Observation of the B0s → χc1(3872)π+π− decay

The first observation of the B0s → (χc1(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 B0s →(ψ(2S) → J/ψπ+π−) π+π− decay is measured to be B (B0s → χc1(3872)π+π−) × B (χc1(3872) → J/ψπ+π−)B (B0s → ψ(2S)π+π−) × B (ψ(2S) → J/ψπ+π−) = (6.8 ± 1.1 ± 0.2) × 10−2, where the first uncertainty is statistical and the second systematic. The mass spectrum of the π+π− system recoiling against the χc1(3872) meson exhibits a large contribution from B0s → χc1(3872) (f0(980) → π+π−) decays.