A neutrino interaction with two vertices topology detected by OPERA

The OPERA experiment has reported the detection of five $\nu_{\tau}$ candidates in the CNGS $\nu_{\mu}$ beam, allowing to reject the background-only hypothesis at the 5.1$\sigma$ level. Besides these events, on May 23$^{rd}$ 2011, OPERA detected a "neutral current like" interaction with two secondary vertices. Such topologies mainly arise from Charged Current interactions of a $\nu_{\tau}$ with associated charm quark production or from Neutral Current interactions of a $\nu_{\mu}$ with production of a charm anti-charm pair. These topologies have generally low probabilities. A dedicated multivariate analysis is in progress to allow discriminating between these two hypotheses. Here the event topology is described in detail and preliminary results of the classifiers for all possible contributions are given.