# OPERA detects its fifth tau neutrino

Cian O'Luanaigh

A particle that left CERN as a muon neutrino underwent oscillation during its 730-kilometre journey to Gran Sasso, arriving as a tau neutrino. Researchers at Gran Sasso announced the result yesterday, naming it 5 sigma on the scale that particle physicists use to describe the certainty of results. OPERA was designed to search for tau neutrinos in the muon-neutrino beam from CERN, which ran during 2006-2012; detecting tau neutrinos in this beam is proof that oscillation occurred during their particles’ 730 km long flight. The pions and kaons then decayed into muons and muon neutrinos in a 1-kilometre long pipe underground. After detecting the first few muon neutrinos produced at CERN in 2006, the experiment collected data from 2008 to the end of 2012.