A joint Fermilab/SLAC publication

# OPERA observes second tau neutrino

06/06/12

A small subset of the OPERA collaboration. In total, the collaboration includes ~200 physicists from 36 institutions in 13 countries. (Photo: OPERA)

Neutrino results continue to pour out of the Neutrino 2012 conference in Japan.

Yesterday, the OPERA collaboration announced its second observation of a tau neutrino, a particle that’s extremely difficult to detect. The experiment, which made its first such observation in 2010, searches for evidence of neutrino oscillation, the process in which neutrinos transform from one type to another.

Several other experiments have shown that neutrinos can spontaneously oscillate as they travel long distances, but OPERA is the first to catch a muon neutrino changing into a tau neutrino.

To do this, OPERA scientists send a beam of muon neutrinos 730 kilometers from CERN to Gran Sasso National Laboratory, a trip that gives a few of the muon neutrinos time to oscillate into tau neutrinos. The OPERA collaboration then searches for the specific set of particles produced when a tau neutrino collides with atoms in the OPERA detector.  The fact that neutrino oscillation is rare, combined with neutrino’s very weak interaction with matter, makes this type of detection very difficult.

Since 2008, the collaboration has observed several thousand neutrino interactions, including the two that involve tau neutrinos. This second observation is an important confirmation of the first sighting, and is strong evidence that neutrinos do indeed oscillate.

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