Publications (69)134.55 Total impact
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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. · 7.94 Impact Factor  [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: The spectral functions of QCD can give us insight into properties of hadrons, and they are useful in probing the QCD vacuum. I will discuss the correlators and spectral functions of charmonium in high temperature two flavour QCD. The spectral functions have been obtained using the Maximum Entropy Method from anisotropic lattice data using the conserved vector current. This work has been done as part of the FASTSUM collaboration. We find that the spectral functions for zero momentum are stable. At nonzero momentum the spectral functions are less stable but still produce resonance and transport peaks. This work is part of our programme to calculate the heavy quark diffusion constant.12/2013;  [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; 
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;  [show abstract] [hide abstract]
ABSTRACT: We report on the calculation by the MILC Collaboration of the electromagnetic effects on kaon and pion masses. These masses are computed in QCD with dynamical (asqtad staggered) quarks plus quenched photons at three lattice spacings varying from 0.12 to 0.06 fm. The masses are fit to staggered chiral perturbation theory with NLO electromagnetic terms, as well as analytic terms at higher order. We extrapolate the results to physical lightquark masses and to the continuum limit. At the current stage of the analysis, most, but not all, of the systematic errors have been estimated. The main goal is the comparison of kaon electromagnetic splittings to those of the pion, i.e., an evaluation of the corrections to "Dashen's theorem." This in turn will allow us to significantly reduce the systematic errors in our determination of m_u/m_d.01/2013; 
Article: Kaon semileptonic vector form factor and determination of V_{us} using staggered fermions
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ABSTRACT: Using staggered fermions and twisted boundary conditions, we calculate the K meson semileptonic decay vector form factor at zero momentum transfer. The HISQ formulation is used for the valence quarks, while the sea quarks are simulated with the asqtad action (MILC N_f=2+1 configurations). For the chiral and continuum extrapolation we use twoloop continuum CHPT, supplemented by partially quenched staggered CHPT at one loop. Our result is f_+^{K\pi}(0) = 0.9667+0.0023+0.0033, where the first error is statistical and the second is the sum in quadrature of the systematic uncertainties. This result is the first N_f=2+1 calculation with two lattice spacings and a controlled continuum extrapolation. It is also the most precise result to date for the vector form factor and, although the central value is larger than previous unquenched lattice calculations, it is compatible with them within errors. Combining our value for f_+^{K\pi}(0) with the latest experimental measurements of K semileptonic decays, we obtain V_{us} = 0.2238+0.0009+0.0005, where the first error is from f_+^{K\pi}(0) and the second one is experimental. As a byproduct of our calculation, we obtain the combination of lowenergy constants [C_{12}^r+C_{34}^r(L_5^r)^2](M_\rho) = (3.62+1.00)x10^{6}.Physical review D: Particles and fields 12/2012; 87(7).  [show abstract] [hide abstract]
ABSTRACT: We study the temperature dependence of bottomonium for temperatures in the range 0.4 Tc < T < 2.1 Tc, using nonrelativistic dynamics for the bottom quark and full relativistic lattice QCD simulations for Nf=2 light flavors. We consider the behaviour of the correlators in Euclidean space, we analyze the associated spectral functions and we study the dependence on the momentum. Our results are amenable to a successful comparison with effective field theories. They help build a coherent picture of the behaviour of bottomonium in the plasma, consistent which the current LHC results.Journal of Physics Conference Series 12/2012; 432(1).  [show abstract] [hide abstract]
ABSTRACT: We present our methods to fit the two point correlators for light, strange, and charmed pseudoscalar meson physics with the highly improved staggered quark (HISQ) action. We make use of the leastsquares fit including the full covariance matrix of the correlators and including Gaussian constraints on some parameters. We fit the correlators on a variety of the HISQ ensembles. The lattice spacing ranges from 0.15 fm down to 0.06 fm. The light sea quark mass ranges from 0.2 times the strange quark mass down to the physical light quark mass. The HISQ ensembles also include lattices with different volumes and with unphysical values of the strange quark mass. We use the results from this work to obtain our preliminary results of $f_D$, $f_{D_s}$, $f_{D_s}/f_{D}$, and ratios of quark masses presented in another talk [1].12/2012;  [show abstract] [hide abstract]
ABSTRACT: We report on the status of our kaon semileptonic form factor calculations using the highlyimproved staggered quark (HISQ) formulation to simulate the valence fermions. We present results for the form factor f_+^{K \pi}(0) on the asqtad N_f=2+1 MILC configurations, discuss the chiralcontinuum extrapolation, and give a preliminary estimate of the total error. We also present a more preliminary set of results for the same form factor but with the sea quarks also simulated with the HISQ action; these results include data at the physical light quark masses. The improvements that we expect to achieve with the use of the HISQ configurations and simulations at the physical quark masses are briefly discussed.11/2012;  [show abstract] [hide abstract]
