Publications (214)578.12 Total impact
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ABSTRACT: The exclusive semileptonic decay B→πℓν is a key process for the determination of the CabibboKobayashiMaskawa matrix element Vub from the comparison of experimental rates as a function of q2 with theoretically determined form factors. The sensitivity of the form factors to the u/d quark mass has meant significant systematic uncertainties in lattice QCD calculations at unphysically heavy pion masses. Here, we give the first lattice QCD calculations of this process for u/d quark masses going down to their physical values, calculating the f0 form factor at zero recoil to 3%. We are able to resolve a longstanding controversy by showing that the softpion theorem result f0(qmax2)=fB/fπ does hold as mπ→0. We use the highly improved staggered quark formalism for the light quarks and show that staggered chiral perturbation theory for the mπ dependence is almost identical to continuum chiral perturbation theory for f0, fB, and fπ. We also give results for other processes such as Bs→Kℓν.  [Show abstract] [Hide abstract]
ABSTRACT: We determine the contribution to the anomalous magnetic moment of the muon from the $\alpha^2_{\mathrm{QED}}$ hadronic vacuum polarization diagram using full lattice QCD and including $u/d$ quarks with physical masses for the first time. We use gluon field configurations that include $u$, $d$, $s$ and $c$ quarks in the sea at multiple values of the lattice spacing, multiple $u/d$ masses and multiple volumes that allow us to include an analysis of finitevolume effects. We obtain a result for $a_{\mu}^{\mathrm{HVP,LO}}$ of $666(6)(12)$, where the first error is from the lattice calculation and the second includes systematic errors from missing QED and isospinbreaking effects and from quarkline disconnected diagrams. Our result implies a discrepancy between the experimental determination of $a_{\mu}$ and the Standard Model of 3$\sigma$.  [Show abstract] [Hide abstract]
ABSTRACT: The quarkline disconnected diagram is a potentially important ingredient in lattice QCD calculations of the hadronic vacuum polarization contribution to the anomalous magnetic moment of the muon. It is also a notoriously difficult one to evaluate. Here, for the first time, we give an estimate of this contribution based on lattice QCD results that have a statistically significant signal, albeit at one value of the lattice spacing and an unphysically heavy value of the $u/d$ quark mass. We use HPQCD's method of determining the anomalous magnetic moment by reconstructing the Adler function from timemoments of the currentcurrent correlator at zero spatial momentum. Our results lead to a total (including $u$, $d$ and $s$ quarks) quarkline disconnected contribution to $a_{\mu}$ of $0.15\%$ of the $u/d$ hadronic vacuum polarization contribution with an uncertainty which is 1\% of that contribution.  [Show abstract] [Hide abstract]
ABSTRACT: We present the first calculation of the electromagnetic form factor of the $\pi$ meson at physical light quark masses. We use configurations generated by the MILC collaboration including the effect of $u$, $d$, $s$ and $c$ sea quarks with the Highly Improved Staggered Quark formalism. We work at three values of the lattice spacing on large volumes and with $u$/$d$ quark masses going down to the physical value. We study scalar and vector form factors for a range in spacelike $q^2$ from 0.0 to 0.1 $\mathrm{GeV}^2$ and from their shape we extract mean square radii. Our vector form factor agrees well with experiment and we find $\langle r^2 \rangle_V = 0.403(18)(6) \,\mathrm{fm}^2$. For the scalar form factor we include quarkline disconnected contributions which have a significant impact on the radius. We give the first results for SU(3) flavoursinglet and octet scalar mean square radii, obtaining: $\langle r^2 \rangle_S^{\mathrm{singlet}} = 0.506(38)(53) \mathrm{fm}^2$ and $\langle r^2 \rangle_S^{\mathrm{octet}} = 0.431(38)(46) \mathrm{fm}^2$. We discuss the comparison with expectations from chiral perturbation theory.  [Show abstract] [Hide abstract]
ABSTRACT: We report our (HPQCD) progress on the calculation of the Hadronic Vacuum Polarisation contribution to the anomalous magnetic moment of muon. In this article we discuss the calculations for the light (up/down) quark connected contribution using our method described in Phys.Rev. D89(2014) 11, 114501 and give an estimate for the disconnected contribution. Our calculation has been carried out on MILC Collaboration's $n_f = 2+1+1$ HISQ ensembles at multiple values of the lattice spacing, multiple volumes and multiple light sea quark masses (including physical pion mass configurations). 
Conference Paper: Phenomenology with Lattice NRQCD b Quarks
