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in isospin one in the J/Psi decay into neutral pion-antiproton-proton, the antiproton-proton 1P1 and 3S1 waves have been replaced by the 31P1 and 33S1 ones and Figs. 1 and 2 have been replaced accordingly.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

CPT\cal CPT-invariant two-fermion Dirac equation with extended hyperfine operator

For the S-states of muonium and positronium, the hyperfine shifts to the order $\alpha^6$ of a recently derived two-fermion equation with explicit $\cal CPT$-invariance are checked against the results of a nonrelativistic reduction, and the leading $\alpha^8$ shifts are calculated. An additional hyperfine operator is discovered which can milden the singularity for $r\to 0$ 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 KˉK\bar{K}K threshold

We improve, in the energy region between $\bar{K}K$ threshold and $\sim~1.4$ GeV, the energy-dependent phase shift analysis of $\pi\pi$ scattering presented in a previous paper. For the S0 wave we have included more data above $\bar{K}K$ threshold and we have taken into account systematically the elasticity data on the reaction $\pi\pi\to\bar{K}K$. 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 $f_2$ 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 $s^{1/2}\geq1.42$ GeV, which we also carry out. We show that this more realistic input produces $\pi\pi$ scattering amplitudes that satisfy better forward dispersion relations, particularly for $\pi^0\pi^0$ scattering.Comment: Plain TeX. 12 figures. Minor anomaly in the K-matrix fit corrected by moving matching point to 932 MeV, and pole $M_1$ to 910.6 MeV. Results unaltere

Breit type equation for mesonic atoms

The finite size effects and relativistic corrections in pionic and kaonic hydrogen are evaluated by generalizing the Breit equation for a spin-0 - spin-1/2 amplitude with the inclusion of the hadron electromagnetic form factors. The agreement of the relativistic corrections to the energies of the mesonic atoms with other methods used to evaluate them is not exact, but reasonably good. The precision values of the energy shifts due to the strong interaction, extracted from data, are however subject to the hadronic form factor uncertainties.Comment: 11 pages Late