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

Hamzeh Khanpour1,2,*, Maryam Soleymaninia2,†, Majid Azizi2,‡, Michael Klasen3,§, Hadi Hashamipour4,∥, Maral Salajegheh5,¶, and Ulf-G. Meißner5,6,7,** (HAPS Collaboration)

  • *Contact author: Hamzeh.Khanpour@cern.ch
  • †Contact author: Maryam_Soleymaninia@ipm.ir
  • ‡Contact author: Ma.Azizi@ipm.ir
  • §Contact author: Michael.Klasen@uni-muenster.de
  • ∥Contact author: Hadi.Hashamipour@lnf.infn.it
  • Contact author: Maral@hiskp.uni-bonn.de
  • **Contact author: Meissner@hiskp.uni-bonn.de
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Phys. Rev. D 113, 114010 – Published 5 June, 2026

DOI: https://doi.org/10.1103/wc54-mnfh

Abstract

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, Ee×Ep=5×41  GeV2 and 18×275  GeV2, corresponding to an extended kinematic reach down to x∼10−5. We focus on longitudinal double-spin asymmetries A1h 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 (Δu¯, Δd¯, Δs) 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 LHAPDF format.

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Phys. Rev. D 113, 114010– Published 5 June, 2026
  • Received 23 February 2026
  • Accepted 17 April 2026
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