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S. Hashimoto

Publications and source records attributed to S. Hashimoto.

At least 145 records · Page 8Linked to original sources
arXiv2002

$B^0-\bar{B}^0$ mixing in quenched lattice QCD

We present our results of lattice calculations of $B$ parameters, which parameterize $ΔB$=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 quark and the $O(a)$-improved Wilson action for light quark. The operators are perturbatively renormalized including the correction of $O(α_s/(aM)^m)$ ($m\ge$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 $α_s$ expansions. We find $B_{B_d}(m_b)=0.84(3)(5)$, $B_{B_s}/B_{B_d}=1.020(21)(^{+15}_{-16})(^{+5}_{-0})$ and $B_{S_s}(m_b)=0.85(1)(5)(^{+1}_{-0})$ in the quenched approximation. The errors represent statistical and systematic as well as the uncertainty in the determination of strange quark mass.

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arXiv2002

I=2 Pion Scattering Phase Shift with Wilson Fermions

We present a lattice QCD calculation of the scattering phase shift for the I=2 $S$-wave two-pion system using the finite size method proposed by Lüscher. We work in the quenched approximation employing the standard plaquette action at $β=5.9$ for gluons and the Wilson fermion action for quarks. The phase shift is extracted from the energy eigenvalues of the two-pion system, which are obtained by a diagonalization of the pion 4-point function evaluated for a set of relative spatial momenta. In order to change momentum of the two-pion system, calculations are carried out on $24^3\times 60$, $32^3\times 60$, and $48^3\times 60$ lattices. The phase shift is successfully calculated over the momentum range $0 < p^2 < 0.3 {\rm GeV}^2$.

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arXiv2002

I=2 Pion Scattering Length with the Wilson Fermion

The calculation of the I=2 pion scattering length in quenched lattice QCD is revisited. The calculation is carried out with the Wilson fermion action employing Lüscher's finite size scaling method at $β=5.9$, 6.1, and 6.3 corresponding to the range of lattice spacing $a\simeq 0.12 - 0.07$ fm. We obtain in the continuum limit $a_0m_π= -0.0410(69)$, which is consistent with the prediction of chiral perturbation theory $a_0m_π=-0.0444(10)$.

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arXiv2002

I=2 Pion Scattering Phase Shift with Wilson Fermions

We present results of phase shift for I=2 $S$-wave $ππ$ system with the Wilson fermions in the quenched approximation. The finite size method proposed by Lüscher is employed, and calculations are carried out at $β=5.9$ ($a^{-1}=1.934(16)$ GeV from $m_ρ$) on $24^3 \times 60$, $32^3 \times 60$, and $48^3 \times 60$ lattices.

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arXiv2002

Light hadron spectrum with two flavors of $O(a)$ improved dynamical quarks : final results from JLQCD

We present the final results of the JLQCD calculation of the light hadron spectrum and quark masses with two flavors of dynamical quarks using the plaquette gauge action and fully $O(a)$-improved Wilson quark action at $β=5.2$. We observe that sea quark effects lead to a closer agreement of the strange meson and baryon masses with experiment and a reduction of quark masses by about 25.

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arXiv2002

An exact Polynomial Hybrid Monte Carlo algorithm for dynamical Kogut-Susskind fermions

We present a polynomial Hybrid Monte Carlo (PHMC) algorithm as an exact simulation algorithm with dynamical Kogut-Susskind fermions. The algorithm uses a Hermitian polynomial approximation for the fractional power of the KS fermion matrix. The systematic error from the polynomial approximation is removed by the Kennedy-Kuti noisy Metropolis test so that the algorithm becomes exact at a finite molecular dynamics step size. We performed numerical tests with $N_f$$=$2 case on several lattice sizes. We found that the PHMC algorithm works on a moderately large lattice of $16^4$ at $β$$=$5.7, $m$$=$0.02 ($m_{\mathrm{PS}}/m_{\mathrm{V}}$$\sim$0.69) with a reasonable computational time.

hep-lat↗
arXiv2002

Polynomial Hybrid Monte Carlo algorithm for lattice QCD with an odd number of flavors

We present a polynomial hybrid Monte Carlo (PHMC) algorithm for lattice QCD with odd numbers of flavors of O(a)-improved Wilson quark action. The algorithm makes use of the non-Hermitian Chebyshev polynomial to approximate the inverse square root of the fermion matrix required for an odd number of flavors. The systematic error from the polynomial approximation is removed by a noisy Metropolis test for which a new method is developed. Investigating the property of our PHMC algorithm in the N_f=2 QCD case, we find that it is as efficient as the conventional HMC algorithm for a moderately large lattice size (16^3 times 48) with intermediate quark masses (m_{PS}/m_V ~ 0.7-0.8). We test our odd-flavor algorithm through extensive simulations of two-flavor QCD treated as an N_f = 1+1 system, and comparing the results with those of the established algorithms for N_f=2 QCD. These tests establish that our PHMC algorithm works on a moderately large lattice size with intermediate quark masses (16^3 times 48, m_{PS}/m_V ~ 0.7-0.8). Finally we experiment with the (2+1)-flavor QCD simulation on small lattices (4^3 times 8 and 8^3 times 16), and confirm the agreement of our results with those obtained with the R algorithm and extrapolated to a zero molecular dynamics step size.

