Parton distributions with small x resummation: evidence for BFKL dynamics in HERA data
Abstract
We present a determination of the parton distribution functions of the proton in which NLO and NNLO fixedorder calculations are supplemented by NLL x small x resummation. Deepinelastic structure functions are computed consistently at NLO+NLLx or NNLO+NLLx, while for hadronic processes small x resummation is included only in the PDF evolution, with kinematic cuts introduced to ensure the fitted data lie in a region where the fixedorder calculation of the hard crosssections is reliable. In all other respects, the fits use the same methodology and are based on the same global dataset as the recent NNPDF3.1 analysis. We demonstrate that the inclusion of small x resummation leads to a quantitative improvement in the perturbative description of the HERA inclusive and charmproduction reduced crosssections in the small x region. The impact of the resummation in our fits is greater at NNLO than at NLO, because fixedorder calculations have a perturbative instability at small x due to large logarithms that can be cured by resummation. We explore the phenomenological implications of PDF sets with small x resummation for the longitudinal structure function F_L at HERA, for parton luminosities and LHC benchmark crosssections, for ultrahighenergy neutrinonucleus crosssections, and for future highenergy leptonproton colliders such as the LHeC.
 Publication:

European Physical Journal C
 Pub Date:
 April 2018
 DOI:
 10.1140/epjc/s1005201857744
 arXiv:
 arXiv:1710.05935
 Bibcode:
 2018EPJC...78..321B
 Keywords:

 High Energy Physics  Phenomenology;
 High Energy Physics  Experiment;
 Nuclear Theory
 EPrint:
 70 pages, many figures. Discussion on uncertainties due to subleading logarithmic contributions. Discussion on fits with pseudodata from future highenergy leptonproton colliders. Updated references. Version to be published in EPJC