The fraction of the longitudinal momentum of 3He that is carried by the isovector combination of u and d quarks is determined using lattice QCD for the first time. The ratio of this combination to that in the constituent nucleons is found to be consistent with unity at the few-percent level from calculations with quark masses corresponding to mπ∼800 MeV, extrapolated to the physical quark masses. This constraint is consistent with, and significantly more precise than, determinations from global nuclear parton distribution function fits. Including the lattice QCD determination of the momentum fraction in the nNNPDF global fitting framework results in the uncertainty on the isovector momentum fraction ratio being reduced by a factor of 2.5, and thereby enables a more precise extraction of the u and d parton distributions in 3He.
@article{arxiv.2009.05522,
title = {Lattice QCD constraints on the parton distribution functions of ${}^3\text{He}$},
author = {William Detmold and Marc Illa and David J. Murphy and Patrick Oare and Kostas Orginos and Phiala E. Shanahan and Michael L. Wagman and Frank Winter},
journal= {arXiv preprint arXiv:2009.05522},
year = {2021}
}