p final-state interaction in the reactions e^+e^- → K^- p and J/ψ→ K^- p

Near-threshold pΛ̅ mass spectra for the reactions e^+e^- → K^- pΛ̅ and J/ψ→ K^- pΛ̅ are investigated with an emphasis on the role played by the interaction in the pΛ̅ system. As guideline for the pΛ̅ interaction a variety of ΛΛ̅ potential models is considered that have been established in the analysis of data on pp̅→ΛΛ̅ in the past. Arguments why the properties of the pΛ̅ and ΛΛ̅ interactions can be expected to be very similar are provided. It is shown that the near-threshold enhancement in the invariant mass observed for the e^+e^- reaction can be reproduced quantitatively by the assumed pΛ̅ final-state interaction in the partial wave suggested by an amplitude analysis of the experiment. The effect of the pΛ̅ final-state interaction in other decays is explored, including the recently measured reactions B^- → J/ψ p̅Λ and B^+ → J/ψ p Λ̅ . It is found that the final-state interaction improves the description of the measured invariant mass near threshold in most cases.