Publications (116)293.43 Total impact

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ABSTRACT: We present a method to couple finitevolume QCD to infinitevolume QED by an appropriate twistaveraging procedure. We demonstrate the prescription numerically for the leadingorder hadronic contribution to the anomalous magnetic moment of the muon and the electromagnetic pion mass splitting. 
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ABSTRACT: We calculate the form factors for B>pi l nu & Bs>K l nu decay in lattice QCD. We use the (2+1)flavor RBCUKQCD gauge fieldensembles generated with the domainwall fermion and Iwasaki gauge actions. For the b quarks we use the anisotropic clover action with the relativistic heavyquark interpretation. We analyze data at 2 lattice spacings a~0.11, 0.086 fm with pion masses as light as M_pi~290 MeV. We extrapolate our numerical results to the physical lightquark masses and to the continuum and interpolate in the pion/kaon energy using SU(2) "hardpion" chiral perturbation theory. We provide complete systematic error budgets for the vector & scalar form factors f+(q^2) & f0(q2) for B>pi l nu & Bs >K l nu at 3 momenta that span the q^2 range accessible in our numerical simulations. Next we extrapolate these results to q^2 = 0 using a modelindependent zparameterization based on analyticity & unitarity. We present our final results for f+(q^2) & f0(q^2) as the z coefficients and matrix of correlations between them; this parameterizes the form factors over the entire kinematic range. Our results agree with other 3flavor latticeQCD determinations using staggered light quarks, and have comparable precision, thereby providing important independent checks. Both B>pi l nu & Bs>K l nu decays enable determinations of the CKM element Vub. To illustrate this, we perform a combined zfit of our numerical B >pi l nu formfactor data with experimental measurements of the branching fraction; we obtain Vub = 3.61(32) x 10^{3}, where the error includes statistical and systematic uncertainties. The same approach can be applied to Bs>K l nu to provide an alternative determination of Vub once the process has been measured experimentally. Finally, we make predictions for B>pi l nu & Bs>K l nu differential branching fractions and forwardbackward asymmetries in the Standard Model. 
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ABSTRACT: We report initial nucleon structure results computed on lattices with 2+1 dynamical M\"obius domain wall fermions at the physical point generated by the RBC and UKQCD collaborations. At this stage, we evaluate only connected quark contributions. In particular, we discuss the nucleon vector and axialvector form factors, nucleon axial charge and the isovector quark momentum fraction. From currently available statistics, we estimate the stochastic accuracy of the determination of $g_A$ and $ _{ud}$ to be around 10%, and we expect to reduce that to 5% within the next year. To reduce the computational cost of our calculations, we extensively use acceleration techniques such as loweigenmode deflation and allmodeaveraging (AMA). We present a method for choosing optimal AMA parameters. 
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ABSTRACT: We present results for several light hadronic quantities ($f_\pi$, $f_K$, $B_K$, $m_{ud}$, $m_s$, $t_0^{1/2}$, $w_0$) obtained from simulations of 2+1 flavor domain wall lattice QCD with large physical volumes and nearlyphysical pion masses at two lattice spacings. We perform a short, O(3)%, extrapolation in pion mass to the physical values by combining our new data in a simultaneous chiral/continuum `global fit' with a number of other ensembles with heavier pion masses. We use the physical values of $m_\pi$, $m_K$ and $m_\Omega$ to determine the two quark masses and the scale  all other quantities are outputs from our simulations. We obtain results with subpercent statistical errors and negligible chiral and finitevolume systematics for these light hadronic quantities, including: $f_\pi$ = 130.2(9) MeV; $f_K$ = 155.5(8) MeV; the average up/down quark mass and strange quark mass in the $\overline {\rm MS}$ scheme at 3 GeV, 2.997(49) and 81.64(1.17) MeV respectively; and the neutral kaon mixing parameter, $B_K$, in the RGI scheme, 0.750(15) and the $\overline{\rm MS}$ scheme at 3 GeV, 0.530(11). 
Article: K_{L}k_{s}.
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ABSTRACT: We report on the first complete calculation of the K_{L}K_{S} mass difference, ΔM_{K}, using lattice QCD. The calculation is performed on a 2+1 flavor, domain wall fermion ensemble with a 330 MeV pion mass and a 575 MeV kaon mass. We use a quenched charm quark with a 949 MeV mass to implement GlashowIliopoulosMaiani cancellation. For these heavierthanphysical particle masses, we obtain ΔM_{K}=3.19(41)(96)×10^{12} MeV, quite similar to the experimental value. Here the first error is statistical, and the second is an estimate of the systematic discretization error. An interesting aspect of this calculation is the importance of the disconnected diagrams, a dramatic failure of the OkuboZweigIizuka rule.Physical Review Letters 09/2014; 113(11):112003. · 7.73 Impact Factor 
