Odd and even partial waves of η π ? and η ′ π ? in π ? p → η ( ′ ) π ? p at 191 GeV / c

摘要

Exclusive production of η π ? 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 / c 2 . 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 a 2 ( 1320 ) and a 4 ( 2040 ) are in line with this similarity. In contrast, a strong enhancement of η ′ π ? over η π ? is found for the L = 1 , 3 , 5 waves, which carry non- q q ˉ quantum numbers. The L = 1 intensity peaks at 1.7 GeV / c 2 in η ′ π ? and at 1.4 GeV / c 2 in η π ? , the corresponding phase motions with respect to L = 2 are different.