15 research outputs found
Polarized Parton Distributions at an Electron-Ion Collider
We study the potential impact of inclusive deep-inelastic scattering data
from a future electron-ion collider (EIC) on longitudinally polarized parton
distribution (PDFs). We perform a PDF determination using the NNPDF
methodology, based on sets of deep-inelastic EIC pseudodata, for different
realistic choices of the electron and proton beam energies. We compare the
results to our current polarized PDF set, NNPDFpol1.0, based on a fit to
fixed-target inclusive DIS data. We show that the uncertainties on the first
moments of the polarized quark singlet and gluon distributions are
substantially reduced in comparison to NNPDFpol1.0, but also that more
measurements may be needed to ultimately pin down the size of the gluon
contribution to the nucleon spin.Comment: 11 pages, 6 figures. Two plots in Fig.5 added and discussion of
extrapolation uncertainties expanded. Final version, published in Phys. Lett.
Progress on neural parton distributions
We give a status report on the determination of a set of parton distributions
based on neural networks. In particular, we summarize the determination of the
nonsinglet quark distribution up to NNLO, we compare it with results obtained
using other approaches, and we discuss its use for a determination of
.Comment: 4 pages, 2 figs, uses dis2007.cls, to appear in the DIS 2007 workshop
proceeding
Recent progress on NNPDF for LHC
We present recent results of the NNPDF collaboration on a full DIS analysis
of Parton Distribution Functions (PDFs). Our method is based on the idea of
combining a Monte Carlo sampling of the probability measure in the space of
PDFs with the use of neural networks as unbiased universal interpolating
functions. The general structure of the project and the features of the fit are
described and compared to those of the traditional approaches.Comment: 4 pages, 6 figures, contribution for the proceedings of the
conference "Rencontres de Moriond, QCD and High Energy Interactions
Unbiased determination of polarized parton distributions and their uncertainties
We present a determination of a set of polarized parton distributions (PDFs)
of the nucleon, at next-to-leading order, from a global set of longitudinally
polarized deep-inelastic scattering data: NNPDFpol1.0. The determination is
based on the NNPDF methodology: a Monte Carlo approach, with neural networks
used as unbiased interpolants, previously applied to the determination of
unpolarized parton distributions, and designed to provide a faithful and
statistically sound representation of PDF uncertainties. We present our
dataset, its statistical features, and its Monte Carlo representation. We
summarize the technique used to solve the polarized evolution equations and its
benchmarking, and the method used to compute physical observables. We review
the NNPDF methodology for parametrization and fitting of neural networks, the
algorithm used to determine the optimal fit, and its adaptation to the
polarized case. We finally present our set of polarized parton distributions.
We discuss its statistical properties, test for its stability upon various
modifications of the fitting procedure, and compare it to other recent
polarized parton sets, and in particular obtain predictions for polarized first
moments of PDFs based on it. We find that the uncertainties on the gluon, and
to a lesser extent the strange PDF, were substantially underestimated in
previous determinations.Comment: 55 pages, 21 figure
A first determination of parton distributions with theoretical uncertainties
The parton distribution functions (PDFs) which characterize the structure of
the proton are currently one of the dominant sources of uncertainty in the
predictions for most processes measured at the Large Hadron Collider (LHC).
Here we present the first extraction of the proton PDFs that accounts for the
missing higher order uncertainty (MHOU) in the fixed-order QCD calculations
used in PDF determinations. We demonstrate that the MHOU can be included as a
contribution to the covariance matrix used for the PDF fit, and then introduce
prescriptions for the computation of this covariance matrix using scale
variations. We validate our results at next-to-leading order (NLO) by
comparison to the known next order (NNLO) corrections. We then construct
variants of the NNPDF3.1 NLO PDF set that include the effect of the MHOU, and
assess their impact on the central values and uncertainties of the resulting
PDFs
Parton distributions from high-precision collider data: NNPDF Collaboration
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 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 NNPDF3.1 PDFs are delivered for the first time both as Hessian sets, and as optimized Monte Carlo sets with a compressed number of replicas.V. B., N. H., J. R., L. R. and E. S. are supported by an European Research Council Starting Grant “PDF4BSM”. R. D. B. and L. D. D. are supported by the UK STFC grants ST/L000458/1 and ST/P000630/1. L. D. D. is supported by the Royal Society, Wolfson Research Merit Award, grant WM140078. S. F. is supported by the European Research Council under the Grant Agreement 740006NNNPDFERC-2016-ADG/ERC-2016-ADG. E. R. N. is supported by the UK STFC grant ST/M003787/1. S. C. is supported by the HICCUP ERC Consolidator grant (614577). M. U. is supported by a Royal Society Dorothy Hodgkin Research Fellowship and partially supported by the STFC grant ST/L000385/1. S. F and Z. K. are supported by the Executive Research Agency (REA) of the European Commission under the Grant Agreement PITN-GA-2012-316704 (HiggsTools). A. G. is supported by the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 659128-NEXTGENPDF
Parton distributions with theory uncertainties: general formalism and first phenomenological studies
Abstract: We formulate a general approach to the inclusion of theoretical uncertainties, specifically those related to the missing higher order uncertainty (MHOU), in the determination of parton distribution functions (PDFs). We demonstrate how, under quite generic assumptions, theory uncertainties can be included as an extra contribution to the covariance matrix when determining PDFs from data. We then review, clarify, and systematize the use of renormalization and factorization scale variations as a means to estimate MHOUs consistently in deep inelastic and hadronic processes. We define a set of prescriptions for constructing a theory covariance matrix using scale variations, which can be used in global fits of data from a wide range of different processes, based on choosing a set of independent scale variations suitably correlated within and across processes. We set up an algebraic framework for the choice and validation of an optimal prescription by comparing the estimate of MHOU encoded in the next-to-leading order (NLO) theory covariance matrix to the observed shifts between NLO and NNLO predictions. We perform a NLO PDF determination which includes the MHOU, assess the impact of the inclusion of MHOUs on the PDF central values and uncertainties, and validate the results by comparison to the known shift between NLO and NNLO PDFs. We finally study the impact of the inclusion of MHOUs in a global PDF determination on LHC cross-sections, and provide guidelines for their use in precision phenomenology. In addition, we also compare the results based on the theory covariance matrix formalism to those obtained by performing PDF determinations based on different scale choices
An open-source machine learning framework for global analyses of parton distributions
Abstract: We present the software framework underlying the NNPDF4.0 global determination of parton distribution functions (PDFs). The code is released under an open source licence and is accompanied by extensive documentation and examples. The code base is composed by a PDF fitting package, tools to handle experimental data and to efficiently compare it to theoretical predictions, and a versatile analysis framework. In addition to ensuring the reproducibility of the NNPDF4.0 (and subsequent) determination, the public release of the NNPDF fitting framework enables a number of phenomenological applications and the production of PDF fits under user-defined data and theory assumptions