ABSTRACT: We present preliminary results for light, strange and charmed pseudoscalar meson physics from simulations using four flavors of dynamical quarks with the highly improved staggered quark (HISQ) action. These simulations include lattice spacings ranging from 0.15 to 0.06 fm, and seaquark masses both above and at their physical value. The major results are charm meson decay constants f_D, f_{D_s} and f_{D_s}/f_D and ratios of quark masses. This talk will focus on our procedures for finding the decay constants on each ensemble, the continuum extrapolation, and estimates of systematic error.10/2012;  [show abstract] [hide abstract]
ABSTRACT: We calculate pseudoscalar masses on gauge configurations containing the effects of 2+1 flavors of dynamical asqtad quarks and quenched electromagnetism. The lattice spacings vary from 0.12 to 0.06 fm. The masses are fit with staggered chiral perturbation theory including NLO electromagnetic terms. We attempt to extract the fit parameters for the electromagnetic contributions, while taking into account the finite volume effects, and extrapolate them to the physical limit.10/2012;  [show abstract] [hide abstract]
ABSTRACT: Using NonRelativistic QCD (NRQCD), we study heavy quark mass dependence of Swave and Pwave bottomonium correlators for 0.42Tc <= T <= 2.09Tc and study spectral functions of Swave bottomonium states moving in a thermal bath at these temperatures using Maximum Entropy Method with NRQCD kernel. For the studied momentum range, the energy of moving states shows quadratic momentumdependence and the width of moving states does not show significant changes as the momentum of bottomonium is increased. Also, we find that in correlator ratios, the temperature effect is larger than the effect caused by 20% change in the bottom quark mass.10/2012;  [show abstract] [hide abstract]
ABSTRACT: We extend our study of bottomonium spectral functions in the quarkgluon plasma to nonzero momentum. We use lattice QCD simulations with two flavours of light quark on highly anisotropic lattices and treat the bottom quark with nonrelativistic QCD (NRQCD). We focus on S wave (Upsilon and eta_b) channels and consider nonrelativistic velocities, v/c < 0.2. A comparison with predictions from effective field theory is made.Journal of High Energy Physics 10/2012; 2013(3). · 5.62 Impact Factor  [show abstract] [hide abstract]
ABSTRACT: The semileptonic decay channel B→Dτν is sensitive to the presence of a scalar current, such as that mediated by a chargedHiggs boson. Recently, the BABAR experiment reported the first observation of the exclusive semileptonic decay B→Dτν̅ , finding an approximately 2σ disagreement with the standardmodel prediction for the ratio R(D)=BR(B→Dτν)/BR(B→Dℓν), where ℓ=e,μ. We compute this ratio of branching fractions using hadronic form factors computed in unquenched lattice QCD and obtain R(D)=0.316(12)(7), where the errors are statistical and total systematic, respectively. This result is the first standardmodel calculation of R(D) from ab initio full QCD. Its error is smaller than that of previous estimates, primarily due to the reduced uncertainty in the scalar form factor f0(q2). Our determination of R(D) is approximately 1σ higher than previous estimates and, thus, reduces the tension with experiment. We also compute R(D) in models with electrically charged scalar exchange, such as the typeII twoHiggsdoublet model. Once again, our result is consistent with, but approximately 1σ higher than, previous estimates for phenomenologically relevant values of the scalar coupling in the typeII model. As a byproduct of our calculation, we also present the standardmodel prediction for the longitudinalpolarization ratio PL(D)=0.325(4)(3).Physical Review Letters 08/2012; 109(7). · 7.94 Impact Factor  [show abstract] [hide abstract]
ABSTRACT: We study SU(3)breaking effects in the neutral BdB̅ d and BsB̅ s systems with unquenched Nf=2+1 lattice quantum chromodynamics (QCD). We calculate the relevant matrix elements on the MILC collaboration’s gauge configurations with asqtadimproved staggered sea quarks. For the valence lightquarks (u, d, and s) we use the asqtad action, while for b quarks we use the Fermilab action. We obtain ξ=fBs√BBs/fBd√BBd=1.268±0.063. We also present results for the ratio of bag parameters BBs/BBd and the ratio of CabibboKobayashiMaskawa matrix elements Vtd/Vts. Although we focus on the calculation of ξ, the strategy and techniques described here will be employed in future extended studies of the B mixing parameters ΔMd,s and ΔΓd,s in the standard model and beyond.Physical Review D 08/2012; 86(3). · 4.69 Impact Factor  Physical review D: Particles and fields 08/2012; 86(3).
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ABSTRACT: We calculate formfactor ratios between the semileptonic decays B̅ 0→D+ℓν̅ and B̅ s0→Ds+ℓν̅ with lattice QCD. These ratios are a key theoretical input in a new strategy to determine the fragmentation fractions of neutral B decays, which are needed for measurements of BR(Bs0→μ+μ). We use the MILC ensembles of gauge configurations with 2+1 flavors of seaquarks at two s of approximately 0.12 fm and 0.09 fm. We use the modelindependent z parametrization to extrapolate our simulation results at small recoil toward maximum recoil. Our results for the formfactor ratios are f0(s)(Mπ2)/f0(d)(MK2)=1.046(44)stat(15)syst and f0(s)(Mπ2)/f0(d)(Mπ2)=1.054(47)stat(17)syst. In contrast to a QCD sumrule calculation, no significant departure from Uspin (d↔s) symmetry is observed.Physical review D: Particles and fields 06/2012; 85(11).
Publication Stats
192  Citations  
134.55  Total Impact Points  
Top Journals
Institutions

2009–2012

University of Utah
 Department of Physics and Astronomy
Salt Lake City, Utah, United States


2011

Swansea University
 Department of Physics
Swansea, WLS, United Kingdom


2002–2010

University of Illinois, UrbanaChampaign
 Department of Physics
Urbana, IL, United States


2005–2007

Trinity College Dublin
 School of Mathematics
Dublin, L, Ireland 
Washington University in St. Louis
 Department of Physics
Saint Louis, MO, United States


2005–2006

Trinity College
 Mathematics
Hartford, Connecticut, United States


1998–2000

University of Iowa
 Department of Physics and Astronomy
Iowa City, IA, United States
