Lattice QCD constraints on the parton distribution functions of ³He

I will report on a recent lattice QCD determination of the fraction of the longitudinal momentum of ³He that is carried by the isovector combination of u and d quarks. 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 a pion mass of 800MeV, 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.