Strangeness Contribution to the Proton Spin from Lattice QCD

TL;DR

This study uses lattice QCD to quantify the small negative contribution of strange quarks to the proton's spin, providing a precise calculation at high energy scales.

Contribution

It presents the first lattice QCD calculation of the strangeness contribution to the proton spin with non-perturbative renormalization and estimates uncertainties from extrapolation.

Findings

Strangeness contribution to proton spin is small and negative.

Calculated Delta s = -0.020(10)(4) at 7.4 GeV scale.

Provides a benchmark for understanding nucleon spin structure.

Abstract

We compute the strangeness and light-quark contributions Delta s, Delta u and Delta d to the proton spin in nf=2 lattice QCD at a pion mass of about 285 MeV and at a lattice spacing a approx 0.073 fm, using the non-perturbatively improved Sheikholeslami-Wohlert Wilson action. We carry out the renormalization of these matrix elements which involves mixing between contributions from different quark flavours. Our main result is the small negative value MSbar scheme value Delta s = -0.020(10)(4), at a scale mu = 7.4 GeV, of the strangeness contribution to the nucleon spin. The second error is an estimate of the uncertainty, due to the missing extrapolation to the physical point.