Flavor changing neutral current charm decays

The DØ collider experiment at Fermilab have studied flavor changing neutral current process c → uµ⁺µ⁻ using a 508 pb⁻¹ data sample of p ¯p collisions ats = 1.96 TeV. We observe the D^± _s → φπ^± → π^±µ⁺µ⁻ final state with a significance above background greater than 7 standard deviations. We also measure 13.2₋ ⁺ ₄ ⁵ ₉ ⁶ of D^± → φπ^± → π^±µ⁺µ⁻ events with a significance of 2.7 standard deviations above background and set a limit on the ratio of branching fractions of B(D^± → φπ^± → π^±µ⁺µ⁻)/B(D^± _s → φπ^± → π^±µ⁺µ⁻) < 0.28 at the 90% confidence level. Using the previously measured values of the D^± _s → φπ^± and φ → µ⁺µ⁻ branching fractions we convert this to a limit on the branching fraction of B(D^± → φπ^± → π^±µ⁺µ⁻) < 3.1×10⁻⁶ at the 90% confidence level.