34 research outputs found
Evolution of Parton Distribution Functions in the Short-Distance Factorization Scheme
Lattice QCD offers the possibility of computing parton distributions from
first principles, although not in the usual factorization
scheme. We study in this paper the evolution of non-singlet parton distribution
functions (PDFs) in the short-distance factorization scheme which notably
arises in lattice calculations in the pseudo-distribution approach. We provide
an assessment of non-perturbative evolution of PDFs from already published
lattice matrix elements, and show how this evolution can be used to reduce the
fluctuation of the lattice data. We compare our result with expectations
obtained thanks to a perturbative matching to . By highlighting
the limitations of the current computations, we advocate for a new strategy
using lattice calculations in small volume.Comment: 57 pages, 28 figure
Gluon helicity from global analysis of experimental data and lattice QCD Ioffe time distributions
We perform a new global analysis of spin-dependent parton distribution
functions with the inclusion of Ioffe time pseudo-distributions computed in
lattice QCD (LQCD), which are directly sensitive to the gluon helicity
distribution, . These lattice data have an analogous relationship to
parton distributions as do experimental cross sections, and can be readily
included in global analyses. We focus in particular on the constraining
capability of current LQCD data on the sign of at intermediate
parton momentum fractions , which was recently brought into question by
analysis of data in the absence of parton positivity constraints. We find that
present LQCD data cannot discriminate between positive and negative
solutions, although significant changes in the solutions for both the gluon and
quark sectors are observed.Comment: 24 pages, 7 figure
Neural-network analysis of Parton Distribution Functions from Ioffe-time pseudodistributions
International audienceWe extract two nonsinglet nucleon Parton Distribution Functions from lattice QCD data for reduced Ioffe-time pseudodistributions. We perform such analysis within the NNPDF framework, considering data coming from different lattice ensembles and dis- cussing in detail the treatment of the different source of systematics involved in the fit. We introduce a recipe for taking care of systematics and use it to perform our extraction of light-cone PDFs
Complementarity of experimental and lattice QCD data on pion parton distributions
We extract pion parton distribution functions (PDFs) in a Monte Carlo global
QCD analysis of experimental data together with reduced Ioffe time
pseudo-distributions and matrix elements of current-current correlators
generated from lattice QCD. By including both experimental and lattice QCD
data, our analysis rigorously quantifies both the uncertainties of the pion
PDFs and systematic effects intrinsic to the lattice QCD observables. The
reduced Ioffe time pseudo-distributions significantly decrease the
uncertainties on the PDFs, while the current-current correlators are limited by
the systematic effects associated with the lattice. Consistent with recent
phenomenological determinations, the behavior of the valence quark distribution
of the pion at large momentum fraction is found to be with .Comment: 46 pages, 15 figure
Toward the Determination of the Gluon Helicity Distribution in the Nucleon from Lattice Quantum Chromodynamics
We present the first exploratory lattice quantum chromodynamics (QCD) calculation of the polarized gluon Ioffe-time pseudodistribution in the nucleon. The Ioffe-time pseudodistribution provides a frame-independent and gauge-invariant framework to determine the gluon helicity in the nucleon from first principles. We employ a high-statistics computation using a 323 × 64 lattice ensemble characterized by a 358 MeV pion mass and a 0.094 fm lattice spacing. We establish the pseudodistribution approach as a feasible method to address the proton spin puzzle with successive improvements in statistical and systematic uncertainties anticipated in the future. Within the statistical precision of our data, we find a good comparison between the lattice determined polarized gluon Ioffe-time distribution and the corresponding expectations from the state-of-the-art global analyses. We find a hint for a nonzero gluon spin contribution to the proton spin from the model-independent extraction of the gluon helicity pseudodistribution over a range of Ioffe-time, ν ≲ 9
Unpolarized Gluon Distribution in the Nucleon From Lattice Quantum Chromodynamics
In this study, we present a determination of the unpolarized gluon Ioffe-time distribution in the nucleon from a first principles lattice quantum chromodynamics calculation. We carry out the lattice calculation on a 323 × 64 ensemble with a pion mass of 358 MeV and lattice spacing of 0.094 fm. We construct the nucleon interpolating fields using the distillation technique, flow the gauge fields using the gradient flow, and solve the summed generalized eigenvalue problem to determine the gluonic matrix elements. Combining these techniques allows us to provide a statistically well-controlled Ioffe-time distribution and unpolarized gluon parton distribution function. We obtain the flow time independent reduced Ioffe-time pseudodistribution and calculate the light-cone Ioffe-time distribution and unpolarized gluon distribution function in the MS scheme at μ = 2  GeV, neglecting the mixing of the gluon operator with the quark singlet sector. Finally, we compare our results to phenomenological determinations