Final-state interactions in the process $\bar pp \to pK^ + \Lambda$

The possibility to determine the pΛ scattering length from the final-state interaction in the reaction p¯p→pK+Λ is investigated experimentally. From a transversely polarized measurement, the K + analyzing power (A N ) which, in principle, allows one to extract the spin triplet scattering length is studied. An unexpected energy dependence of the forward/backward symmetric part of A N is found. The influence of N * resonances on the pΛ invariant mass spectrum is investigated by exploiting the large acceptance for the process p¯p→pK+Λ→pK+pπ− and is found to be the main source of uncertainty for determining the pΛ scattering length