114 research outputs found
High-Precision c and b Masses, and QCD Coupling from Current-Current Correlators in Lattice and Continuum QCD
We extend our earlier lattice-QCD analysis of heavy-quark correlators to
smaller lattice spacings and larger masses to obtain new values for the c mass
and QCD coupling, and, for the first time, values for the b mass:
m_c(3GeV,n_f=4)=0.986(6)GeV, alpha_msb(M_Z,n_f=5)=0.1183(7), and
m_b(10GeV,n_f=5)=3.617(25)GeV. These are among the most accurate determinations
by any method. We check our results using a nonperturbative determination of
the mass ratio m_b(mu,n_f)/m_c(mu,n_f); the two methods agree to within our 1%
errors and taken together imply m_b/m_c=4.51(4). We also update our previous
analysis of alpha_msb from Wilson loops to account for revised values for r_1
and r_1/a, finding a new value alpha_\msb(M_Z,n_f=5)=0.1184(6); and we update
our recent values for light-quark masses from the ratio m_c/m_s. Finally, in
the Appendix, we derive a procedure for simplifying and accelerating
complicated least-squares fits.Comment: 16 pages, 10 figures, 3 table
Critical behaviour of the O(3) nonlinear sigma model with topological term at theta=pi from numerical simulations
We investigate the critical behaviour at theta=pi of the two-dimensional O(3)
nonlinear sigma model with topological term on the lattice. Our method is based
on numerical simulations at imaginary values of theta, and on scaling
transformations that allow a controlled analytic continuation to real values of
theta. Our results are compatible with a second order phase transition, with
the critical exponent of the SU(2)_1 Wess-Zumino-Novikov-Witten model, for
sufficiently small values of the coupling.Comment: Revised version. 24 pages, 7 figure
Update: Precision D_s decay constant from full lattice QCD using very fine lattices
We update our previous determination of both the decay constant and the mass
of the meson using the Highly Improved Staggered Quark formalism. We
include additional results at two finer values of the lattice spacing along
with improved determinations of the lattice spacing and improved tuning of the
charm and strange quark masses. We obtain = 1.9691(32) GeV, in good
agreement with experiment, and = 0.2480(25) GeV. Our result for
is 1.6 lower than the most recent experimental average
determined from the leptonic decay rate and using from CKM
unitarity. Combining our with the experimental rate we obtain a
direct determination of , or alternatively using a probability distribution for statistical errors for this
quantity which vanishes above 1. We also include an accurate prediction of the
decay constant of the , = 0.3947(24) GeV, as a calibration
point for other lattice calculations.Comment: 24 pages, 20 figures. Updated to include new experimental results
from BaBar, new experimental averages from HFAG and consequent discussion of
theory/experiment comparison. Other minor typographical changes. Version
accepted by Phys. Rev.
High Precision determination of the pi, K, D and D_s decay constants from lattice QCD
We determine and decay constants from lattice QCD with 2% errors, 4
times better than experiment and previous theory: = 241(3) MeV,
= 207(4) MeV and = 1.164(11).
We also obtain = 1.189(7) and =
0.979(11). Combining with experiment gives =0.2262(14) and
of 4.43(41). We use a highly improved quark discretization on
MILC gluon fields that include realistic sea quarks fixing the and
masses from the , , and meson masses. This allows a stringent
test against experiment for and masses for the first time (to within
7 MeV).Comment: 4 pages, 2 figures. Published version - changes from original include
a more extensive discussion of errors and an error budget table covering more
quantities. There are very small changes in some of the values reporte
Highly Improved Staggered Quarks on the Lattice, with Applications to Charm Physics
We use perturbative Symanzik improvement to create a new staggered-quark
action (HISQ) that has greatly reduced one-loop taste-exchange errors, no
tree-level order a^2 errors, and no tree-level order (am)^4 errors to leading
order in the quark's velocity v/c. We demonstrate with simulations that the
resulting action has taste-exchange interactions that are at least 3--4 times
smaller than the widely used ASQTAD action. We show how to estimate errors due
to taste exchange by comparing ASQTAD and HISQ simulations, and demonstrate
with simulations that such errors are no more than 1% when HISQ is used for
light quarks at lattice spacings of 1/10 fm or less. The suppression of (am)^4
errors also makes HISQ the most accurate discretization currently available for
simulating c quarks. We demonstrate this in a new analysis of the psi-eta_c
mass splitting using the HISQ action on lattices where a m_c=0.43 and 0.66,
with full-QCD gluon configurations (from MILC). We obtain a result of~111(5)
MeV which compares well with experiment. We discuss applications of this
formalism to D physics and present our first high-precision results for D_s
mesons.Comment: 21 pages, 8 figures, 5 table
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