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Using 448.0 × 10 6 ψ(3686) events collected with the BESIII detector, an amplitude analysis is performed for ψ(3686) → γχc1, χc1 → ηπ + π − decays. The most dominant two-body structure observed is a0 (980) ± π ∓ ; a0(980) ± → ηπ ± . The a0(980) line shape is modeled using a dispersion relation, and a significant non-zero a0(980) coupling to the η ′ π channel is measured. We observe χc1 → a2(1700)π production for the first time, with a significance larger than 17σ. The production of mesons with exotic quantum numbers, J P C = 1 −+ , is investigated, and upper limits for the branching fractions χc1 → π1(1400) ± π ∓ , χc1 → π1(1600) ± π ∓ , and χc1 → π1(2015) ± π ∓ , with subsequent π1(X) ± → ηπ ± decay, are determined.

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