Analysis of the Λp Final State Interaction in the Reaction p + p → K + ( Λp )

The missing mass spectrum measured in high resolution studies of the reaction pp → K + X is analyzed with respect to the strong final state interaction near the Λp production threshold. The observed spectrum can be described by factorizing the reaction amplitude in terms of a production amplitude and a final state scattering amplitude. Parametrizing the Λp final state interaction in terms of the inverse Jost function allows a direct extraction of the low-energy phase-equivalent potential parameters. Constraints on the singlet and triplet scattering lengths and effective ranges are deduced in a simultaneous fit of the Λp invariant mass spectrum and the total cross section data of the free Λp scattering using the effective range approximation.