著者

Hirai H. Tanaka T. Kawamura T. Yamamoto Y. Yagi T.

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.68, no.17, pp.172102, 2003-11

被引用文献数

53 45

---

High-pressure experiments on methane hydrate were performed in the pressure range of 0.2–42 GPa using diamond-anvil cell. In situ x-ray-diffraction study revealed that methane hydrate of a high-pressure form, filled ice structure, survived up to 42 GPa. Pressure versus volume data were obtained in the pressure region. The filled ice structure represented large anisotropic compressibility and the volume change attained 40% at 42 GPa. The anisotropic compressibility was explained by the characteristic channel framework of the filled ice structure.

著者

Aoki S. Fukugita M. Ishikawa K-I. Ishizuka N. Iwasaki Y. Kanaya K. Kaneko T. Kuramashi Y. Okawa M. Ukawa A. Yamazaki T. Yoshié T.

出版者

American Physical Society

雑誌

Physical review D (ISSN:15507998)

巻号頁・発行日

vol.71, no.9, pp.094504, 2005-05

被引用文献数

68

---

We calculate the two-pion wave function in the ground state of the I=2 S-wave system and find the interaction range between two pions, which allows us to examine the validity of the necessary condition for the finite-volume method for the scattering length proposed by Lüscher. We work in the quenched approximation employing a renormalization group improved gauge action for gluons and an improved Wilson action for quarks at 1/a=1.207(12) GeV on 163×80, 203×80, and 243×80 lattices. We conclude that the necessary condition is satisfied within the statistical errors for the lattice sizes L>=24 (3.92 fm) when the quark mass is in the range that corresponds to mpi2=0.273–0.736 GeV2. We obtain the scattering length with a smaller statistical error from the wave function than from the two-pion time correlator.

著者

Yamada N. Aoki S. Fukugita M. Hashimoto S. Ishikawa K-I. Ishizuka N. Iwasaki Y. Kanaya K. Kaneko T. Kuramashi Y. Okawa M. Taniguchi Y. Tsutsui N. Ukawa A. Yoshié T.

出版者

American Physical Society

雑誌

Physical review D (ISSN:15507998)

巻号頁・発行日

vol.71, no.5, pp.054505, 2005-03

被引用文献数

16 19

---

We perform a nonperturbative determination of the O(a)-improvement coefficient cSW for the Wilson quark action in three-flavor QCD with the plaquette gauge action. Numerical simulations are carried out in a range of beta=12.0–5.2 on a single lattice size of 83×16 employing the Schrödinger functional setup of lattice QCD. As our main result, we obtain an interpolation formula for cSW and the critical hopping parameter Kc as a function of the bare coupling. This enables us to remove the O(a) scaling violation from physical observables in future numerical simulation in the wide range of beta. Our analysis with a perturbatively modified improvement condition for cSW suggests that finite volume effects in cSW are not large on the 83×16 lattice. We investigate Nf dependence of cSW by additional simulations for Nf=4, 2, and 0 at beta=9.6. As a preparatory step for this study, we also determine cSW in two-flavor QCD at beta=5.2. At this beta, several groups have carried out large-scale calculations of the hadron spectrum, while no systematic determination of cSW has been performed.

著者

Yamada N. Aoki S. Fukugita M. Hashimoto S. Ishikawa K-I. Ishizuka N. Iwasaki Y. Kanaya K. Kaneko T. Kuramashi Y. Okawa M. Taniguchi Y. Tsutsui N. Ukawa A. Yoshié T.

出版者

American Physical Society

雑誌

Physical review D (ISSN:15507998)

巻号頁・発行日

vol.71, no.5, pp.054505, 2005-03

被引用文献数

16 19

---

We perform a nonperturbative determination of the O(a)-improvement coefficient cSW for the Wilson quark action in three-flavor QCD with the plaquette gauge action. Numerical simulations are carried out in a range of beta=12.0–5.2 on a single lattice size of 83×16 employing the Schrödinger functional setup of lattice QCD. As our main result, we obtain an interpolation formula for cSW and the critical hopping parameter Kc as a function of the bare coupling. This enables us to remove the O(a) scaling violation from physical observables in future numerical simulation in the wide range of beta. Our analysis with a perturbatively modified improvement condition for cSW suggests that finite volume effects in cSW are not large on the 83×16 lattice. We investigate Nf dependence of cSW by additional simulations for Nf=4, 2, and 0 at beta=9.6. As a preparatory step for this study, we also determine cSW in two-flavor QCD at beta=5.2. At this beta, several groups have carried out large-scale calculations of the hadron spectrum, while no systematic determination of cSW has been performed.

