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

Near-threshold pΛ mass spectra for the reactions e⁺e⁻ → K⁻ pΛ and J/ψ → K⁻ pΛ are investigated with an emphasis on the role played by the interaction in the pΛ system. As guideline for the pΛ interaction a variety of ΛΛ potential models is considered that have been established in the analysis of data on p p→ ΛΛ in the past. Arguments why the properties of the pΛ and ΛΛ 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 pΛ final-state interaction in the partial wave suggested by an amplitude analysis of the experiment. The effect of the pΛ final-state interaction in other decays is explored, including the recently measured reactions B⁻ → J/ψ\, p Λ and B⁺ → J/ψ\, p Λ. It is found that the final-state interaction improves the description of the measured invariant mass near threshold in most cases.