243 research outputs found
Issues in determining alpha_s from hadronic tau decay and electroproduction data
We discuss some key issues associated with duality-violating and
non-perturbative OPE contributions to the theoretical representations of light
quark current-current two-point functions and relevant to precision
determinations of alpha_s from hadronic tau decay and electroproduction
cross-section data. We demonstrate that analyses with an explicit
representation of duality-violating effects are required to bring theoretical
errors in such extractions under control, motivating the accompanying paper in
these proceedings, which presents the results of such an analysis.Comment: 5 pages, 4 figures. Prepared for the Proceedings of the International
Workshop on e+e- collisions from Phi to Psi (PHIPSI11), Sep. 19-22, 2011,
BINP, Novosibirsk, Russi
Duality Violation and the K --> pi pi Electroweak Penguin Operator Matrix Elements from Hadronic Tau Decays
We discuss a preliminary study of the impact of duality violations on
extractions from tau decay data of the D=6 VEVs which determine chiral limit
Standard Model K-->pi pi matrix elements of the electroweak penguin operators.Comment: 4 pages, 5 figures, prepared for the Proceedings of the 11th Particle
and Nuclear Intersections Conference (PANIC 2011), Boston, USA, July 24-29,
201
Isospin-Breaking Vacuum-to-Pi^0,Eta Pseudoscalar Matrix Elements at Next-to-Leading Order in the Chiral Expansion
We employ Chiral Perturbation Theory (ChPT) to evaluate the complete set of
pseudoscalar matrix elements, , with P_f any of the
flavor-diagonal pseudoscalar currents (f=u,d,s), to order (m_d-m_u), and to
next-to-leading order in the chiral expansion. These matrix elements represent
the basic input to a QCD sum rule analysis of isospin breaking in the pi NN
couplings using the three-point-function method. We discuss also how one could
use the results to construct a one parameter family of interpolating fields for
the , all of whose members have zero vacuum-to- matrix element,
and explain how this could in principle be used to provide non-trivial tests of
the reliability of the assumptions underlying the use of the
three-point-function method. It is shown that the isospin-breaking mixing
parameters required for this construction receive significant corrections
beyond leading order in the chiral expansion.Comment: 9 pages, 1 postscript figur
Isospin Breaking and -> Decay
We study decay up to including all orders of the chiral
expansion and one-loop level of mesons in formlism of chiral constituent quark
model. This G-parity forbidden decay is caused by and
electromagnetic interaction of mesons. We illustrate that in the formlism both
nonresonant contact interaction and resonance exchange contribute to
this process, and the contribution from resonance exchange is dominant.
We obtain that transition matrix element is
MeV, and
isospin breaking parameter is MeV at energy scale .Comment: Revtex file, 16 pages, four eps figur
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
The discovery and properties of pentaquarks
The pentaquarks are exotic baryons formed of four quarks and an antiquarks.
Their existence has been discussed in the literature over the last 30 years or
more, first in connection with kaon nucleon scattering data. The subject has
been revived by the end of 2002 when experimental evidence of a narrow baryon
of strangeness = + 1, and mass 1530 MeV has been found. This is
interpreted as the lightest member of an SU(3)-flavor antidecuplet. Here we
shall mainly review the predictions of pentaquark properties as e.g. mass, spin
and parity, within constituent quark models.
Both light and heavy pentaquarks will be presented.Comment: Plenary talk, MESON2004 Conference Proceedings, Crakow, June 4-8 200
Z^* Resonances: Phenomenology and Models
We explore the phenomenology of, and models for, the Z^* resonances, the
lowest of which is now well established, and called the Theta. We provide an
overview of three models which have been proposed to explain its existence
and/or its small width, and point out other relevant predictions, and potential
problems, for each. The relation to what is known about KN scattering,
including possible resonance signals in other channels, is also discussed.Comment: 29 pages, uses RevTeX4; expanded version (published form
Duality violations in tau hadronic spectral moments
Evidence is presented for the necessity of including duality violations in a
consistent description of spectral function moments employed in the precision
determination of from decay. A physically motivated ansatz
for duality violations in the spectral functions enables us to perform fits to
spectral moments employing both pinched and unpinched weights. We describe our
analysis strategy and provide some preliminary findings. Final numerical
results await completion of an ongoing re-determination of the ALEPH covariance
matrices incorporating correlations due to the unfolding procedure which are
absent from the currently posted versions. To what extent this issue affects
existing analyses and our own work will require further study.Comment: 6 pages, 3 figures. Talk given at 11th International Workshop on Tau
Lepton Physics, Manchester, UK, 13-17 September 201
- …