The strange and light quark contributions to the nucleon mass from Lattice QCD

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We determine the strangeness and light quark fractions of the nucleon mass by computing the quark line connected and disconnected contributions to the matrix elements mq <N|qbar q|N> in lattice QCD, 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 approx 0.073 fm. The renormalization of the matrix elements involves mixing between contributions from different quark flavours. The pion-nucleon sigma-term is extrapolated to physical quark masses exploiting the sea quark mass dependence of the nucleon mass. We obtain the renormalized values σπₙ = 38(12) MeV at the physical point and fₜₛ=σₛ/mₙ= 0.012(14)⁺¹⁰₋₃ for the strangeness contribution at our larger than physical sea quark mass.