Impact of low-$x$ resummation on QCD analysis of HERA data

Fits to the final combined HERA deep-inelastic scattering cross-section data within the conventional DGLAP framework of QCD have shown some tension at low x and low $Q^2$ . A resolution of this tension incorporating $\ln (1/x)$ -resummation terms into the HERAPDF fits is investigated using the xFitter program. The kinematic region where this resummation is important is delineated. Such high-energy resummation not only gives a better description of the data, particularly of the longitudinal structure function $F_L$ , it also results in a gluon PDF which is steeply rising at low x for low scales, $Q^2 \simeq 2.5\,\hbox {GeV}^2$ , contrary to the fixed-order NLO and NNLO gluon PDF.