DELPHI has shown a preliminary result . on the decay Ds --> tau nu at the HEP97 conference in Jerusalem. The Ds meson was tagged using the cascade decay Ds* --> Ds gamma.
The L3 collaboration has obtained a result on the same channel.
More recently a more inclusive analysis has been done by ALEPH using mainly the lepton inclusive distributions.
The main interest in these measurements is to extract the decay constant fDs and to compare its value to results from lattice QCD. These results can then be used to obtain a value for fB, the corresponding decay constant for b mesons.
An important limitation on the accuracy of the fDs determination originates in the uncertainty attached to the Ds production rate in jets coming from the poor determination of absolute values of Ds decay branching fractions. A better understanding of b and c quark hadronisation mechanism can allow in a near future to have a better control of the Ds production rate in c jets (expect a factor 2 improvement).