SEARCH FOR NU(MU)-]NU(TAU) OSCILLATION

The fine granularity of the CHARM-II detector has been exploited to se arch, in the CERN-SPS wide band neutrino beam, for quasi-elastic nu(ta u) interactions followed by the decay tau --> pinu(tau). Since the sam pling thickness of the target calorimeter corresponds to approximately 1/9 of an interaction length, these events appear in the detector as a single track followed by a hadronic shower. The study of the ''singl e pion'' events is used to set limits on the nu(mu) --> nu(tau) oscill ation parameters. The maximum sensitivity to the mixing angle theta is reached for DELTAm2 = 50 eV2 allowing to exclude values of sin2 20 gr eater than 6.4 x 10(-3) at 90% CL.