Model-independent analysis of the neutron-proton final-state interaction region in the pp -> pn pi^+ reaction

Experimental data on the pp -> pn pi^+ reaction measured in an exclusive two-arm experiment at 800 MeV show a narrow peak arising from the strong proton-neutron final-state interaction. It was claimed, within the framework of a certain model, that this peak contained up to a 25% spin-singlet final state contribution. By comparing the data with those of pp -> d pi^+ in a largely model-independent way, it is here demonstrated that at all the angles measured the whole of the peak could be explained as being due to spin-triplet final states, with the spin-singlet being at most a few percent. Good qualitative agreement with the measured proton analysing power is also found within this approach.