Photon or meson formation in J/ψ decays into pp¯

Abstract

The measurements of the J/ψ → γpp decays by the BES Collaboration indicate an enhancement at the pp threshold which, however, is not present in the J/ψ decays into ωpp and into πpp. Here, two processes for describing the decays J/ψ → Bpp where B = γ, ω are presented in some detail and the cases B = φ, π are briefly touched on. The first one, applied not only to the radiative decay to reproduce the threshold peak but also to the ωpp decay channel to improve the description of the spectrum, postulates a direct emission of the boson before the baryon pair is formed. The second process assumes that the boson B is emitted from the baryon pair following the J/ψ decay and includes for the decays into γpp a final state nucleon-antinucleon interaction based on the Paris N N potential. The reproduction of the pp distribution in the J/ψ → ωpp decays needs a final state interaction involving a N (2050) 3/2 − resonance. The photon-and meson-emission rates are reproduced in a semi-quantitative way. PACS numbers: 12.39.Pn, 13.20Gd, 13.60.le, 13.75.Cs, 14.65Dw an enhancement close to the pp threshold has been observed by the BES 1 Collaboration [4,5]. We note that both the J/ψ and the photon have J P C = 1 −− . There are three final pp states allowed by parity, P , and charge-conjugation, 1 Beijing Electron Sprectrometer

Extraction of baryonia from the lightest anti-protonic atoms

“…The short distance parameter β is extracted from electron or pion scattering experiments and fixed to reproduce the zeros of charge form-factors. Thus for 3 He, α = 0.45, β = 1.753 [23,24], and for 4 He, α = 0.846, β = 1.20 [22], all in fm −1 units. Reference [25] finds (with a different N N potential) a 2% higher order corrections to the 2P levels in deuterium.…”

“…The separation, average recoil energies and the spread of recoil energies are given in Table III. These values and the separation energies indicate that three atoms 2 H, 3 He, 4 He cover disjoint energy regions from about -5 down to -40 MeV. Therefore, a model is required for the sub-threshold extrapolation.…”

“…The downward shift of 33 P 1 required by the deuteron levels does not remove the inconsistency. Apparently there is another source of the difficulty and the 4 He atoms indicate a new possibility. [11] 18±2 45±5…”

“…Interpretation, in the J/ψ → γpp process, of the close to pp threshold enhancement in terms of N N potentials [4,5] leads to the conclusion that there exist a broad spin singlet S-wave quasi-bound state. However, the state obtained [5] by Bonn potential is formed in the isospin I=1.…”

“…In this work we study the level shifts and widths due to pN interactions in the lightest atoms (levels): 2 H(2P ), 3 He(2P , 3D) and 4 He(2P , 3D). The number of states is limited to those characterized by very low atomic-nuclear overlaps.…”