Lattice QCD constraints on the parton distribution functions of ${}^3\text{He}$

Understand

The fraction of the longitudinal momentum of ${}^3\text{He}$ 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 $m_\pi\sim 800$ 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 ${}^3\text{He}$.