Studying χc1 → ηπ+π− decays at BESIII

Abstract

Abstract. Based on 447.5 × 10 6 ψ(3686) produced at BESIII, we present results from an Amplitude Analysis of the ψ(3686) → γχ c1 ; χ c1 → ηπ + π − decays. Strong evidence for a two-body structure in ηπ + + c.c. decays, with the invariant mass, width and spin consistent with the a 2 (1700) is found. This decay mode of the χ c1 has not been reported before. Using a dispersion relation to model the a 0 (980) → ηπ line shape, a non-zero value for the a 0 (980) → η π coupling is measured for the first time. The production of mesons with exotic quantum numbers, J PC = 1 −+ , decaying to the ηπ final state in the mass range 1.4-2.0 GeV/c 2 is investigated, and the upper limits at 90% confidence level for the production of the π 1 (1400), π 1 (1600) and π 1 (2015) are determined.