The energy dependence of the virtual photoabsorption cross section in deep inelastic scattering (DIS) at low $x = Q^2/W^2 < 0.1$ may be described in terms of the saturation scale that in our approach depends on the energy, $\Lambda^2_{ sat} = \Lambda^2_{ sat} (W^2)$. 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.
Categories: hep-ph