Search for the decay B ⁰ → ϕμ ⁺ μ ⁻

A search for the decay B⁰→ ϕμ⁺μ⁻ is performed using proton-proton collisions at centre-of-mass energies of 7, 8, and 13 TeV collected by the LHCb experiment and corresponding to an integrated luminosity of 9 fb⁻¹. No evidence for the B⁰→ ϕμ⁺μ⁻ decay is found and an upper limit on the branching fraction, excluding the ϕ and charmonium regions in the dimuon spectrum, of 4.4 × 10⁻³ at a 90% credibility level, relative to that of the Bs0→ ϕμ⁺μ⁻ decay, is established. Using the measured Bs0→ ϕμ⁺μ⁻ branching fraction and assuming a phase-space model, the absolute branching fraction of the decay B⁰→ ϕμ⁺μ⁻ in the full q² range is determined to be less than 3.2 × 10⁻⁹ at a 90% credibility level. [Figure not available: see fulltext.]