369 research outputs found
Extracting m_s From Flavor Breaking in Hadronic Tau Decays
New finite energy sum rules (FESR's) for extracting m_s from hadronic tau
decay data are constructed which (1) significantly reduce potential theoretical
uncertainties present in existing sum rule analyses and (2) remove problems
associated with both the poor convergence of the OPE representation of the
longitudinal part of the vector and axial vector correlators and the large
statistical errors in the spectral data above the K^* region.Comment: 4 pages, 1 figure. Report of presentations to International
Conference on Quark Nuclear Physics, Adelaide, Feb. 21-25, 2000, 16th
International Conference on Problems in Few-Body Physics, Taipei, March 6-10,
2000, and 7th Conference on the Intersections of Particle and Nuclear
Physics, Quebec City, May 22-28, 200
OPE Constraints and the Leading Order Hadronic Contribution to (g-2)_mu
OPE constraints are studied as a means of distinguishing between the versions
of the I=1 vector spectral function extracted from (i) inclusive I=1 hadronic
electroproduction cross-sections and (ii) inclusive I=1 hadronic tau decay
data, with the goal of clarifying expectations for the leading order hadronic
contribution to a_mu = (g-2)_mu /2 in the Standard Model. The constraints are
shown to, at present, favor the tau decay data, and hence a Standard Model
prediction for a_mu compatible with the BNL E821 experimental result. The
relative role of the 2pi and 4pi contributions to the discrepancy between the
integrated electroproduction results and the corresponding OPE constraints is
also investigated, and the significance, in this context, of forthcoming
re-measurements of the e^+e^- --> pi^+ pi^- pi^0 pi^0 cross-sections pointed
out.Comment: 6 pages, 5 figures, prepared for the Proceedings of the 9th
International Workshop on Tau Lepton Physic
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.
Constraints on Hadronic Spectral Functions From Continuous Families of Finite Energy Sum Rules
Hadronic tau decay data is used to study the reliability of various finite energy sum rules (FESR's). For intermediate scales (of order 2-3 GeV^2), those FESR's with weights s^k are found to have significant errors, whereas those with weights having a zero at the juncture (s=s_0) of the cut and circular part of the contour work very well. It is also shown that a combination of two such sum rules allows rather strong constraints to be placed on the hadronic spectral function without sacrificing the excellent agreement between OPE and hadronic representations. The method then is applied to the strangeness -1 and pseudoscalar isovector channels, where it is shown to provide novel constraints on those ansatze for the unmeasured continuum parts of the spectral functions employed in existing extractions of m_u+m_d, m_s. The continuum ansätz in the latter channel, in particular, is shown to produce a rather poor match to the corresponding OPE representation, hence re-opening the question of the value of the light quark mass combination m_u+m_d
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
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