著者

Umeda T. Isoya J. Morishita N. Ohshima T. Kamiya T.

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.69, pp.121201, 2004-03

被引用文献数

42

---

The EI5 and EI6 centers are typical intrinsic defects in radiation-damaged and semi-insulating 4H-SiC. So far, their origins have been assigned to positively charged carbon vacancies (VC+) and silicon antisites (SiC+), respectively. However, our complete set of 29Si hyperfine (HF) data clearly reveals that both the centers should originate from VC+ but their locations are different, i.e., quasicubic sites for EI5 and hexagonal sites for EI6, as recently predicted by the first-principle calculation [M. Bockstedte et al., Phys. Rev. B 67, 193102 (2003)]. The two types of VC+ centers showed remarkable differences in their atomic structures as well as in the temperature dependence of HF interactions, which are closely related to the nature of the two sites.

著者

Kaminski A. Rosenkranz S. Fretwell H. M. Mesot J. Randeria M. Campuzano J. C. Norman M. R. Li Z. Z. Raffy H. Sato T. Takahashi T. Kadowaki K.

出版者

American Physical Society

雑誌

Physical review B (ISSN:01631829)

巻号頁・発行日

vol.69, pp.212509, 2004-06

被引用文献数

31 34

---

One of the interesting features of the photoemission spectra of the high temperature cuprate superconductors is the presence of a large signal (referred to as the "background") in the unoccupied region of the Brillouin zone. Here we present data indicating that the background signal is a component of the photocurrent that is separate from the spectral function and is most likely due to strong scattering of the photoelectrons. We also present an analytical method that can be used to subtract the background signal.

著者

Namekawa Y. Aoki S. Fukugita M. Ishikawa K.-I. Ishizuka N. Iwasaki Y. Kanaya K. Kaneko T. Kuramashi Y. Lesk V. I. Okawa M. Ukawa A. Umeda T. Yoshié T.

出版者

American Physical Society

雑誌

Physical review D (ISSN:15507998)

巻号頁・発行日

vol.70, no.7, pp.074503, 2004-10

被引用文献数

24 31

---

We extend the study of the light hadron spectrum and the quark mass in two-flavor QCD to smaller sea quark mass, corresponding to mPS/mV=0.60–0.35. Numerical simulations are carried out using the RG-improved gauge action and the meanfield-improved clover quark action at beta=1.8 (a=0.2 fm from rho meson mass). We observe that the light hadron spectrum for small sea quark mass does not follow the expectation from chiral extrapolations with quadratic functions made from the region of mPS/mV=0.80–0.55. Whereas fits with either polynomial or continuum chiral perturbation theory (ChPT) fail, the Wilson ChPT (WChPT) that includes a2 effects associated with explicit chiral symmetry breaking successfully fits the whole data: In particular, WChPT correctly predicts the light quark mass spectrum from simulations for medium heavy quark mass, such as mPS/mV>~0.5. Reanalyzing the previous data with the use of WChPT, we find the mean up and down quark mass being smaller than the previous result from quadratic chiral extrapolation by approximately 10%, mudMS-bar(µ=2 GeV)=3.11(17) [MeV] in the continuum limit.

著者

Yamazaki T. Aoki S. Fukugit M. Ishikawa K-I. Ishizuka N. Iwasaki Y. Kanaya K. Kaneko T. Kuramashi Y. Okawa M. Ukawa A. Yoshié T.

