
[Show abstract] [Hide abstract] ABSTRACT: We generate $2+1$ flavor QCD configurations near the physical point on a
$96^4$ lattice employing the 6APE stout smeared Wilson clover action with a
nonperturbative $c_{\rm SW}$ and the Iwasaki gauge action at $\beta=1.82$. The
physical point is estimated based on the chiral perturbation theory using
several data points generated by the reweighting technique from the simulation
point, wherer $m_\pi$,$m_K$ and $m_\Omega$ are used as physical inputs. The
physics results include the quark masses, the hadron spectrum, the pseudoscalar
meson decay constants and nucleon sigma terms, using the nonperturbative
renormalization factors evaluated with the Schrodinger functional method. Article · Nov 2015

[Show abstract] [Hide abstract] ABSTRACT: We present the quark mass and axial current renormalization factors for the
RGimproved Iwasaki gauge action and three flavors of the stout smeared
$O(a)$improved Wilson quark action. We employ $\alpha=0.1$ and
$n_{\mathrm{step}}=6$ for the stout link smearing parameters and all links in
the quark action are replaced with the smeared links. Using the Schr\"{o}dinger
functional scheme we evaluate the renormalization factors at $\beta=1.82$ where
large scale simulations are being carried out. Article · Nov 2015

[Show abstract] [Hide abstract] ABSTRACT: Scattering lengths for two pseudoscalar meson systems, $\pi\pi(I=2)$,
$KK(I=1)$ and $\pi K(I=3/2,\ 1/2)$, are calculated from lattice QCD by using
the finite size formula. We perform the calculation with $N_f=2+1$ gauge
configurations generated on $32^3 \times 64$ lattice using the Iwasaki gauge
action and nonperturbatively ${\cal O}(a)$improved Wilson action at $a^{1} =
2.19$ GeV. The quark masses correspond to $m_\pi = 0.17  0.71$ GeV. For $\pi
K(I=1/2)$ system, we use the variational method with the two operators,
$\bar{s}u$ and $\pi K$, to separate the contamination from the higher states.
In order to obtain the scattering length at the physical quark mass, we fit our
results at the several quark masses with the formula of the ${\cal O}(p^4)$
chiral perturbation theory (ChPT) and that including the effects of the
discretization error from the Wilson fermion, Wilson chiral perturbation theory
(WChPT). We found that the mass dependence of our results near $m_\pi=0.17$ GeV
are described well by WChPT but not by ChPT. The scattering lengths at the
physical point are given as $a_0^{(2)} m_\pi =0.04263(22)(41)$, $a_0^{(1)} m_K
=0.310(17)(32)$, $a_0^{(3/2)}\mu_{\pi K}=0.0469(24)(20)$ and
$a_0^{(1/2)}\mu_{\pi K}=0.142(14)(27)$. Possible systematic errors are also
discussed. Article · Nov 2013 · Physical Review D

[Show abstract] [Hide abstract] ABSTRACT: We present our results for the $K\to\pi\pi$ decay amplitudes for both the
$\Delta I=1/2$ and $3/2$ channels. Calculations are carried out with $N_f=2+1$
gauge configurations generated with the Iwasaki gauge action and
nonperturbatively $O(a)$improved Wilson fermion action at $a=0.091\,{\rm
fm}$, $m_\pi=280\,{\rm MeV}$ and $m_K=580\,{\rm MeV}$ on a $32^3\times 64$
($La=2.9\,{\rm fm}$) lattice. For the quark loops in the penguin and
disconnected contributions in the $I=0$ channel, the combined hopping parameter
expansion and truncated solver method work very well for variance reduction. We
obtain, for the first time with a Wilsontype fermion action, that ${\rm Re}A_0
= 60(36) \times10^{ 8}\,{\rm GeV}$ and ${\rm Im}A_0 =67(56)
\times10^{12}\,{\rm GeV}$ for a matching scale $q^* =1/a$. The dependence on
the matching scale $q^*$ for these values is weak. Article · Nov 2013 · Physical Review D

