Low-x scaling in γ∗p total cross sections

We show that the experimental data for the total virtual-photon proton cross section, σγ∗p(W2,Q2), for xbj≲0.1 lie on a universal curve, when plotted against η=(Q2+m20)/Λ2(W2), where Λ2(W2)=C1(W2+W20)C2 is determined by the parameters C1,C2 and W20. The observed scaling law follows from the generalized-vector-dominance/colour-dipole picture (GVD/CDP) of low-x deep inelastic scattering.