Search for the flavor-changing neutral current decay D0 --> mu+ mu- with the HERA-B detector

We report on a search for the flavor-changing neutral current decay D0→μ+μ- using 50×106 events recorded with a dimuon trigger in interactions of 920 GeV protons with nuclei by the HERA-B experiment. We find no evidence for such decays and set a 90% confidence level upper limit on the branching fraction B(D0→μ+μ-)<2.0×10-6. © 2004 Elsevier B.V.