1,787 research outputs found
K -> pion Semileptonic Form Factors from Two-Flavor Lattice QCD
We present new lattice results of the K -> pion semileptonic form factors
obtained from simulations with two flavors of dynamical twisted-mass fermions,
using pion masses as light as 260 MeV. Our main result is f+(0) = 0.9560 (84),
which, combined with the latest experimental data for Kl3 decays, leads to
|V_{us}| = 0.2267 (5)_exp (20)_f+(0). Using the PDG(2008) determinations of
|Vud| and |Vub| our result implies for the unitarity relation |Vud|**2 +
|Vus|**2 + |Vub|**2 = 1.0004 (15). For the O(p**6) term of the chiral expansion
of f+(0) we get Df = f+(0) - 1 - f2 = -0.0214 (84).Comment: 4 pages, 4 figures, 1 table, revte
Vector and scalar form factors for K- and D-meson semileptonic decays from twisted mass fermions with Nf = 2
We present lattice results for the form factors relevant in the K -> pion and
D -> pion semileptonic decays, obtained from simulations with two flavors of
dynamical twisted-mass fermions and pion masses as light as 260 MeV. For K ->
pion decays we discuss the estimates of the main sources of systematic
uncertainties, including the quenching of the strange quark, leading to our
final result f+(0) = 0.9560 (57) (62). Combined with the latest experimental
data, our value of f+(0) implies for the CKM matrix element |Vus| the value
0.2267 (5) (20) consistent with the first-row CKM unitarity. For D -> pion
decays the application of Heavy Meson Chiral Perturbation Theory allows to
extrapolate our results for both the scalar and the vector form factors at the
physical point with quite good accuracy, obtaining a nice agreement with the
experimental data. In particular at zero-momentum transfer we obtain f+(0) =
0.64 (5).Comment: 8 pages, 4 figures, 1 table, proceedings of the XXVII Int'l Symposium
on Lattice Field Theory (LAT2009), July 26-31 2009, Peking University,
Beijing (China
semileptonic form factors with Twisted Mass fermions
We present a lattice QCD determination of the vector and scalar form factors
of the semileptonic decay which are relevant for the
extraction of the CKM matrix element from experimental data. Our
results are based on the gauge configurations produced by the European Twisted
Mass Collaboration with dynamical fermions, which include in the
sea, besides two light mass degenerate quarks, also the strange and the charm
quarks. We use data simulated at three different values of the lattice spacing
and with pion masses as small as MeV. Our final result for the vector
form factor at zero momentum transfer is , where the
uncertainty is both statistical and systematic combined in quadrature. Using
the latest experimental value of from decays, we
obtain , which allows to test the unitarity constraint
of the Standard Model below the permille level once the determination of
from superallowed nuclear decays is adopted. A slight
tension with unitarity at the level of standard deviations is
observed. Moreover we present our results for the semileptonic scalar
and vector form factors in the whole range of values of
the squared four-momentum transfer measured in decays,
obtaining a very good agreement with the momentum dependence of the
experimental data. We provide a set of synthetic data points representing our
results for the vector and scalar form factors at the physical point for
several selected values of .Comment: 37 pages, 5 tables, 9 figures; version to appear in PR
Leading isospin-breaking corrections to pion, kaon and charmed-meson masses with Twisted-Mass fermions
We present a lattice computation of the isospin-breaking corrections to
pseudoscalar meson masses using the gauge configurations produced by the
European Twisted Mass collaboration with dynamical quarks at
three values of the lattice spacing ( and fm)
with pion masses in the range MeV. The strange and
charm quark masses are tuned at their physical values. We adopt the RM123
method based on the combined expansion of the path integral in powers of the
- and -quark mass difference () and of the
electromagnetic coupling . Within the quenched QED approximation,
which neglects the effects of the sea-quark charges, and after the
extrapolations to the physical pion mass and to the continuum and infinite
volume limits, we provide results for the pion, kaon and (for the first time)
charmed-meson mass splittings, for the prescription-dependent parameters
, \epsilon_\gamma(\overline{MS}, 2~\mbox{GeV}),
\epsilon_{K^0}(\overline{MS}, 2~\mbox{GeV}), related to the violations of the
Dashen's theorem, and for the light quark mass difference (\widehat{m}_d -
\widehat{m}_u)(\overline{MS}, 2~\mbox{GeV}).Comment: 47 pages, 20 figures, 4 tables; comments on QED and QCD splitting
prescriptions added; version to appear in PR
\Delta S=2 and \Delta C=2 bag parameters in the SM and beyond from Nf=2+1+1 twisted-mass LQCD
We present unquenched lattice QCD results for the matrix elements of
four-fermion operators relevant to the description of the neutral K and D
mixing in the Standard Model and its extensions. We have employed simulations
with Nf = 2 + 1 + 1 dynamical sea quarks at three values of the lattice
spacings in the interval 0.06 - 0.09 fm and pseudoscalar meson masses in the
range 210 - 450 MeV. Our results are extrapolated to the continuum limit and to
the physical pion mass. Renormalization constants have been determined
non-perturbatively in the RI-MOM scheme. In particular, for the Kaon
bag-parameter, which is relevant for the \overline{K}^0-K^0 mixing in the
Standard Model, we obtain B_K^{RGI} = 0.717(24).Comment: Added comments to error budget discussion; fig.19 corrected. Version
to appear in PR
First lattice calculation of the QED corrections to leptonic decay rates
The leading-order electromagnetic and strong isospin-breaking corrections to
the ratio of and decay rates are evaluated for the
first time on the lattice, following a method recently proposed. The lattice
results are obtained using the gauge ensembles produced by the European Twisted
Mass Collaboration with dynamical quarks. Systematics effects
are evaluated and the impact of the quenched QED approximation is estimated.
Our result for the correction to the tree-level decay
ratio is to be compared to the estimate based
on Chiral Perturbation Theory and adopted by the Particle Data Group.Comment: 5 pages, 6 figures; extended supplemental material with 1 table and 1
figure, results unchange
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