First observation of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"><mml:msubsup><mml:mi>B</mml:mi><mml:mi>s</mml:mi><mml:mn>0</mml:mn></mml:msubsup><mml:mo>→</mml:mo><mml:mi>J</mml:mi><mml:mo stretchy="false">/</mml:mo><mml:mi>ψ</mml:mi><mml:msub><mml:mi>f</mml:mi><mml:mn>0</mml:mn></mml:msub><mml:mo stretchy="false">(</mml:mo><mml:mn>980</mml:mn><mml:mo stretchy="false">)</mml:mo></mml:math> 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.