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ABSTRACT: The HPQCD collaboration has used radiativelyimproved NonRelativistic QCD (NRQCD) for $b$ quarks in bottomonium to determine the decay rate of $\Upsilon$ and $\Upsilon^\prime$ mesons to leptons in lattice QCD. Using timemoments of vector bottomonium currentcurrent correlators, we are also able to determine the $b$ quark mass in the $\overline{\mathrm{MS}}$ scheme. We use the same NRQCD $b$ quarks and Highly Improved Staggered Quark (HISQ) light quarks  with masses down to their physical values  to give a complete picture of heavylight meson decay constants including those for vector mesons. We also study the semileptonic $B\rightarrow\pi\ell\nu$ decay at zero recoil to show that lattice QCD is consistent with the soft pion theorem for this decay: $f_0(q^2_{\mathrm{max}})=f_B/f_\pi$ in the massless pion limit. Finally, we present preliminary results for the $B_c \rightarrow \eta_c \ell \nu$ semileptonic decay form factors. This is a showcase for the comparison of results for NRQCD $b$ quarks with those from HISQ $b$ quarks (both with HISQ $c$ quarks). We give the first 3point results from our `heavy HISQ' programme, which will allow us to improve the normalisation of NRQCDHISQ currents for other calculations.  [Show abstract] [Hide abstract]
ABSTRACT: The exclusive semileptonic decay $B \rightarrow \pi \ell \nu$ is a key process for the determination of the CabibboKobayashiMaskawa matrix element $V_{ub}$ from the comparison of experimental rates as a function of $q^2$ with theoretically determined form factors. The sensitivity of the form factors to the $u/d$ quark mass has meant significant systematic uncertainties in lattice QCD calculations at unphysically heavy pion masses. Here we give the first lattice QCD calculations of this process for u/d quark masses going down to their physical values, calculating the $f_0$ form factor at zero recoil to 3\%. We are able to resolve a longstanding controversy by showing that the softpion theorem result $f_0(q^2_{max}) = f_B/f_{\pi}$ does hold as $m_{\pi} \rightarrow 0$. We use the Highly Improved Staggered Quark formalism for the light quarks and show that staggered chiral perturbation theory for the $m_{\pi}$ dependence is almost identical to continuum chiral perturbation theory for $f_0$, $f_B$ and $f_{\pi}$. We also give results for other processes such as $B_s \rightarrow K \ell \nu$.  [Show abstract] [Hide abstract]
ABSTRACT: We present a lattice QCD calculation of the $B \rightarrow D l \nu$ semileptonic decay form factors $f_+(q^2)$ and $f_0(q^2)$ for the entire physical $q^2$ range. Nonrelativistic QCD (NRQCD) bottom quarks and Highly Improved Staggered Quark (HISQ) charm and light quarks are employed together with $N_f = 2+1$ MILC gauge configurations. A joint fit to our lattice and BaBar experimental data allows an extraction of the CKM matrix element $V_{cb}$. We also determine the phenomenologically interesting ratio $R(D) = {\cal B}(B \rightarrow D \tau \nu_\tau) / {\cal B}(B \rightarrow D l \nu_l)$ ($l = e, \mu$). We find $V_{cb}_{excl.}^{B \rightarrow D} = 0.0402(17)(13)$, where the first error consists of the lattice simulation errors and the experimental statistical error and the second error is the experimental systematic error. For the branching fraction ratio we find $R(D) = 0.300(8)$.  [Show abstract] [Hide abstract]
ABSTRACT: We extend the picture of $B$meson decay constants obtained in lattice QCD beyond those of the $B$, $B_s$ and $B_c$ to give the first full lattice QCD results for the $B^*$, $B^*_s$ and $B^*_c$. We use improved NonRelativistic QCD for the valence $b$ quark and the Highly Improved Staggered Quark (HISQ) action for the lighter quarks on gluon field configurations that include the effect of $u/d$, $s$ and $c$ quarks in the sea with $u/d$ quark masses going down to physical values. For the ratio of vector to pseudoscalar decay constants, we find $f_{B^*}/f_B$ = 0.941(26), $f_{B^*_s}/f_{B_s}$ = 0.953(23) (both $2\sigma$ less than 1.0) and $f_{B^*_c}/f_{B_c}$ = 0.988(27). Taking correlated uncertainties into account we see clear indications that the ratio increases as the mass of the lighter quark increases. We compare our results to those using the HISQ formalism for all quarks and find good agreement both on decay constant values when the heaviest quark is a $b$ and on the dependence on the mass of the heaviest quark in the region of the $b$. Finally, we give an overview plot of decay constants for goldplated mesons, the most complete picture of these hadronic parameters to date.  [Show abstract] [Hide abstract]
ABSTRACT: We present the first lattice QCD calculation of the $B_s$ and $B_d$ mixing parameters with physical light quark masses. We use MILC gluon field configurations that include $u$, $d$, $s$ and $c$ sea quarks at 3 values of the lattice spacing and with 3 values of the $u/d$ quark mass going down to the physical value. We use improved NRQCD for the valence $b$ quarks. Preliminary results show significant improvements over earlier values.  [Show abstract] [Hide abstract]
