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

TL;DR

This paper reports the measurement of the ratio of branching fractions for D_s+ decays to mu+ nu_mu and phi mu+ nu_mu, and determines the decay constant f_{D_s} using data from Fermilab experiment E653.

Contribution

It provides the first measurement of the branching ratio and decay constant of D_s+ mesons using purely leptonic decay channels in a fixed-target experiment.

Findings

Measured B(D_s+ -> mu+ nu_mu) / B(D_s+ -> phi mu+ nu_mu) = 0.16 ± 0.06 ± 0.03

Determined the decay constant f_{D_s} = 194 ± 35 ± 20 ± 14 MeV

Observed 23.2 ± 6.0_{-0.9}^{+1.0} leptonic decay events

Abstract

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