Final State Interactions and Polarization Observables in the Reaction pp → pKΛ

Due to the lack of high quality hyperon beams, final state interactions in hyperon production reactions are a compelling tool to study hyperon-nucleon interactions. The COSY-TOF experiment has recently been upgraded in order to reconstruct the pK A final state with sufficient precision to determine the spin triplet pA scattering length with a polarized proton beam. We find an unexpected behavior of the K analyzing power which prevents the extraction method to be used with the available statistics. A theoretical explanation is pending. Furthermore, the polarized beam together with the self analyzing decay of the A allows us to determine the A depolarization. This is especially sensitive to K and 7r exchange in the production mechanism. Our finding verifies, to a large extent, the result from DISTO [2] that has so far been the only measurement close to the production threshold.