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arXiv2002

Light Hadron Spectrum and Quark Masses from Quenched Lattice QCD

We present 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 32^3x56 - 64^3x112 lattices at four lattice spacings (a \approx 0.1-0.05 fm) and the spatial extent of 3 fm. Hadronic observables are calculated at five quark masses (m_{PS}/m_V \approx 0.75 - 0.4), assuming the u and d quarks being 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. We take m_π, m_ρand m_K (or m_ϕ) as input. 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 meson hyperfine splitting is too small, and the octet masses and the decuplet mass splittings 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 m_{ud}=4.29(14)^{+0.51}_{-0.79} MeV. The s quark mass depends on the strange hadron mass chosen for input: m_s = 113.8(2.3)^{+5.8}_{-2.9} MeV from m_K and m_s = 142.3(5.8)^{+22.0}_{-0} MeV from m_ϕ, indicating again a failure of the quenched approximation. We obtain Λ_{\bar{MS}}^{(0)}= 219.5(5.4) MeV. An O(10%) deviation from experiment is observed in the pseudoscalar meson decay constants.

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arXiv2002

Charmonium Spectrum from Quenched Anisotropic Lattice QCD

We present a detailed study of the charmonium spectrum using anisotropic lattice QCD. We first derive a tree-level improved clover quark action on the anisotropic lattice for arbitrary quark mass. The heavy quark mass dependences of the improvement coefficients, i.e. the ratio of the hopping parameters $ζ=K_t/K_s$ and the clover coefficients $c_{s,t}$, are examined at the tree level. We then compute the charmonium spectrum in the quenched approximation employing $ξ= a_s/a_t = 3$ anisotropic lattices. Simulations are made with the standard anisotropic gauge action and the anisotropic clover quark action at four lattice spacings in the range $a_s$=0.07-0.2 fm. The clover coefficients $c_{s,t}$ are estimated from tree-level tadpole improvement. On the other hand, for the ratio of the hopping parameters $ζ$, we adopt both the tree-level tadpole-improved value and a non-perturbative one. We calculate the spectrum of S- and P-states and their excitations. The results largely depend on the scale input even in the continuum limit, showing a quenching effect. When the lattice spacing is determined from the $1P-1S$ splitting, the deviation from the experimental value is estimated to be $\sim$30% for the S-state hyperfine splitting and $\sim$20% for the P-state fine structure. Our results are consistent with previous results at $ξ= 2$ obtained by Chen when the lattice spacing is determined from the Sommer scale $r_0$. We also address the problem with the hyperfine splitting that different choices of the clover coefficients lead to disagreeing results in the continuum limit.

hep-lat↗
arXiv2001

Heavy quark expansion parameters from lattice NRQCD

Using the lattice NRQCD action for heavy quark, we calculate the heavy quark expansion parameters $μ_π^2$ and $μ_G^2$ for heavy-light mesons and heavy-light-light baryons. The results are compared with the mass differences among heavy hadrons to test the validity of HQET relations on the lattice.

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arXiv2001

Exploration of sea quark effects in two-flavor QCD with the O(a)-improved Wilson quark action

We explore sea quark effects in the light hadron mass spectrum in a simulation of two-flavor QCD using the nonperturbatively O(a)-improved Wilson fermion action. In order to identify finite-size effects, light meson masses are measured on 12^3x48, 16^3x48 and 20^3x48 lattices with a~0.1 fm. On the largest lattice, where the finite-size effect is negligible, we find a significant increase of the strange vector meson mass compared to the quenched approximation. We also investigate the quark mass dependence of pseudoscalar meson masses and decay constants and test the consistency with (partially quenched) chiral perturbation theory.

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arXiv2001

I=2 Pion Scattering Length and Phase Shift with Wilson Fermions

We present preliminary results of scattering length and phase shift for I=2 S-wave $ππ$ system with the Wilson fermions in the quenched approximation. The finite size method presented by Lüscher is employed, and calculations are carried out at $β=5.9$ on a $24^3\times 60$ and $32^3\times 60$ lattice.

hep-lat↗
arXiv2001

Chiral property of domain-wall fermion from eigenvalues of 4D Wilson-Dirac Operator

We investigate a chiral property of the domain-wall fermion (DWF) system using the four-dimensional hermitian Wilson-Dirac operator $H_W$. A formula expressing the Ward-Takahashi identity quark mass $m_{5q}$ with eigenvalues of this operator is derived, which well explains the $N_5$ dependence of $m_{5q}$ observed in previous numerical simulations. We further discuss the chiral property of DWF in the large volume in terms of the spectra of $H_W$.

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arXiv2001

Maximum entropy analysis of hadron spectral functions and excited states in quenched lattice QCD

Employing the maximum entropy method we extract the spectral functions from meson correlators at four lattice spacings in quenched QCD with the Wilson quark action. We confirm that the masses and decay constants, obtained from the position and the area of peaks, agree well with the results from the conventional exponential fit. For the first excited state, we obtain $m_{π_1} = 660(590)$ MeV, $m_{ρ_1} = 1540(570)$ MeV, and $f_{ρ_1} = 0.085(36)$ in the continuum limit.

hep-lat↗
arXiv2001

Charmonium spectrum from quenched QCD on anisotropic lattices

We present our final results of the charmonium spectrum in quenched QCD on anisotropic lattices. Simulations are made with the plaquette gauge action and a tadpole improved clover quark action employing $ξ= a_s/a_t = 3$. We calculate the spectrum of S- and P-states and their excitation, and study the scaling behavior of mass splittings. Comparison is made with the experiment and previous lattice results. The issue of hyperfine splitting for different choices of the clover coefficients obtained by Klassen is discussed.

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