We present the first results of the PACS-CS project which aims to simulate 2 þ 1 flavor lattice QCD on the physical point with the nonperturbatively OðaÞ-improved Wilson quark action and the Iwasaki gauge action. Numerical simulations are carried out at ¼ 1:9, corresponding to the lattice spacing of a ¼ 0:0907ð13Þ fm, on a 32 3 Â 64 lattice with the use of the domain-decomposed HMC algorithm to reduce the up-down quark mass. Further algorithmic improvements make possible the simulation whose up-down quark mass is as light as the physical value. The resulting pseudoscalar meson masses range from 702 MeV down to 156 MeV, which clearly exhibit the presence of chiral logarithms. An analysis of the pseudoscalar meson sector with SU(3) chiral perturbation theory reveals that the next-to-leading order corrections are large at the physical strange quark mass. In order to estimate the physical up-down quark mass, we employ the SU(2) chiral analysis expanding the strange quark contributions analytically around the physical strange quark mass. The SU(2) low energy constants " l 3 and " l 4 are comparable with the recent estimates by other lattice QCD calculations. We determine the physical point together with the lattice spacing employing m , m K and m as input. The hadron spectrum extrapolated to the physical point shows an agreement with the experimental values at a few % level of statistical errors, albeit there remain possible cutoff effects. We also find that our results of f , f K and their ratio, where renormalization is carries out perturbatively at one loop, are compatible with the experimental values. For the physical quark masses we obtain m MS ud and m MS s extracted from the axial-vector Ward-Takahashi identity with the perturbative renormalization factors. We also briefly discuss the results for the static quark potential.

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We perform a lattice QCD study of the meson decay from the N f ¼ 2 þ 1 full QCD configurations generated with a renormalization group improved gauge action and a nonperturbatively OðaÞ-improved Wilson fermion action. The resonance parameters, the effective ! coupling constant and the resonance mass, are estimated from the P-wave scattering phase shift for the isospin I ¼ 1 two-pion system. The finite size formulas are employed to calculate the phase shift from the energy on the lattice. Our calculations are carried out at two quark masses, m ¼ 410 MeV (m =m ¼ 0:46) and m ¼ 300 MeV (m =m ¼ 0:35), on a 32 3 Â 64 (La ¼ 2:9 fm) lattice at the lattice spacing a ¼ 0:091 fm. We compare our results at these two quark masses with those given in the previous works using N f ¼ 2 full QCD configurations and the experiment.

We present the results of the physical point simulation in 2 þ 1 flavor lattice QCD with the nonperturbatively OðaÞ-improved Wilson quark action and the Iwasaki gauge action at ¼ 1:9 on a 32 3 Â 64 lattice. The physical quark masses together with the lattice spacing is determined with m , m K and m as physical inputs. There are two key algorithmic ingredients to make possible the direct simulation at the physical point: One is the mass-preconditioned domain-decomposed HMC algorithm to reduce the computational cost. The other is the reweighting technique to adjust the hopping parameters exactly to the physical point. The physics results include the hadron spectrum, the quark masses and the pseudoscalar meson decay constants. The renormalization factors are nonperturbatively evaluated with the Schrödinger functional method. The results are compared with the previous ones obtained by the chiral extrapolation method.