Single-Pion Production in pp Collisions at =.95 GeV/c (I)

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The single-pion production reactions pp→ dπ+, pp→ npπ+ and pp→ ppπ⁰ were measured at a beam momentum of 0.95 GeV/c (Tₚ ≈ 400 MeV) using the short version of the COSY-TOF spectrometer. The implementation of a central calorimeter provided particle identification, energy determination and neutron detection in addition to time-of-flight and angle measurements. Thus all pion production channels were recorded with 1-4 overconstraints. The total and differential cross sections obtained are compared to previous data and theoretical calculations. Main emphasis is put on the discussion of the ppπ⁰ channel, where we obtain angular distributions different from previous experimental results, however, partly in good agreement with recent phenomenological and theoretical predictions. In particular we observe very large anisotropies for the π⁰ angular distributions in the kinematical region of small relative proton momenta revealing there a dominance of proton spinflip transitions associated with π⁰ s- and d-partial waves and emphasizing the important role of π⁰ d-waves.