出版者

American Physical Society

雑誌

Physical review D (ISSN:15507998)

巻号頁・発行日

vol.70, no.7, pp.074513, 2004-10

被引用文献数

82 94

---

We present a lattice QCD calculation of phase shift including the chiral and continuum extrapolations in two-flavor QCD. The calculation is carried out for I=2 S-wave pipi scattering. The phase shift is evaluated for two momentum systems, the center of mass and laboratory systems, by using the finite-volume method proposed by Lüscher in the center of mass system and its extension to general systems by Rummukainen and Gottlieb. The measurements are made at three different bare couplings beta=1.80, 1.95 and 2.10 using a renormalization group improved gauge and a tadpole improved clover fermion action, and employing a set of configurations generated for hadron spectroscopy in our previous work. The illustrative values we obtain for the phase shift in the continuum limit are delta(deg.)=-3.50(64), -9.5(30) and -16.9(64) for sqrt(s)(GeV)=0.4, 0.6 and 0.8, which are consistent with experiments.

著者

Kaminski A. Fretwell H. M. Norman M. R. Randeria M. Rosenkranz S. Chatterjee U. Campuzano J. C. Mesot J. Sato T. Takahashi T. Terashima T. Takano M. Kadowaki K. Li Z. Z. Raffy H.

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.71, pp.014517, 2005-01

被引用文献数

83 80

---

We examine the momentum and energy dependence of the scattering rate of the high-temperature cuprate superconductors using angle-resolved photoemission spectroscopy. The scattering rate is of the form a + bomega around the Fermi surface for under-and optimal doping. The inelastic coefficient b is found to be isotropic. The elastic term a, however, is found to be highly anisotropic for under-and optimally doped samples, with an anisotropy which correlates with that of the pseudogap. This is contrasted with heavily overdoped samples, which show an isotropic scattering rate and an absence of the pseudogap above Tc. We find this to be a generic property for both single-and double-layer compounds.

著者

Kakeya I. Wada T. Nakamura R. Kadowaki K.

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.72, pp.014540, 2005-07

被引用文献数

14 10

---

Josephson plasma excitations in the high-Tc superconductor Bi2Sr2CaCu2O8+delta have been investigated in a wide microwave frequency region (9.8–75 GHz)—in particular, in a magnetic field applied parallel to the ab plane of the single crystal. In sharp contrast to the case for magnetic fields parallel to the c axis or tilted from the ab plane, it was found that there are two kinds of resonance modes, which are split in energy and possess two distinctly different magnetic field dependences. One always lies higher in energy than the other and has a shallow minimum at about 0.8 kOe, then increases linearly with magnetic field. On the other hand, another mode begins to appear only in a magnetic field (from a few kOe and higher) and has a weakly decreasing tendency with increasing magnetic field. By comparing with a recent theoretical model the higher-energy mode can naturally be attributed to the Josephson plasma resonance mode propagating along the primitive reciprocal lattice vector of the Josephson vortex lattice, whereas the lower-frequency mode is assigned to the novel phase collective mode of the Josephson vortex lattice, which has never been observed before.

著者

Takeda S. Aoki S. Fukugita M. Ishikawa K-I. Ishizuka N. Iwasaki Y. Kanaya K. Kaneko T. Kuramashi Y. Okawa M. Taniguchi Y. Ukawa A. Yoshié T.

出版者

American Physical Society

雑誌

Physical review D (ISSN:15507998)

巻号頁・発行日

vol.70, no.7, pp.074510, 2004-10

被引用文献数

16 23

---

We study the scaling behavior of the step scaling function for SU(3) gauge theory, employing the renormalization-group improved Iwasaki gauge action and the perturbatively improved Lüscher-Weisz gauge action. We confirm that the step scaling functions from the improved gauge actions agree with that previously obtained from the plaquette action within errors in the continuum limit at both weak and strong coupling regions. We also investigate how different choices of boundary counterterms for the improved gauge actions affect the scaling behavior. In the extrapolation to the continuum limit, we observe that the cutoff dependence becomes moderate for the Iwasaki action, if a perturbative reduction of scaling violations is applied to the simulation results. We also measure the low energy scale ratio with the Iwasaki action and confirm its universality.

著者

Aoki S. Fukugita M. Ishizuka N. Iwasaki Y. Kanaya K. Kaneko T. Kuramashi Y. Okawa M. Taniguchi Y. Ukawa A. Yoshié T.

