366 research outputs found
Measurement of coherent ϕ-meson photoproduction from the deuteron at low energies
The cross section and decay angular distributions for the coherent ϕ-meson photoproduction on the deuteron have been measured for the first time up to a squared four-momentum transfer t=(pγ−pϕ)2=−2 GeV2/c2, using the CLAS detector at the Thomas Jefferson National Accelerator Facility. The cross sections are compared with predictions from a rescattering model. In a framework of vector meson dominance, the data are consistent with the total ϕ-N cross section σϕN at about 10 mb. If vector meson dominance is violated, a larger σϕN is possible by introducing a larger t slope for the ϕN→ϕN process than that for the γN→ϕN process. The decay angular distributions of the ϕ are consistent with helicity conservation
Photonic SUSY Two-Loop Corrections to the Muon Magnetic Moment
Photonic SUSY two-loop corrections to the muon magnetic moment are
contributions from diagrams where an additional photon loop is attached to a
SUSY one-loop diagram. These photonic corrections are evaluated exactly,
extending a leading-log calculation by Degrassi and Giudice. Compact analytical
expressions are provided and the numerical behaviour is discussed. The photonic
corrections reduce the SUSY one-loop result by 7...9%. The new terms are
typically around ten times smaller than the leading logarithms, but they can be
larger and have either sign in cases with large SUSY mass splittings. We also
provide details on renormalization and regularization and on how to incorporate
the photonic corrections into a full SUSY two-loop calculation.Comment: 25 page
A Pair Polarimeter for Linearly Polarized High Energy Photons
A high quality beam of linearly polarized photons of several GeV will become
available with the coherent bremsstrahlung technique at JLab. We have developed
a polarimeter which requires about two meters of the beam line, has an
analyzing power of 20% and an efficiency of 0.02%. The layout and first results
of a polarimeter test on the laser back-scattering photon beam at SPring-8/LEPS
are presented
Status of KLOE-2
In a few months the KLOE-2 detector is expected to start data taking at the
upgraded DANE -factory of INFN Laboratori Nazionali di
Frascati. It aims to collect 25 fb at the peak, and about 5
fb in the energy region between 1 and 2.5 GeV. We review the status and
physics program of the projectComment: 6 pages, 5 figures, to appear in the Proceedings of the PHIPSI09
Workshop, Oct 13-16, 2009, Beijing, Chin
Forward coherent -meson photoproduction from deuterons near threshold
Differential cross sections and decay asymmetries for coherent -meson
photoproduction from deuterons were measured for the first time at forward
angles using linearly polarized photons at = 1.5-2.4 GeV. This
reaction offers a unique way to directly access natural-parity Pomeron dynamics
and gluon exchange at low energies. The cross sections at zero degrees increase
with increasing photon energy. The decay asymmetries demonstrate a complete
dominance of natural-parity exchange processes, showing that isovector
unnatural-parity -meson exchange is small. Nevertheless the deduced cross
sections of -mesons from nucleons contributed by isoscalar t-channel
exchange processes are not well described by the conventional Pomeron model.Comment: 14 pages, 6 figures. Final published versio
Development of portable NMR polarimeter system for polarized HD target
A portable NMR polarimeter system has been developed to measure the
polarization of a polarized Hydrogen-Deuteride (HD) target for hadron
photoproduction experiments at SPring-8. The polarized HD target is produced at
the Research Center for Nuclear Physics (RCNP), Osaka university and is
transported to SPring-8. The HD polarization should be monitored at both
places. We have constructed the portable NMR polarimeter system by replacing
the devices in the conventional system with the software system with PCI
eXtensions for Instrumentation (PXI). The weight of the NMR system is downsized
from 80 kg to 7 kg, and the cost is reduced to 25%. We check the performance of
the portable NMR polarimeter system. The signal-to-noise (S/N) ratio of the NMR
signal for the portable system is about 50% of that for the conventional NMR
system. This performance of the portable NMR system is proved to be compatible
with the conventional NMR system for the polarization measurement.Comment: 6 page, 8 figures, 2011/Mar/9 Replace Author
New results on the hadronic vacuum polarization to the muon g-2
Results on the lowest-order hadronic vacuum polarization contribution to the
muon magnetic anomaly are presented. They are based on the latest published
experimental data used as input to the dispersion integral. Thus recent results
on tau to nutau pi pi0 decays from Belle and on e+ e- annihilation to pi+ pi-
from BABAR and KLOE are included. The new data, together with improved
isospin-breaking corrections for tau decays, result into a much better
consistency among the different results. A discrepancy between the Standard
Model prediction and the direct g-2 measurement is found at the level of 3
sigma.Comment: proceedings of the PhiPsi09 conference, Oct. 13-16, 2009, Beijing,
Chin
Photoproduction of Lambda(1405) and Sigma^{0}(1385) on the proton at E_\gamma = 1.5-2.4 GeV
Differential cross sections for and reactions have been measured in the photon energy range
from 1.5 to 2.4 GeV and the angular range of for the
scattering angle in the center-of-mass system. This data is the first
measurement of the photoproduction cross section. The
lineshapes of \LamS measured in and decay modes
were different with each other, indicating a strong interference of the isospin
0 and 1 terms of the scattering amplitudes. The ratios of \LamS
production to \SigS production were measured in two photon energy ranges: near
the production threshold ( GeV) and far from it ( GeV). The observed ratio decreased in the higher photon energy
region, which may suggest different production mechanisms and internal
structures for these hyperon resonances
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