A lattice study of the strangeness content of the nucleon

We determine the quark contributions to the nucleon spin Δ s , Δ u and Δ d 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 n F = 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 σ π N = ( 38 ± 12 )  MeV at the physical point and the strangeness fraction f T s = σ s / m N = 0.012 ( 14 ) − 3 + 10 at our larger than physical sea quark mass. For the strangeness contribution to the nucleon spin we obtain Δ s M S ¯ ( 7.4 GeV ) = − 0.020 ( 10 ) ( 1 ) .