Publications (163)274.14 Total impact
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ABSTRACT: We report on a calculation of the B*Bpi coupling in lattice QCD. The strong matrix element for a B* to Bpi transition is directly related to the leading order lowenergy constant in heavy meson chiral perturbation theory (HMChPT) for B mesons. We carry out our calculation directly at the bquark mass using a nonperturbatively tuned clover action that controls discretization effects of order pa and (ma)^n for all n. Our analysis is performed on RBC/UKQCD gauge configurations using domainwall fermions and the Iwasaki gauge action at two lattice spacings of ainverse = 1.729(25) GeV, ainverse = 2.281(28) 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 HMChPT coupling g_b = 0.56(3)stat(7)sys in the continuum and at the physical lightquark masses. This is the first calculation performed directly at the physical bquark 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.  [Show abstract] [Hide abstract]
ABSTRACT: The second workshop to discuss the development of liquid argon time projection chambers (LArTPCs) in the United States was held at Fermilab on July 89, 2014. The workshop was organized under the auspices of the Coordinating Panel for Advanced Detectors, a body that was initiated by the American Physical Society Division of Particles and Fields. All presentations at the workshop were made in six topical plenary sessions: $i)$ Argon Purity and Cryogenics, $ii)$ TPC and High Voltage, $iii)$ Electronics, Data Acquisition and Triggering, $iv)$ Scintillation Light Detection, $v)$ Calibration and Test Beams, and $vi)$ Software. This document summarizes the current efforts in each of these areas. It primarily focuses on the work in the US, but also highlights work done elsewhere in the world.Journal of Instrumentation 04/2015; 9(05). DOI:10.1088/17480221/9/05/T05005 · 1.53 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We present a latticeQCD calculation of the $B\to\pi\ell\nu$ semileptonic form factors and a new determination of the CKM matrix element $V_{ub}$. We use the MILC asqtad 2+1flavor lattice configurations at four lattice spacings and lightquark masses down to 1/20 of the physical strangequark mass. We extrapolate the lattice form factors to the continuum using staggered chiral perturbation theory in the hardpion and SU(2) limits. We employ a modelindependent $z$ parameterization to extrapolate our lattice form factors from largerecoil momentum to the full kinematic range. We introduce a new functional method to propagate information from the chiralcontinuum extrapolation to the $z$ expansion. We present our results together with a complete systematic error budget, including a covariance matrix to enable the combination of our form factors with other latticeQCD and experimental results. To obtain $V_{ub}$, we simultaneously fit the experimental data for the $B\to\pi\ell\nu$ differential decay rate obtained by the BaBar and Belle collaborations together with our lattice formfactor results. We find $V_{ub}=(3.72\pm 0.16)\times 10^{3}$ where the error is from the combined fit to lattice plus experiments and includes all sources of uncertainty. Our formfactor results bring the QCD error on $V_{ub}$ to the same level as the experimental error. We also provide results for the $B\to\pi\ell\nu$ vector and scalar form factors obtained from the combined lattice and experiment fit, which are more preciselydetermined than from our latticeQCD calculation alone. These results can be used in other phenomenological applications and to test other approaches to QCD. 
Article: The $B \to D \ell \nu$ form factors at nonzero recoil and $V_{cb}$ from $2+1$flavor lattice QCD
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ABSTRACT: We present the first unquenched latticeQCD calculation of the hadronic form factors for the exclusive decay $\overline{B} \rightarrow D \ell \overline{\nu}$ at nonzero recoil. We carry out numerical simulations on fourteen ensembles of gaugefield configurations generated with 2+1 flavors of asqtadimproved staggered sea quarks. The ensembles encompass a wide range of lattice spacings (approximately 0.045 to 0.12 fm) and ratios of light (up and down) to strange seaquark masses ranging from 0.05 to 0.4. For the $b$ and $c$ valence quarks we use improved Wilson fermions with the Fermilab interpretation, while for the light valence quarks we use asqtadimproved staggered fermions. We extrapolate our results to the physical point using rooted staggered heavylight meson chiral perturbation theory. We then parameterize the form factors and extend them to the full kinematic range using modelindependent functions based on analyticity and unitarity. We present our final results for $f_+(q^2)$ and $f_0(q^2)$, including statistical and systematic errors, as coefficients of a series in the variable $z$ and the covariance matrix between these coefficients. We then fit the lattice formfactor data jointly with the experimentally measured differential decay rate from BaBar to determine the CKM matrix element, $V_{cb}=(39.6 \pm 1.7_{\rm QCD+exp} \pm 0.2_{\rm QED})\times 10^{3}$. As a byproduct of the joint fit we obtain the form factors with improved precision at large recoil. Finally, we use them to update our calculation of the ratio $R(D)$ in the Standard Model, which yields $R(D) = 0.299(11)$.  [Show abstract] [Hide abstract]
