The Purely Leptonic Decays D+ -> mu+ nu and Ds+-> lepton+ nu at CLEO

Abstract

We update our previous results by increasing the luminosity, the efficiency, and for the Ds+ the number of tags. We determine f{D+}=(205.8 +/- 8.5 +/- 2.5) MeV, and an interim preliminary value of f{Ds+}=(267.9 +/- 8.2 +/- 3.9) MeV, where both results are radiatively corrected. We agree with the recent most precise unquenched Lattice-QCD calculation for the D+, but are in disagreement for the Ds+. Several consequences are discussed, including the possibility of physics beyond the Standard Model.

4 pages, 6 figures, to appear in Proceedings of Flavor Physics and CP Violation 2008 (FPCP 2008), and Rencontres de Moriond QCD and High Energy Interactions (2008)