Strangeness Contribution to the Proton Spin from Lattice QCD

TL;DR

The main result is the small negative value Δs(MS)(√(7.4) GeV)=-0.020(10)(4) of the strangeness contribution to the nucleon spin, an estimate of the uncertainty, due to the missing extrapolation to the physical point.

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.

Figures (2)

• Figure 1: The disconnected ratio $R^{\mathrm{dis}}$ versus $t_{\mathrm{f}}$ on the $40^364$ volume at $\kappa_{\mathrm{val}}=\kappa_{\mathrm{cur}}=\kappa_s$ for smeared-smeared (SS) and smeared-point (SP) source-sink combinations.
• Figure 2: Volume and valence quark mass dependence of the unrenormalized $\Delta s^{\mathrm{lat}}$.