Observation of B ̄ (s) 0 → J / ψ f 1 (1285) decays and measurement of the f 1 (1285) mixing angle

Abstract

Decays of B̄s0 and B̄0 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. B̄(s)0→J/ψf1(1285) decays are seen for the first time, and the branching fractions are measured. Using these rates, the f1(1285) mixing angle between strange and nonstrange components of its wave function in the qq̄ structure model is determined to be ±(24.0-2.6-0.8+3.1+0.6). Implications on the possible tetraquark nature of the f1(1285) are discussed. © 2014 CERN, for the LHCb Collaboration.