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

Abstract Near-threshold p p Λ ¯ mass spectra for the reactions e^+e^- K^- p e + e - → K - p Λ ¯ and J/ K^- p J / ψ → K - p Λ ¯ are investigated with an emphasis on the role played by the interaction in the p p Λ ¯ system. As guideline for the p p Λ ¯ interaction a variety of Λ Λ ¯ potential models is considered that have been established in the analysis of data on pp p p ¯ → Λ Λ ¯ in the past. Arguments why the properties of the p p Λ ¯ and Λ Λ ¯ 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^- e + e - reaction can be reproduced quantitatively by the assumed p p Λ ¯ final-state interaction in the partial wave suggested by an amplitude analysis of the experiment. The effect of the p p Λ ¯ final-state interaction in other decays is explored, including the recently measured reactions B^- J/ \, p B - → J / ψ p ¯ Λ and B^+ J/ \, p 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.