出版者

American Physical Society

雑誌

Physical review D (ISSN:15507998)

巻号頁・発行日

vol.70, no.3, pp.034503, 2004-08

被引用文献数

4

---

We report on a nonperturbative evaluation of the renormalization factors for the vector and axial-vector currents, ZV and ZA, in the quenched domain-wall QCD (DWQCD) with plaquette and renormalization-group-improved gauge actions. We take the Dirichlet boundary condition for both gauge and domain-wall fermion fields on the finite box, and introduce flavor-chiral Ward-Takahashi identities to calculate the renormalization factors. As a test of the method, we numerically confirm the expected relation that ZV~=ZA in DWQCD. Employing two different box sizes for the numerical simulations at several values of the gauge coupling constant g2 and the domain-wall height M, we extrapolate ZV to infinite volume to remove a/L errors. We finally give the interpolation formula of ZV in the infinite volume as a function of g2 and M.

著者

Aoki S. Fukugita M. Hashimoto S. Ishikawa K.-I. Ishizuka N. Iwasaki Y. Kanaya K. Kaneko T. Kuramashi Y. Okawa M. Tsutsui N. Ukawa A. Yamada N. Yoshié T.

出版者

American Physical Society

雑誌

Physical review D (ISSN:05562821)

巻号頁・発行日

vol.69, no.9, pp.094512, 2004-05

被引用文献数

5

---

We present a lattice QCD calculation of the heavy quark expansion parameters µpi2 and µG2 for heavy-light mesons and heavy-light-light baryons. The calculation is carried out on a 203×48 lattice at beta=6.0 in the quenched approximation, using the lattice NRQCD action for heavy quarks. We obtain the parameters µpi2 and µG2 in two different methods: a direct calculation of the matrix elements and an indirect calculation through the mass spectrum, and confirm that both the methods give consistent results. We also discuss an application to the lifetime ratios.

著者

Iwasaki Y. Kanaya K. Kaya S. Sakai S. Yoshié T.

出版者

American Physical Society

雑誌

Physical review D (ISSN:05562821)

巻号頁・発行日

vol.69, pp.014507, 2004-01

被引用文献数

66

---

We investigate the phase structure of lattice QCD for the general number of flavors in the parameter space of gauge coupling constant and quark mass, employing the one-plaquette gauge action and the standard Wilson quark action. Performing a series of simulations for the number of flavors NF = 6–360 with degenerate-mass quarks, we find that when NF>=7 there is a line of a bulk first order phase transition between the confined phase and a deconfined phase at a finite current quark mass in the strong coupling region and the intermediate coupling region. The massless quark line exists only in the deconfined phase. Based on these numerical results in the strong coupling limit and in the intermediate coupling region, we propose the following phase structure, depending on the number of flavors whose masses are less than Lambdad which is the physical scale characterizing the phase transition in the weak coupling region: When NF>=17, there is only a trivial IR fixed point and therefore the theory in the continuum limit is free. On the other hand, when 16>=NF>=7, there is a nontrivial IR fixed point and therefore the theory is nontrivial with anomalous dimensions, however, without quark confinement. Theories which satisfy both quark confinement and spontaneous chiral symmetry breaking in the continuum limit exist only for NF<=6.

著者

Aoki S. Burkhalter R. Fukugita M. Hashimoto S. Ishikawa K.-I. Ishizuka N. Iwasaki Y. Kanaya K. Kaneko T. Kuramashi Y. Okawa M. Onogi T. Tsutsui N. Ukawa A. Yamada N. Yoshié T.

出版者

American Physical Society

雑誌

Physical review D (ISSN:05562821)

巻号頁・発行日

vol.68, no.5, pp.054502, 2003-09

被引用文献数

98 238

---

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 β=5.2, where the lattice spacing is found to be a=0.0887(11) fm from the ρ meson mass, on a 203×48 lattice. At each of five sea quark masses corresponding to mPS/mV≃0.8–0.6, we generate 12 000 trajectories using a symmetrically preconditioned Hybrid Monte Carlo algorithm. Finite spatial volume effects are investigated employing 123×48, 163×48 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 mudMS̅ (2 GeV)=3.223(-0.069+0.046) MeV and msMS̅ (2 GeV)=84.5(-1.7+12.0) MeV which are about 20% smaller than in quenched QCD.

著者

Umeda T. Aoki S. Fukugita M. Ishikawa K.-I. Ishizuka N. Iwasaki Y. Kanaya K. Kuramashi Y. Lesk V. I. Namekawa Y. Okawa M. Taniguchi Y. Ukawa A. Yoshié T.