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ABSTRACT: The composition of nucleons has long been known to be subatomic particles called quarks and gluons, which interact through the strong force and theoretically can be described by Quantum Chromodynamics (QCD). Lattice QCD (LQCD), in which the continuous spacetime is translated into grid points on a fourdimensional lattice and ab initio Monte Carlo simulations are performed, is by far the only modelindependent method to study QCD with controllable errors. We report the successful application of a novel algorithm, AllModeAveraging, in the LQCD calculations of nucleon internal structure on the Gordon supercomputer our award of roughly 6 million service units through XSEDE. The application of AMA resulted in as much as a factor of 30 speedup in computational efficiency. 
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ABSTRACT: The form factor that yields the lightbylight scattering contribution to the muon anomalous magnetic moment is computed in lattice QCD+QED and QED. A nonperturbative treatment of QED is used and is checked against perturbation theory. The hadronic contribution is calculated for unphysical quark and muon masses, and only the diagram with a single quark loop is computed. Statistically significant signals are obtained. Initial results appear promising, and the prospect for a complete calculation with physical masses and controlled errors is discussed.Physical Review Letters 07/2014; 114(1). DOI:10.1103/PhysRevLett.114.012001 · 7.73 Impact Factor 
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ABSTRACT: Neutral $B$ meson mixing matrix elements and $B$ meson decay constants are calculated. Static approximation is used for $b$ quark and domainwall fermion formalism is employed for light quarks. The calculations are carried out on $2+1$ flavor dynamical ensembles generated by RBC/UKQCD Collaborations with lattice spacings $0.086$fm ($a^{1}\sim 2.3$GeV) and $0.11$fm ($1.7$GeV), and a fixed physical spatial volume of about $(2.7{\rm fm})^3$. In the static quark action, linksmearings are used to improve the signaltonoise ratio. We employ two kinds of linksmearings, HYP1 and HYP2, and their results are combined in taking the continuum limit. For the matching between the lattice and the continuum theory, oneloop perturbative $O(a)$ improvements are made to reduce discretization errors. As the most important quantity of this work, we obtain SU(3) breaking ratio $\xi=1.208(60)$, where the error includes statistical and systematic one. We also find other neutral $B$ meson mixing quantities $f_B\sqrt{\hat{B}_B}=240(22)$MeV, $f_{B_s}\sqrt{\hat{B}_{B_s}}=290(22)$MeV, $\hat{B}_B=1.17(22)$, $\hat{B}_{B_s}=1.22(13)$ and $B_{B_s}/B_B=1.028(74)$, $B$ meson decay constants $f_B=219(17)$MeV, $f_{B_s}=264(19)$MeV and $f_{B_s}/f_B=1.193(41)$, in the static limit of $b$ quark. 
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ABSTRACT: We report on the first complete calculation of the $K_LK_S$ mass difference, $\Delta M_K$, using lattice QCD. The calculation is performed on a 2+1 flavor, domain wall fermion (DWF) ensemble with a 330~MeV pion mass and a 575~MeV kaon mass. We use a quenched charm quark with a 949~MeV mass to implement GlashowIliopoulosMaiani (GIM) cancellation. For these heavierthanphysical particle masses, we obtain $\Delta M_K =3.19(41)(96)\times 10^{12}$~MeV, quite similar to the experimental value. Here the first error is statistical and the second is an estimate of the systematic discretization error. An interesting aspect of this calculation is the importance of the disconnected diagrams, a dramatic failure of the OZI rule.Physical Review Letters 06/2014; 113(11). DOI:10.1103/PhysRevLett.113.112003 · 7.73 Impact Factor 
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ABSTRACT: We calculate the Bmeson decay constants f_B, f_Bs, and their ratio in unquenched lattice QCD using domainwall light quarks and relativistic bquarks. We use gaugefield ensembles generated by the RBC and UKQCD collaborations using the domainwall fermion action and Iwasaki gauge action with three flavors of light dynamical quarks. We analyze data at two lattice spacings of a ~ 0.11, 0.086 fm with unitary pion masses as light as M_pi ~ 290 MeV; this enables us to control the extrapolation to the physical lightquark masses and continuum. For the bquarks we use the anisotropic clover action with the relativistic heavyquark interpretation, such that discretization errors from the heavyquark action are of the same size as from the lightquark sector. We renormalize the lattice heavylight axialvector current using a mostly nonperturbative method in which we