ABSTRACT: The charmonium system has several excited states below the energy threshold for decay into $D$ and $\bar{D}$ mesons, which can in principle be studied accurately in lattice QCD. Studies that include many states in the spectrum have typically only been done at one value of the lattice spacing and with relatively heavy light quarks in the sea. Here we give preliminary results for radial and orbital excitation energies for charmonium from a calculation on 2+1+1 MILC configurations at multiple lattice spacings and including physical values for $u/d$ quark masses. We use the HISQ formulation for $c$ to obtain small discretisation errors and smeared operators to improve excited state overlap.  [Show abstract] [Hide abstract]
ABSTRACT: We describe a new technique (presented in arXiv:1403.1778) to determine the contribution to the anomalous magnetic moment (g2) of the muon coming from the hadronic vacuum polarisation using lattice QCD. Our method uses Pad\'{e} approximants to reconstruct the Adler function from its derivatives at $q^2=0$. These are obtained simply and accurately from timemoments of the vector currentcurrent correlator at zero spatial momentum. We test the method using strange quark correlators calculated on MILC Collaboration's $n_f$ = 2+1+1 HISQ ensembles at multiple values of the lattice spacing, multiple volumes and multiple light sea quark masses (including physical pion mass configurations). 
Article: The $\Upsilon$ and $\Upsilon^{\prime}$ Leptonic Widths, $a_{\mu}^b$ and $m_b$ from full lattice QCD
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ABSTRACT: We determine the decay rate to leptons of the groundstate $\Upsilon$ meson and its first radial excitation in lattice QCD for the first time. We use radiativelyimproved NRQCD for the $b$ quarks and include $u$, $d$, $s$ and $c$ quarks in the sea with $u/d$ masses down to their physical values. We find $\Gamma(\Upsilon \rightarrow e^+e^)$ = 1.19(11) keV and $\Gamma(\Upsilon^{\prime} \rightarrow e^+e^)$ = 0.69(9) keV, both in good agreement with experiment. The decay constants we obtain are included in a summary plot of meson decay constants from lattice QCD given in the Conclusions. We also test timemoments of the vector currentcurrent correlator against values determined from the $b$ quark contribution to $\sigma(e^+e^ \rightarrow \mathrm{hadrons})$ and calculate the $b$quark piece of the hadronic vacuum polarisation contribution to the anomalous magnetic moment of the muon, $a_{\mu}^b = 0.271(37) \times 10^{10}$. Finally we determine the $b$quark mass, obtaining in the $\overline{MS}$ scheme, $\overline{m}_b(\overline{m}_b, n_f=5)$ = 4.196(23) GeV, the most accurate result from lattice QCD to date.  [Show abstract] [Hide abstract]
ABSTRACT: We present a new lattice QCD analysis of heavyquark pseudoscalarpseudoscalar correlators, using gluon configurations from the MILC collaboration that include vacuum polarization from $u$, $d$, $s$ and $c$ quarks ($n_f=4$). We extract new values for the QCD coupling and for the $c$ quark's $\mathrm{\overline{MS}}$ mass: $\alpha_\mathrm{\overline{MS}}(M_Z,n_f=5) = 0.11881(86)$ and $m_c(3\,\mathrm{GeV}, n_f=4) = 0.9896(69)$GeV. These agree well with our earlier simulations using $n_f=3$ sea quarks, vindicating the perturbative treatment of $c$ quarks in that analysis. A joint $n_f=3$, $n_f=4$ analysis gives improved values for the coupling and heavyquark masses: $\alpha_\mathrm{\overline{MS}}(M_Z,n_f=5) = 0.11856(53)$, $m_c(3\,\mathrm{GeV}, n_f=4) = 0.9864(41)$GeV, $m_b(10\,\mathrm{GeV}, n_f=5) = 3.625(25)$GeV, and $m_b/m_c=4.54(3)$. Finally we obtain a new nonperturbative result for the ratio of $c$ and $s$ quark masses: $m_c/m_s=11.652(65)$. This ratio implies $m_s(2\,\mathrm{GeV}, n_f=3)=94.0(6)$MeV when it is combined with our best $c$ mass. Combining $m_c/m_s$ with our new $m_b/m_c$ gives $m_b/m_s=52.90(44)$, which is several standard deviations away from the GeorgiJarlskop prediction from certain GUTs. 
Article: Bs→Kℓν form factors from lattice QCD
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ABSTRACT: We report the first lattice QCD calculation of the form factors for the standard model treelevel decay $B_s\to K \ell\nu$. In combination with future measurement, this calculation will provide an alternative exclusive semileptonic determination of $V_{ub}$. We compare our results with previous model calculations, make predictions for differential decay rates and branching fractions, and predict the ratio of differential branching fractions between $B_s\to K\tau\nu$ and $B_s\to K\mu\nu$. We also present standard model predictions for differential decay rate forwardbackward asymmetries, polarization fractions, and calculate potentially useful ratios of $B_s\to K$ form factors with those of the fictitious $B_s\to\eta_s$ decay. Our lattice simulations utilize NRQCD $b$ and HISQ light quarks on a subset of the MILC $2+1$ asqtad gauge configurations, including two lattice spacings and a range of light quark masses.  [Show abstract] [Hide abstract]
