Evidence for resonance behaviour of A1 and A3 mesons coherently produced on nuclei

An analysis of about 60 000 events produced in the reaction π-A → (π+π-π-)A on nine different nuclear targets A at 8.9, 12.9, and 15.1 GeV/c has been performed using the Illinois PWA program. In the A1 region our "coherent" sample of events (which contains about 11% of incoherently produced events) is described by only four partial waves: the 1+S and 1+P amplitudes, which both show a peak, and the O-S and O-P waves, which are rather constant. We observed variations of both 1+S and 1+P phases relative to the O-P phase by about 90° across the A1 peak. This observation suggests the presence of resonant 1+ waves in the A1 mass region (∼1.1 GeV). In the A3 region we observe that the 2- state shows resonance behaviour and that fπ and ρ{variant}π are two decays modes with amplitudes of opposite signs.