Abstract
We determine the quark contributions to the nucleon spin Δs, Δu and Δd as well as their contributions to the nucleon mass, the σ-terms. This is done by computing both, the quark line connected and disconnected contributions to the respective matrix elements, using the non-perturbatively improved Sheikholeslami–Wohlert Wilson Fermionic action. We simulate nF=2 mass degenerate sea quarks with a pion mass of about 285 MeV and a lattice spacing a≈0.073 fm. The renormalization of the matrix elements involves mixing between contributions from different quark flavours. The pion–nucleon σ-term is extrapolated to physical quark masses exploiting the sea quark mass dependence of the nucleon mass. We obtain the renormalized value σπN=(38±12) MeV at the physical point and the strangeness fraction fTs=σs/mN=0.012(14)−3+10 at our larger than physical sea quark mass. For the strangeness contribution to the nucleon spin we obtain ΔsMS¯(7.4GeV)=−0.020(10)(1).
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