Study of lattice QCD by large scale numerical simulations including dynamical quark effects

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Including dynamical quark loop effects in lattice QCD simulations is one of the most important problem to make quantitative study of strong interaction and to obtain phenomenologically important hadronic matrix elements. In fact, in the quenched approximation where the dynamical quark loop effect is neglected, it has been shown that the evaluated hadron mass spectra deviate from experimental values by about 5-10%. It has also been shown recently that about half part of the deviation in hadron mass spectra observed in the quenched approximation disappears with the inclusion of the dynamical loop effect of u and d quarks. In the real world, however, there are three light quarks, u,d and s quarks, and it is important to verify if the remaining deviation disappears by the inclusion of the s quark loop effect. For this purpose we have made realistic (2+1) flavor QCD simulation with O(a) improved Wilson fermions in which the discretization error of lattice QCD simulation is known to be O(a^2) with a the lattice spacing. We have calculated hadron mass spectra on two lattices having lattice spacing a【approximately equal】 0.1fm and 0.12fm. We have extrapolated hadron masses to a=0 assuming a^2 dependence of hadron masses evaluated on lattices with finite a, and found that preliminary values of extrapolated hadron masses are consistent with experimental values. Evaluation of phenomenologically important various hadronic matrix elements such as decay constants have also been done including the dynamical loop effect of u and d quarks.