Publications (196)328.88 Total impact

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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. 
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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. 
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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. 
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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. 
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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. 
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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. 
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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.Physical Review D 03/2014; 89(11). DOI:10.1103/PhysRevD.89.114501 · 4.86 Impact Factor 
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. 
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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 $M_{\pi} \rightarrow 0$. } 
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ABSTRACT: We determine the rate for $D_s^* \rightarrow D_s \gamma$ for the first time from lattice QCD and include the full effect of $u$, $d$ and $s$ sea quarks. The valence quarks are implemented using the Highly Improved Staggered Quark (HISQ) formalism and we normalise the vector current nonperturbatively. We obtain $M(D_s^*)M(D_s)$ of 148(4) MeV, in good agreement with experiment. The value of the decay constant of the $D_s^*$ we find to be 274(6) MeV, so that $f_{D_s^*}/f_{D_s} = 1.10(2)$. For the radiative decay we find $\Gamma(D_s^* \rightarrow D_s \gamma)$ = 0.066(26) keV. Given the experimental branching fraction for this decay we predict a total width for the $D_s^*$ of 0.070(28) keV, making this the longest lived charged vector meson.Physical Review Letters 12/2013; 112(21). DOI:10.1103/PhysRevLett.112.212002 · 7.73 Impact Factor 
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ABSTRACT: We determine the complete set of axial and vector form factors for the Ds to {\phi}l{\nu} decay from full lattice QCD for the first time. The valence quarks are implemented using the Highly Improved Staggered Quark action and we normalise the appropriate axial and vector currents fully nonperturbatively. The q^2 and angular distributions we obtain for the differential rate agree well with those from the BaBar experiment and, from the total branching fraction, we obtain Vcs = 1.017(63), in good agreement with that from D to Kl{\nu} semileptonic decay. We also find the mass and decay constant of the {\phi} meson in good agreement with experiment, showing that its decay to K{\bar{K}} (which we do not include here) has at most a small effect. We include an Appendix on nonperturbative renormalisation of the complete set of staggered vector and axial vector bilinears needed for this calculation. 
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ABSTRACT: We calculate, for the first time using unquenched lattice QCD form factors, the standard model differential branching fractions dB/dq^{2}(B→Kℓ^{+}ℓ^{}) for ℓ=e, μ, τ and compare with experimental measurements by Belle, BABAR, CDF, and LHCb. We report on B(B→Kℓ^{+}ℓ^{}) in q^{2} bins used by experiment and predict B(B→Kτ^{+}τ^{})=(1.41±0.15)×10^{7}. We also calculate the ratio of branching fractions R_{e}^{μ}=1.00029(69) and predict R_{ℓ}^{τ}=1.176(40), for ℓ=e, μ. Finally, we calculate the "flat term" in the angular distribution of the differential decay rate F_{H}^{e,μ,τ} in experimentally motivated q^{2} bins.Physical Review Letters 10/2013; 111(16):162002. · 7.73 Impact Factor 
Physical Review D 10/2013; 88(7). DOI:10.1103/PhysRevD.88.079901 · 4.86 Impact Factor

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ABSTRACT: We calculate, for the first time using unquenched lattice QCD, form factors for the rare decay B→Kℓ^{+}ℓ^{} in and beyond the Standard Model. Our lattice QCD calculation utilizes a nonrelativistic QCD formulation for the b valence quarks and the highly improved staggered quark formulation for the light valence quarks. We employ the MILC 2+1 asqtad ensembles. The form factor results, based on the z expansion, are valid over the full kinematic range of q^{2}. We construct the ratios f_{0}/f_{+} and f_{T}/f_{+}, which are useful in constraining new physics and verifying effective theory form factor symmetry relations. We also discuss the calculation of Standard Model observables.Physical Review D 09/2013; 88(5). DOI:10.1103/PhysRevD.88.054509 · 4.86 Impact Factor 
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ABSTRACT: Calculations of pseudoscalar decay constants of B, Bs, K and pi mesons with physical light quarks are presented. We use HISQ ensembles that include u,d,s and c sea quarks at three lattice spacings. HISQ is used for the valence light quarks and a radiatively improved NRQCD action for the heavy quarks. The key results are f_{B^+}=0.184(4)$ GeV, f_{B_s}=0.224(4) GeV, f_{B_s}/f_{B^+}=1.217(8), f_{K^+}/f_{pi^+}=1.1916(21), f_{K^+}=155.37(34) MeV, giving a significant improvement over previous results that required chiral extrapolation. We also calculate the Wilson flow scale w_0, finding w_0=0.1715(9) fm. 
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ABSTRACT: We calculate, for the first time using unquenched lattice QCD form factors, the Standard Model differential branching fractions $dB/dq^2(B \to Kll)$ for $l=e, \mu, \tau$ and compare with experimental measurements by Belle, BABAR, CDF, and LHCb. We report on $\mathcal{B}(B \to Kll)$ in $q^2$ bins used by experiment and predict $\mathcal{B}(B \to K \tau \tau) = (1.41 \pm 0.15) 10^{7}$. We also calculate the ratio of branching fractions $R^\mu_e = 1.00029(69)$ and predict $R^\tau_l = 1.176(40)$, for $l=e, \mu$. Finally, we calculate the "flat term" in the angular distribution of the differential decay rate $F_H^{e, \mu, \tau}$ in experimentally motivated $q^2$ bins.Physical Review Letters 06/2013; 111(16). DOI:10.1103/PhysRevLett.111.162002 · 7.73 Impact Factor 
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ABSTRACT: We present a new study of the form factors for D > K semileptonic decay from lattice QCD that allows us to compare the shape of the vector form factor to experiment and, for the first time, to extract V_cs using results from all experimental q^2 bins. The valence quarks are implemented with the Highly Improved Staggered Quark action on MILC configurations that include u, d and s sea quarks. The scalar and vector currents are nonperturbatively normalised and, using phased boundary conditions, we are able to cover the full q^2 range accessible to experiment. Our result is V_cs = 0.963(5)_{expt}(14)_{lattice}. We also demonstrate that the form factors are insensitive to whether the spectator quark is u/d or s, which has implications for other decay channels. 
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ABSTRACT: We determine the decay constants of the pi and K mesons on gluon field configurations from the MILC collaboration including u, d, s and c quarks. We use three values of the lattice spacing and u/d quark masses going down to the physical value. We use the w_0 parameter to fix the relative lattice spacing and f_pi to fix the overall scale. This allows us to obtain a value for f{K^+}/f{pi^+} = 1.1916(21). Comparing to the ratio of experimental leptonic decay rates gives Vus = 0.22564(28){Br(K^+)}(20){EM}(40){latt}(5){Vud} and the test of unitarity of the first row of the CabibboKobayashiMaskawa matrix: Vud^2+Vus^2+Vub^2  1 = 0.00009(51).Physical Review D 03/2013; 88(7). DOI:10.1103/PhysRevD.88.074504 · 4.86 Impact Factor
Publication Stats
13k  Citations  
328.88  Total Impact Points  
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Institutions

2014

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


1988–2014

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


1979–2014

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


2001

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


1999

Simon Fraser University
 Department of Physics
Burnaby, British Columbia, Canada


1998

Southern Methodist University
Dallas, Texas, United States


1977–1989

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