Observation of ¯B0(s)→J/ψ f1(1285) Decays and Measurement of the f1(1285) Mixing Angle

Abstract

Decays of ¯ B 0 s and ¯ B 0 mesons into J / ψ π + π − π + π − final states, produced in p p collisions at the LHC, are investigated using data corresponding to an integrated luminosity of 3 fb − 1 collected with the LHCb detector. ¯ B 0 ( s ) → 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 q ¯ q structure model is determined to be ± ( 24 . 0 + 3.1 + 0.6 − 2.6 − 0.8 ) ° . Implications on the possible tetraquark nature of the f 1 ( 1285 ) are discussed.