ABSTRACT: We discuss the sources of uncertainty in calculations of the partial widths of the Higgs boson within the Standard Model. The uncertainties come from two sources: the truncation of perturbation theory and the uncertainties in input parameters. We review the current status of perturbative calculations and note that these are already reaching the partspermil level of accuracy for the major decay modes. The main sources of uncertainty will then come from the parametric dependences on alpha_s, m_b, and m_c. Knowledge of these parameters is systematically improvable through lattice gauge theory calculations. We estimate the precision that lattice QCD will achieve in the next decade and the corresponding precision of the Standard Model predictions for Higgs boson partial widths. 
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ABSTRACT: We describe a new technique to determine the contribution to the anomalous magnetic moment of the muon coming from the hadronic vacuum polarization using lattice QCD. Our method reconstructs the Adler function, using Pad\'{e} approximants, from its derivatives at $q^2=0$ obtained simply and accurately from timemoments of the vector currentcurrent correlator at zero spatial momentum. We test the method using strange quark correlators on largevolume gluon field configurations that include the effect of up and down (at physical masses), strange and charm quarks in the sea at multiple values of the lattice spacing and multiple volumes and show that 1% accuracy is achievable. For the charm quark contributions we use our previously determined moments with up, down and strange quarks in the sea on very fine lattices. We find the (connected) contribution to the anomalous moment from the strange quark vacuum polarization to be $a_\mu^s = 53.41(59) \times 10^{10}$, and from charm to be $a_\mu^c = 14.42(39)\times 10^{10}$. These are in good agreement with flavourseparated results from nonlattice methods, given caveats about the comparison. The extension of our method to the light quark contribution and to that from the quarkline disconnected diagram is straightforward. 
Article: Nonperturbative tests of the renormalization of mixed cloverstaggered currents in lattice QCD
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ABSTRACT: The Fermilab Lattice and MILC collaborations have shown in oneloop lattice QCD perturbation theory that the renormalization constants of vector and axialvector mixed cloverasqtad currents are closely related to the product of those for cloverclover and asqtadasqtad (local) vector currents. To be useful for future higher precision calculations this relationship must be valid beyond oneloop and very general. We test its validity nonperturbatively using clover and Highly Improved Staggered (HISQ) strange quarks, utilising the absolute normalization of the HISQ temporal axial current. We find that the renormalization of the mixed current differs from the square root of the product of the pure HISQ and pure clover currents by $23\%$. We also compare discretization errors between the clover and HISQ formalisms. 
Conference Paper: Bottomonium and B results from full lattice QCD
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ABSTRACT: We have developed two methods for handling $b$ quarks in lattice QCD. One uses NRQCD (now improved to include radiative corrections) and the other uses Highly Improved Staggered Quarks (HISQ), extrapolating to the $b$ quark from lighter masses and using multiple lattice spacings to control discretisation errors. Comparison of results for the two different methods gives confidence in estimates of lattice QCD systematic errors, since they are very different in these two cases. Here we show results for heavyonium hyperfine splittings and vector currentcurrent correlator moments using HISQ quarks, to add to earlier results testing the heavy HISQ method with pseudoscalar mesons. We also show the form factor for $B \rightarrow \pi l \nu$ decay at zero recoil using NRQCD $b$ quarks and $u/d$ quarks with physical masses. This allows us to test the soft pion theorem relation ($f_0(q^2_{max})=f_B/f_{\pi}$) accurately and we find good agreement as $M_{\pi} \rightarrow 0$. }
Publication Stats
15k  Citations  
578.12  Total Impact Points  
Top Journals
Institutions

19792015

Cornell University
 • Laboratory for Elementary Particle Physics
 • Department of Physics
Итак, New York, United States


19952014

University of Glasgow
 School of Physics and Astronomy
Glasgow, Scotland, United Kingdom


19882014

University of Cambridge
 Department of Applied Mathematics and Theoretical Physics
Cambridge, England, United Kingdom


2001

The Ohio State University
 Department of Physics
Columbus, OH, United States


1998

Southern Methodist University
 Department of Physics
Dallas, Texas, United States


19771979

Stanford University
 SLAC National Accelerator Laboratory
Palo Alto, California, United States
