Toward precision helicity PDFs from global DIS and SIDIS fits with projected EIC measurements

We present HAPS-pPDF1.0, a new global determination of the helicity-dependent parton distribution functions (PDFs) of the proton, based on inclusive deep-inelastic scattering (DIS) and semi-inclusive DIS (SIDIS) data within a consistent next-to-leading order (NLO) QCD framework. In addition to existing measurements, we incorporate simulated pseudodata for the future Electron-Ion Collider (EIC), considering two beam-energy configurations, E e × E p = 5 × 41 GeV 2 and 18 × 275 GeV 2 , corresponding to an extended kinematic reach down to x ∼ 10 − 5 . We focus on longitudinal double-spin asymmetries A 1 h for charge-separated pion and kaon production in SIDIS off a longitudinally polarized proton target. These projected measurements significantly improve the flavor separation of sea-quark polarized PDFs ( Δ u ¯ , Δ d ¯ , Δ s ) and reduce the uncertainties on both quark and gluon helicity distributions, with the largest impact at small x . Polarized PDFs are extracted using a neural-network parametrization and a Monte Carlo replica methodology to propagate experimental uncertainties, while theoretical constraints such as positivity are imposed during the fit. We demonstrate that the inclusion of EIC pseudodata leads to a substantially more precise determination of polarized PDFs, with the largest impact in the small- x region. The resulting polarized PDF sets are provided in the format.