Emil Avsar, Gösta Gustafson
Geometric scaling and QCD dynamics in DIS

JHEP 0704:067,2007


DIS data from HERA show a striking regularity as \sigma^{\gamma^* p} is a function of the ratio \tau=Q^2/Q_s^2(x) only. The scaling function shows a break at \tau ~ 1, which has been taken as an indication for saturation. However, besides saturation also the transition between dominance of k_t-ordered (DGLAP) and k_t-non-ordered (BFKL) evolution contributes to a break around this value of \tau, as well as the suppression for small Q^2 due to finite quark masses and confinement. In this paper we use a dipole cascade model based on Mueller's dipole model, which also includes energy conservation and pomeron mergins, to investigate the contributions of these different effects to the scaling behaviour. As a result we predict that the scaling function for \tau < 1 will be modified when data for Q^2 > 1 GeV^2 become available. We also investigate the scaling properties of the charm contribution and the impact parameter dependence of the saturation scale.

LU TP 06-47, hep-ph/0702087