Odd and even partial waves of f ηπ−ηπ− and η′π−η′π− in π−p→η(′)π−pπ−p→η(′)π−p at 191 GeV/c

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-q¯q 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.