出版者

American Physical Society

雑誌

Physical review D (ISSN:05562821)

巻号頁・発行日

vol.68, no.3, pp.034503, 2003-08

被引用文献数

15

---

We report on our study of two-flavor full QCD on anisotropic lattices using O(a)-improved Wilson quarks coupled with a renormalization-group-improved glue. The bare gauge and quark anisotropies corresponding to the renormalized anisotropy ξ=as/at=2 are determined as functions of β and κ, which cover the region of spatial lattice spacings as≈0.28–0.16 fm and mPS/mV≈0.6–0.9. The calibrations of the bare anisotropies are performed with the Wilson loop and the meson dispersion relation at four lattice cutoffs and 5–6 quark masses. Using the calibration results we calculate the meson mass spectrum and the Sommer scale r0. We confirm that the values of r0 calculated for the calibration using pseudoscalar and vector meson energy momentum dispersion relations coincide in the continuum limit within errors. This work serves to lay the groundwork for studies of heavy quark systems and the thermodynamics of QCD including the extraction of the equation of state in the continuum limit using Wilson-type quark actions.

著者

Noaki J. Aoki S. Aoki Y. Burkhalter R. Ejiri S. Fukugita M. Hashimoto S. Ishizuka N. Iwasaki Y. Izubuchi T. Kanaya K. Kaneko T. Kuramashi Y. Lesk V. Nagai K. I. Okawa M. Taniguch Y. Ukawa A. Yoshié T.

出版者

American Physical Society

雑誌

Physical review D (ISSN:05562821)

巻号頁・発行日

vol.68, no.1, pp.014501, 2003-07

被引用文献数

45 146

---

We explore the application of the domain wall fermion formalism of lattice QCD to calculate the K→ππ decay amplitudes in terms of the K+→π+ and K0→0 hadronic matrix elements through relations derived in chiral perturbation theory. Numerical simulations are carried out in quenched QCD using the domain-wall fermion action for quarks and a renormalization group-improved gauge action for gluons on a 163×32×16 and 243×32×16 lattice at β=2.6 corresponding to the lattice spacing 1/a≈2 GeV. Quark loop contractions which appear in Penguin diagrams are calculated by the random noise method, and the ΔI=1/2 matrix elements which require subtractions with the quark loop contractions are obtained with a statistical accuracy of about 10%. We investigate the chiral properties required of the K+→π+ matrix elements. Matching the lattice matrix elements to those in the continuum at μ=1/a using the perturbative renormalization factor to one loop order, and running to the scale μ=mc=1.3 GeV with the renormalization group for Nf=3 flavors, we calculate all the matrix elements needed for the decay amplitudes. With these matrix elements, the ΔI=3/2 decay amplitude Re A2 shows a good agreement with experiment after an extrapolation to the chiral limit. The ΔI=1/2 amplitude Re A0, on the other hand, is about 50–60 % of the experimental one even after chiral extrapolation. In view of the insufficient enhancement of the ΔI=1/2 contribution, we employ the experimental values for the real parts of the decay amplitudes in our calculation of ɛ′/ɛ. The central values of our result indicate that the ΔI=3/2 contribution is larger than the ΔI=1/2 contribution so that ɛ′/ɛ is negative and has a magnitude of order 10-4. We discuss in detail possible systematic uncertainties, which seem too large for a definite conclusion on the value of ɛ′/ɛ.

著者

Lesk V. I. Aoki S. Burkhalter R. Fukugita M. Ishikawa K.-I. Ishizuka N. Iwasaki Y. Kanaya K. Kuramashi Y. Okawa M. Taniguchi Y. Ukawa A. Umeda T. Yoshie T.

