Observation of the decay B0s→ϕπ+π−Bs0→ϕπ+π− and evidence for B0→ϕπ+π−

The first observation of the rare decay B 0 s → ϕ π + π − and evidence for B 0 → ϕ π + π − are reported, using p p collision data recorded by the LHCb detector at center-of-mass energies √ s = 7 and 8 TeV, corresponding to an integrated luminosity of 3     fb − 1 . The branching fractions in the π + π − invariant mass range 400 < m ( π + π − ) < 1600     MeV / c 2 are [ 3.48 ± 0.23 ± 0.17 ± 0.35 ] × 10 − 6 and [ 1.82 ± 0.25 ± 0.41 ± 0.14 ] × 10 − 7 for B 0 s → ϕ π + π − and B 0 → ϕ π + π − respectively, where the uncertainties are statistical, systematic and from the normalization mode B 0 s → ϕ ϕ . A combined analysis of the π + π − mass spectrum and the decay angles of the final-state particles identifies the exclusive decays B 0 s → ϕ f 0 ( 980 ) , B 0 s → ϕ f 2 ( 1270 ) , and B 0 s → ϕ ρ 0 with branching fractions of [ 1.12 ± 0.1 6 + 0.09 − 0.08 ± 0.11 ] × 10 − 6 , [ 0.61 ± 0.1 3 + 0.12 − 0.05 ± 0.06 ] × 10 − 6 and [ 2.7 ± 0.7 ± 0.2 ± 0.2 ] × 10 − 7 , respectively.