Observation of the decay canal B⁰_s → η_cφ with LHCb experiment

The interference between B⁰_s meson decay amplitudes to CP final state directly or via mixing gives rise to a measurable CP-violating phase φ_s, which is predicted to be φ_s^SM = (-0.0370 ± 0.0006) rad in the Standard Model. However, such process may receive contributions from New Physics and change the value of φ_s. At present, the most precise measurement of φ_s is given by the LHCb experiment and the world average is φ_s^exp = (-0.021 ± 0.032) rad, with uncertainty still dominated by the statistics. In this context, a study of B⁰_s → η_cφ decays is performed using pp collision data corresponding to an integrated luminosity of 3.0 fb^-1, collected with the LHCb detector during the Run 1 of the LHC. The observation of the decay B⁰_s → η_cφ is reported, where the η_c meson is reconstructed in the pp-bar, 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 B⁰_s → J/ψφ is used as a normalisation channel. The measured branching fraction is B(B⁰_s → η_cφ) = (5.01 ± 0.53 ± 0.27 ± 0.63) x 10^-4, where the first uncertainty is statistical, the second systematic and the third uncertainty is due to the limited knowledge of the external branching fractions. (author)