Publications (149)140.3 Total impact
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ABSTRACT: We compute the leptonic decay constants $f_{D^+}$, $f_{D_s}$, and $f_{K^+}$, and the quarkmass ratios $m_c/m_s$ and $m_s/m_l$ in unquenched lattice QCD using the experimentally determined value of $f_{\pi^+}$ for normalization. We use the MILC Highly Improved Staggered Quark (HISQ) ensembles with four dynamical quark flavors  up, down, strange, and charm  and with both physical and unphysical values of the light seaquark masses. The use of physical pions removes the need for a chiral extrapolation, thereby eliminating a significant source of uncertainty in previous calculations. Four different lattice spacings ranging from $a\approx 0.06$ fm to $0.15$ fm are included in the analysis to control the extrapolation to the continuum limit. Our primary results are $f_{D^+} = 212.6(0.4)({}^{+1.0}_{1.2})\ \mathrm{MeV}$, $f_{D_s} = 249.0(0.3)({}^{+1.1}_{1.5})\ \mathrm{MeV}$, and $f_{D_s}/f_{D^+} = 1.1712(10)({}^{+29}_{32})$, where the errors are statistical and total systematic, respectively. The errors on our results for the charm decay constants and their ratio are approximately two to four times smaller than those of the most precise previous lattice calculations. We also obtain $f_{K^+}/f_{\pi^+} = 1.1956(10)({}^{+26}_{18})$, updating our previous result, and determine the quarkmass ratios $m_s/m_l = 27.35(5)({}^{+10}_{7})$ and $m_c/m_s = 11.747(19)({}^{+59}_{43})$. When combined with experimental measurements of the decay rates, our results lead to precise determinations of the CKM matrix elements $V_{us} = 0.22487(51) (29)(20)(5)$, $V_{cd}=0.217(1) (5)(1)$ and $V_{cs}= 1.010(5)(18)(6)$, where the errors are from this calculation of the decay constants, the uncertainty in the experimental decay rates, structuredependent electromagnetic corrections, and, in the case of $V_{us}$, the uncertainty in $V_{ud}$, respectively.07/2014;  [Show abstract] [Hide abstract]
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.04/2014;  [Show abstract] [Hide abstract]
ABSTRACT: We present a study of the $D$ and $B$ leptonic decay constants on the MILC $N_f=2+1$ asqtad gauge ensembles using asqtadimproved staggered light quarks and clover heavy quarks in the Fermilab interpretation. Our previous analysis \cite{Bazavov:2011aa} computed the decay constants at lattice spacings $a \approx 0.14, 0.11$ and $0.083$ fm. We have extended the simulations to finer $a \approx 0.058$ and $0.043$ fm lattice spacings, and have also increased statistics; this allows us to address many important sources of uncertainty. Technical advances include a twostep twopoint fit procedure, better tuning of the heavy quark masses and a better determination of the axialvector current matching. The present analysis remains blinded, so here we focus on the improvements and their predicted impact on the error budget compared to the prior analysis.03/2014;  [Show abstract] [Hide abstract]
ABSTRACT: We calculate the kaon semileptonic form factor f+(0) from lattice QCD, working, for the first time, at the physical lightquark masses. We use gauge configurations generated by the MILC Collaboration with Nf=2+1+1 flavors of sea quarks, which incorporate the effects of dynamical charm quarks as well as those of up, down, and strange. We employ data at three lattice spacings to extrapolate to the continuum limit. Our result, f+(0)=0.9704(32), where the error is the total statistical plus systematic uncertainty added in quadrature, is the most precise determination to date. Combining our result with the latest experimental measurements of K semileptonic decays, one obtains the CabibboKobayashiMaskawa matrix element Vus=0.22290(74)(52), where the first error is from f+(0) and the second one is from experiment. In the firstrow test of CabibboKobayashiMaskawa unitarity, the error stemming from Vus is now comparable to that from Vud.Physical Review Letters 03/2014; 112(11):112001. · 7.73 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We compute the zerorecoil form factor for the semileptonic decay $\bar{B}^0\to D^{*+}\ell^\bar{\nu}$ (and modes related by isospin and charge conjugation) using lattice QCD with three flavors of sea quarks. We use an improved staggered action for the light valence and sea quarks (the MILC \asqtad\ configurations), and the Fermilab action for the heavy quarks. Our calculations incorporate higher statistics, finer lattice spacings, and lighter quark masses than our 2008 work. As a byproduct of tuning the new data set, we obtain the $D_s$ and $B_s$ hyperfine splittings with fewMeV accuracy. For the zerorecoil form factor, we obtain $\mathcal{F}(1)=0.906(4)(12)$, where the first error is statistical and the second is the sum in quadrature of all systematic errors. With the latest HFAG average of experimental results and a cautious treatment of QED effects, we find $V_{cb} = (39.04 \pm 0.49_\text{expt} \pm 0.53_\text{QCD} \pm 0.19_\text{QED})\times10^{3}$. The QCD error is now commensurate with the experimental error.03/2014;  [Show abstract] [Hide abstract]
