Odd and even partial waves of ηπ^- and η^'π^- in π^-p→η^(')π^-

Exclusive production of ηπ^- and η^'π^- has been studied with a 191 GeV/c π^- beam impinging on a hydrogen target at COMPASS (CERN). Partial-wave analyses reveal different odd/even angular momentum (L) characteristics in the inspected invariant mass range up to 3 GeV/c². A striking similarity between the two systems is observed for the L=2, 4, 6 intensities (scaled by kinematical factors) and the relative phases. The known resonances a₂(1320) and a₄(2040) are in line with this similarity. In contrast, a strong enhancement of η^'π^- over ηπ^- is found for the L=1, 3, 5 waves, which carry non-qq- quantum numbers. The L=1 intensity peaks at 1.7 GeV/c² in η^'π^- and at 1.4 GeV/c² in ηπ^-, the corresponding phase motions with respect to L=2 are different.