Decays of ${\overline{B}}_s^0$ and ${\overline{B}}^0$ mesons into $J/\psi$ ${\pi }^{+}$${\pi }^{-}$${\pi }^{+}$${\pi }^{-}$ final states, produced in $pp$ collisions at the LHC, are investigated using data corresponding to an integrated luminosity of $3\mathrm{fb}{}^{-1}$ collected with the LHCb detector. ${\overline{B}}_{(s)}^0\to J/\psi f_1(1285)$ 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 $q\overline{q}$ structure model is determined to be $\pm (24.0_{-2.6-0.8}^{+3.1+0.6})°$. Implications on the possible tetraquark nature of the $f_1(1285)$ are discussed.

• Received 8 October 2013

DOI:https://doi.org/10.1103/PhysRevLett.112.091802

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© 2014 CERN, for the LHCb Collaboration