Measurement of spin observables in the quasi-free np-> {pp}_s pi- reaction at 353 MeV

Abstract

The transverse spin correlations A_{x,x} and A_{y,y} have been measured in the pol{d} pol{p} -> p_spec {pp}_s pi- reaction at COSY-ANKE at 353 MeV per nucleon. Here {pp}_s denotes a proton-proton pair with low excitation energy, which is dominantly in the 1S0 state. By measuring three protons in the final state it was possible to extract events where there was a spectator proton p_spec so that the reaction could be interpreted in terms of quasi-free pol{n} pol{p} -> {pp}_s pi-. The proton analyzing power in this reaction was also deduced from this data set by averaging over the polarization of the deuteron beam. The values of A_y^p were shown to be consistent with a refined analysis of our earlier results obtained with a polarized proton incident on a deuterium target. Taking these data in combination with our earlier measurements of the differential cross sections and analyzing powers in the pol{p} p -> {pp}_s pi^0 reaction, a more robust partial wave decomposition was achieved. Three different acceptable solutions were found and the only way of resolving this ambiguity without further theoretical input would be through a measurement of the mixed spin-correlation parameter A_{x,z}.