18 research outputs found
Exploratory lattice QCD study of the rare kaon decay
In Ref [1] we have presented the results of an exploratory lattice QCD
computation of the long-distance contribution to the
decay amplitude. In the present paper we describe the details of this
calculation, which includes the implementation of a number of novel techniques.
The decay amplitude is dominated by short-distance
contributions which can be computed in perturbation theory with the only
required non-perturbative input being the relatively well-known form factors of
semileptonic kaon decays. The long-distance contributions, which are the target
of this work, are expected to be of O(5%) in the branching ratio. Our study
demonstrates the feasibility of lattice QCD computations of the
decay amplitude, and in particular of the
long-distance component. Though this calculation is performed on a small
lattice () and at unphysical pion, kaon and charm quark masses,
MeV, MeV and m_c^{\overline{\mathrm{MS}}}(\mbox{2
GeV})=863 MeV, the techniques presented in this work can readily be applied to
a future realistic calculation.Comment: 74 pages, 12 figure
The pion's electromagnetic form factor at small momentum transfer in full lattice QCD
We compute the electromagnetic form factor of a "pion" with mass m_pi=330MeV
at low values of Q^2\equiv -q^2, where q is the momentum transfer. The
computations are performed in a lattice simulation using an ensemble of the
RBC/UKQCD collaboration's gauge configurations with Domain Wall Fermions and
the Iwasaki gauge action with an inverse lattice spacing of 1.73(3)GeV. In
order to be able to reach low momentum transfers we use partially twisted
boundary conditions using the techniques we have developed and tested earlier.
For the pion of mass 330MeV we find a charge radius given by
_{330MeV}=0.354(31)fm^2 which, using NLO SU(2) chiral perturbation
theory, extrapolates to a value of =0.418(31)fm^2 for a physical pion,
in agreement with the experimentally determined result. We confirm that there
is a significant reduction in computational cost when using propagators
computed from a single time-slice stochastic source compared to using those
with a point source; for m_pi=330MeV and volume (2.74fm)^3 we find the
reduction is approximately a factor of 12.Comment: 20 pages, 3 figure
Calculation of the hadronic vacuum polarization contribution to the muon anomalous magnetic moment
We present a first-principles lattice QCD+QED calculation at physical pion
mass of the leading-order hadronic vacuum polarization contribution to the muon
anomalous magnetic moment. The total contribution of up, down, strange, and
charm quarks including QED and strong isospin breaking effects is found to be
, where the first error is
statistical and the second is systematic. By supplementing lattice data for
very short and long distances with experimental R-ratio data using the
compilation of Ref. [1], we significantly improve the precision of our
calculation and find with lattice statistical, lattice systematic, R-ratio statistical,
and R-ratio systematic errors given separately. This is the currently most
precise determination of the leading-order hadronic vacuum polarization
contribution to the muon anomalous magnetic moment. In addition, we present the
first lattice calculation of the light-quark QED correction at physical pion
mass.Comment: 12 pages, 11 figure
Domain wall QCD with physical quark masses
We present results for several light hadronic quantities (, ,
, , , , ) obtained from simulations of 2+1
flavor domain wall lattice QCD with large physical volumes and nearly-physical
pion masses at two lattice spacings. We perform a short, O(3)%, extrapolation
in pion mass to the physical values by combining our new data in a simultaneous
chiral/continuum `global fit' with a number of other ensembles with heavier
pion masses. We use the physical values of , and to
determine the two quark masses and the scale - all other quantities are outputs
from our simulations. We obtain results with sub-percent statistical errors and
negligible chiral and finite-volume systematics for these light hadronic
quantities, including: = 130.2(9) MeV; = 155.5(8) MeV; the
average up/down quark mass and strange quark mass in the scheme
at 3 GeV, 2.997(49) and 81.64(1.17) MeV respectively; and the neutral kaon
mixing parameter, , in the RGI scheme, 0.750(15) and the
scheme at 3 GeV, 0.530(11).Comment: 131 pages, 30 figures. Updated to match published versio