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Prospects for the Precision Measurement of {alpha}{sub s}

Description: The prospects for the measurement of the strong coupling constant {alpha}{sub MS}(M{sub Z}) to a relative uncertainty of 1 % are discussed. Particular emphasis is placed on the implications relating to future High Energy Physics facilities.
Date: December 1996
Creator: Burrows, P. N.; Dixon, L. & El-Khadra, A. X.
Partner: UNT Libraries Government Documents Department

The B {r{underscore}arrow} D*{ell}{nu} form factor at zero recoil

Description: The authors describe a model independent lattice QCD method for determining the deviation from unity for h{sub A{sub 1}}, the B {r{underscore}arrow} D*{ell}{nu} form factor at zero recoil. They extend the double ratio method previously used to determine the B {r{underscore}arrow} D{ell}{nu} form factor. The bulk of statistical and systematic errors cancel in the double ratios they consider, yielding form factors which promise to reduce present theoretical uncertainties in the determination of {vert{underscore}bar}V{sub cb}{vert{underscore}bar}. They present results from a prototype calculation at a single lattice spacing corresponding to {beta} = 5.7.
Date: January 26, 2000
Creator: Simone, J.N.; Hashimoto, S.; El-Khadra, A.X.; Kronfeld, A.S.; Mackenzie, P.B. & Ryan, S.M.
Partner: UNT Libraries Government Documents Department

$D$ semileptonic form factors and $|V_{cs(d)}|$ from 2+1 flavor lattice QCD

Description: The measured partial widths of the semileptonic decays D {yields} K{ell}{nu} and D {yields} {pi}{ell}{nu} can be combined with the form factors calculated on the lattice to extract the CKM matrix elements |V{sub cs}| and |V{sub cd}|. The lattice calculations can be checked by comparing the form factor shapes from the lattice and experiment. We have generated a sizable data set by using heavy clover quarks with the Fermilab interpretation for charm and asqtad staggered light quarks on 2+1 flavor MILC ensembles with lattice spacings of approximately 0.12, 0.09, 0.06, and 0.045 fm. Preliminary fits to staggered chiral perturbation theory suggest that we can reduce the uncertainties in the form factors at q{sup 2} = 0 to below 5%.
Date: November 1, 2011
Creator: Bailey, Jon A.; Bazavov, A.; El-Khadra, A.X.; Gottlieb, Steven; Jain, R.D.; Kronfeld, A.S. et al.
Partner: UNT Libraries Government Documents Department

B and D meson decay constants from 2+1 flavor improved staggered simulations

Description: We give an update on simulation results for the decay constants f{sub B}; f{sub B{sub s}}, f{sub D} and f{sub D{sub s}}. These decay constants are important for precision tests of the standard model, in particular entering as inputs to the global CKM unitarity triangle fit. The results presented here make use of the MILC (2+1)-flavor asqtad ensembles, with heavy quarks incorporated using the clover action with the Fermilab method. Partially quenched, staggered chiral perturbation theory is used to extract the decay constants at the physical point. In addition, we give error projections for a new analysis in progress, based on an extended data set.
Date: December 1, 2011
Creator: Neil, E.T.; Bailey, Jon A.; Bazavov, A.; Bernard, C.; Bouchard, C.M.; DeTar, C. et al.
Partner: UNT Libraries Government Documents Department

$B_s\to D_s/B\to D$ Semileptonic Form-Factor Ratios and Their Application to BR($B^0_s\to \mu^+\mu^-$)

Description: We calculate form-factor ratios between the semileptonic decays {bar B}{sup 0} {yields} D{sup +} {ell}{sup -}{bar {nu}} and {bar B}{sub s}{sup 0} {yields} D{sub s}{sup +}{ell}{sup -}{bar {nu}} with lattice QCD. These ratios are a key theoretical input in a new strategy to determine the fragmentation fractions of the neutral B decays, which are needed for measurements of BR(B{sub s}{sup 0} {yields} {mu}{sup +}{mu}{sup -}). They use the MILC ensembles of gauge configurations with 2 + 1 flavors of sea quarks at two lattice spacings of approximately 0.12 fm and 0.09 fm. We use the model-independent z parametrization to extrapolate their simulation results at small recoil toward maximum recoil. The results for the form-factor ratios are {line_integral}{sub 0}{sup (s)} (M{sub {pi}}{sup 2})/{line_integral}{sub 0}{sup (d)} (M{sub K}{sup 2}) = 1.046(44){sub stat.}(15){sub syst.} and {line_integral}{sub 0}{sup (s)} (M{sub {pi}}{sup 2})/{line_integral}{sub 0}{sup (d)} (M{sub {pi}}{sup 2}) = 1.054(47){sub stat.}(17){sub syst.}. In contrast to a QCD sum-rule calculation, no significant departure from U-spin (d {leftrightarrow} s) symmetry is observed.
Date: February 1, 2012
Creator: Bailey, Jon A.; Bazavov, A.; Bernard, C.; Bouchard, C. M.; DeTar, C.; Du, Daping et al.
Partner: UNT Libraries Government Documents Department

