4,591 research outputs found
Semileptonic Decays: an Update Down Under
Heavy-meson semileptonic decays calculations on the lattice are reviewed. The
focus is upon obtaining reliable matrix elements. Errors that depend upon the
lattice spacing, , are an important source of systematic error. Full
improvement of matrix elements for arbitrary-mass four-component quarks is
discussed. With improvement, bottom-quark matrix elements can be calculated
directly using current lattices. Momentum dependent errors for -improved
quarks and statistical noise limit momenta to around 1 GeV/c with current
lattices. Hence, maximum recoil momenta can be reached for decays while
only a fraction of the maximum recoil momentum can be reliably studied for the
light-meson decay modes of the . Differential decay rates and partial widths
are phenomenologically important quantities in decays that can be reliably
determined with present lattices.Comment: 14 pages, 9 postscript figures, requires espcrc2.st
Chiral Perturbation Theory and Weak Matrix Elements
I describe recent developments in quenched chiral perturbation theory (QChPT)
and the status of weak matrix elements involving light quarks. I illustrate
how, with improved statistical errors, and with calculations of the masses of
baryons containing non-degenerate quarks, there is now a clear need for
extrapolations of higher order than linear in the quark mass. I describe how
QChPT makes predictions for the functional forms to use in such extrapolations,
and emphasize the distinction between contributions coming from chiral loops
which are similar to those present in unquenched theories, and those from
loops which are pure quenched artifacts. I describe a fit to the baryon
masses using the predictions of QChPT. I give a status report on the numerical
evidence for loops, concluding that they are likely present, and are
characterized by a coupling . I use the difference between
chiral loops in QCD and quenched QCD to estimate the quenching errors in a
variety of quantities. I then turn to results for matrix elements, largely from
quenched simulations. Results for quenched decay constants cannot yet be
reliably extrapolated to the continuum limit. By contrast, new results for
suggest a continuum, ``quenched'' value of , based on a quadratic extrapolation in . The theoretical
basis for using a quadratic extrapolation has been confirmed. For the first
time there is significant evidence that unquenching changes , and my
estimate for the value in QCD is .
Here the second error is a conservative estimate of the systematic error due to
uncertainties in the effect of quenching. A less conservative viewpoint reduces
to .Comment: 16 pages, 11 figures, Latex using espcrc2.sty and psfig. Talk
presented at LATTICE96(phenomenology
Status of Heavy Quark Physics on the Lattice
The status of lattice calculations of some phenomenology of heavy quarks is
presented. Emphasis is on progress made in calculating those quantities
relevant to estimating parameters of the quark mixing matrix, namely leptonic
decay constants, the bag parameter of neutral mixing, and semileptonic form
factors. New results from studies of quarkonia are highlighted.Comment: LATTICE98(Plenary Review Talk), to be published in Nucl. Phys. Proc.
Suppl.; LaTeX, 15 pages, 9 PostScript figures, uses espcrc2.st
Heavy Light Weak Matrix Elements
I review the status of lattice calculations of heavy-light weak matrix
elements, concentrating on semileptonic B decays to light mesons, B -> K*
gamma, the B meson decay constant, f_B, and the mixing parameter B_B.Comment: 12 pages, LaTeX2e with 6 postscript figures. Uses espcrc2.sty and
epsf.sty (included). Talk presented at LATTICE96(heavy quarks
Renormalization of the effective theory for heavy quarks at small velocity
The slope of the Isgur-Wise function at the normalization point,
,is one of the basic parameters for the extraction of the
matrix element from exclusive semileptonic decay data. A method for
measuring this parameter on the lattice is the effective theory for heavy
quarks at small velocity . This theory is a variant of the heavy quark
effective theory in which the motion of the quark is treated as a perturbation.
In this work we study the lattice renormalization of the slow heavy quark
effective theory. We show that the renormalization of is not
affected by ultraviolet power divergences, implying no need of difficult
non-perturbative subtractions. A lattice computation of with
this method is therefore feasible in principle. The one-loop renormalization
constants of the effective theory for slow heavy quarks are computed to order
together with the lattice-continuum renormalization constant of
. We demonstrate that the expansion in the heavy-quark velocity
reproduces correctly the infrared structure of the original (non-expanded)
theory to every order. We compute also the one-loop renormalization constants
of the slow heavy quark effective theory to higher orders in and the
lattice-continuum renormalization constants of the higher derivatives of the
function. Unfortunately, the renormalization constants of the higher
derivatives are affected by ultraviolet power divergences, implying the
necessity of numerical non-perturbative subtractions. The lattice computation
of higher derivatives of the Isgur-Wise function seems therefore problematic.Comment: Latex, 43 pages, 5 figures available by fax upon request. To be
published in Nucl. Phys
Heavy quark physics from lattice QCD
I review the current status of lattice calculations of heavy quark
quantities. Particular emphasis is placed on leptonic and semileptonic decay
matrix elements.Comment: Lattice2001(plenary), 12 pages, 6 figures. Table 1 updated and typos
in Figure 6 correcte
A precise determination of the Bc mass from dynamical lattice QCD
We perform a precise calculation of the mass of the B_c meson using
unquenched configurations from the MILC collaboration including 2+1 flavours of
improved staggered quarks. Lattice NRQCD and the Fermilab formalism are used to
describe the b and c quarks respectively. We find the mass of the B_c meson to
be 6.304(16) GeVComment: Talk presented at Lattice2004(heavy), Fermilab, June 21-26. 3 pages,
2 figure
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