First Observation of B0s → J/ψ f0(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 B0s → J/ψ f0(980) is observed. This CP eigenstate mode could be used to measure mixing-induced CP violation in the B0s system. Using a fit to the π+ π− mass spectrum with interfering resonances gives R(f0/φ) ≡ Γ(B0s → J/ψ f0, f0 → π+ π−)/Γ(B0s → J/ψ φ, φ → K+ K−) = 0.252(−0.032−0.033)(+0.046+0.027). In the interval ±90 MeV around 980 MeV, corresponding to approximately two full f0 widths we also find R′ ≡ Γ(B0s → J/ψ π+ π− ,|m(π+ π−)−980 MeV|<90 MeV)/Γ(B0s → J/ψ φ, φ → K+ K−) = 0.162 ± 0.022 ± 0.016, where in both cases the uncertainties are statistical and systematic, respectively.