498 research outputs found
A model-independent analysis of final-state interactions in \bar B_{d/s}^0 --> J/psi pi pi
Exploiting -meson decays for Standard Model tests and beyond requires a
precise understanding of the strong final-state interactions that can be
provided model-independently by means of dispersion theory. This formalism
allows one to deduce the universal pion-pion final-state interactions from the
accurately known phase shifts and, in the scalar sector, a
coupled-channel treatment with the kaon-antikaon system. In this work an
analysis of the decays and is presented. We find very good agreement with the data up
to 1.05 GeV with a number of parameters reduced significantly compared to a
phenomenological analysis. In addition, the phases of the amplitudes are
correct by construction, a crucial feature when it comes to studies of
violation in heavy-meson decays.Comment: 25 pages, 6 figures, version published in JHE
Isospin violation in the vector form factors of the nucleon
A quantitative understanding of isospin violation is an increasingly
important ingredient for the extraction of the nucleon's strange vector form
factors from experimental data. We calculate the isospin violating electric and
magnetic form factors in chiral perturbation theory to leading and
next-to-leading order respectively, and we extract the low-energy constants
from resonance saturation. Uncertainties are dominated largely by limitations
in the current knowledge of some vector meson couplings. The resulting bounds
on isospin violation are sufficiently precise to be of value to on-going
experimental studies of the strange form factors.Comment: 13 pages, 8 figures, uses RevTe
Towards an improved understanding of eta --> gamma^* gamma^*
We argue that high-quality data on the reaction
will allow one to determine the double off-shell form factor in a model-independent way with controlled accuracy. This is
an important step towards a reliable evaluation of the hadronic light-by-light
scattering contribution to the anomalous magnetic moment of the muon. When
analyzing the existing data for in the range of
total energies , we demonstrate that the
double off-shell form factor is
consistent with the commonly employed factorization ansatz at least for
, if the effect of the meson is taken into account.
However, better data are needed to draw firm conclusions.Comment: 7 pages, 3 figure
Effects of states and bottom meson loops on transitions
We study the dipion transitions . In particular, we consider the effects of the two
intermediate bottomoniumlike exotic states and as
well as bottom meson loops. The strong pion-pion final-state interactions,
especially including channel coupling to in the -wave, are taken
into account model-independently by using dispersion theory. Based on a
nonrelativistic effective field theory we find that the contribution from the
bottom meson loops is comparable to those from the chiral contact terms and the
-exchange terms. For the decay, the result shows that including the effects of the
-exchange and the bottom meson loops can naturally reproduce the two-hump
behavior of the mass spectra. Future angular distribution data are
decisive for the identification of different production mechanisms. For the
decay, we show that there is
a narrow dip around 1 GeV in the invariant mass distribution, caused
by the final-state interactions. The distribution is clearly different from
that in similar transitions from lower states, and needs to be
verified by future data with high statistics. Also we predict the decay width
and the dikaon mass distribution of the process.Comment: 25 pages, 8 figures, predictions of the decay width and the dikaon
mass distribution of the
process added, more discussions adde
Efficient and realistic device modeling from atomic detail to the nanoscale
As semiconductor devices scale to new dimensions, the materials and designs
become more dependent on atomic details. NEMO5 is a nanoelectronics modeling
package designed for comprehending the critical multi-scale, multi-physics
phenomena through efficient computational approaches and quantitatively
modeling new generations of nanoelectronic devices as well as predicting novel
device architectures and phenomena. This article seeks to provide updates on
the current status of the tool and new functionality, including advances in
quantum transport simulations and with materials such as metals, topological
insulators, and piezoelectrics.Comment: 10 pages, 12 figure
Electric and magnetic form factors of strange baryons
Predictions for the electromagnetic form factors of the Lambda$, Sigma and Xi
hyperons are presented. The numerical calculations are performed within the
framework of the fully relativistic constituent-quark model developed by the
Bonn group. The computed magnetic moments compare favorably with the
experimentally known values. Most magnetic form factors G_M(Q^2) can be
parametrized in terms of a dipole with cutoff masses ranging from 0.79 to 1.14
GeV.Comment: 15 pages, 8 figures, 3 tables, submitted to Eur. Phys. J.
Strange form factors and Chiral Perturbation Theory
We review the contributions of Chiral Perturbation Theory to the theoretical
understanding or not-quite-yet-understanding of the nucleon matrix elements of
the strange vector current.Comment: 4 pages, 6 figures, presented at the International Workshop on Parity
Violation and Hadronic Structure (PAVI04), Grenoble, France, 8-11 Jun 200
Isospin breaking in the vector current of the nucleon
Extraction of the nucleon's strange form factors from experimental data
requires a quantitative understanding of the unavoidable contamination from
isospin violation. A number of authors have addressed this issue during the
past decade, and their work is reviewed here. The predictions from early models
are largely consistent with recent results that rely as much as possible on
input from QCD symmetries and related experimental data. The resulting bounds
on isospin violation are sufficiently precise to be of value to on-going
experimental and theoretical studies of the nucleon's strange form factors.Comment: 5 pages, 3 figures. Presented at the International Workshop "From
Parity Violation to Hadronic Structure and more...", Milos, Greece, 16-20 May
2006. Version 2 is only to update Refs. [21] and [25
Диагностика частотной области изоляции трансформатора
The first part of paper deals with the base information about diagnostics of power transformers. In this part are presented differently insulating methods, for example method of recovery voltage method, method of polarization and depolarization currents and chromatographic analysis. The second part of paper deals use of method of frequency domain spectroscopy for oil power transformers. This method is used in analysis insulating condition of power transformer with system of oil-paper. It was found, that the results of these tests are highly impacted by the operating temperature during the experimental measurement. Moisture and conductivity between insulating paper and oil in an insulating system are highly dependent from temperature. In the other part, the paper presents experimental results of the frequency diagnostic measurement for a real single-phase traction transformer 110/27 kV at different operating temperatures and states (with oil and without). Finally in the last part, the paper presents comparing frequency insulating measurements among several the same single-phase transformers 110/27 kV
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