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

TL;DR

This paper reports updated measurements of leptonic decay constants for D+ and Ds+ mesons at CLEO, comparing results with theoretical predictions and discussing implications for physics beyond the Standard Model.

Contribution

The study provides new, more precise measurements of fD+ and an interim value for fDs+ using increased data and improved analysis techniques.

Findings

fD+ = 205.8 +/- 8.5 +/- 2.5 MeV, consistent with lattice QCD

fDs+ = 267.9 +/- 8.2 +/- 3.9 MeV, preliminary and in disagreement with some theories

Results have implications for new physics beyond the Standard Model

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.