Publications (157)176.94 Total impact
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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.01/2015;  [Show abstract] [Hide abstract]
ABSTRACT: We present the status of our updated D and Bmeson decayconstant analysis, based on the MILC $N_f = 2+1$ asqtad gauge ensembles. Heavy quarks are incorporated using the Wilson clover action with the Fermilab interpretation. This analysis includes ensembles at five lattice spacings from a $\approx$ 0.045 to 0.15 fm, and light seaquark masses down to 1/20th of the strangequark mass. Projected error budgets for ratios of decay constants, in particular between bottom and charmmeson decay constants, are presented.01/2015;  [Show abstract] [Hide abstract]
ABSTRACT: We report on the status of our calculation of the hadronic matrix elements for neutral $B$meson mixing with asqtad sea and valence light quarks and using the Wilson clover action with the Fermilab interpretation for the $b$ quark. We calculate the matrix elements of all five local operators that contribute to neutral $B$meson mixing both in and beyond the Standard Model. We use MILC ensembles with $N_f=2+1$ dynamical flavors at four different lattice spacings in the range $a \approx 0.045$$0.12$~fm, and with light seaquark masses as low as 0.05 times the physical strange quark mass. We perform a combined chiralcontinuum extrapolation including the socalled wrongspin contributions in simultaneous fits to the matrix elements of the five operators. We present a complete systematic error budget and conclude with an outlook for obtaining final results from this analysis.12/2014;  [Show abstract] [Hide abstract]
ABSTRACT: We present an update on our calculation of the shortdistance $D^0$meson mixing hadronic matrix elements. The analysis is performed on the MILC collaboration's $N_f=2+1$ asqtad configurations. We use asqtad light valence quarks and the SheikoleslamiWohlert action with the Fermilab interpretation for the valence charm quark. SU(3), partially quenched, rooted, staggered heavymeson chiral perturbation theory is used to extrapolate to the chiralcontinuum limit. Systematic errors arising from the chiralcontinuum extrapolation, heavyquark discretization, and quarkmass uncertainties are folded into the statistical errors from the chiralcontinuum fits with methods of Bayesian inference. A preliminary error budget for all five operators is presented.11/2014;  [Show abstract] [Hide abstract]
ABSTRACT: We compute the $B\to\pi\ell\nu$ semileptonic form factors and update the determination of the CKM matrix element $V_{ub}$. We use the MILC asqtad ensembles with $N_f=2+1$ sea quarks at four different lattice spacings in the range $a \approx 0.045$~fm to $0.12$~fm. The lattice form factors are extrapolated to the continuum limit using SU(2) staggered chiral perturbation theory in the hard pion limit, followed by an extrapolation in $q^2$ to the full kinematic range using a functional $z$parameterization. The extrapolation is combined with the experimental measurements of the partial branching fraction to extract $V_{ub}$. Our preliminary result is $V_{ub}=(3.72\pm 0.14)\times 10^{3}$, where the error reflects both the lattice and experimental uncertainties, which are now on par with each other.11/2014;  [Show abstract] [Hide abstract]
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. We use the MILC highly improved staggered quark (HISQ) ensembles with four dynamical quark flavors. 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. 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.11/2014;  [Show abstract] [Hide abstract]
ABSTRACT: We report on a preliminary scale determination with gradientflow techniques on the $N_f = 2 + 1 + 1$ HISQ ensembles generated by the MILC collaboration. The ensembles include four lattice spacings, ranging from 0.15 to 0.06 fm, and both physical and unphysical values of the quark masses. The scales $\sqrt{t_0}/a$ and $w_0/a$ are computed using Symanzik flow and the cloverleaf definition of $\langle E \rangle$ on each ensemble. Then both scales and the meson masses $aM_\pi$ and $aM_K$ are adjusted for mistunings in the charm mass. Using a combination of continuum chiral perturbation theory and a Taylor series ansatz in the lattice spacing, the results are simultaneously extrapolated to the continuum and interpolated to physical quark masses. Our preliminary results are $\sqrt{t_0} = 0.1422(7)$fm and $w_0 = 0.1732(10)$fm. We also find the continuum massdependence of $w_0$.11/2014;  [Show abstract] [Hide abstract]
ABSTRACT: We report on the MILC Collaboration calculation of electromagnetic effects on light pseudoscalar mesons. The simulations employ asqtad staggered dynamical quarks in QCD plus quenched photons, with lattice spacings varying from 0.12 to 0.06 fm. Finite volume corrections for the MILC realization of lattice electrodynamics have been calculated in chiral perturbation theory and applied to the lattice data. These corrections differ from those calculated by Hayakawa and Uno because our treatment of zero modes differs from theirs. Updated results for the corrections to "Dashen's theorem" are presented.09/2014;  [Show abstract] [Hide abstract]
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;
Publication Stats
1k  Citations  
176.94  Total Impact Points  
Top Journals
Institutions

2006–2014

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, New York, 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
