Yasutaka Taniguchi

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 by matching the Hamiltonian on the lattice and in the continuum. The heavy quark mass dependence of the improvement coefficients, i.e., the ratio of the hopping parameters z5Kt /Ks and the clover coefficients c s,t , is examined at the tree level, and effects of the choice of the spatial Wilson parameter r s are discussed. We then compute the charmonium spectrum in the quenched approximation employing j5as /at53 anisotropic lattices. Simulations are made with the standard anisotropic gauge action and the anisotropic clover quark action with r s51 at four lattice spacings in the range as50.07‐0.2 fm. The clover coefficientsc s,t are estimated from tree-level tadpole improvement. On the other hand, for the ratio of the hopping parameters z, we adopt both the tree-level tadpole-improved value and a non-perturbative one. The latter employs the condition that the speed of light calculated from the meson energy-momentum relation be unity. We calculate the spectrum of S and P states and their excitations using both the pole and kinetic masses. We find that the combination of the pole mass and the tadpole-improved value of z to yield the smoothest approach to the continuum limit, which we then adopt for the continuum extrapolation of the spectrum. 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 1 P-1S splitting, the deviation from the experimental value is estimated to be ;30% for the S-state hyperfine splitting and ;20% for the P-state fine structure. Our results are consistent with previous results at j52 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. Making a leading order analysis based on potential models we show that a large hyperfine splitting ;95 MeV obtained by Klassen with a different choice of the clover coefficients is likely an overestimate.

Light-quark masses from unquenched lattice QCD

We calculate the light meson spectrum and the light quark masses by lattice QCD simulation, treating all light quarks dynamically and employing the Iwasaki gluon action and the nonperturbatively O(a)-improved Wilson quark action. The calculations are made at the squared lattice spacings at an equal distance a{sup 2}{approx_equal}0.005, 0.01, and 0.015 fm{sup 2}, and the continuum limit is taken assuming an O(a{sup 2}) discretization error. The light meson spectrum is consistent with experiment. The up, down, and strange quark masses in the MS scheme at 2 GeV are m=(m{sub u}+m{sub d})/2=3.55{sub -0.28}{sup +0.65} MeV and m{sub s}=90.1{sub -6.1}{sup +17.2} MeV where the error includes statistical and all systematic errors added in quadrature. These values contain the previous estimates obtained with the dynamical u and d quarks within the error.

Charmed baryons at the physical point in 2+1 flavor lattice QCD

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 × 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 baryon mass gives a 1 = 2.194(10) GeV, and thus the spatial extent becomes L = 32a = 2.88(1) fm. Our results for the charmed baryon masses are consistent with experimental values, �

Nonperturbative O(a) improvement of the Wilson quark action with the renormalization-group-improved gauge action using the Schrödinger functional method

We perform a nonperturbative determination of the O(a)-improvement coefficient c{sub SW} and the critical hopping parameter {kappa}{sub c} for N{sub f}=3, 2, and 0 flavor QCD with the (RG) renormalization-group-improved gauge action using the Schroedinger functional method. In order to interpolate c{sub SW} and {kappa}{sub c} as a function of the bare coupling, a wide range of {beta} from the weak coupling region to the moderately strong coupling points used in large-scale simulations is studied. Corrections at finite lattice size of O(a/L) turned out to be large for the RG-improved gauge action, and hence we make the determination at a size fixed in physical units using a modified improvement condition. This enables us to avoid O(a) scaling violations which would remain in physical observables if c{sub SW} determined for a fixed lattice size L/a is used in numerical simulations.

Non-perturbative renormalization of quark mass in N-f=2+1 QCD with the Schrodinger functional scheme

We present an evaluation of the quark mass renormalization factor for Nf = 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

Isoscalar dipole transition as a probe for asymmetric clustering

\overline {\text{MS}}

2+1 Flavor QCD Simulation on a

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 Nf = 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 Nf = 2 + 1 simulations; previous work of the CP -PACS/JLQCD collaboration, which covered the up-down quark mass range heavier than mπ ∼ 500 MeV and that of PACS-CS collaboration for much lighter quark masses down to mπ = 155MeV. The quark mass renormalization factor is used to renormalize bare PCAC masses in these simulations.

96^4

Background: The sharp 1− resonances with enhanced isoscalar dipole transition strengths are observed in many light nuclei at relatively small excitation energies, but their nature has been unclear. Purpose: We show those resonances can be attributed to the cluster states with asymmetric configurations such as α+O16. We explain why asymmetric cluster states are strongly excited by the isoscalar dipole transition. We also provide a theoretical prediction of the isoscalar dipole transitions in Ne20 and Ti44. Method: The transition matrix is analytically derived to clarify the excitation mechanism. The nuclear model calculations by Brink–Bloch wave function and antisymmetrized molecular dynamics are also performed to provide a theoretical prediction for Ne20 and Ti44. Results: It is shown that the transition matrix is as large as the Weisskopf estimate even though the ground state is an ideal shell-model state. Furthermore, it is considerably amplified if the ground state has cluster correlation. The nuclear model calculations predict large transition matrix to the α+O16 and α+Ca40 cluster states comparable with or larger than the Weisskopf estimate. Conclusions: We conclude that the asymmetric cluster states are strongly excited by the isoscalar dipole transition. Combined with the isoscalar monopole transition that populates the 0+ cluster states, the isoscalar transitions are promising probes for asymmetric clusters.

Lattice

We generate

Cluster structures and superdeformation in Si 28

2+1