Amplitude Analysis of the χ_{c1} → ηπ⁺π⁻ Decays

Using 448.0 x 10⁶ ψ(3686) events collected with the BESIII detector, an amplitude analysis is performed for ψ(3686)→γχ_{c1}, χ_{c1} → ηπ⁺π⁻ decays. The most dominant two-body structure observed is α₀(980)^± π^∓; α₀(980)^±→ηπ^±. The α₀(980) line shape is modeled using a dispersion relation, and a significant nonzero α₀(980) coupling to the η′π channel is measured. We observe χ_{c1} → α₂(1700)π production for the first time, with a significance larger than 17σ. The production of mesons with exotic quantum numbers, J^{PC} = 1⁻⁺, is investigated, and upper limits for the branching fractions χ_{c1}→π₁(1400)^±π^∓, χ_{c1} → π₁(1600)^±π^∓, and χ_{c1} → π₁(2015)^±π^∓, with subsequent π₁(X)^± → ηπ^± decay, are determined.

Branching fractions (Nuclear physics), Hadrons—Decay, Collisions (Nuclear physics), Mesons
National Key Basic Research Program of China (2015CB856700); National Natural Science Foundation of China (NSFC) (11235011, 11322544, 11335008, 11425524); NSFC and Chinese Academy of Sciences (CAS) (U1232201, U1332201; U1532258); CAS (KJCX2-YW-N29, KJCX2-YW-N45); Koninklijke Nederlandse Akademie van Wetenschappen (KNAW) (530-4CDP03); Ministry of Development of Turkey (DPT2006K-120470); U.S. Department of Energy (DE-FG02-05ER41374, DE-SC-0010504, DE-SC0012069); National Research Foundation of Korea (R32-2008-000-10155-0).
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