A Global Fit to Scattering Data with NLL BFKL Resummations

Abstract

We calculate DIS-scheme splitting and coefficient functions for electromagnetic deep inelastic scattering with small x resummations, as given by the NLL BFKL equation with running coupling and approximate NLL resummed impact factors. The resummations are combined with a NLO fixed order expansion, and the improved quantities thus obtained are stable at small x and significantly suppressed with respect to LL results. These results are implemented in a global fit to DIS and related data, and the results compared to a NLO fixed order DIS-scheme fit and with a previous LL resummed fit. The NLL resummed fit quality is excellent, and constitutes a marked improvement over the purely fixed order approach. The input gluon, at Q_0^2=1GeV^2, obtained from the resummed fit is positive and slightly increasing as x-->0, in contrast to the result obtained at fixed order. A resummed prediction for the longitudinal structure function F_L is presented. It is positive definite and growing with energy at low x and Q^2, where the fixed order results show a significant perturbative instability.