ABSTRACT: These reports present the results of the 2013 Community Summer Study of the APS Division of Particles and Fields ("Snowmass 2013") on the future program of particle physics in the U.S. Chapter 9, on Computing, discusses the computing challenges for future experiments in the Energy, Intensity, and Cosmic Frontiers, for accelerator science, and for particle theory, as well as structural issues in supporting the intense uses of computing required in all areas of particle physics.01/2014;  [Show abstract] [Hide abstract]
ABSTRACT: We present recent results on the QCD equation of state with 2+1+1 flavors of highly improved staggered quarks (HISQ). We focus on three sets of ensembles with temporal extent 6, 8 and 10, that reach up to temperatures of 967, 725 and 580 MeV, respectively. The strange and charm quark masses are tuned to the physical values and the light quarks mass is set to one fifth of the strange. This corresponds to a Goldstone pion of about 300 MeV.12/2013;  [Show abstract] [Hide abstract]
ABSTRACT: We calculate the form factors for the semileptonic decays $B_s\to K\ell\nu$ and $B\to K\ell\ell$ with lattice QCD. We work at several lattice spacings and a range of light quark masses, using the MILC 2+1flavor asqtad ensembles. We use the Fermilab method for the $b$ quark. We obtain chiralcontinuum extrapolations for $E_K$ up to $\sim1.2$ GeV and then extend to the entire kinematic range with the modelindependent $z$ expansion.12/2013;  [Show abstract] [Hide abstract]
ABSTRACT: We calculate the kaon semileptonic form factor $f_+(0)$ from lattice QCD, working, for the first time, at the physical lightquark masses. We use gauge configurations generated by the MILC collaboration with $N_f=2+1+1$ flavors of sea quarks, which incorporate the effects of dynamical charm quarks as well as those of up, down, and strange. We employ data at three lattice spacings to extrapolate to the continuum limit. Our result, $f_+(0) = 0.9704(32)$, where the error is the total statistical plus systematic uncertainty added in quadrature, is the most precise determination to date. Combining our result with the latest experimental measurements of $K$ semileptonic decays, one obtains the CabibboKobayashiMaskawa matrix element $V_{us}=0.22290(74)(52)$, where the first error is from $f_+(0)$ and the second one is from experiment. In the firstrow test of CabibboKobayashiMaskawa unitarity, the error stemming from $V_{us}$ is now comparable to that from $V_{ud}$.12/2013;  [Show abstract] [Hide abstract]
ABSTRACT: We have analyzed the semileptonic decays $B\rightarrow D\ell\nu$ and $B\rightarrow D^*\ell\nu$ on the full suite of MILC (2+1)flavor asqtad ensembles with lattice spacings as small as 0.045 fm and lighttostrangequark mass ratios as low as 1/20. We use the Fermilab interpretation of the clover action for heavy valence quarks and the asqtad action for light valence quarks. We compute the hadronic form factors for $B\rightarrow D$ at both zero and nonzero recoil and for $B\rightarrow D^*$ at zero recoil. We report our results for $V_{cb}$.11/2013;  [Show abstract] [Hide abstract]
ABSTRACT: We update our determinations of $f_{D^+}$, $f_{D_s}$, $f_K$, and quark mass ratios from simulations with four flavors of HISQ dynamical quarks. The availability of ensembles with light quarks near their physical mass means that we can extract physical results with only small corrections for valence and seaquark mass mistunings instead of a chiral extrapolation. The adjusted valencequark masses and lattice spacings may be determined from an ensemblebyensemble analysis, and the results for the quark mass ratios then extrapolated to the continuum limit. Our central values of the charmed meson decay constants, however, come from an alternative analysis, which uses staggered chiral perturbation theory for the heavylight mesons, and allows us to incorporate data at unphysical quark masses where statistical errors are often smaller. A jackknife analysis propagated through all of these steps takes account of the correlations among all the quantities used in the analysis. Systematic errors from the finite spatial size and EM effects are estimated by varying the parameters in the analysis, and systematic errors from the assumptions in the continuum extrapolation are estimated from the spread of values from different extrapolations.11/2013;  [Show abstract] [Hide abstract]
