Observation of B_((s))~0 → J/ψ f_1(1285) Decays and Measurement of the f_1 (1285) Mixing Angle

摘要

Decays of B_s~0 and B~0 mesons into J/ψ π~+π~-π~+π~- final states, produced in pp collisions at the LHC, are investigated using data corresponding to an integrated luminosity of 3 fb~(-1) collected with the LHCb detector. B_((s))~0 → J/ψ f_1 (1285) decays are seen for the first time, and the branching fractions are measured. Using these rates, the f_1(1285) mixing angle between strange and nonstrange components of its wave function in the qq structure model is determined to be ±(24.0_(-2.6-0.8)~(+3.1+0.6))~o. Implications on the possible tetraquark nature of the f_1(1285) are discussed.