FIG. 1. Lattice calculation of the pion valence quark PDF at momentum P^z = 1.9 GeV with different orders of perturbative matching, and with/without renormalization group resummation (RGR) and leading-renormalon resummation (LRR). The comparison shows that the perturbation theory becomes unreliable at x ∼ 0.2, which is consistent with the power counting rule that ΛQCD/(2xP^z ) << 1. Credit: Xiangdong Ji

This workshop covered a wide range of topics related to parton distributions and nucleon structure in both nuclear and particle physics, including lattice QCD calculations of parton distribution functions (PDFs), transverse-momentum-dependent distributions (TMDs) and generalized parton distributions (GPDs), as well as electroweak PDFs, higher-order corrections to semi-inclusive deep inelastic scattering, TMDs at leading and subleading powers, and small-x physics. The talks and discussions focused on the theoretical foundations, such as QCD factorization, evolution, resummation, renormalon and power corrections, as well as the most recent applications to lattice calculations and phenomenology. One of the highlights was the lattice calculation of the pion valence quark PDF with next-to-next-to-leading order matching, next-to-leading order DGLAP evolution, and leading-renormalon resummation, as shown in Fig. 1. This analysis helps determine in which region of x perturbation theory is reliable, thus achieving an important step towards fully systematic control.

Another highlight was the analysis of the impact of beyond-Standard-Model physics, which is described by the Standard Model Effective Field Theory (SMEFT), on the global analyses of PDFs. Using the projected high luminosity (HL) LHC (HL-LHC) data, a simultaneous fit of the gluon PDF and SMEFT Wilson coefficients to the top sector shows significant impact on the gluon PDF, as displayed in Fig. 2. This could potentially lead to the discovery of new physics at HL-LHC.

22-83W Workshop Webpage