The Energy Dependence of the Saturation Scale
  At low $x \cong Q^2/W^2 << 1$, in deep inelastic scattering, the photon fluctuates into a $q \bar q$ vector state that interacts via two gluons with the proton. The energy dependence is determined by the saturation scale, in our approach given by $\Lambda^2_{sat} (W^2) \sim (W^2)^{C_2}$. Imposing DGLAP evolution, we find $C_2^{theory} = 0.27$ in agreement with the model-independent analysis of the HERA data. Different values of the exponent $C_2$ are correlated with different ratios of the longitudinal to transverse structure function. This stresses the need for experiments to separate longitudinal and transverse contributions in deep inelastic scattering. 
Masaaki Kuroda and Dieter Schildknecht