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Light hadron spectrum with 2+1 flavor dynamical $O(a)$-improved Wilson quarks

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 Added by Naoya Ukita
 Publication date 2007
  fields
and research's language is English




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We present preliminary results for the light harden spectrum in $N_f=2+1$ lattice QCD obtained with the nonperturbatively $O(a)$-improved Wilson quark action and the Iwasaki gauge action. Simulations are carried out at $beta=1.90$ on a $32^3 times 64$ lattice using the PACS-CS computer. We employ Luschers domain-decomposed HMC algorithm to reduce the up-down quark masses toward the physical value. The pseudoscalar meson masses range from 730 MeV down to 210 MeV. We compare the light harden spectrum extrapolated to the physical point with the experimental values.



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We present simulation details and results for the light hadron spectrum in N f = 2 + 1 lattice QCD with the nonperturbatively O(a)-improved Wilson quark action and the Iwasaki gauge action. Simulations are carried out at a lattice spacing of 0.09 fm on a (2.9fm)^3 box using the PACS-CS computer. We employ the Luschers domain-decomposed HMC algorithm with several improvements to reduce the degenerate up-down quark mass toward the physical value. So far the resulting pseudoscalar meson mass is ranging from 702MeV down to 156MeV. We discuss on the stability and the efficiency of the algorithm. The light harden spectrum extrapolated at the physical point is compared with the experimental values. We also present the values of the quark masses and the pseudoscalar meson decay constants.
We present a summary of results of the joint CP-PACS and JLQCD project toward a 2+1 flavor full QCD simulation with the O(a)-improved Wilson quark formalism and the Iwasaki gauge action. Configurations were generated during 2002-2005 at three lattice spacings, a~0.076, 0.100 and 0.122 fm, keeping the physical volume constant at (2.0fm)^3. Up and down quark masses are taken in the range m_{PS}/m_V~0.6-0.78. We have completed the analysis for the light meson spectrum and quark masses in the continuum limit using the full configuration set. The predicted meson masses reproduce experimental values in the continuum limit at a 1% level. The average up and down, and strange quark masses turn out to be m_{ud}^{bar{MS}}(mu=2 GeV)=3.50(14)({}^{+26}_{-15}) MeV and m_s^{bar{MS}}(mu=2 GeV)=91.8(3.9)({}^{+6.8}_{-4.1}) MeV. We discuss our future strategy toward definitive results on hadron spectroscopy with the Wilson-clover formalism.
We report on a calculation of the light hadron spectrum and quark masses in three-flavor dynamical QCD using the non-perturbatively O(a)-improved Wilson quark action and a renormalization-group improved gauge action. Simulations are carried out on a 16^3 times 32 lattice at beta=1.9, where a^{-1} simeq 2GeV, with 6 ud quark masses corresponding to m_{pi}/m_{rho} simeq 0.64-0.77 and 2 s quark masses close to the physical value. We observe that the inclusion of dynamical strange quark brings the lattice QCD meson spectrum to good agreement with experiment. Dynamical strange quarks also lead to a reduction of the uds quark masses by about 15%.
We present a high statistics study of the light hadron spectrum and quark masses in QCD with two flavors of dynamical quarks. Numerical simulations are carried out using the plaquette gauge action and the O(a)-improved Wilson quark action at beta=5.2, where the lattice spacing is found to be a=0.0887(11)fm from rho meson mass, on a 20^3times 48 lattice. At each of five sea quark masses corresponding to m_{PS}/m_{V} simeq 0.8-0.6, we generate 12000 trajectories using the symmetrically preconditioned Hybrid Monte Carlo algorithm. Finite spatial volume effects are investigated employing 12^3 times 48, 16^3 times 48 lattices. We also perform a set of simulations in quenched QCD with the same lattice actions at a similar lattice spacing to those for the full QCD runs. In the meson sector we find clear evidence of sea quark effects. The J parameter increases for lighter sea quark masses, and the full QCD meson masses are systematically closer to experiment than in quenched QCD. Careful finite-size studies are made to ascertain that these are not due to finite-size effects. Evidence of sea quark effects is less clear in the baryon sector due to larger finite-size effects. We also calculate light quark masses and find m_{ud}^{MS}(2GeV) =3.223(+0.046/-0.069)MeV and m_s^{MS}(2GeV)=84.5(+12.0/-1.7)MeV which are about 20% smaller than in quenched QCD.
We report on our study of light hadron spectrum and quark masses in QCD with two flavors of dynamical quarks. Simulations are made with the plaquette gauge action and the non-perturbatively $O(a)$ improved Wilson quark action. We simulate 5 sea qaurk masses corresponding to $m_{PS}/m_{V} simeq 0.8$--0.6 at $beta=5.2$ on $12^3 times 48$, $16^3 times 48$ and $20^3 times 48$ lattices. A comparison with previous calculations in quenched QCD indicates sea quark effects in meson and quark masses.
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