Direct, Resonant Production of States with Positive Charge Conjugation in Electron-Positron Annihilation

Recent theory results on direct production of resonances with positive charge conjugationin electron-positron annihilation are reviewed. The strong modeldependence is emphasized, with predictions varying between 0.03 eV and 0.43 eV for the charmonium state with JPC = 1++ and between0.16 eV and4.25 eV for the state with JPC =2++. For the state with JPC = 0++ the cross section is of O $ \left( {\mathop m\nolimits_e^2 /\mathop M\nolimits_x^2 } \right) $ and thus negligeable for all practical purpose. The importance of the relative phase of the production amplitude is emphasized.

Diffractive hadron production at ultrahigh energies

Diffractive production is considered in the ultrahigh energy region where pomeron exchange amplitudes are transformed into black disk ones due to rescattering corrections. The corresponding corrections in hadron reactions h1 + h3 → h1 + h2 + h3 with small momenta transferred [Formula: see text] are calculated in terms of the K-matrix technique modified for ultrahigh energies. Small values of the momenta transferred are crucial for introducing equations for amplitudes. The three-body equation for hadron diffractive production reaction h1 + h3 → h1 + h2 + h3 is written and solved precisely in the eikonal approach. In the black disk regime final state scattering processes do not change the shapes of amplitudes principally but dump amplitudes by a factor ~ ¼; initial state rescatterings result in additional factor ~ ½. In the resonant disk regime initial and final state scatterings damp strongly the production amplitude that corresponds to σ inel /σ tot → 0 at [Formula: see text] in this mode.

ADVANCES IN A FIELD-THEORETIC UNDERSTANDING OF PION PRODUCTION IN NUCLEON–NUCLEON COLLISIONS

We study the production amplitude for the reaction NN → NNπ up to next-to-leading order in chiral perturbation theory. We show that the irreducible chiral loops at this order exactly cancel those terms that arise from the off-shell parts of the πN rescattering vertex. This cancellation is required for formal consistency of the whole scheme. The net effect of the inclusion of all next-to-leading order loops is to enhance the leading rescattering amplitude by a factor of 4/3 compared to phenomenological studies, bringing its contribution to the cross section for pp → dπ+ close to the experimental value.