Parton distributions from high-precision collider data

Abstract

We present a new set of parton distributions, NNPDF3.1, which updates NNPDF3.0, the first global set of PDFs determined using a methodology validated by a closure test. The update is motivated by recent progress in methodology and available data, and involves both. On the methodological side, we now parametrize and determine the charm PDF alongside the light-quark and gluon ones, thereby increasing from seven to eight the number of independent PDFs. On the data side, we now include the D0 electron and muon W asymmetries from the final Tevatron dataset, the complete LHCb measurements of W and Z production in the forward region at 7 and 8 TeV, and new ATLAS and CMS measurements of inclusive jet and electroweak boson production. We also include for the first time top-quark pair differential distributions and the transverse momentum of the Z bosons from ATLAS and CMS. We investigate the impact of parametrizing charm and provide evidence that the accuracy and stability of the PDFs are thereby improved. We study the impact of the new data by producing a variety of determinations based on reduced datasets. We find that both improvements have a significant impact on the PDFs, with some substantial reductions in uncertainties, but with the new PDFs generally in agreement with the previous set at the one-sigma level. The most significant changes are seen in the light-quark flavor separation, and in increased precision in the a e-mail: stefano.forte@mi.infn.it determination of the gluon. We explore the implications of NNPDF3.1 for LHC phenomenology at Run II, compare with recent LHC measurements at 13 TeV, provide updated predictions for Higgs production cross-sections and discuss the strangeness and charm content of the proton in light of our improved dataset and methodology. The NNPDF3

CT14 intrinsic charm parton distribution functions from CTEQ-TEA global analysis

“…These core questions must be raised to appraise the range of validity of the PDF models with nonperturbative charm in our work and in the other recent studies [33,34,39,40,44]. We address them by starting from the fundamental QCD result, the factorization theorem for DIS cross sections with massive fermions.…”

“…For a valence-like model, it was found to be JHEP02(2018)059 less than about 2.5%, at the 90% confidence level (C.L.). Recently, several analyses by the NNPDF group [37][38][39][40] established a smaller fitted charm momentum fraction. NNPDF determined a fitted charm momentum fraction equal to (0.26±0.42)% at 68% C.L.…”

“…NNPDF determined a fitted charm momentum fraction equal to (0.26±0.42)% at 68% C.L. just above the charm mass threshold, with the charm quark pole mass taken to be 1.51 GeV [40], and equal to (0.34±0.14)% when the EMC data [41] on SIDIS charm production were included.…”

LHC and its impact on nCTEQ15 PDFs

“…The W /Z pPb data are sensitive to the heavier quark flavors (especially the strange PDF), so this provides important information on the nuclear flavor decomposition. Improved information on the nuclear corrections from the LHC lead data can also help reduce proton PDF uncertainties as (at present) fixed-target nuclear data is essential for distinguishing the individual flavors [13]. The next step is to incorporate this new data into the nPDF fit to help separately disentangle issues of flavor differentiation and nuclear corrections.…”

Prompt photon production and photon-jet correlations at the LHC

“…For the NLO and NLO+PS predictions, we employ the recent PDF set NNPDF3.1 NLO based on high-precision collider data [47]. For the LO predictions, we use instead the preceding set NNPDF2.3QED LO [48], which (while based on a similar theoretical approach) was in particular employed in the Monash 2013 tune of PYTHIA 8 [49].…”