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 ensembles include four lattice spacings, ranging from approximately 0.15 to 0.06 fm, and both physical and unphysical values of the quark masses. The scales $\sqrt{t_0}/a$ and $w_0/a$ and their treelevel improvements, $\sqrt{t_{0,{\rm imp}}}$ and $w_{0,{\rm imp}}$, are computed on each ensemble using Symanzik flow and the cloverleaf definition of the energy density $E$. Using a combination of continuum chiral perturbation theory and a Taylorseries ansatz for the latticespacing and strongcoupling dependence, the results are simultaneously extrapolated to the continuum and interpolated to physical quark masses. We determine the scales $\sqrt{t_0} = 0.1416({}_{5}^{+8})$ fm and $w_0 = 0.1717({}_{11}^{+12})$ fm, where the errors are sums, in quadrature, of statistical and all systematic errors. The precision of $w_0$ and $\sqrt{t_0}$ is comparable to or more precise than the best previous estimates, respectively. We also find the continuum massdependence of $w_0$ that will be useful for estimating the scales of other ensembles. We also estimate the integrated autocorrelation length of $\langle E(t) \rangle$. For long flow times, the autocorrelation length of $\langle E \rangle$ appears to be comparable to or smaller than that of the topological charge.  [Show abstract] [Hide abstract]
ABSTRACT: A ShortBaseline Neutrino (SBN) physics program of three LArTPC detectors located along the Booster Neutrino Beam (BNB) at Fermilab is presented. This new SBN Program will deliver a rich and compelling physics opportunity, including the ability to resolve a class of experimental anomalies in neutrino physics and to perform the most sensitive search to date for sterile neutrinos at the eV massscale through both appearance and disappearance oscillation channels. Using data sets of 6.6e20 protons on target (P.O.T.) in the LAr1ND and ICARUS T600 detectors plus 13.2e20 P.O.T. in the MicroBooNE detector, we estimate that a search for muon neutrino to electron neutrino appearance can be performed with ~5 sigma sensitivity for the LSND allowed (99% C.L.) parameter region. In this proposal for the SBN Program, we describe the physics analysis, the conceptual design of the LAr1ND detector, the design and refurbishment of the T600 detector, the necessary infrastructure required to execute the program, and a possible reconfiguration of the BNB target and horn system to improve its performance for oscillation searches.  [Show abstract] [Hide abstract]
ABSTRACT: At the 17th JPARC PAC, which was held on September 2013, we proposed the sterile neutrino search at JPARC MLF. After reviewing the proposal, PAC recommended to have a background measurement at the detector's candidate site location in their report to investigate whether the background rates can be manageable for the real experiment or not. Therefore, we have performed the background measurements (MLF; 2013BU1301 test experiment) during the summer of 2014, also following the 18th JPARC PAC recommendations, and the measurements results are described here.  [Show abstract] [Hide abstract]
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.  [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.  [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.  [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.  [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.  [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.  [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 $w_0$.  [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.  [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.Physical Review D 07/2014; 90(7). DOI:10.1103/PhysRevD.90.074509 · 4.86 Impact Factor  [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.  [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.  [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.
Publication Stats
2k  Citations  
274.14  Total Impact Points  
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Institutions

2008–2015

Los Alamos National Laboratory
 Materials Physics and Applications Division
ЛосАламос, California, United States 
Bucknell University
Lewisburg, Pennsylvania, United States


2006–2015

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


2009–2012

Brookhaven National Laboratory
 Physics Department
New York City, New York, United States 
University of Alabama
Tuscaloosa, Alabama, United States 
Louisiana State University
 Department of Physics & Astronomy
Baton Rouge, Louisiana, United States


2003–2006

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