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

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 left angle N vertical stroke anti qq vertical stroke N right angle 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 ∼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 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. (orig.)