Odd and even partial waves of ηπ−ηπ− and η′π−η′π− in π−p→η(′)π−pπ−p→η(′)π−p at 191 GeV/c191 GeV/c

Exclusive production of ηπ−ηπ− and η′π−η′π− has been studied with a 191 GeV/c191 GeV/cπ−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/c23 GeV/c2. A striking similarity between the two systems is observed for the L=2,4,6L=2,4,6 intensities (scaled by kinematical factors) and the relative phases. The known resonances a2(1320)a2(1320) and a4(2040)a4(2040) are in line with this similarity. In contrast, a strong enhancement of η′π−η′π− over ηπ−ηπ− is found for the L=1,3,5L=1,3,5 waves, which carry non-qq¯ quantum numbers. The L=1L=1 intensity peaks at 1.7 GeV/c21.7 GeV/c2 in η′π−η′π− and at 1.4 GeV/c21.4 GeV/c2 in ηπ−ηπ−, the corresponding phase motions with respect to L=2L=2 are different.