Measurement of B(D_s+ -> mu+ nu_mu)/B(D_s+ -> phi mu+ nu_mu) and Determination of the Decay Constant f_{D_s}

Abstract

We have observed $23.2\pm 6.0_{-0.9}^{+1.0}$ purely-leptonic decays of $D_s^{+}->\hat{I}{¼}^{+}\hat{I}{½}_{\hat{I}}¼$ from a sample of muonic one prong decay events detected in the emulsion target of Fermilab experiment E653. Using the $D_s^{+}->\ddot{I}•\hat{I}{¼}^{+}\hat{I}{½}_{\hat{I}}¼$ yield measured previously in this experiment, we obtain $B(D_s^{+}-->\hat{I}{¼}^{+}\hat{I}{½}_{\hat{I}}¼)/B(D_s^{+}-->\ddot{I}•\hat{I}{¼}^{+}\hat{I}{½}_{\hat{I}}¼)=0.16\pm 0.06\pm 0.03$. In addition, we extract the decay constant $f_{D_s}=194\pm 35\pm 20\pm 14MeV$.

15 pages including one figure