SEARCH FOR HEAVY ISOSINGLET NEUTRINOS

A new search for decays of heavy isosinglet neutrinos produced by neut ral-current neutrino interactions in the CERN wide-band neutrino beam has been conducted by the CHARM-II Collaboration. We searched for heav y neutrinos created by scattering muon neutrinos on nucleons and decay ing into mu(+) mu(-) v(mu). Production and decay of heavy neutrinos wo uld appear as double events in the detector. Each double event candida te was tested wheather the measured quantities are compatible with the kinematics of this process. No event passed this test. The analysis i s based on 2 x 10(7) neutral-current neutrino events collected from 19 87-1991. The experiment is sensitive to heavy neutrinos in the mass ra nge 0.3-2.4 GeV/c(2). The best limit for the mixing parameter is \U-mu i\(2) < 3 X 10(-5) for a mass around 2 GeV/c(2). The analysis improve d by an order of magnitude previous results derived from wide-band neu trino beam exposures of the CHARM detector.