[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 non-perturbatively ${\cal O}(a)$-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.
Physical Review D 11/2013; 89(5). DOI:10.1103/PhysRevD.89.054502 · 4.64 Impact Factor
[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
non-perturbatively $O(a)$-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 Wilson-type 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.
[Show abstract][Hide abstract] ABSTRACT: The S-wave π 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_π = 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 quark-mass dependence of the scattering lengths and also discuss the
limitation of chiral perturbation theory.
[Show abstract][Hide abstract] ABSTRACT: We investigate the charmed baryon mass spectrum using the relativistic heavy
quark action on 2+1 flavor PACS-CS configurations previously generated on $32^3
\times 64$ lattice. The dynamical up-down 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.
[Show abstract][Hide abstract] ABSTRACT: We review the work of the PACS-CS 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 long-term 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 non-perturbative Schrodinger functional approach to figure out the non-perturbative 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 multi-hadron 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.
Progress of Theoretical and Experimental Physics 08/2012; DOI:10.1093/ptep/pts002 · 2.49 Impact Factor
[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 up-down 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 non-perturbatively $O(a)$-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
non-perturbative QCD renormalization.
[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 non-perturbatively $O(a)$-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 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, $m_\pi=410\,{\rm MeV}$ ($m_\pi/m_\rho=0.46$) 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.
[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 non-perturbatively $O(a)$-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 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, $m_\pi=410\,{\rm MeV}$ ($m_\pi/m_\rho=0.46$) 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.
[Show abstract][Hide abstract] ABSTRACT: We investigate the charm quark system using the relativistic heavy quark
action on 2+1 flavor PACS-CS configurations previously generated on $32^3
\times 64$ lattice. The dynamical up-down 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
spin-averaged 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 charmed-strange 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.
[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 PACS-CS Collaboration. The decay width is
estimated from the $P$-wave scattering phase shift for the isospin $I=1$
two-pion system. The finite size formula presented by L\"uscher in the center
of mass frame and its extension to non-zero 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.
[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 non-perturbative 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 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 up-down quark mass range heavier
than m
π
∼ 500 MeV and that of PACS-CS 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.
Journal of High Energy Physics 06/2010; 2010(8):1-27. DOI:10.1007/JHEP08(2010)101 · 6.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The S-wave 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 quark-mass dependence of the scattering lengths and also discuss the limitation of chiral perturbation theory.
[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 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 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
Physical Review D 11/2009; 81(7). DOI:10.1103/PhysRevD.81.074503 · 4.64 Impact Factor
[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 quark-mass 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
[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 non-perturbative 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 three-flavor to four-flavor 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 non-perturbatively 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 CP-PACS/JL-QCD collaboration [1], which covered the up-down 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 .
Journal of High Energy Physics 10/2009; 2009(10):053. DOI:10.1088/1126-6708/2009/10/053 · 6.11 Impact Factor
[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 one-loop order. The baryon mass data used for the analyses are obtained for the degenerate up-down 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 meson-baryon 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
[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.
[Show abstract][Hide abstract] ABSTRACT: We study heavy-heavy and heavy-light quark systems for charm with a relativistic heavy quark action in 2+1 flavor lattice QCD. Configurations are generated by the PACS-CS 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.
[Show abstract][Hide abstract] ABSTRACT: 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 Luscher's 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.
[Show abstract][Hide abstract] ABSTRACT: We investigate the quark mass dependence of meson and baryon masses obtained from 2+1 flavor dynamical quark simulations performed by the PACS-CS Collaboration. With the use of SU(2) and SU(3) chiral perturbation theories up to NLO, we examine the chiral behavior of the pseudoscalar meson masses and the decay constants in terms of the degenerate up-down quark mass ranging form 3 MeV to 24 MeV and two choices of the strange quark mass around the physical value. We discuss the convergence of the SU(2) and SU(3) chiral expansions and present the results for the low energy constants. We find that the SU(3) expansion is not convergent at NLO for the physical strange quark mass. The chiral behavior of the nucleon mass is also discussed based on the SU(2) heavy baryon chiral perturbation theory up to NNLO. Our results show that the expansion is well behaved only up to m_pi^2 ~ 0.2 GeV^2. Comment: 7 Pages, 8 figures, talk presented at the XXVI International Symposium on Lattice Field Theory, July 14-19, 2008, Williamsburg, Virginia, USA