Geometric Scaling and QCD Dynamics in DIS

DIS data from HERA show a striking regularity as σ^{γ^* p} is a function of the ratio τ=Q^2/Q_s^2(x) only. The scaling function shows a break at τ~ 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 τ, 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 τ< 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.

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