Speaker
Description
A phenomenological study of the final combined HERA data on inclusive deep inelastic scattering (DIS) has been performed. The data are presented and investigated for a kinematic range extending from values of the four-momentum transfer, $Q^2$, above $10^4$ GeV$^2$ down to the lowest values observable at
HERA of $Q^2 = 0.045$ GeV$^2$ and Bjorken $x$, $x_{\rm Bj} = 6 \times 10^{−7}$. The data are well described by fits based on perturbative quantum chromodynamics (QCD) using collinear factorisation and evolution of the parton densities encompassed in the DGLAP formalism from the highest $Q^2$ down to $Q^2$ of a few GeV$^2$. The standard DGLAP evolution was augmented by including an additional higher-twist term in the description of the longitudinal structure function, $F_L$. This additional term, $F_L A_L^{\rm HT}/Q^2$, improves the description of the reduced cross sections significantly. The resulting predictions for F_L suggest that further corrections are required for $Q^2$ less than about 2 GeV$^2$. The Regge formalism can describe the data up to $Q^2 \sim 0.65$ GeV$^2$. The complete data set can be described by a new fit using the ALLM parameterisation. The region between the Regge and the perturbative QCD regimes is of particular interest.
