260 research outputs found
Isospin Breaking in the Extraction of Isovector and Isoscalar Spectral Functions from e^+e^- --> hadrons
A finite energy sum rule (FESR) analysis of the isospin-breaking vector
current correlator is used to determine the
isospin-breaking electromagnetic (EM) decay constants of the low-lying vector
mesons. These results are used to evaluate the corrections required to extract
the flavor diagonal 33 and 88 resonance contributions from the full resonance
EM contributions to the EM spectral function. A large (~15%) correction is
found in the case of the omega contribution to the isoscalar spectral function.
The implications of these results for sum rules based on the
isovector-isoscalar spectral difference are considered.Comment: Presentation to the 3rd International Conference on Symmetries in
Subatomic Physics, Adelaide, Mar. 13-17, 200
Strong Isospin Breaking in CP-even and CP-odd K -> pi pi Decays
Complete next-to-leading (chiral) order (NLO) expressions for the strong
isospin-breaking (IB) contributions in K -> pi pi are used to discuss (1) for
CP-even, the impact on the magnitude of the Delta I=1/2 Rule, and (2) for
CP-odd, the strong IB correction, Omega_st, for the gluonic penguin
contribution to epsilon'/epsilon, with particular emphasis on the strong
low-energy constant (LEC) and loop contributions, numerical values for which
are model-independent at NLO.Comment: 4 pages. Contribution to the proceedings of the 7th Conference on the
Intersections of Particle and Nuclear Physics (CIPANP), May 22-28 2000,
Quebec City, Canada. Uses AIP 6x9 LaTeX styl
Violation of the I=1/2 rule in the nonmesonic weak decay of hypernuclei
Violations of the I=1/2 rule are investigated in the nonmesonic weak
hypernuclear decay using a weak NNN transition potential based on
meson exchange. While the weak I=3/2 matrix elements of baryons with
pseudoscalar mesons are known to be very small, the same matrix elements of
baryons with vector mesons, evaluated in the factorization approximation, are
found to be significant. Within the uncertainties of the factorization
approximation we find that the total rate increases by at most 6% lying within
the error bars of the more recent experimental result. The neutron- to
proton-induced rate, on the other hand, can change by up to a factor of two,
while the asymmetry parameter is strongly affected as well.Comment: 17 pages. Paper related to a contribution presented at the
International Conference on Hypernuclear and Strange Particle Physics
(HYP97). Submitted to Phys. Lett.
O(m_d-m_u) Effects in CP-even and CP-odd K-->pi pi Decays
Strong isospin-breaking (IB) effects in CP-even and CP-odd K-->pi pi decays are computed to next-to-leading order (NLO) in the chiral expansion. The impact of these corrections on the magnitude of the Delta I=1/2 Rule and on the size of the IB correction, Omega_IB, to the gluonic penguin contribution to epsilon'/epsilon are discussed
V_us From Hadronic Tau Decays
We study extractions of |V_us| based on finite energy sum rule (FESR)
analyses of hadronic tau decay data. We show (i) that the ``(0,0) spectral
weight'' implementation (proposed previously in the literature as a favorable
version of this analysis) suffers from significant convergence problems, but
(ii) that alternate implementations exist which bring these problems under
control. Results based on present spectral data are shown to be in agreement
with those of other approaches, though with, at present, somewhat larger
experimental errors. Sub-1% determinations of |V_us| are also shown to be
expected from these alternate analyses once tau data from the B factories
becomes available.Comment: 4 pages, prepared for the proceedings of the 9th Conference on the
Intersections of Particle and Nuclear Physics (CIPANP06), Westin Rio Mar
Resort, Puerto Rico, May 30-June 3, 200
Decay constants, light quark masses and quark mass bounds from light quark pseudoscalar sum rules
The flavor and pseudoscalar correlators are investigated using
families of finite energy sum rules (FESR's) known to be very accurately
satisfied in the isovector vector channel. It is shown that the combination of
constraints provided by the full set of these sum rules is sufficiently strong
to allow determination of both the light quark mass combinations ,
and the decay constants of the first excited pseudoscalar mesons in
these channels. The resulting masses and decay constants are also shown to
produce well-satisfied Borel transformed sum rules, thus providing non-trivial
constraints on the treatment of direct instanton effects in the FESR analysis.
The values of and obtained are in good agreement with the
values implied by recent hadronic decay analyses and the ratios obtained
from ChPT. New light quark mass bounds based on FESR's involving weight
functions which strongly suppress spectral contributions from the excited
resonance region are also presented.Comment: 28 pages, 10 figure
The Strange Quark Mass From Flavor Breaking in Hadronic Tau Decays
The strange quark mass is extracted from a finite energy sum rule (FESR)
analysis of the flavor-breaking difference of light-light and light-strange
quark vector-plus-axial-vector correlators, using spectral functions determined
from hadronic tau decay data. We point out problems for existing FESR
treatments associated with potentially slow convergence of the perturbative
series for the mass-dependent terms in the OPE over certain parts of the FESR
contour, and show how to construct alternate weight choices which not only cure
this problem, but also (1) considerably improve the convergence of the
integrated perturbative series, (2) strongly suppress contributions from the
region of s values where the errors on the strange current spectral function
are still large and (3) essentially completely remove uncertainties associated
with the subtraction of longitudinal contributions to the experimental decay
distributions. The result is an extraction of m_s with statistical errors
comparable to those associated with the current experimental uncertainties in
the determination of the CKM angle, V_{us}. We find m_s(1 GeV)=158.6\pm 18.7\pm
16.3\pm 13.3 MeV (where the first error is statistical, the second due to that
on V_{us}, and the third theoretical).Comment: 13 pages, 2 figures; final version to appear in Phys. Rev. D;
expanded versions of Figure 2 and Reference 3
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