[Show abstract] [Hide abstract] ABSTRACT: The Swave πK scattering lengths are calculated for both the isospin 1/2 and 3/2 channels in the lattice QCD by using the finite size formula.
We perform the calculation with Nf = 2+1 gauge configurations generated on 323 ×64 lattice using the Iwasaki gauge action and nonperturbatively O(a)improved Wilson action at 1/a = 2.17 GeV. The quark masses correspond to mπ= 0.29  0.70 GeV. For I = 1/2, to separate the contamination from excited states, we construct a 2 ×2 matrix of the time correlation function and
diagonalize it. Here, we adopt the two kinds of operators, s̅u and πK. It is found that the signs of the scattering lengths are in agreement with experiment, namely attraction in I = 1/2 and repulsion in I = 3/2. We investigate the quarkmass dependence of the scattering lengths and also discuss the limitation of chiral perturbation
theory. Article · May 2013 · Progress of Theoretical Physics Supplement

Source Available from: M. Okawa
[Show abstract] [Hide abstract] ABSTRACT: We investigate the charmed baryon mass spectrum using the relativistic heavy
quark action on 2+1 flavor PACSCS configurations previously generated on $32^3
\times 64$ lattice. The dynamical updown and strange quark masses are tuned to
their physical values, reweighted from those employed in the configuration
generation. At the physical point, the inverse lattice spacing determined from
the $\Omega$ baryon mass gives $a^{1}=2.194(10)$ GeV, and thus the spatial
extent becomes $L = 32 a = 2.88(1)$ fm. Our results for the charmed baryon
masses are consistent with experimental values, except for the mass of
$\Xi_{cc}$, which has been measured by only one experimental group so far and
has not been confirmed yet by others. In addition, we report values of other
doubly and triply charmed baryon masses, which have never been measured
experimentally. Fulltext Article · Jan 2013 · Physical review D: Particles and fields

[Show abstract] [Hide abstract] ABSTRACT: We review the work of the PACSCS Collaboration, which aimed to realize lattice quantum chromodynamics (QCD) calculations at the physical point, i.e., those with quark masses set at physical values. This has been a longterm goal of lattice QCD simulation since its inception in 1979. After reviewing the algorithmic progress, which played a key role in this development, we summarize the simulations that explored the quark mass dependence of hadron masses down to values close to the physical point. In addition to allowing a reliable determination of the light hadron mass spectrum, this work provided clues on the validity range of chiral perturbation theory, which is widely used in phenomenology. We then describe the application of the technique of quark determinant reweighting, which enables lattice QCD calculations exactly on the physical point. The physical quark masses and the strong coupling constants are fundamental constants of the strong interaction. We describe a nonperturbative Schrodinger functional approach to figure out the nonperturbative renormalization needed to calculate them. There are a number of physical applications that can benefit from lattice QCD calculations carried out either near or at the physical point. We take up three illustrative examples: calculation of the physical properties of the rho meson as a resonance, the electromagnetic form factor and charge radius of the pion, and charmed meson spectroscopy. Bringing single hadron properties under control opens up a number of new areas for serious lattice QCD research. One such area is electromagnetic effects in hadronic properties. We discuss the combined QCD plus QED simulation strategy and present results on electromagnetic mass difference. Another area is multihadron states, or nuclei. We discuss the motivations and difficulties in this area, and describe our work for deuteron and helium as our initial playground. We conclude with a brief discussion on the future perspective of lattice QCD. Article · Aug 2012 · Progress of Theoretical and Experimental Physics

Source Available from: M. Okawa
[Show abstract] [Hide abstract] ABSTRACT: We present the results of 1+1+1 flavor QCD+QED simulation at the physical
point, in which the dynamical quark effects in QED and the updown quark mass
difference are incorporated by the reweighting technique. The physical quark
masses together with the lattice spacing are determined with $m_{\pi^+}$,
$m_{K^+}$, $m_{K^0}$ and $m_{\Omega^}$ as physical inputs. Calculations are
carried out using a set of 2+1 flavor QCD configurations near the physical
point generated by the nonperturbatively $O(a)$improved Wilson quark action
and the Iwasaki gauge action at $\beta=1.9$ on a $32^3\times 64$ lattice. We
evaluate the values of the up, down and strange quark masses individually with
nonperturbative QCD renormalization. Fulltext Article · May 2012 · Physical review D: Particles and fields

