Parton distributions with QED corrections

Abstract

We present a set of parton distribution functions (PDFs), based on the NNPDF2.3 set, which includes a photon PDF, and QED contributions to parton evolution. We describe the implementation of the combined QCD+QED evolution in the NNPDF framework. We then provide a first determination of the full set of PDFs based on deep-inelastic scattering data and LHC data for W and Z/γ * Drell-Yan production, using leading-order QED and NLO or NNLO QCD. We compare the ensuing NNPDF2.3QED PDF set to the older MRST2004QED set. We perform a preliminary investigation of the phenomenological implications of NNPDF2.3QED: specifically, photon-induced corrections to direct photon production at HERA, and high-mass dilepton and W pair production at the LHC.

W + W − pair production in proton-proton collisions: small missing terms

“…Here, in the QCD improved calculations µ 2 F = m 2 t was used as the factorization scale. Let us show also our predictions obtained with the NNPDF2.3 QED photon distributions [38], (see figure 11). In the left panel of figure 11 we concentrate on the biggest inelastic-inelastic contribution.…”

“…Recently the NNPDF collaboration presented a detailed study of uncertainties of a photon PDF in the framework of so-called neural network PDFs [38]. This analysis suggests that inelastic photon-induced contributions may have rather big uncertainies.…”

APFEL Web: a web-based application for the graphical visualization of parton distribution functions

“…[2]. interface for the visualization of PDFs with a wide range of formats: absolute plots, ratio plots, compare PDFs from different groups, compare error PDF from a single set, plot all PDF flavor combinations at the same time, compute parton luminosities and finally compute also DIS structure functions and APPLgrid observables.…”

Forward and small-x physics at CMS

“…Even though demonstrated only at a qualitative level, an increase of the gluon density at small-x values tends to be preferred for a consistent description of measurements at central and forward pseudorapidities. In particular, it has been observed that the description of charged-particle multiplicity at high pseudorapidities [17] provided by tunes using the NNPDF2.3LO PDF [18], e.g. Monash [19] and CUETP8M1 [17], is better than tunes using other PDF sets.…”