Theory compared with experiment in the quenched approximation and in full QCD.
Background.
Significant progress has been made in
lattice phenomelogy during the past five years through the use of
improved staggered fermions. This progress is illustrated
in the figure in the upper right in which the ratio of lattice results to experimental
results for a number of experimentally well determined quantities is plotted.
The panel on the left shows lattice results from the quenched approximation
in which vacuum polarization effects are neglected, while the panel on the
right shows lattice results for full QCD.
Other notable results include
calculations of mass splittings in the charmonium and bottomonium spectra,
the strong coupling constant and
the Cabibbo-Kobayashi-Maskawa (CKM) matrix
element Vus to the same accuracy as their experimental determinations.
The lattice gauge theory community has moved from the validation of techniques
through the calculation of quantities that are well known experimentally to
the successful prediction of quantities that had not previously been measured.
Three cases in which predictions were subsequently confirmed by experiment
were the calculations of the leptonic decay constants of the D and Ds
mesons and the mass of the Bc meson. Another example was the successful
prediction of the form factor for the decay of the D meson into a K meson
and leptons, which is illustrated in the figure at the left. The orange band
is the lattice prediction and the blue plotting symbols are the results of
the Belle Collaboration.
Shape of the form factor for the decay of a D meson into a kaon and leptons
predicted by lattice QCD (orange band) and measured by experiment (purple diamonds).
Project Goals.
This project aims at a comprehensive analysis of the physics of heavy-light mesons with particular
emphasis on physics relevant to determinations of CKM matrix elements and quark masses.
It uses the unquenched, improved staggered fermion gauge configurations of the MILC collaboration,
improved staggered light valence quarks, and (so far) clover heavy quarks with the Fermilab interpretation.
Ultimately, we aim at determinations of B and D meson decay constants, semileptonic form factors, and
B B bar mixing parameters on the full MILC data set.
2008/2009 Goals.
Abstract of 2008 proposal: We propose to extend our broad program of calculating matrix elements for the leptonic and semileptonic decays of mesons containing a heavy quark. These calculations have influenced, and will continue to influence, flavor-physics studies in the experiments BaBar, Belle, CDF, CLEO-c, D0 and, later, LHC-b and BES. We will use gauge configurations that include effects of 2+1 species of improved staggered sea quarks, with ml = (mu + md )/2 as close to the chiral limit as 0.1ms , and the strange quark mass ms fixed at its physical value. For the heavy quark we will use either the standard or an improved version of the Fermilab method.
The specific computational goals of the 2008/2009 proposal included the completion of the analysis of the heavy-to-light semileptonic form factors, the B→D(*)lν (heavy-to-heavy) semileptonic form factor, the leptonic decay constants of B, Bs, D, and Ds, mesons, and the B0-B0 bar mixing amplitude, with a statistical data set four times larger than we had used in previous analyses. We proposed to do these analyses on the new MILC fine lattice ensembles (a=0.09 fm, ml={0.1, 0.15, 0.2} ms). We have since decided to extend our goals for improved statistics to the other find (a=0.09 fm) and coarse (a=0.12 fm) ensembles.
Selected References
- The B -> πlν semileptonic form factor from three-flavor lattice QCD: A model-independent determination of |V(ub)|.
J. Bailey et al. FERMILAB-PUB-08-541-T, Nov 2008, arXiv:0811.3640 [hep-lat], sumitted to Phys. Rev. D.
- The Anti-B -> D* l anti-ν form factor at zero recoil from three-flavor lattice QCD: A Model independent determination of |V(cb)|,
C. Bernard et al. FERMILAB-PUB-08-316-T,
Submitted to Phys. Rev. D, arXiv:0808.2519 [hep-lat].
- Charmed meson decay constants in three-flavor lattice QCD.
C. Aubin et al. FERMILAB-PUB-05-257-T, Jun 2005. 4pp.
Published in Phys.Rev.Lett.95:122002,2005
- Mass of the B(c) meson in three-flavor lattice QCD.
By HPQCD Collaboration and Fermilab Lattice Collaboration and UKQCD Collaboration (Ian F. Allison et al.). FERMILAB-PUB-04-349-T, Nov 2004. 4pp.
Published in Phys.Rev.Lett.94:172001,2005
- Semileptonic decays of D mesons in three-flavor lattice QCD.
By Fermilab Lattice Collaboration and MILC Collaboration and HPQCD Collaboration (C. Aubin et al.). FERMILAB-PUB-04-195-T, Aug 2004. 4pp.
Published in Phys.Rev.Lett.94:011601,2005
- High precision lattice QCD confronts experiment.
C.T.H. Davies et al. FERMILAB-PUB-03-297-T, Apr 2003. 4pp.
Published in Phys.Rev.Lett.92:022001,2004
e-Print Archive: hep-lat/0304004.
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