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

TL;DR

This paper uses lattice QCD to determine the momentum distribution of quarks in helium-3, providing more precise constraints than previous global fits and improving our understanding of nuclear parton distributions.

Contribution

First lattice QCD calculation of the isovector quark momentum fraction in helium-3, enhancing the precision of nuclear parton distribution constraints.

Findings

The isovector momentum fraction ratio is consistent with unity.

Lattice results reduce the uncertainty in parton distribution extractions.

Improved constraints enable more accurate modeling of nuclear structure.

Abstract

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 ${}^3\text{He}$.