Observation of sizeable ω contribution to χ_c1(3872) → π⁺π⁻J/ψ decays

Resonant structures in the dipion mass spectrum from χ_c1(3872)→π⁺π⁻J/ψ decays, produced via B⁺ → K⁺χ_c1(3872) decays, are analyzed using proton-proton collision data collected by the LHCb experiment, corresponding to an integrated luminosity of 9  fb⁻¹. A sizeable contribution from the isospin conserving χ_c1(3872) → ωJ/ψ decay is established for the first time, (21.4±2.3±2.0)%, with a significance of more than 7.1σ. The amplitude of isospin violating decay, χ_c1(3872) → ρ⁰J/ψ, relative to isospin conserving decay, χ_c1(3872) → ωJ/ψ, is properly determined, and it is a factor of 6 larger than expected for a pure charmonium state.