Observation of the decay Bs0 → ηc ϕ and evidence for Bs0 → ηc π + π −

A study of Bs0 → ηcϕ and Bs0 → ηcπ+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 Bs0 → ηcϕ is reported, where the ηc meson is reconstructed in the pp¯¯¯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 Bs0 → J/ψϕ is used as a normalisation channel. Evidence is also reported for the decay Bs0 → ηcπ+π−, where the ηc meson is reconstructed in the pp¯¯¯pp¯ decay mode, using the decay Bs0 → J/ψπ+π− as a normalisation channel. The measured branching fractions are B(B0s→ηcϕ)=(5.01±0.53±0.27±0.63)×10−4,B(B0s→ηcπ+π−)=(1.76±0.59±0.12±0.29)×10−4, B(Bs0→ηcϕ)=(5.01±0.53±0.27±0.63)×10−4,B(Bs0→ηcπ+π−)=(1.76±0.59±0.12±0.29)×10−4, 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.