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.]