Measurement of diffractive 3pi production on a polarized target at 17 GeV/c

The reaction pi /sup -/p/sub pol./ to pi /sup -/ pi /sup +/ pi /sup - /p has been measured at 17 GeV/c using a polarized target. The data sample contains about 60000 interactions on polarized protons. The nucleon polarization as a function of momentum transfer is very similar to elastic pi /sup -/p scattering and is nearly independent of the 3 pi mass, except for a possible structure around 1.2 GeV. Using the isobar model, the authors have performed a partial-wave analysis and extracted the 3 pi amplitudes. The generalized 3 pi density matrix elements agree with earlier determinations. Relative phases obtained from density matrix elements agree well with the ones obtained from transversity amplitudes. This proves the validity of the coherence assumption made in the interpretation of unpolarized target results. The results confirm the existence of an A/sub 1/ resonance in the region 1.2-1.3 GeV. (20 refs).