Strangeness contribution to the proton spin from lattice QCD

Abstract

We compute the strangeness and light-quark contributions Δs, Δu, and Δd to the proton spin in nf=2 lattice QCD at a pion mass of about 285 MeV and at a lattice spacing a≈0.073 fm, using the nonperturbatively improved Sheikholeslami-Wohlert Wilson action. We carry out the renormalization of these matrix elements, which involves mixing between contributions from different quark flavors. Our main result is the small negative value ΔsMS̅ (√7.4 GeV)=-0.020(10)(4) 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.