compute the bulk of the matching factor nonperturbatively, with a small correction, that is close to unity, in lattice perturbation theory. We also improve the lattice heavylight current through O(alpha_s a). We extrapolate our results to the physical lightquark masses and continuum using SU(2) heavymeson chiral perturbation theory, and provide a complete systematic error budget. We obtain f_B0 = 196.2(15.7) MeV, f_B+ = 195.4(15.8) MeV, f_Bs = 235.4(12.2) MeV, f_Bs/f_B0 = 1.193(59), and f_Bs/f_B+ = 1.220(82), where the errors are statistical and total systematic added in quadrature. These results are in good agreement with other published results and provide an important independent cross check of other threeflavor determinations of Bmeson decay constants using staggered light quarks. 
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ABSTRACT: The real and imaginary parts of the $K_LK_S$ mixing matrix receive contributions from all three charge2/3 quarks: up, charm and top. These give both short and longdistance contributions which are accessible through a combination of perturbative and lattice methods. We will discuss a strategy to compute both the mass difference, $\Delta M_K$ and $\epsilon_K$ to subpercent accuracy, looking in detail at the contributions from each of the three CKM matrix element products $V_{id}^*V_{is}$ for $i=u, c$ and $t$ as described in Ref. [1] 
Article: Covariant approximation averaging
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ABSTRACT: We present a new class of statistical error reduction techniques for MonteCarlo simulations. Using covariant symmetries, we show that correlation functions can be constructed from inexpensive approximations without introducing any systematic bias in the final result. We introduce a new class of covariant approximation averaging techniques, known as allmode averaging (AMA), in which the approximation takes account of contributions of all eigenmodes through the inverse of the Dirac operator computed from the conjugate gradient method with a relaxed stopping condition. In this paper we compare the performance and computational cost of our new method with traditional methods using correlation functions and masses of the pion, nucleon, and vector meson in $N_f=2+1$ lattice QCD using domainwall fermions. This comparison indicates that AMA significantly reduces statistical errors in MonteCarlo calculations over conventional methods for the same cost. 
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ABSTRACT: Neutral B meson mixing matrix elements and B meson decay constants are calculated. Static approximation is used for b quark and domainwall fermion formalism is employed for light quarks. The calculations are done on 2+1 flavor dynamical ensembles, whose lattice spacings are 0.086 fm and 0.11 fm with a fixed physical spatial volume of about (2.7 fm)^3. In the static quark action, linksmearings are used to improve the signaltonoise ratio. We employ two kinds of linksmearings and their results are combined in taking a continuum limit. For the matching between the lattice and the continuum theory, oneloop perturbative calculations are used including O(a) improvements to reduce discretization errors. We obtain SU(3) braking ratio \xi=1.222(60) in the static limit of b quark. 
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ABSTRACT: We report on a calculation of the effects of isospin breaking in Lattice QCD+QED. This involves using Chiral Perturbation Theory with Electromagnetic corrections to find the renormalized, nondegenerate, light quark masses. The calculations are carried out on QCD ensembles generated by the RBC and UKQCD collaborations using Domain Wall Fermions and the Iwasaki and Iwasaki+DSDR Gauge Actions with unitary pion masses down to 170 MeV. Noncompact QED is treated in the quenched approximation. The simulations use a $32^3$ lattice size with $a^{1}=2.28(3)$ GeV (Iwasaki) and 1.37(1) (Iwasaki+DSDR). This builds on previous work from the RBC/UKQCD collaboration with lattice spacing $a^{1}=1.78(4)$ GeV. 
Conference Paper: The origin of mass
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ABSTRACT: The origin of mass is one of the deepest mysteries in science. Neutrons and protons, which account for almost all visible mass in the Universe, emerged from a primordial plasma through a cataclysmic phase transition microseconds after the Big Bang. However, most mass in the Universe is invisible. The existence of dark matter, which interacts with our world so weakly that it is essentially undetectable, has been established from its galacticscale gravitational effects. Here we describe results from the first truly physical calculations of the cosmic phase transition and a groundbreaking firstprinciples investigation into composite dark matter, studies impossible with previous stateoftheart methods and resources. By inventing a powerful new algorithm, "DSDR," and implementing it effectively for contemporary supercomputers, we attain excellent strong scaling, perfect weak scaling to the LLNL BlueGene/Q two million cores, sustained speed of 7.2 petaflops, and timetosolution speedup of more than 200 over the previous stateoftheart.Proceedings of the International Conference on High Performance Computing, Networking, Storage and Analysis; 11/2013 
