Search for the rare decays B⁰ₛ → μ⁺ μ⁻ and B⁰ → μ⁺ μ⁻

A search for the decays Bₛ⁰→μ⁺μ⁻ and B⁰→μ⁺μ⁻ is performed with about 37 pb⁻¹ of $pp$ collisions at √s = 7 TeV collected by the LHCb experiment at the Large Hadron Collider at CERN. The observed numbers of events are consistent with the background expectations. The resulting upper limits on the branching ratios are B(Bₛ⁰→μ⁺μ⁻) < 5.6 × 10⁻⁸ and B(B⁰→μ⁺μ⁻) < 1.5 × 10⁻⁸ at 95% confidence level.