出版者

American Physical Society

雑誌

Physical review D (ISSN:05562821)

巻号頁・発行日

vol.67, no.7, pp.074503, 2003-04

被引用文献数

16

---

We present results for the mass of the η′ meson in the continuum limit for two-flavor lattice QCD, calculated on the CP-PACS computer, using a renormalization-group-improved gauge action, and the Sheikoleslami-Wohlert fermion action with a tadpole-improved csw. The correlation functions are measured at three values of the coupling β corresponding to the lattice spacing a≈0.22, 0.16, 0.11 fm and for four values of the quark mass parameter κ corresponding to mπ/mρ≈0.8, 0.75, 0.7, 0.6. For each (β, κ) pair, 400–800 gauge configurations are used. The two-loop diagrams are evaluated using a noisy source method. We calculate η′ propagators using both smeared and local sources, and find that excited state contaminations are much reduced by smearing. A full analysis for the smeared propagators gives mη′=0.960(87)-0.248+0.036 GeV in the continuum limit, where the second error represents the systematic uncertainty coming from varying the functional form for chiral and continuum extrapolations.

著者

Aoki S. Boyd G. Burkhalter R. Ejiri S. Fukugita M. Hashimoto S. Iwasaki Y. Kanaya K. Kaneko T. Kuramashi Y. Nagai K. Okawa M. Shanahan H. P. Ukawa A. Yoshié T.

出版者

American Physical Society

雑誌

Physical review D (ISSN:05562821)

巻号頁・発行日

vol.67, no.3, pp.034503, 2003-02

被引用文献数

75

---

We present the details of simulations for the light hadron spectrum in quenched QCD carried out on the CP-PACS parallel computer. Simulations are made with the Wilson quark action and the plaquette gauge action on lattices of size 323×56–643×112 at four values of lattice spacings in the range a≈0.1–0.05 fm and spatial extent Lsa≈3 fm. Hadronic observables are calculated at five quark masses corresponding to mPS/mV≈0.75–0.4, assuming the u and d quarks are degenerate, but treating the s quark separately. We find that the presence of quenched chiral singularities is supported from an analysis of the pseudoscalar meson data. The physical values of hadron masses are determined using mπ, mρ, and mK (or mφ) as input to fix the physical scale of lattice spacing and the u, d, and s quark masses. After chiral and continuum extrapolations, the agreement of the calculated mass spectrum with experiment is at a 10% level. In comparison with the statistical accuracy of 1%–3% and systematic errors of at most 1.7% we have achieved, this demonstrates a failure of the quenched approximation for the hadron spectrum: the hyperfine splitting in the meson sector is too small, and in the baryon sector the octet masses and mass splitting of the decuplet are both smaller than experiment. Light quark masses are calculated using two definitions: the conventional one and the one based on the axial-vector Ward identity. The two results converge toward the continuum limit, yielding mud=4.29(14)-0.79+0.51 MeV where the first error is statistical and the second one is systematic due to chiral extrapolation. The s quark mass depends on the strange hadron mass chosen for input: ms=113.8(2.3)-2.9+5.8 MeV from mK and ms=142.3(5.8)-0+22.0 MeV from mφ, indicating again a failure of the quenched approximation. We obtain the scale of QCD, ΛMS̅ (0)=219.5(5.4) MeV with mρ used as input. An O(10%) deviation from experiment is observed in the pseudoscalar meson decay constants.

著者

Aoki S. Fukugita M. Hashimoto S. Ishikawa K-I. Ishizuka N. Iwasaki Y. Kanaya K. Kaneko T. Kuramashi Y. Okawa M. Onogi T. Tsutsui N. Ukawa A. Yamada N. Yoshié T.

出版者

American Physical Society

雑誌

Physical review D (ISSN:05562821)

巻号頁・発行日

vol.67, no.1, pp.014506, 2003-01

被引用文献数

14 49

---

We present our results of lattice calculations of B parameters, which parametrize ΔB=2 transition amplitudes together with the leptonic decay constant. Calculations are made in the quenched approximation at β=5.7, 5.9, 6.0 and 6.1, using NRQCD action for heavy quarks and the O(a)-improved Wilson action for light quarks. The operators are perturbatively renormalized including the correction of O(αs/(aM)m) (m>~0). We examine the scaling behavior of B parameters, and discuss the systematic uncertainties based on the results with several different truncations of higher order terms in 1/M and αs expansions. We find BBd(mb)=0.84(3)(5), BBs/BBd=1.020(21)(-16+15)(-0+5) and BSs(mb)=0.85(1)(5)(-0+1) in the quenched approximation. The errors represent statistical and systematic errors as well as the uncertainty in the determination of strange quark mass.