172 research outputs found
Antiproton-Proton Channels in J/psi Decays
The recent measurements by the BES Collaboration of J/psi decays into a
photon and a proton-antiproton pair indicate a strong enhancement at the
proton-antiproton threshold not observed in the decays into a neutral pion and
a proton-antiproton pair. Is this enhancement due to a proton-antiproton
quasi-bound state or a baryonium? A natural explanation follows from a
traditional model of proton-antiproton interactions based on G-parity
transformation. The observed proton-antiproton structure is due to a strong
attraction in the 1S0 state, and possibly to a near-threshold quasi-bound state
in the 11S0 wave.Comment: 6 pages, 5 figures. The antiproton-proton pair being in isospin one
in the J/Psi decay into neutral pion-antiproton-proton, the antiproton-proton
1P1 and 3S1 waves have been replaced by the 31P1 and 33S1 ones and Figs. 1
and 2 have been replaced accordingly. Conclusions are unchanged. Most of the
content of the paper is published in Phys. Rev. C72, 011001 (2005
-invariant two-fermion Dirac equation with extended hyperfine operator
For the S-states of muonium and positronium, the hyperfine shifts to the
order of a recently derived two-fermion equation with explicit -invariance are checked against the results of a nonrelativistic reduction,
and the leading shifts are calculated. An additional hyperfine
operator is discovered which can milden the singularity for of the
Dirac hyperfine operator, such that the resulting extended operator can be used
nonperturbatively. The binding correction to magnetic moments is mentioned
Antihyperon polarization in high-energy inclusive reactions
We propose a model for the antihyperon polarization in high-energy
proton-nucleus inclusive reactions, based on the final-state interactions
between the antihyperons and other produced particles (predominantly pions). To
formulate this idea, we use the previously obtained low-energy
pion-(anti-)hyperon interaction using effective chiral Lagrangians, and a
hydrodynamic parametrization of the background matter, which expands and
decouples at a certain freezeout temperature.Comment: 17 pages, 10 figure
The pion-pion scattering amplitude. II: Improved analysis above threshold
We improve, in the energy region between threshold and
GeV, the energy-dependent phase shift analysis of scattering presented
in a previous paper. For the S0 wave we have included more data above
threshold and we have taken into account systematically the
elasticity data on the reaction . We here made a coupled
channel fit. For the D0 wave we have considered information on low energy
parameters, and imposed a better fit to the resonance. For both waves the
expressions we now find are substantially more precise than the previous ones.
We also provide slightly improved D2 and P waves, including the estimated
inelasticity for the first, and a more flexible parametrization between 1 and
1.42 GeV for the second. The accuracy of our amplitudes is now such that it
requires a refinement of the Regge analysis, for GeV, which
we also carry out. We show that this more realistic input produces
scattering amplitudes that satisfy better forward dispersion relations,
particularly for scattering.Comment: Plain TeX. 12 figures. Minor anomaly in the K-matrix fit corrected by
moving matching point to 932 MeV, and pole to 910.6 MeV. Results
unaltere
Antiproton-proton resonant like channels in J/Psi decays into photon, proton and antiproton
The BES collaboration has recently observed a strong enhancement close to the
proton-antiproton threshold in the J/Psi decays into photon, proton and
antiproton. Such a structure can be explained by a traditional
nucleon-antinucleon model. The near threshold 1S0 bound state and/or the
well-established 3P0 resonant state found in this nucleon-antinucleon
interaction can adequately describe the BES data.Comment: Invited talk at the 10th International Symposium on Meson-Nucleon
Physics and the Structure of the Nucleon (MENU 2004), Beijing, China, August
29 - September 4, 2004 - 4 pages, 2 figure
Eight-component two-fermion equations
An eight-component formalism is proposed for the relativistic two-fermion
problem. In QED, it extends the applicability of the Dirac equation with
hyperfine interaction to the positronium case. The use of exact relativistic
two-body kinematics entails a CP-invariant spectrum which is symmetric in the
total cms energy. It allows the extension of recent \alpha^6 recoil corrections
to the positronium case, and implies new recoil corrections to the fine and
hyperfine structures and to the Bethe logarithm.Comment: Revtex, accepted for publication in Phys. Rev.
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