[Show abstract] [Hide abstract] ABSTRACT: We perform a lattice QCD study of the $\rho$ meson decay from the $N_f=2+1$
full QCD configurations generated with a renormalization group improved gauge
action and a nonperturbatively $O(a)$improved Wilson fermion action. The
resonance parameters, the effective $\rho\to\pi\pi$ coupling constant and the
resonance mass, are estimated from the $P$wave scattering phase shift for the
isospin I=1 twopion 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, $m_\pi=410\,{\rm MeV}$ ($m_\pi/m_\rho=0.46$) and
$m_\pi=300\,{\rm MeV}$ ($m_\pi/m_\rho=0.35$), on a $32^3\times 64$
($La=2.9\,{\rm fm}$) lattice at the lattice spacing $a=0.091\,{\rm fm}$. We
compare our results at these two quark masses with those given in the previous
works using $N_f=2$ full QCD configurations and the experiment. Article · Nov 2011

Source Available from: M. Okawa
[Show abstract] [Hide abstract] ABSTRACT: We perform a lattice QCD study of the $\rho$ meson decay from the $N_f=2+1$
full QCD configurations generated with a renormalization group improved gauge
action and a nonperturbatively $O(a)$improved Wilson fermion action. The
resonance parameters, the effective $\rho\to\pi\pi$ coupling constant and the
resonance mass, are estimated from the $P$wave scattering phase shift for the
isospin I=1 twopion 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, $m_\pi=410\,{\rm MeV}$ ($m_\pi/m_\rho=0.46$) and
$m_\pi=300\,{\rm MeV}$ ($m_\pi/m_\rho=0.35$), on a $32^3\times 64$
($La=2.9\,{\rm fm}$) lattice at the lattice spacing $a=0.091\,{\rm fm}$. We
compare our results at these two quark masses with those given in the previous
works using $N_f=2$ full QCD configurations and the experiment. Fulltext Article · Jun 2011 · Physical review D: Particles and fields

Source Available from: M. Okawa
[Show abstract] [Hide abstract] ABSTRACT: We investigate the charm quark system using the relativistic heavy quark
action on 2+1 flavor PACSCS configurations previously generated on $32^3
\times 64$ lattice. The dynamical updown and strange quark masses are set to
the physical values by using the technique of reweighting to shift the quark
hopping parameters from the values employed in the configuration generation. At
the physical point, the lattice spacing equals $a^{1}=2.194(10)$ GeV and the
spatial extent $L=2.88(1)$ fm. The charm quark mass is determined by the
spinaveraged mass of the 1S charmonium state, from which we obtain $m_{\rm
charm}^{\msbar}(\mu = m_{\rm charm}^{\msbar}) = 1.260(1)(6)(35)$ GeV, where the
errors are due to our statistics, scale determination and renormalization
factor. An additional systematic error from the heavy quark is of order
$\alpha_s^2 f(m_Q a)(a \Lambda_{QCD})$, which is estimated to be a percent
level if the factor $f(m_Q a)$ analytic in $m_Q a$ is of order unity. Our
results for the charmed and charmedstrange meson decay constants are
$f_D=226(6)(1)(5)$ MeV, $f_{D_s}=257(2)(1)(5)$ MeV, again up to the heavy quark
errors of order $\alpha_s^2 f(m_Q a)(a \Lambda_{QCD})$. Combined with the CLEO
values for the leptonic decay widths, these values yield $V_{cd} =
0.205(6)(1)(5)(9)$, $V_{cs} = 1.00(1)(1)(3)(3)$, where the last error is on
account of the experimental uncertainty of the decay widths. Fulltext Article · Apr 2011 · Physical review D: Particles and fields

