On the Energy Dependence of DIS in the Diffraction Region of Low X

The energy dependence of the virtual photoabsorption cross section in deep inelastic scattering (DIS) at low $x=Q^2\mathrm{/}{W}^2<0.1$ may be described in terms of the saturation scale that in our approach depends on the energy, ${\mathrm{\Lambda }}_{sat}^2={\mathrm{\Lambda }}_{sat}^2(W^2)$. We briefly summarize our recent findings that allow us to predict the exponent $C_2$ of $\Lambda^2_{sat} (W^2) \sim (W^2)^{C_2}$ in agreement with the previous result obtained from fitting the experimental data. The exponent $C_2$ depending on the relative magnitude of the longitudinal and transverse contribution to the structure function, direct measurements of the longitudinal part are urgently needed.