Gluon Quasi-Parton-Distribution Functions from Lattice QCD

Area of Science:

• High Energy Physics
• Quantum Chromodynamics
• Nuclear Physics

Background:

• Understanding the nucleon's internal structure is crucial in high energy physics.
• Parton-distribution functions (PDFs) describe the momentum distribution of quarks and gluons within nucleons.
• Accessing the x-dependence of gluon PDFs from first principles is computationally challenging.

Purpose of the Study:

• To present the first lattice-based approach to determine the x-dependence of the gluon unpolarized parton-distribution function (PDF).
• To utilize the large-momentum effective theory (LMET) framework for this investigation.

Main Methods:

• Employed lattice quantum chromodynamics (LQCD) simulations with (2+1)-flavor domain-wall fermions.
• Calculated gluon quasi-PDF matrix elements at unphysically high pion masses (340 and 678 MeV).
• Utilized nucleon momenta up to 0.93 GeV and a lattice spacing of 0.111 fm.

Main Results:

• The study provides the first lattice determination of the gluon unpolarized PDF's x-dependence.
• Results for the gluon quasi-PDF matrix elements are consistent with the Fourier transform of global fits (CT14, PDF4LHC15 NNLO).
• Consistency is observed within statistical uncertainties and systematic effects like power corrections and perturbative matching.

Conclusions:

• This work demonstrates the feasibility of accessing gluon PDFs using LMET and lattice simulations.
• The findings validate the LMET approach and provide a crucial step towards ab initio calculations of nucleon structure.
• Future improvements can refine the precision and extend the kinematic reach of these calculations.