Why are higher-order partial waves enhanced in reactions of pp-bar → YY-bar type

A considerable backward-forward asymmetry is observed in cross sections of binary reactions of the type pp-bar → YY-bar. This anisotropy can be phenomenologically explained due to relative enchancement of the higher-order partial wave contribution compared to the lower-order one. As an example for pp-bar → ΛΛ-bar reaction is shown that the enchancement is due to the initial- and final-state interaction. The derived formulas explain the reason of the enchancement in the model where the initial and final state interaction potential is approximated by a square-well complex potential