Investigation into the limits of perturbation theory at low Q^2 using HERA deep inelastic scattering data

Abstract

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 $x$, $x_{\mathrm{Bj}}$ = 6 $\cdot$ 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 Regge formalism can describe the data up to $Q^2\approx$ 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.

38 pages, 13 figures