Observation of neutrino induced diffractive $D_s^{*+}$ production and subsequent decay $D_s^{*+} \to D_s^+ \to \tau^+ \to \mu^+$

We report on the first direct observation of a neutrino induced charged-current interaction with two subsequent decays of short-lived particles close to the interaction vertex. This rare double- kink signature in the CHORUS emulsion target is interpreted as a $D_s^{*+}$ production followed by the decay chain $D_s^{*+} \rightarrow D_s^+ \gamma, D_s^+ \rightarrow \tau^+ \nu_\tau ,$ \linebr eak $\tau^+\rightarrow \mu^+\nu_\mu\bar{\nu_\tau}$. The event is characterised by small $Q^2$ and small four-momentum transfer squared $t$ to the target nucleon, which indicates a diffractive pr oduction mechanism. A complete analysis of the event is presented.