Observation of the decay B_s ⁰ → η_c φ and evidence for B_s ⁰ → η_c π ⁺ π ⁻

A study of B_s ⁰ → η_cϕ and B_s ⁰ → η_cπ⁺π⁻ decays is performed using pp collision data corresponding to an integrated luminosity of 3.0 fb⁻¹, collected with the LHCb detector in Run 1 of the LHC. The observation of the decay B_s ⁰ → η_cϕ is reported, where the η_c meson is reconstructed in the pp¯ , K⁺K⁻π⁺π⁻, π⁺π⁻π⁺π⁻ and K⁺K⁻K⁺K⁻ decay modes and the ϕ(1020) in the K⁺K⁻ decay mode. The decay B_s ⁰ → J/ψϕ is used as a normalisation channel. Evidence is also reported for the decay B_s ⁰ → η_cπ⁺π⁻, where the η_c meson is reconstructed in the pp¯ decay mode, using the decay B_s ⁰ → J/ψπ⁺π⁻ as a normalisation channel. The measured branching fractions are(Formula Presented.)where in each case the first uncertainty is statistical, the second systematic and the third uncertainty is due to the limited knowledge of the external branching fractions.[Figure not available: see fulltext.].