Calculation of $K\to\pi l\nu$ Form Factors with $N_f = 2+1$ Flavors of Staggered Auarks

Description: We report on the status of the Fermilab-MILC calculation of the form factor f{sub +}{sup K}{pi}(q{sup 2} = 0), needed to extract the CKM matrix element |V{sub us}| from experimental data on K semileptonic decays. The HISQ formulation is used in the simulations for the valence quarks, while the sea quarks are simulated with the asqtad action (MILC N{sub f} = 2 + 1 configurations). We discuss the general methodology of the calculation, including the use of twisted boundary conditions to get values of the momentum transfer close to zero and the different techniques applied for the correlators fits. We present initial results for lattice spacings a {approx} 0.12 fm and a {approx} 0.09 fm, and several choices of the light quark masses.
Date: November 1, 2011
Creator: Gamiz, E.; DeTar, C.; El-Khadra, A. X.; Kronfeld, A. S.; Mackenzie, P. B. & Simone, J.
Partner: UNT Libraries Government Documents Department

The decay constants f(B) and f(D+) from three-flavor lattice QCD

Description: We present new preliminary results for the leptonic decay constants f{sub B} and f{sub D+} determined in 2+1 flavor lattice QCD at lattice spacings a = 0.09, 0.12 and 0.15 fm. Results are obtained using the MILC Collaboration gauge configuration ensembles, clover heavy quarks in the Fermilab interpretation and improved staggered light quarks. Decay constants, computed at partially quenched combinations of the valence and sea light quark masses, are used to determine the low-energy parameters of staggered chiral perturbation theory. The physical decay constants are found in an extrapolation using the parameterized chiral formula.
Date: January 1, 2007
Creator: Bernard, C.; DeTar, C.; Di Pierro, M.; El-Khadra, A. X.; Evans, R. T.; Freeland, E. et al.
Partner: UNT Libraries Government Documents Department

B and D Meson Decay Constants

Description: We present an update of our calculations of the decay constants of the D, D{sub s}, B, and B{sub s} mesons in unquenched 2+1 flavor QCD. We use the MILC library of improved staggered gauge ensembles at lattice spacings 0.09, 0.12, and 0.15 fm, clover heavy quarks with the Fermilab normalizations, and improved staggered light valence quarks.
Date: April 1, 2009
Creator: Bernard, C.; DeTar, C.; Di Pierro, M.; El-Khadra, A. X.; Evans, R. T.; Freeland, Elizabeth Dawn et al.
Partner: UNT Libraries Government Documents Department

Visualization of semileptonic form factors from lattice QCD

Description: Comparisons of lattice-QCD calculations of semileptonic form factors with experimental measurements often display two sets of points, one each for lattice QCD and experiment. Here we propose to display the output of a lattice-QCD analysis as a curve and error band. This is justified, because lattice-QCD results rely in part on fitting, both for the chiral extrapolation and to extend lattice-QCD data over the full physically allowed kinematic domain. To display an error band, correlations in the fit parameters must be taken into account. For the statistical error, the correlation comes from the fit. To illustrate how to address correlations in the systematic errors, we use the Becirevic-Kaidalov parametrization of the D {yields} {pi}{ell}{nu} and D {yields} K{ell}{nu} form factors, and a analyticity-based fit for the B {yields} {pi}{ell}{nu} form factor f{sub +}.
Date: June 1, 2009
Creator: Bernard, C.; DeTar, C.; Di Pierro, M.; El-Khadra, A. X.; Evans, R. T.; Freeland, E. D. et al.
Partner: UNT Libraries Government Documents Department

The Ds and D+ Leptonic Decay Constants from Lattice QCD

Description: We present the leptonic decay constants f{sub D{sub s}} and f{sub D{sup +}} computed on the MILC collaboration's 2+1 flavor asqtad gauge ensembles. We use clover heavy quarks with the Fermilab interpretation and improved staggered light quarks. The simultaneous chiral and continuum extrapolation, which determines both decay constants, includes partially-quenched lattice results at lattice spacings a {approx} 0.09, 0.12 and 0.15 fm. We have made several recent improvements in our analysis: (a) we include terms in the fit describing leading order heavy-quark discretization effects, (b) we have adopted a more precise input r{sub 1} value consistent with our other D and B meson studies, (c) we have retuned the input bare charm masses based upon the new r{sub 1}. Our preliminary results are f{sub D{sub s}} = 260 {+-} 10 MeV and f{sub D{sup +}} = 217 {+-} 10 MeV.
Date: December 1, 2009
Creator: Bazavov, A.; Bernard, C.; DeTar, C.; Freeland, E. D.; Gamiz, E.; Gottlieb, Steven et al.
Partner: UNT Libraries Government Documents Department