Source Available from: M. Okawa
[Show abstract] [Hide abstract] ABSTRACT: We present preliminary results on the $\rho$ meson decay width from $N_f=2+1$
full QCD configurations generated by PACSCS Collaboration. The decay width is
estimated from the $P$wave scattering phase shift for the isospin $I=1$
twopion system. The finite size formula presented by L\"uscher in the center
of mass frame and its extension to nonzero total momentum frame by Rummukainen
and Gottlieb are employed for the calculations of the phase shift. Our
calculations are carried out at $m_\pi=410\ {\rm MeV}$ ($m_\pi/m_\rho=0.46$)
and $a=0.091\ {\rm fm}$ on a $32^3\times 64$ ($La=2.9 {\rm fm}$) lattice. Fulltext Article · Nov 2010

Source Available from: M. Okawa
[Show abstract] [Hide abstract] ABSTRACT: We present an evaluation of the quark mass renormalization factor for N
f
= 2 + 1 QCD. The Schrödinger functional scheme is employed as the intermediate scheme to carry out nonperturbative running from the low energy region, where renormalization of bare mass is performed on the lattice, to deep in the high energy perturbative region, where the conversion to the renormalization group invariant mass or the \( \overline {\text{MS}} \) scheme is safely carried out. For numerical simulations we adopted the Iwasaki gauge action and nonperturbatively improved Wilson fermion action with the clover term. Seven renormalization scales are used to cover from low to high energy regions and three lattice spacings to take the continuum limit at each scale. The regularization independent step scaling function of the quark mass for the N
f
= 2 + 1 QCD is obtained in the continuum limit. Renormalization factors for the pseudo scalar density and the axial vector current are also evaluated for the same action and the bare couplings as two recent large scale N
f
= 2 + 1 simulations; previous work of the CP PACS/JLQCD collaboration, which covered the updown quark mass range heavier than m
π
∼ 500 MeV and that of PACSCS collaboration for much lighter quark masses down to m
π
= 155MeV. The quark mass renormalization factor is used to renormalize bare PCAC masses in these simulations. Fulltext Article · Jun 2010 · Journal of High Energy Physics

[Show abstract] [Hide abstract] ABSTRACT: The Swave pi K scattering lengths are calculatedfor both the isospin 1/2 and 3/2 channels in the lattice QCD by using the finite size formula. We perform the calculation with N_f = 2+1 gauge configurations generated on 32^3 × 64 lattice using the Iwasaki gauge action and nonperturbatively O(a)improved Wilson action at 1/a = 2.17 GeV. The quark masses correspond to m_pi = 0.29  0.70 GeV. For I = 1/2, to separate the contamination from excited states, we construct a 2 × 2 matrix of the time correlation function and diagonalize it. Here, we adopt the two kinds of operators, bar{s}u and e;pi K. It is found that the signs of the scattering lengths are in agreement with experiment, namely attraction in I = 1/2 and repulsion in I = 3/2. We investigate the quarkmass dependence of the scattering lengths and also discuss the limitation of chiral perturbation theory. Article · Jan 2010 · Progress of Theoretical Physics Supplement

Source Available from: M. Okawa
[Show abstract] [Hide abstract] ABSTRACT: We present the results of the physical point simulation in 2+1 flavor lattice QCD with the nonperturbatively $O(a)$improved Wilson quark action and the Iwasaki gauge action at $\beta=1.9$ on a $32^3 \times 64$ lattice. The physical quark masses together with the lattice spacing is determined with $m_\pi$, $m_K$ and $m_\Omega$ as physical inputs. There are two key algorithmic ingredients to make possible the direct simulation at the physical point: One is the masspreconditioned domaindecomposed 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 Schr{\"o}dinger functional method. The results are compared with the previous ones obtained by the chiral extrapolation method. Comment: 20 pages, 17 figures, version to appear in Phys. Rev. D Fulltext Article · Nov 2009 · Physical Review D

