Amplitude analysis of B⁺→ ψ(2S)K⁺π⁺π⁻ decays

The first full amplitude analysis of B⁺ → ψ(2S)K⁺π⁺π⁻ decays is performed using proton-proton collision data corresponding to an integrated luminosity of 9 fb⁻¹ recorded with the LHCb detector. The rich K⁺π⁺π⁻ spectrum is studied and the branching fractions of the resonant substructure associated with the prominent K₁(1270)⁺ contribution are measured. The data cannot be described by conventional strange and charmonium resonances only. An amplitude model with 53 components is developed comprising 11 hidden-charm exotic hadrons. New production mechanisms for charged charmonium-like states are observed. Significant resonant activity with spin-parity J^P = 1⁺ in the ψ(2S)π⁺ system is confirmed and a multi-pole structure is demonstrated. The spectral decomposition of the ψ(2S)π⁺π⁻ invariant-mass structure, dominated by X⁰ → ψ(2S)ρ(770)⁰ decays, broadly resembles the J/ψϕ spectrum observed in B⁺ → J/ψϕK⁺ decays. Exotic ψ(2S)K⁺π⁻ resonances are observed for the first time.