100 research outputs found
Hadronic effects in leptonic systems: muonium hyperfine structure and anomalous magnetic moment of muon
Contributions of hadronic effects to the muonium physics and anomalous
magnetic moment of muon are considered. Special attention is paid to
higher-order effects and the uncertainty related to the hadronic contribution
to the hyperfine structure interval in the ground state of muonium.Comment: Presented at PSAS 2002 (St. Petersburg
Measurement of (1020) meson leptonic width with CMD-2 detector at VEPP-2M Collider
The (1020) meson leptonic width has been determined from the combined
analysis of 4 major decay modes of the resonance () studied with the CMD-2 detector at
the VEPP-2M collider. The following value has been obtained:
keV.
The meson parameters in four main decay channels have been also
recalculated: , , , .Comment: 14 pages, 3 figure
Electromagnetic form factors of charged and neutral kaons in an extended vector-meson-dominance model
A model is developed for electromagnetic form factors of the charged and
neutral K-mesons. The formalism is based on ChPT Lagrangians with vector
mesons. The form factors, calculated without fitting parameters, are in a good
agreement with experiment for space-like and time-like photon momenta.
Contribution of the two-kaon channels to the muon anomalous magnetic moment
a_\mu is calculated.Comment: 23 pages, 11 figures, accepted for publication in Eur. Phys. J.
Reevaluation of the hadronic contribution to the muon magnetic anomaly using new e+e- -> pi+pi- cross section data from BABAR
Using recently published, high-precision pi+pi- cross section data by the
BABAR experiment from the analysis of e+e- events with high-energy photon
radiation in the initial state, we reevaluate the lowest order hadronic
contribution a_mu[had,LO] to the anomalous magnetic moment of the muon. We
employ newly developed software featuring improved data interpolation and
averaging, more accurate error propagation and systematic validation. With the
new data, the discrepancy between the e+e- and tau-based results for the
dominant two-pion mode reduces from previously 2.4 sigma to 1.5 sigma in the
dispersion integral, though significant local discrepancies in the spectra
persist. We obtain for the e+e- based evaluation amu[had,LO] = (695.5 +- 4.1)
10^-10, where the error accounts for all sources. The full Standard Model
prediction of a_mu differs from the experimental value by 3.2 sigma.Comment: 9 pages, 7 figures. Version published in Eur. Phys. J. C. The theory
vs. experiment discrepancy increased by 0.1 \sigma, using the updated
experimental g-2 value with the new \mu_\mu/\mu_p rati
Contribution to muon g-2 from the \pi0\gamma and \eta\gamma intermediate states in the vacuum polarization
Using new experimental data, we have calculated the contribution to the
anomalous magnetic moment of the muon from the \pi0\gamma and \eta\gamma
intermediate states in the vacuum polarization with high precision:
a{\mu}(\pi0\gamma)+a{\mu}(\eta\gamma)=(54.7\pm 1.5)\times 10^{-11}. We have
also found the small contribution from e+e-\pi0, e+e-\eta and \mu+\mu-\pi0
intermediate states equal to 0.5\times 10^{-11}.Comment: 6 pages, 2 figures, revte
Radiative decays of light vector mesons in a quark level linear sigma model
We calculate the P0 to gamma gamma, V0 to P0 gamma and V0to V'0 gamma gamma
decays in the framework of a U(3)xU(3) linear sigma model which includes
constituent quarks. For the first two decays this approach improves results
based on the anomalous Wess-Zumino term, with contributions due to SU(3)
symmetry breaking and vector mixing. The phi to (omega,rho) gamma gamma decays
are dominated by resonant eta' exchange . Our calculation for the later decays
improves and update similar calculations in the -closely related- framework of
vector meson dominance. We obtain BR(phi to rho gamma gamma)=2.5x10^{-5} and
BR(phi to omega gamma gamma)=2.8x10^{-6} within the scope of the
high-luminosity phi factories.Comment: 8 pages, submitted to Phys. Rev.
Study of the Process in the C.M.Energy Range 1.05-1.38 GeV with CMD-2
The process has been studied with the CMD-2 detector
using about 950 events detected in the center-of-mass energy range from 1.05 to
1.38 GeV. The cross section exceeds the expectation based on the contributions
of the rho(770), omega(782) and phi(1020) mesons only.Comment: 12 pages, 3 figures, uses elsart.cls, submitted to Physics Letters
High-statistics measurement of the pion form factor in the rho-meson energy range with the CMD-2 detector
We present a measurement of the pion form factor based on e+e- annihilation
data from the CMD-2 detector in the energy range 0.6<sqrt(s)<1.0 GeV with a
systematic uncertainty of 0.8%. A data sample is five times larger than that
used in our previous measurement.Comment: 18 pages, 10 figures. Added comparison with KLOE measurement, minor
updates. Accepted by PL
Study of the Process e+ e- --> omega pi0 --> pi0 pi0 gamma in c.m. Energy Range 920--1380 MeV at CMD-2
The cross section of the process e+ e- --> omega pi0 --> pi0 pi0 gamma has
been measured in the c.m. energy range 920-1380 MeV with the CMD-2 detector.
Its energy dependence is well described by the interference of the rho(770) and
rho'(1450) mesons decaying to omega pi0. Upper limits for the cross sections of
the direct processes e+ e- --> pi0 pi0 gamma, eta pi0 gamma have been set.Comment: Accepted for publication in PL
The Discrepancy Between tau and e+e- Spectral Functions Revisited and the Consequences for the Muon Magnetic Anomaly
We revisit the procedure for comparing the pi pi spectral function measured
in tau decays to that obtained in e+e- annihilation. We re-examine the
isospin-breaking corrections using new experimental and theoretical input, and
find improved agreement between the tau- --> pi- pi0 nu_tau branching fraction
measurement and its prediction using the isospin-breaking-corrected e+e- -->
pi+pi- spectral function, though not resolving all discrepancies. We recompute
the lowest order hadronic contributions to the muon g-2 using e+e- and tau data
with the new corrections, and find a reduced difference between the two
evaluations. The new tau-based estimate of the muon magnetic anomaly is found
to be 1.9 standard deviations lower than the direct measurement.Comment: 10 pages, 6 figures, submitted to Eur. Phys. J. C; (v2): Revised
version with improved and uniform treatment of tau and e+e- data with
HVPTools and a few minor bug fixes; (v3): Final version accepted for
publicatio
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