We calculate connected and disconnected contributions to the flavour singlet scalar density amplitude of the nucleon in a full QCD lattice simulation with n f = 2 dynamical Wilson fermions at β = 5.6 on a 16 3 × 32 lattice. We find that both contributions are of similar size at the light quark mass. We arrive at the estimate σ πN = 18(5)MeV. Its smallness is directly related to the apparent decrease of u, d quark masses when unquenching QCD lattice simulations. The y parameter can be estimated from a semi-quenched analysis, in which there are no strange quarks in the sea, the result being y = 0.59(13).

We present the final analysis of the light and strange hadron spectra from a full QCD lattice simulation with two degenerate dynamical sea quark flavours at β = 5.6 on a 16 3 × 32 lattice. Four sets of sea quark masses corresponding to the range .69 ≤ m π /m ρ ≤ .83 are investigated. For reference we also ran a quenched simulation at β eff = 6.0, which is the point of equal lattice spacing, a −1 ρ . In the light sector, we find the chiral extrapolation to physical u-and d-masses to present a major source of uncertainty, comparable to the expected size of unquenching effects. From linear and quadratic fits we can estimate the errors on the hadron masses made from light quarks to be on a 15 % level prior to the continuum extrapolation. For the hadrons with strange valence quark content, the N F = 2 approximation to QCD appears not to cure the well-known failure of quenched QCD to reproduce the physical K − K * splitting.2

We perform a lattice mass analysis in the flavor singlet pseudoscalar channel on the SESAM and TL full QCD vacuum configurations, with 2 active flavors of dynamical Wilson fermions at ␤ϭ5.6. At our inverse lattice spacing, a Ϫ1 Ϸ2.3 GeV, we retrieve by a chiral extrapolation to the physical light quark masses the value m Ј ϭ3.7 Ϫ4 ϩ8 m . A crude extrapolation from (N f ϭ3) phenomenology would suggest m Ј Ϸ5.1m for N f ϭ2 QCD. We verify that the mass gap between the singlet state Ј and the flavor triplet state is due to gauge configurations with nontrivial topology.1 In our N f ϭ2 world we have a triplet ͑rather than an octet͒ of flavor non-singlet mesons. Moreover, working with massdegenerate quarks, our 's are exactly mass degenerate too.2 Upper ͑lower͒ case letters refer to masses in physical ͑lattice͒ units.

We determine the masses of the light and the strange quarks in the M S-scheme using our high-statistics lattice simulation of QCD with dynamical Wilson fermions. For the light quark mass we find m light MS (2 GeV) = 2.7(2) MeV, which is lower than in quenched simulations. For the strange quark, in a sea of two dynamical light quarks, we obtain m strange MS (2 GeV) = 140(20) MeV.

We present results for the bb spectrum obtained using an O(M b v 6 )-correct non-relativistic lattice QCD action, where M b denotes the bare b-quark mass and v 2 is the mean squared quark velocity. Propagators are evaluated on SESAM's three sets of dynamical gauge configurations generated with two flavours of Wilson fermions at β = 5.6. These results, the first of their kind obtained with dynamical Wilson fermions, are compared to a quenched analysis at equivalent lattice spacing, β = 6.0. Using our three sea-quark values we perform the "chiral" extrapolation to m eff = m s /3, where m s denotes the strange quark mass. The light quark mass dependence is found to be small in relation to the statistical errors. Comparing the full QCD result to our quenched simulation we find better agreement of our dynamical data with experimental results in the spin-independent sector but observe no unquenching effects in hyperfine-splittings. To pin down the systematic errors we have also compared quenched results in different "tadpole" schemes as well as using a lower order action. We find * email: spitz@hlrz.kfa-juelich.de † email: hoeber@theorie.physik.uni-wuppertal.de 1 that spin-splittings with an O(M b v 4 ) action are O(10 %) higher compared to O(M b v 6 ) results. Relative to the results obtained with the plaquette method the Landau gauge mean link tadpole scheme raises the spin splittings by about the same margin so that our two improvements are opposite in effect.2