Search

The single-pion production reactions pp $ \rightarrow$ d $ \pi^{+}_{}$ , pp $ \rightarrow$ np $ \pi^{+}_{}$ and pp $ \rightarrow$ pp $ \pi^{0}_{}$ were measured at a beam momentum of 0.95GeV/c ( Tp $ \approx$ 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 np $ \pi^{+}_{}$ 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 pp $ \pi^{0}_{}$ channel we observe in the np $ \pi^{+}_{}$ channel a strong influence of the $ \Delta$ excitation. In particular, the pion angular distribution exhibits a (3 cos2 $ \Theta$ + 1) -dependence, typical for a pure s -channel $ \Delta$ excitation and identical to that observed in the d $ \pi^{+}_{}$ channel. Since the latter is understood by a s -channel resonance in the 1 D2 pn partial wave, we discuss an analogous scenario for the pn $ \pi^{+}_{}$ channel. [ABSTRACT FROM AUTHOR]

The single-pion production reactions pp → dπ+, pp → npπ+ and pp → ppπ0 were measured at a beam momentum of 0.95GeV/c ( T p ≈ 400MeV) 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. [ABSTRACT FROM AUTHOR]

Data accumulated recently for the exclusive measurement of the pp $ \rightarrow$ pp $ \pi^{+}_{}$ $ \pi^{-}_{}$ reaction at a beam energy of 0.793GeV using the COSY-TOF spectrometer have been analyzed with respect to possible events from the pp $ \rightarrow$ nn $ \pi^{+}_{}$ $ \pi^{+}_{}$ reaction channel. The latter is expected to be the only $ \pi$ $ \pi$ production channel, which contains no major contributions from resonance excitation close to threshold and hence should be a good testing ground for chiral dynamics in the $ \pi$ $ \pi$ production process. No single event has been found, which meets all conditions for being a candidate for the pp $ \rightarrow$ nn $ \pi^{+}_{}$ $ \pi^{+}_{}$ reaction. This gives an upper limit for the cross-section of 0.16μb (90% C.L.), which is more than an order of magnitude smaller than the cross-sections of the other two-pion production channels at the same incident energy. [ABSTRACT FROM AUTHOR]