Observation of the Bs0→X(3872)ϕ Decay

Using a data sample of proton-proton collisions at √s = 13  TeV, corresponding to an integrated luminosity of 140  fb⁻¹ collected by the CMS experiment in 2016–2018, the B⁰_s → X(3872)ϕ decay is observed. Decays into J/ψπ⁺π⁻ and K⁺K⁻ are used to reconstruct, respectively, the X(3872) and ϕ. The ratio of the product of branching fractions B[B⁰_s → X(3872)ϕ]B[X(3872) → J/ψπ⁺π−] to the product B[B⁰_s → ψ(2S)ϕ]B[ψ(2S) → J/ψπ⁺π−] is measured to be [2.21±0.29(stat)±0.17(syst)]%. The ratio B[B⁰_s → X(3872)ϕ]/B[B⁰ → X(3872)K⁰] is found to be consistent with one, while the ratio B[B⁰_s → X(3872)ϕ]/B[B⁺ → X(3872)K⁺] is two times smaller. This suggests a difference in the production dynamics of the X(3872) in B⁰ and B⁰_s meson decays compared to B⁺. The reported observation may shed new light on the nature of the X(3872) particle.