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ABSTRACT: After a brief selfcontained introduction to the muon anomalous magnetic moment, (g2), we review the status of lattice calculations of the hadronic vacuum polarization contribution and present first results from lattice QCD for the hadronic lightbylight scattering contribution. The signal for the latter is consistent with model calculations. While encouraging, the statistical error is large and systematic errors are mostly uncontrolled. The method is applied first to pure QED as a check. 
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ABSTRACT: We develop and demonstrate techniques needed to compute the long distance contribution to the $K_{L}$$K_{S}$ mass difference, $\Delta M_K$, in lattice QCD and carry out a first, exploratory calculation of this fundamental quantity. The calculation is performed on 2+1 flavor, domain wall fermion, $16^3\times32$ configurations with a 421 MeV pion mass. We include only currentcurrent operators and drop all disconnected and double penguin diagrams. The short distance part of the mass difference in a 2+1 flavor calculation contains a quadratic divergence cut off by the lattice spacing. Here, this quadratic divergence is eliminated through the GIM mechanism by introducing a valence charm quark. The inclusion of the charm quark makes the complete calculation accessible to lattice methods provided the discretization errors associated with the charm quark can be controlled. The long distance effects are discussed for each parity channel separately. While we can see a clear signal in the parity odd channel, the signal to noise ratio in the parity even channel is exponentially decreasing as the separation between the two weak operators increases. We obtain a mass difference $\Delta M_K$ which ranges from $5.12(24)\times 10^{12}$ MeV to $9.31(66)\times 10^{12}$ MeV for kaon masses varying from 563 MeV to 839 MeV. Extensions of these methods are proposed which promise accurate results for both $\Delta M_K$ and $\epsilon_K$, including long distance effects.Physical review D: Particles and fields 12/2012; 88(1). DOI:10.1103/PhysRevD.88.014508 · 4.86 Impact Factor 
Article: Error reduction technique using covariant approximation and application to nucleon form factor
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ABSTRACT: We demonstrate the new class of variance reduction techniques for hadron propagator and nucleon isovector form factor in the realistic lattice of $N_f=2+1$ domainwall fermion. Allmode averaging (AMA) is one of the powerful tools to reduce the statistical noise effectively for wider varieties of observables compared to existing techniques such as lowmode averaging (LMA). We adopt this technique to hadron twopoint functions and threepoint functions, and compare with LMA and traditional sourceshift method in the same ensembles. We observe AMA is much more cost effective in reducing statistical error for these observables. 
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ABSTRACT: We describe the computation of the amplitude A2 for a kaon to decay into two pions with isospin I=2. The results presented in [ T. Blum et al. Phys. Rev. Lett. 108 141601 (2012)] from an analysis of 63 gluon configurations are updated to 146 configurations giving ReA2=1.381(46)stat(258)syst108 GeV and ImA2=6.54(46)stat(120)syst1013 GeV. ReA2 is in good agreement with the experimental result, whereas the value of ImA2 was hitherto unknown. We are also working toward a direct computation of the K→(ππ)I=0 amplitude A0 but, within the Standard Model, our result for ImA2 can be combined with the experimental results for ReA0, ReA2 and ε′/ε to give ImA0/ReA0=1.61(28)×104. Our result for ImA2 implies that the electroweak penguin (EWP) contribution to ε′/ε is Re(ε′/ε)EWP=(6.25±0.44stat±1.19syst)×104.Physical review D: Particles and fields 10/2012; 86(7). DOI:10.1103/PhysRevD.86.074513 · 4.86 Impact Factor 
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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.08/2012; DOI:10.1093/ptep/pts002
Publication Stats
2k  Citations  
293.43  Total Impact Points  
Top Journals
Institutions

2002–2015

Brookhaven National Laboratory
 Physics Department
New York, New York, United States


2012

University of Connecticut
 Department of Physics
Storrs, CT, United States


2001–2009

Kanazawa University
 Institute for Theoretical Physics
Kanazawa, Ishikawa, Japan


2005–2006

RIKEN
Вако, Saitama, Japan


1997–2002

University of Tsukuba
 Centre for Computational Sciences
Tsukuba, Ibaraki, Japan