B -> D* l nu at zero recoil: an update

Description: We present an update of our calculation of the form factor for {bar B} {yields} D*{ell}{bar {nu}} at zero recoil, with higher statistics and finer lattices. As before, we use the Fermilab action for b and c quarks, the asqtad staggered action for light valence quarks, and the MILC ensembles for gluons and light quarks (Luescher-Weisz married to 2+1 rooted staggered sea quarks). In this update, we have reduced the total uncertainty on F(1) from 2.6% to 1.7%.
Date: November 1, 2010
Creator: Bailey, Jon A.; Bazavov, A.; Bernard, C.; Bouchard, C.M.; DeTar, C.; El-Khadra, A.X. et al.
Partner: UNT Libraries Government Documents Department

$B^0_s$ and $B^0$ Mixing in the Standard Model and Beyond: A Progress Report

Description: We give a progress report on the calculation of B meson mixing matrix elements, focusing on contributions that could arise beyond the Standard Model. The calculation uses asqtad (light quark) and Fermilab (heavy quark) valence actions and MILC ensembles with 2+1 flavors of asqtad sea quarks. We report preliminary B{sub s}{sup 0} fit results, at a lattice spacing of 0.12 fm, for the SUSY basis of effective four-quark mixing operators and include an estimate for the final error budget.
Date: November 1, 2010
Creator: Bouchard, C.; /Illinois U., Urbana /Fermilab; El-Khadra, A.X.; /Illinois U., Urbana; Freeland, E.D.; /Illinois U., Urbana /Washington U., St. Louis et al.
Partner: UNT Libraries Government Documents Department

Semileptonic decays of K and D mesons in 2+1 flavor QCD

Description: The experimentally measured rates of the semileptonic decays K {yields} {pi}/{nu} and D {yields} K({pi})/{nu} can be combined with lattice calculations of the associated form factors to precisely extract the CKM matrix elements |V{sub us}| and |V{sub cs(d)}|. We report on the status of form factor calculations with Fermilab charm quarks and staggered light quarks on the 2+1 flavor asqtad staggered MILC ensembles. Analysis of data for the D {yields} {pi}/{nu} form factor provides a nontrivial test of our methods via comparison with CLEO data. We discuss the use of HISQ valence quarks to calculate the K {yields} {pi}/{nu} form factor f{sub +}{sup K{pi}}(0) and describe tests of our method.
Date: November 1, 2010
Creator: Bailey, Jon A.; Bazavov, A.; Bernard, C.; Bouchard, C.M.; DeTar, C.; El-Khadra, A.X. et al.
Partner: UNT Libraries Government Documents Department

Semi-leptonic news

Description: We present our recent results for the semi-leptonic decays K {yields} {pi}e{nu}, D {yields} Ke{nu}, D {yields} {pi}e{nu} and some exploratory data on B {yields} De{nu} and B {yields} {pi}e{nu}. 20 refs., 5 figs., 2 tabs.
Date: January 1, 1989
Creator: Bernard, C.W. (California Univ., Santa Barbara, CA (USA). Inst. for Theoretical Physics); El-Khadra, A.X. & Soni, A. (Brookhaven National Lab., Upton, NY (USA))
Partner: UNT Libraries Government Documents Department

Semi-leptonic decays on the lattice: The exclusive 0 sup minus to 0 sup minus case

Description: We present our results for the meson form factors of several semi- leptonic decays. They are computed from the corresponding matrix elements evaluated on the lattice as ratios of Greens functions. The renormalization of the local operators is calculated nonperturbatively. The dependence of the form factors on the four momentum transfer q{sup 2} is studied by injecting external three momenta to the initial and final state mesons. We study the pseudoscalar decays K {yields} {pi}{ell}{nu}, D {yields} K{ell}{nu}, D {yields} {pi}{ell}{nu}, D{sub s} {yields} {eta}{ell}{nu} and D{sub s} {yields} K{ell}{nu} on different lattices. We also analyze scaling, finite size and SU(3) symmetry breaking effects. The uncertainties in some lattice parameters, e.g. a{sup {minus}1}, as a source of systematic errors in this calculation are discussed. 35 refs., 15 figs., 13 tabs.
Date: January 1, 1990
Creator: Bernard, C.W. (California Univ., Santa Barbara, CA (USA). Inst. for Theoretical Physics); El-Khadra, A.X. (Fermi National Accelerator Lab., Batavia, IL (USA)) & Soni, A. (California Univ., Santa Barbara, CA (USA). Inst. for Theoretical Physics Brookhaven National Lab., Upton, NY (USA))
Partner: UNT Libraries Government Documents Department