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

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