Observation of the Bs0→ χ_c1(3872)π⁺π⁻ decay

The first observation of the B_s⁰→ (χ_c1(3872) → J/ψπ⁺π⁻)π⁺π⁻ decay is reported using proton-proton collision data, corresponding to integrated luminosities of 1, 2 and 6 fb⁻¹, collected by the LHCb experiment at centre-of-mass energies of 7, 8 and 13 TeV, respectively. The ratio of branching fractions relative to the B_s⁰→ (ψ(2S) → J/ψπ⁺π⁻)π⁺π⁻ decay is measured to be (Formula presented.) where the first uncertainty is statistical and the second systematic. The mass spectrum of the π⁺π⁻ system recoiling against the χ_c1(3872) meson exhibits a large contribution from B_s⁰→ χ_c1(3872) (f₀(980) → π⁺π⁻) decays.