2,420 research outputs found
Charmonium properties from lattice QCD + QED: hyperfine splitting, leptonic width, charm quark mass and
We have performed the first lattice QCD computations of the
properties (masses and decay constants) of ground-state charmonium mesons. Our
calculation uses the HISQ action to generate quark-line connected two-point
correlation functions on MILC gluon field configurations that include
quark masses going down to the physical point, tuning the quark mass from
and including the effect of the quark's electric charge
through quenched QED. We obtain (connected) =
120.3(1.1) MeV and interpret the difference with experiment as the impact on
of its decay to gluons, missing from the lattice calculation. This
allows us to determine =+7.3(1.2) MeV,
giving its value for the first time. Our result of 0.4104(17)
GeV, gives =5.637(49) keV, in agreement
with, but now more accurate than experiment. At the same time we have improved
the determination of the quark mass, including the impact of quenched QED
to give = 0.9841(51) GeV. We have also used
the time-moments of the vector charmonium current-current correlators to
improve the lattice QCD result for the quark HVP contribution to the
anomalous magnetic moment of the muon. We obtain , which is 2.5 higher than the value derived using moments
extracted from some sets of experimental data on . This value for includes our determination of
the effect of QED on this quantity, .Comment: Added extra discussion on QED setup, some new results to study the
effects of strong isospin breaking in the sea (including new Fig. 1) and a
fit stability plot for the hyperfine splitting (new Fig. 7). Version accepted
for publication in PR
Numerical simulations of the flow and sediment transport regimes surrounding a short cylinder
Author Posting. © IEEE, 2007. This article is posted here by permission of IEEE for personal use, not for redistribution. The definitive version was published in IEEE Journal of Oceanic Engineering 32 (2007): 249-259, doi:10.1109/JOE.2007.890986.The 3-D flow field and bed stress surrounding a short cylinder in response to combined wave and mean-flow forcing events is examined. Model simulations are performed with a 3-D nonhydrostatic computational fluid dynamics model, FLOW-3D. The model is forced with a range of characteristic tidal and wave velocities as observed in 12–15 m of water at the Martha's Vineyard Coastal Observatory (MVCO, Edgartown, MA). The 2.4-m-long and 0.5-m diameter cylinder is buried 10% of the diameter on a flat, fixed bed. Regions of incipient motion are identified through local estimates of the Shields parameter exceeding the critical value. Potential areas of sediment deposition are identified with local estimates of the Rouse parameter exceeding ten. The model predictions of sediment response are in general in agreement with field observations of seabed morphology obtained over a one-week period during the 2003–2004 MVCO mine burial experiment. Both observations and simulations show potential transport occurring at the ends of the mine in wave-dominated events. Mean flows greater than 10 cm/s lead to the formation of larger scour pits upstream of the cylinder. Deposition in both cases tends to occur along the sides, near the center of mass of the mine. However, the fixed-bed assumption prohibits the prediction of full perimeter scour as is observed in nature. Predicted scour and burial regimes for a range of wave and mean-flow combinations are established.This work was supported in part by the U.S. Office of Naval
Research under the mine burial project N00014-00-1-0570. The work of K. A.
Hatton was supported by the National Science Foundation Graduate Research
Fellowship
Renormalisation of the tensor current in lattice QCD and the tensor decay constant
Lattice QCD calculations of form factors for rare Standard Model processes
such as use tensor currents that require
renormalisation. These renormalisation factors, , have typically been
calculated within perturbation theory and the estimated uncertainties from
missing higher order terms are significant. Here we study tensor current
renormalisation using lattice implementations of momentum-subtraction schemes.
Such schemes are potentially more accurate but have systematic errors from
nonperturbative artefacts. To determine and remove these condensate
contributions we calculate the ground-state charmonium tensor decay constant,
, which is also of interest in beyond the Standard Model studies.
We obtain GeV, with
ratio to the vector decay constant of 0.9569(52), significantly below 1. We
also give factors, converted to the scheme, corrected
for condensate contamination. This contamination reaches 1.5\% at a
renormalisation scale of 2 GeV (in the preferred RI-SMOM scheme) and so must be
removed for accurate results.Comment: 12 pages, version accepted for publication in PR
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