Scalar densities and baryon mass differences in lattice QCD with Wilson fermions

We compute the normalization constant and the proton matrix elements of the scalar quark densities on a 103x20 lattice, at β = 6.0, in the quenched approximation and for three values of the Wilson parameter: K = 0.1515, 0.1530, 0.1545. The normalization constant is in agreement with a new Ward identity derived in this paper. In terms of the usual D and F terms of the baryon octet mass differences, we find D/F = 0.4±0.2, in agreement with the experimental value (D/F)exp = -0.3. We observe that D/F decreases in absolute value for large quark mass, as suggested by the constituent quark model. Using a previous lattice determination of quark masses, we find MΞ-Mp = 210±60 MeV, to be compared with the measured value (MΞ-mp)exp = 380 MeV. We also determine the nucleon σ-term to be σ = 15±4 MeV. (orig.)