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The Kaon B-parameter in mixed action chiral perturbation theory

Description: We calculate the kaon B-parameter, B{sub K}, in chiral perturbation theory for a partially quenched, mixed action theory with Ginsparg-Wilson valence quarks and staggered sea quarks. We find that the resulting expression is similar to that in the continuum, and in fact has only two additional unknown parameters. At one-loop order, taste-symmetry violations in the staggered sea sector only contribute to flavor-disconnected diagrams by generating an {Omicron}(a{sup 2}) shift to the masses of taste-singlet sea-sea mesons. Lattice discretization errors also give rise to an analytic term which shifts the tree-level value of B{sub K} by an amount of {Omicron}(a{sup 2}). This term, however, is not strictly due to taste-breaking, and is therefore also present in the expression for B{sub K} for pure G-W lattice fermions. We also present a numerical study of the mixed B{sub K} expression in order to demonstrate that both discretization errors and finite volume effects are small and under control on the MILC improved staggered lattices.
Date: September 1, 2006
Creator: Aubin, C.; U., /Columbia; Laiho, Jack; Van de Water, Ruth S. & /Fermilab
Partner: UNT Libraries Government Documents Department

Semileptonic B to D Decays at Nonzero Recoil with 2+1 Flavors of Improved Staggered Quarks

Description: The Fermilab Lattice-MILC collaboration is completing a comprehensive program of heavy-light physics on the MILC (2+1)-flavor asqtad ensembles with lattice spacings as small as 0.045 fm and light-to-strange-quark mass ratios as low as 1/20. We use the Fermilab interpretation of the clover action for heavy valence quarks and the asqtad action for light valence quarks. The central goal of the program is to provide ever more exacting tests of the unitarity of the CKM matrix. We give a progress report on one part of the program, namely the analysis of the semileptonic decay B to D at both zero and nonzero recoil. Although final results are not presented, we discuss improvements in the analysis methods, the statistical errors, and the parameter coverage that we expect will lead to a significant reduction in the final error for |V{sub cb}| from this decay channel.
Date: November 1, 2011
Creator: Qiu, Si-Wei; U., /Utah; DeTar, Carleton; U., /Utah; Du, Daping; U., /Iowa et al.
Partner: UNT Libraries Government Documents Department

Taste violations in the scalar correlator in mixed action simulations

Description: We study the behavior of the isovector scalar correlator, which is particularly sensitive to lattice artifacts, using domain-wall valence quarks on a staggered sea (generated by the MILC collaboration). We analyze this according to the prediction from chiral perturbation theory determined by Prelovsek, which indicates that the leading unitarity violations come from taste breaking effects. We show that our data behaves in the way predicted by Prelovsek, thus verifying that the largest contribution to the violations of unitarity which arise at finite lattice spacing can be described by the mixed-action chiral perturbation theory.
Date: October 1, 2007
Creator: Aubin, C.; Coll., /Columbia U. /William-Mary; Laiho, Jack; /Fermilab /Washington U., St. Louis; Van de Water, Ruth S. & /Fermilab
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

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

The kaon B-parameter from unquenched mixed action lattice QCD

Description: We present a preliminary calculation of B{sub K} using domain-wall valence quarks and 2+1 flavors of improved staggered sea quarks. Both the size of the residual quark mass, which measures the amount of chiral symmetry breaking, and of the mixed meson splitting Delta{sub mix}, a measure of taste-symmetry breaking, show that discretization effects are under control in our mixed action lattice simulations. We show preliminary data for pseudoscalar meson masses, decay constants and B{sub K}. We discuss general issues associated with the chiral extrapolation of lattice data, and, as an example, present a preliminary chiral and continuum extrapolation of f{sub pi}. The quality of our data shows that the good chiral properties of domain-wall quarks, in combination with the light sea quark masses and multiple lattice spacings available with the MILC staggered configurations, will allow for a precise determination of B{sub K}.
Date: October 1, 2007
Creator: Aubin, Christopher A.; Laiho, Jack & Van de Water, Ruth S.
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

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