7,481 research outputs found
Electron-Positron Annihilation into Hadron-Antihadron Pairs
The reactions of electron-positron to nucleon-antinucleon pairs are studied
in a non-perturbative quark model. The work suggests that the two-step process,
in which the primary quark-antiquark pair forms first a vector meson which in
turn decays into a hadron pair, is dominant over the one-step process in which
the primary quark-antiquark pair is directly dressed by additional
quark-antiquark pairs to form a hadron pair. To reproduce the experimental data
of the reactions of electron-positron to proton-antiproton and
electron-positron to neutron-antineutron a D-wave omega-like vector meson with
a mass of around 2 GeV has to be introduced.Comment: 15 pages, 6 figure
Detection of Cherenkov light from air showers with Geiger-APDs
We have detected Cherenkov light from air showers with Geiger-mode APDs
(G-APDs). G-APDs are novel semiconductor photon-detectors, which offer several
advantages compared to conventional photomultiplier tubes in the field of
ground-based gamma-ray astronomy. In a field test with the MAGIC telescope we
have tested the efficiency of a G-APD / light catcher setup to detect Cherenkov
light from air showers. We estimate a detection efficiency, which is 60% higher
than the efficiency of a MAGIC camera pixel. Ambient temperature dark count
rates of the tested G-APDs are below the rates of the night sky light
background. According to these recent tests G-APDs promise a major progress in
ground-based gamma-ray astronomy.Comment: 4 pages, 5 figures, to appear in the proceedings of the 30th
International Cosmic Ray Conference, Merida, July 200
Electromagnetic form factors in the J/\psi mass region: The case in favor of additional resonances
Using the results of our recent analysis of e^+e^- annihilation, we plot the
curves for the diagonal and transition form factors of light hadrons in the
time-like region up to the production threshold of an open charm quantum
number. The comparison with existing data on the decays of J/\psi into such
hadrons shows that some new resonance structures may be present in the mass
range between 2 GeVand the J/\psi mass. Searching them may help in a better
understanding of the mass spectrum in both the simple and a more sophisticated
quark models, and in revealing the details of the three-gluon mechanism of the
OZI rule breaking in K\bar K channel.Comment: Formulas are added, typo is corrected, the text is rearranged.
Replaced to match the version accepted in Phys Rev
Evidence for Quark Spin-flip in Pomeron Exchange
Spin-parity analyses of the system in the reaction for photon laboratory energies from 20 to 70 GeV have shown that
production of the meson dominates, with a
background at the level of 20%. Using vector-meson dominance arguments, this
background is shown to be consistent with the data on .
The energy dependence of the data imply that the mechanism is a combination of
Reggeon and Pomeron exchange. Assuming that the latter is relevant only for the
component and extrapolating to W=200 GeV, it is argued that this
accounts for most of the preliminary signal observed by the H1
Collaboration in the same reaction. A residual peak can be ascribed to the
, which requires a quark spin-flip from Pomeron exchange. Precisely
the same mechanism occurs in the reaction .Comment: 6 pages, 3 figure
Isoscalar resonances with J^{PC}=1^{--} in e^+e^-annihilation
The analysis of the vector isoscalar excitations in the energy range between
1 and 2 GeV of the annihilation is presented for the final states
, , , and
. The effects of both the resonance mixing and the
successive opening of multiparticle channels, with the energy dependent partial
widths, are taken into account. The work extends our previous analysis
hep-ph/9609216 of the vector isovector excitations and is aimed to compare the
existing data with the predictions of the model. It is shown that
this hypothesis does not contradict the data.Comment: 16 pages, revtex, 6 ps figures. Clarifying remarks, a table, and
references are added. Accepted in Phys. Rev.
Precise method for the determination of the neutron electric form factor based on a relativistic analysis of the process $d(e,e'n)p
We generalize the recoil polarization method for the determination of the
proton form factor to the case of the disintegration of vector polarized
deuterons by longitudinally polarized electrons, . We
suggest to measure for this reaction, in the kinematics of quasi-elastic
-scattering, the ratio of the asymmetries induced by the
- and -components of the deuteron vector polarization. In the framework
of the relativistic impulse approximation the ratio is sensitive to
in a wide interval of momentum transfer squared, whereas it depends
weakly on the details of the -interaction and on the choice of the deuteron
wave function. Moreover, in the range 1.5 GeV, the ratio
shows a smooth dependence on , making the analysis simpler.Comment: 7 pages, 4 figs, 1 tabl
Does fix the Electromagnetic Form Factor at ?
We show that the decay is a reliable
source of information for the electromagnetic form factor of the pion at
by using general arguments to estimate, or
rather, put upper bounds on, the background processes that could spoil this
extraction. We briefly comment on the significance of the resulting
.Comment: 10 pages revtex manuscript, one figure--not included, U. of MD PP
#94-00
Rho primes in analyzing e+e- annihilation, MARK III, LASS and ARGUS data
The results of an analysis are presented of some recent data on the reactions
, with the
subtracted events, , , , , the decays
,
, upon taking into account both the strong energy
dependence of the partial widths on energy and the previously neglected mixing
of the type resonances. The above effects are shown to exert an
essential influence on the specific values of masses and coupling constants of
heavy resonances and hence are necessary to be accounted for in establishing
their true nature.Comment: 20 pages, ReVTeX, 9 Postscript figures As compared to hep-ph/9607398,
new material concerning the analysis of the ARGUS data on the tau decays into
four pion hadronic states is adde
Lithium ion-induced damage in silicon detectors
Silicon diodes processed by CNM on standard and oxygenated silicon substrates have been irradiated by 58 MeV lithium ions. The radiation-induced effects are very similar to the one observed after proton irradiation: substrate space charge sign inversion (SCSI), lower increase of the effective substrate doping concentration after SCSI for the oxygenated devices. The experimental radiation hardness factor has been determined to be 45.01, within 8.2% with the expected value. These results suggest that 58 MeV Li ions are a suitable radiation source for radiation hardness studies by ions heavier than protons for the future very high luminosity hadron colliders
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