News from the Frontiers of Cosmology: A companion to the book The Edge of Physics
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OPERA tunes into first-ever tau neutrinos

OPERA

The OPERA experiment in the underground Gran Sasso Laboratory in Italy has likely seen the first tau neutrino, making it the first time that a neutrino type may have been seen “appearing” rather than “disappearing”.

Before we dig further into this strange statement and why it’s important, here’s a bit of background on neutrino appearances and disappearances. Neutrinos come in three flavours: electron, muon and tau. During the 1960s, neutrino detectors showed that there was a deficit of neutrinos coming from the sun. This came to be called the mystery of the missing solar neutrinos. Eventually, physicists figured out that the neutrinos were morphing from one type to another on their journey from the sun to the Earth. So if a detector was sensitive to only one type of neutrino, then it would see less of that type than was being emitted by the sun, since that particular neutrino type had changed into another type along the way, and hence could not be seen by the detector. This phenomenon is called neutrino oscillation.

This “disappearance” of a neutrino type has been detected by various detectors worldwide.

But how about detecting the reverse process? Say a neutrino source is spewing out muon neutrinos, and some of them are changing to tau neutrinos on their way to the detector. How about detecting the “appearance” of the neutrino which was not produced at the source?

That’s exactly what OPERA has done. A neutrino source at the CERN Accelerator Complex has been generating muon neutrinos. These neutrinos travel 730 kilometres to the OPERA detector (in about 2.4 milliseconds). Now, OPERA has most likely found one tau neutrino from among the many billions of muon neutrinos produced at CERN. This tau neutrino “appeared”—it is of course equivalent to a muon neutrino disappearing. But still, it’s a first.

Why is all this important? It turns out that neutrino oscillations require neutrinos to have mass, something which is not allowed in the standard model of particle physics. New physics is required to explain the process, and the more we study neutrino oscillations, the clearer the new physics will become.

Hitoshi Murayama, a theoretical physicist at the University of California, Berkeley, wrote about the announcement of the discovery of neutrino oscillations in Japan in 1998 (quoted in The Edge of Physics): “It was a moving moment. Uncharacteristically for a physics conference, people gave the speaker a standing ovation. I stood up too. Having survived every experimental challenge since the late 1970s, the Standard Model had finally fallen. The results showed that at the very least the theory is incomplete.”

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3 comments

1 Tweets that mention OPERA tunes into first-ever tau neutrinos — The Edge of Physics Blog -- Topsy.com { 05.31.10 at 12:59 pm }

[...] This post was mentioned on Twitter by Jez and Jez, Anil Ananthaswamy. Anil Ananthaswamy said: OPERA tunes into first-ever tau neutrino "appearance": http://edgeofphysics.com/blog/opera-tunes-into-first-ever-tau-neutrinos [...]

2 Roy Johnstone { 06.08.10 at 3:41 am }

Hi Anil, thanks for another interesting article!
This is a very timely finding in light of the recent idea that neutrinos may yet hold the key to, not just dark matter content, but dark energy and cosmic expansion!

The idea is predicated on a cyclic universe model where, in the contraction phase, neutrino density increases to the point where it becomes a condensate which effectively acts like a superfluid, avoiding any loss of energy to friction . This neutrino condensate would contain an enormous amount of energy, plenty to drive a very rapid inflation phase which may fit the inflationary model very well. This could answer one of the unanswered questions of that (Guth) model, which is, what inflated? The same effect could obviously also arise in the collapse forming a black hole, so that (very speculatively) a universe (ours?) could inflate inside a black hole? This idea is also motivated by an apparent correlation between neutrino oscillation rates and vacuum energy density. The picture is that as neutrinos move through the primordial condensate, the varying coupling causes them to oscillate according to the CKM?PMNS? mixing matrix. It’s like the neutrino equivalent of the normal SM particles moving through the Higgs field gaining mass.

Would appreciate your thoughts?
Roy

3 Alan Hayes { 06.10.10 at 6:45 pm }

The idea is predicated on a cyclic universe model where, in the contraction phase, neutrino density increases to the point where it becomes a condensate which effectively acts like a superfluid, avoiding any loss of energy to friction . This neutrino condensate would contain an enormous amount of energy, plenty to drive a very rapid inflation phase which may fit the inflationary model very well. This could answer one of the unanswered questions of that (Guth) model, which is, what inflated? The same effect could obviously also arise in the collapse forming a black hole, so that (very speculatively) a universe (ours?) could inflate inside a black hole? This idea is also motivated by an apparent correlation between neutrino oscillation rates and vacuum energy density. The picture is that as neutrinos move through the primordial condensate, the varying coupling causes them to oscillate according to the CKM?PMNS? mixing matrix. It’s like the neutrino equivalent of the normal SM particles moving through the Higgs field gaining mass.
+1

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