Wednesday, October 18th, 2017
Evidence for BFKL dynamics in HERA data
In a paper submitted today to the arXiv, the NNPDF Collaboration has presented a new global PDF determination in which NLO and NNLO fixed-order calculations are supplemented by NLLx small-x resummation. This analysis demonstrates for the first time that the inclusion of small-x resummation leads to a quantitative improvement in the perturbative description of the HERA inclusive and charm production cross-sections at small x and small Q, providing unambiguous evidence for the onset of BFKL dynamics. Crucially, the impact of the resummation in our fits is greater at NNLO than at NLO, because fixed-order calculations have a perturbative instability at small x due to large logarithms that are cured by resummation. This paper then explores the phenomenological implications of PDF sets with small-x resummation for the longitudinal structure function FL at HERA, for parton luminosities and LHC benchmark cross-sections, for ultra-high energy neutrino-nucleus cross-sections, and for future high-energy lepton-proton colliders such as the LHeC.