New results on the numu-nutau and nue-nutau oscillation search with the CHORUS detector

Abstract

The present results on the $\numtonut$ oscillation search by the CHORUS experiment at CERN are summarized. A fraction of the neutrino interactions collected in 1994-1997 has been analysed, searching for $\nu_{\tau}$ charged current interactions followed by the $\tau$ lepton decay into a negative hadron, electron, or into a muon. A sample of 126,229 events with an identified muon in the final state and 19,436 events without an identified muon in the final state have been located in the emulsion target. Within the applied cuts, no $\nu_{\tau}$ candidate has been found. This result leads to a 90% C.L. limit $P(\numtonut)< 4.0\cdot 10^{-4}$ on the mixing probability. A $\nuetonut$ exclusion plot is also presented corresponding to 90% C.L. limit on the mixing probability of $P(\nuetonut)<~3.0\cdot~10^{-2}$.