ABSTRACT: We present results for the form factor $f_+^{K \pi}(0)$, needed to extract the CKM matrix element $V_{us}$ from experimental data on semileptonic $K$ decays, on the HISQ $N_f=2+1+1$ MILC configurations. The HISQ action is also used for the valence sector. The data set used for our final result includes three different values of the lattice spacing and data at the physical light quark masses. We discuss the error budget and how this calculation improves on our previous determination of $f_+^{K \pi}(0)$ on the asqtad $N_f=2+1$ MILC configurations.11/2013;  [Show abstract] [Hide abstract]
ABSTRACT: We present the status of our calculation of hadronic matrix elements for $D$ and $B$meson mixing. We use a large set of the MILC collaboration's $N_f=2+1$ asqtad ensembles, which includes lattice spacings in the range $a\approx0.12$0.045 fm, and up/down to strange quark mass ratios as low as 0.05. The asqtad action is also employed for the light valence quarks. For the heavy quarks we use the SheikholeslamiWohlert action with the Fermilab interpretation. Our calculation covers the complete set of five local operators needed to describe $B$meson mixing in the Standard Model and Beyond. In the charm sector, our calculation of local mixing matrix elements may be used to constrain new physics models. We present final correlator fit results on the full data set for the $B$meson mixing project and preliminary fit results for the $D$meson mixing project.11/2013; 
Article: $B\to\pi\ell\nu$ and $B\to\pi\ell^+\ell^$ semileptonic form factors from unquenched lattice QCD
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ABSTRACT: We update the lattice calculation of the $B\to\pi$ semileptonic form factors, which have important applications to the CKM matrix element $V_{ub}$ and the $B\to\pi\ell^+\ell^$ rare decay. We use MILC asqtad ensembles with $N_f=2+1$ sea quarks and over a range of lattice spacings $a \approx 0.045$$0.12$ fm. We perform a combined chiral and continuum extrapolation of our lattice data using SU(2) staggered chiral perturbation theory in the hard pion limit. To extend the results for the form factors to the full kinematic range, we take a functional approach to parameterize the form factors using the BourrelyCapriniLellouch formalism in a modelindependent way. Our analysis is still blinded with an unknown offset factor which will be disclosed when we present the final results.11/2013; 
Article: Charged Leptons
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ABSTRACT: This is the report of the Intensity Frontier Charged Lepton Working Group of the 2013 Community Summer Study "Snowmass on the Mississippi", summarizing the current status and future experimental opportunities in muon and tau lepton studies and their sensitivity to new physics. These include searches for charged lepton flavor violation, measurements of magnetic and electric dipole moments, and precision measurements of the decay spectrum and parityviolating asymmetries.11/2013;  [Show abstract] [Hide abstract]
ABSTRACT: We report on a calculation of the $B^*B\pi$ coupling in lattice QCD. The strong matrix element $\langle B \pi  B^*\rangle$ is directly related to the leading order lowenergy constant in heavy meson chiral perturbation theory (HM$\chi$PT) for $B$mesons. We carry out our calculation directly at the $b$quark mass using a nonperturbatively tuned clover action that controls discretisation effects of order $\vec{p}a$ and $(ma)^n$ for all $n$. Our analysis is performed on RBC/UKQCD gauge configurations using domain wall fermions and the Iwasaki gauge action at two lattice spacings of $a^{1}=1.73(3)$ GeV, $a^{1}=2.28(3)$ GeV, and unitary pion masses down to 290 MeV. We achieve good statistical precision and control all systematic uncertainties, giving a final result for the HM$\chi$PT coupling $g_b = 0.569(48)_{stat}(59)_{sys}$ in the continuum and at the physical lightquark masses. This is the first calculation performed directly at the physical $b$quark mass and lies in the region one would expect from carrying out an interpolation between previous results at the charm mass and at the static point.11/2013; 
