Single-pion production in pp collisions at 0.95 GeV/c (II)

The single-pion production reactions pp → d π + , pp → np π+ and pp → pp π0 were measured at a beam momentum of 0.95GeV/c ( T p ≈ 400 MeV) using the short version of the COSY-TOF spectrometer. The central calorimeter provided particle identification, energy determination and neutron detection in addition to time-of-flight and angle measurements from other detector parts. Thus all pion production channels were recorded with 1-4 overconstraints. The main emphasis is put on the presentation and discussion of the npπ+ channel, since the results on the other channels have already been published previously. The total and differential cross-sections obtained are compared to theoretical calculations. In contrast to the ppπ0 channel we observe in the npπ+ channel a strong influence of the Δ excitation. In particular, the pion angular distribution exhibits a (3 cos2 Θ + 1) -dependence, typical for a pure s -channel Δ excitation and identical to that observed in the d φ+ channel. Since the latter is understood by a s -channel resonance in the 1 D 2 pn partial wave, we discuss an analogous scenario for the pn π+ channel. © 2009 SIF, Springer-Verlag Berlin Heidelberg.