## Monday, May 31, 2010 ... //

### CERN sends muon neutrinos, Gran Sasso detected one tau neutrino

For three years or so, a gadget at CERN has been sending muon neutrinos to Gran Sasso which is 730 km away. No, the source of the muon neutrinos has been something else than the LHC - a device that has suffered from the first big power cut since the bird attack by a baguette on Friday.

The neutrinos had to travel through the Earth (the maximum depth is 11.4 km) but they don't mind. ;-)

Today, the OPERA Collaboration in Gran Sasso in Central Italy and CERN announced the first ever detection of a tau neutrino created by muon-tau neutrino oscillations:

Particle chameleon caught in the act of changing
Neutrinos are hard to see and they don't oscillate much. Moreover, the distance is big and the focusing is not too good. These three facts combine so that it took a lot of time to observe a single tau neutrino despite the fact that it was a muon neutrino, the SU(2) partner of the charged muon mass eigenstate, that was created at CERN.

In Gran Sasso, it collided with some matter, exchanged charge with it via a virtual W-boson, and became a charged tau lepton which is traced by scintillators.

It has been known for decades that neutrino oscillate - see e.g. my 1998 lectures on neutrinos (Majorana vs Dirac) that discuss the oscillations on pages 12-13. But it was easier to argue that the oscillations had to occur because of lost particles: newly created unusual species of particles are always harder.

CERN video:

Wait for some time or go to YouTube for the video. Double-click for full screen.