Helicity-dependent, or polarised, parton distribution functions describe the longitudinal polarisation of quarks, antiquarks, and gluons inside a polarised nucleon. They encode how the spin of a fast-moving proton or neutron is shared among its partonic constituents and are therefore central to the modern understanding of nucleon spin structure in Quantum Chromodynamics. Helicity PDFs are extracted from global QCD analyses of polarised hard-scattering data, including inclusive deep-inelastic scattering, semi-inclusive deep-inelastic scattering, and polarised proton-proton collisions. This article reviews the definition and physical interpretation of polarised PDFs, the perturbative QCD framework used to determine them, the experimental observables that constrain the different parton flavours, and the statistical methodology of global analyses. The state of the art in polarised PDF determination is presented, together with the impact expected from future measurements at the Electron-Ion Collider.
We present an extraction of the unpolarised transverse momentum dependent (TMD) parton distribution functions (PDFs) for the valence quarks in the pion from experimental mea- surements of the Drell-Yan process. The procedure adopted in this project relies on the framework of TMD factorisation, and the inputs of nucleon...
W. Chang, Chia-Yu Hsieh, C. Kao et al.· 0 citations
Precise determination of the partonic structure of real photons has attracted renewed interest in view of ongoing studies of high-energy photon-induced processes in ultraperipheral collisions (UPCs) at the Large Hadron Collider (LHC) and the future Electron-Ion Collider (EIC). Despite being fundamental in their own rig...
M. Chithirasreemadam, V. Guzey, F. Hekhorn et al.· 0 citations
Generalized Parton Distributions (GPDs) encode the three-dimensional structure of hadrons, yet their modification in nuclear matter remains largely unconstrained. We report the first derivation of resummed QCD power corrections to deeply virtual Compton scattering on nuclei. Extending techniques from inclusive deep ine...
Unraveling the partonic origin of the proton spin requires precise determinations of polarized parton distribution functions (PDFs), which depend on comparably precise theoretical predictions for polarized scattering, particularly in view of the high-precision measurements anticipated at the future Electron-Ion Collide...
Liang Dong, Shen Fang, Jun Gao et al.· 0 citations
We compute quark and meson spectral functions in low-energy QCD, including all-order scatterings and decays of pions and the scalar $\sigma$-mode. For low energies the gluons decouple and the dynamics of two-flavour QCD is well-described by a Quark-Meson model. The computations are performed directly in Minkowski space...
Konrad Kockler, J. M. Pawlowski, Franz R. Sattler et al.· 0 citations
Higher twists in deep-inelastic scattering (DIS) and related hard scattering processes provide a unique window on nonperturbative QCD dynamics, encoding quark-gluon correlations and multiparton interactions beyond the leading-twist parton model. We present an overview of the theoretical foundations of higher twists in...
W. Melnitchouk· 0 citations
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