Article: Symanzik flow on HISQ ensembles
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ABSTRACT: We report on a scale determination with gradientflow techniques on the $N_f = 2 + 1 + 1$ HISQ ensembles generated by the MILC collaboration. The lattice scale $w_0/a$, originally proposed by the BMW collaboration, is computed using Symanzik flow at four lattice spacings ranging from 0.15 to 0.06 fm. With a Taylor series ansatz, the results are simultaneously extrapolated to the continuum and interpolated to physical quark masses. We give a preliminary determination of the scale $w_0$ in physical units, along with associated systematic errors, and compare with results from other groups. We also present a first estimate of autocorrelation lengths as a function of flowtime for these ensembles.11/2013; 
Article: The form factors for B > pi l nu semileptonic decay from 2+1 flavors of domainwall fermions
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ABSTRACT: We present a calculation of the B > pi l nu form factors with domainwall light quarks and relativistic bquarks on the lattice. We work with the 2+1 flavor domainwall fermion and Iwasaki gaugefield ensembles generated by the RBC and UKQCD Collaborations. The chiralcontinuum extrapolation is performed using SU(2) hardpion chiral perturbation theory. To extrapolate the lattice form factors to the full kinematic range, we use the model independent zparameterization and impose the kinematic constraint f_+(0) = f_0(0) at zero momentum transfer.11/2013;  [Show abstract] [Hide abstract]
ABSTRACT: This report represents the response of the Intensity Frontier Quark Flavor Physics Working Group to the Snowmass charge. We summarize the current status of quark flavor physics and identify many exciting future opportunities for studying the properties of strange, charm, and bottom quarks. The ability of these studies to reveal the effects of new physics at high mass scales make them an essential ingredient in a wellbalanced experimental particle physics program.11/2013;  [Show abstract] [Hide abstract]
ABSTRACT: Dark sectors, consisting of new, light, weaklycoupled particles that do not interact with the known strong, weak, or electromagnetic forces, are a particularly compelling possibility for new physics. Nature may contain numerous dark sectors, each with their own beautiful structure, distinct particles, and forces. This review summarizes the physics motivation for dark sectors and the exciting opportunities for experimental exploration. It is the summary of the Intensity Frontier subgroup "New, Light, Weaklycoupled Particles" of the Community Summer Study 2013 (Snowmass). We discuss axions, which solve the strong CP problem and are an excellent dark matter candidate, and their generalization to axionlike particles. We also review dark photons and other darksector particles, including subGeV dark matter, which are theoretically natural, provide for dark matter candidates or new dark matter interactions, and could resolve outstanding puzzles in particle and astroparticle physics. In many cases, the exploration of dark sectors can proceed with existing facilities and comparatively modest experiments. A rich, diverse, and lowcost experimental program has been identified that has the potential for one or more gamechanging discoveries. These physics opportunities should be vigorously pursued in the US and elsewhere.10/2013;
Publication Stats
1k  Citations  
140.30  Total Impact Points  
Top Journals
Institutions

2006–2013

Fermi National Accelerator Laboratory (Fermilab)
 Theoretical Physics Department
Batavia, Illinois, United States


2012

Seoul National University
 Department of Physics and Astronomy
Sŏul, Seoul, South Korea


2009–2012

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


2008–2012

Los Alamos National Laboratory
Los Alamos, California, United States 
University of Alabama
Tuscaloosa, Alabama, United States


2007–2009

Columbia University
 Department of Physics
New York City, NY, United States


2003–2006

University of Washington Seattle
 Department of Physics
Seattle, WA, United States
