Measurement of the decay constant fDs+ using Ds+→l+ν

Abstract

We measure the decay constant fDs+ using the Ds+→+ν channel, where the + designates either a μ+ or a τ+, when the τ+→π+ν ̄. Using both measurements we find fDs+=274±13±7MeV. Combining with our previous determination of fD+, we compute the ratio fDs+/fD+=1.23±0.11±0.04. We compare with theoretical estimates. © 2007 The American Physical Society.