.

Domaines: Physique Générale [physics.gen-ph]; Physique des Hautes Energies - Phénoménologie [hep-ph]

E. Iancu, K. Itakura, S. Munier. Saturation and BFKL dynamics in the HERA data at small-$x$. Physics Letters B, 2004, 590, pp.199-208. ⟨hal-00170462⟩