First observation of Bs0→J/ψf0(980) decays

Using data collected with the LHCb detector in proton-proton collisions at a centre-of-mass energy of 7 TeV, the hadronic decay Bs0→J/ψf0(980) is observed. This CP eigenstate mode could be used to measure mixing-induced CP violation in the Bs0 system. Using a fit to the π+π− mass spectrum with interfering resonances gives Rf0/ϕ≡Γ(Bs0→J/ψf0,f0→π+π−)Γ(Bs0→J/ψϕ,ϕ→K+K−)=0.252−0.032−0.033+0.046+0.027. In the interval ±90MeV around 980 MeV, corresponding to approximately two full f0 widths we also find R′≡Γ(Bs0→J/ψπ+π−,|m(π+π−)−980MeV|<90MeV)Γ(Bs0→J/ψϕ,ϕ→K+K−)=0.162±0.022±0.016, where in both cases the uncertainties are statistical and systematic, respectively.