[Show abstract] [Hide abstract] ABSTRACT: The $S$wave $\pi K$ scattering lengths are calculated for both the isospin 1/2 and 3/2 channels in the lattice QCD by using the finite size formula. We perform the calculation with $N_f=2+1$ gauge configurations generated on $32^3 \times 64$ lattice using the Iwasaki gauge action and nonperturbatively $O(a)$improved Wilson action at $1/a = 2.17$ GeV. The quark masses correspond to $m_\pi = 0.30  0.70$ GeV. For $I=1/2$, to separate the contamination from excited states, we construct a $2 \times 2$ matrix of the time correlation function and diagonalize it. Here, we adopt the two kinds of operators, $\bar{s}u$ and $\pi K$. It is found that the signs of the scattering lengths are in agreement with experiment, namely attraction in $I=1/2$ and repulsion in $I=3/2$. We investigate the quarkmass dependence of the scattering lengths and also discuss the limitation of chiral perturbation theory. Comment: 7 pages, 3 figures, Talk presented at Lattice2009, Peking University, Beijing, China Article · Nov 2009

Source Available from: M. Okawa
[Show abstract] [Hide abstract] ABSTRACT: We present an evaluation of the running coupling constant for Nf = 2+1 QCD. The Schrödinger functional scheme is used as the intermediate scheme to carry out nonperturbative running from the low energy region, where physical scale is introduced, to deep in the high energy perturbative region, where conversion to the scheme is safely performed. Possible systematic errors due to the use of perturbation theory occur only in the conversion from threeflavor to fourflavor running coupling constant near the charm mass threshold, where higher order terms beyond 5th order in the β function may not be negligible. For numerical simulations we adopted Iwasaki gauge action and nonperturbatively improved Wilson fermion action with the clover term. Seven renormalization scales are used to cover from low to high energy region and three lattice spacings to take the continuum limit at each scale. A physical scale is introduced from the previous Nf = 2+1 simulation of the CPPACS/JLQCD collaboration [1], which covered the updown quark mass range heavier than mπ ~ 500 MeV. Our final result is = 0.12047(81)(48)(+0−173) and = 239(10)(6)(+0−22) MeV . Fulltext Article · Oct 2009 · Journal of High Energy Physics

Source Available from: M. Okawa
[Show abstract] [Hide abstract] ABSTRACT: We investigate the quark mass dependence of baryon masses in 2+1 flavor lattice QCD using SU(3) heavy baryon chiral perturbation theory up to oneloop order. The baryon mass data used for the analyses are obtained for the degenerate updown quark mass of 3 MeV to 24 MeV and two choices of the strange quark mass around the physical value. We find that the SU(3) chiral expansion fails to describe both the octet and the decuplet baryon data if phenomenological values are employed for the mesonbaryon couplings. The SU(2) case is also examined for the nucleon. We observe that higher order terms are controlled only around the physical point. We also evaluate finite size effects using SU(3) heavy baryon chiralperturbation theory, finding small values of order 1% even at the physical point. Comment: 26 pages, 10 tables, 58 figures Fulltext Article · May 2009 · Physical review D: Particles and fields

Naruhito Ishizuka
[Show abstract] [Hide abstract] ABSTRACT: I present derivation of L\"uscher's finite size formula for the elastic $N\pi$ and the $NN$ scattering system for several angular momenta from the relativistic quantum field theory. Article · Jan 2009

Source Available from: M. Okawa
[Show abstract] [Hide abstract] ABSTRACT: We study heavyheavy and heavylight quark systems for charm with a relativistic heavy quark action in 2+1 flavor lattice QCD. Configurations are generated by the PACSCS Collaboration at the lattice spacing is $a=0.09$ fm with the lattice size of $32^3\times 64$ employing the $O(a)$improved Wilson quark action and the Iwasaki gauge action. We present preliminary results for the charmonium spectrum and the $D$ and $D_s$ meson decay constants evaluated at 3.5 MeV$< m_{\rm ud}<$ 12 MeV with $m_{\rm s}$ around the physical value. We investigate the dynamical quark mass dependences of the hyperfine and the orbital splittings. The decay constants are compared with the recent experimental values. Fulltext Article · Nov 2008