Amplitude analysis and branching fraction measurement of B̄s0→J/ψK⁺K^-

An amplitude analysis of the final state structure in the B̄s0→J/ψK ⁺K ^- decay mode is performed using 1.0 fb ^-1 of data collected by the LHCb experiment in 7 TeV center-of-mass energy pp collisions produced by the LHC. A modified Dalitz plot analysis of the final state is performed using both the invariant mass spectra and the decay angular distributions. Resonant structures are observed in the K ⁺K ^- mass spectrum as well as a significant nonresonant S-wave contribution over the entire K ⁺K ^- mass range. The largest resonant component is the (1020), accompanied by f ₀(980), f2′(1525), and four additional resonances. The overall branching fraction is measured to be B(B̄s0→J/ψK ⁺K ^-)=(7. 70±0.08±0.39±0.60)×10 ^-4, where the first uncertainty is statistical, the second systematic, and the third due to the ratio of the number of B̄s0 to B ^- mesons produced. The mass and width of the f2′(1525) are measured to be 1522.2±2.8-2.0+5.3 MeV and 84±6-5+10 MeV, respectively. The final state fractions of the other resonant states are also reported.