Evidence for Neutrino Disappearance

decowski writes "Results from the first six months of experiments at KamLAND, an underground neutrino detector in central Japan, show that anti-neutrinos emanating from nearby nuclear reactors are "disappearing," which indicates they have mass and can oscillate or change from one type to another. As anti-neutrinos are the anti-matter counterpart to neutrinos, these results provide independent confirmation of earlier studies involving solar neutrinos and show that the Standard Model of Particle Physics, which has successfully explained fundamental physics since the 1970's, is in need of updating. The results also point the way to the first direct measurements of the total radioactivity of the earth."

Comments

What about earthquakes?

[Futurepower(R)]

Isn't being underground in Japan dangerous because of earthquake activity?

Answering my own question:

[Futurepower(R)]

Answering my own question:

I sent and email to KamLAND, and this was the answer:

"Not really. I haven't heard of any mine caverns collapsed because of an earthquake in Japan. Much bigger risk is the human-induced quakes because of the blasts and instability due to large caverns in a mine. This of course can happen anywhere. SNO for example saw quite a big quake in the Sudbury nickel mine this way even though it is geologically old and stable."

Hitoshi

Re:Answering my own question:

[JDizzy]

Earth quakes do more damage on land than they do under the land. Thsi is because of the ultra-low sound waves disrupt the air molecules more efficiently than solid earth dirt molecules. It is a fact, it is safer to be under ground in an earth quake than in an other place.

Minor quibble, or addendum

[aminorex]

I think it's been suspected since 1995 when the Brookhaven Muon g-2 experiment results began to get published, and very clear since 1998 or so, as they expanded and were corroborated, that there are defects, omissions, from the Standard Model that go beyond the little detail of overlooking gravitation.

Check out this search for more info on the anomalous magnetic moment of the muon.

Re:Minor quibble, or addendum

[Peter T Ermit]

IIRC, the publication of the g-2 results was in 2001 and 2002. There's probably a third release coming, where they release the mu-plus results, too.

When it comes down to it, the g-2 stuff is just a three-sigma deviation from the standard model -- interesting, and better than most other three-sigma results out there, but not definitive. The neutrino results, first at Super-K, SNO, and K2K, and now at KamLAND, are pretty much definitive.

Besides, the g-2 result and the neutrino results each require different modifications to the standard model; the latter requires supersymmetry or some extension of the model, whereas the former requires the assumption of mass in existing particles.

Re:Minor quibble, or addendum

[yomegaman]

I don't think either the g-2 or the neutrino oscillations really pose much problem to the Standard Model, unfortunately. Nonzero neutrino masses can be easily incorporated into the SM, there's nothing there that requires them to be massless. You just add the mass terms to the Lagrangian and throw in a mixing matrix, sure the masses are arbritrary but they are for all other particles too. I don't quite know what to make of the g-2 measurement. After the first results came out there was so much arguing about the theoretical prediction that it started to look like you could get any answer you wanted. First there was a lot of heat about the hadronic correction term, then the light-by-light scattering part turned out to have the wrong sign, etc. It's not at all obvious to me that there is a really firm SM prediction to compare the experimental results too, it's like the kaon mixing epsilon'/epsilon business all over again. The g-2 people seem to be a bit too eager pushing a "new physics" interpretation for my taste, although I guess it's understandable why they are doing it. The last time I looked the discrepancy was 2.2 sigma, which is certainly not 'very clear' evidence that the SM is wrong.

Re:Minor quibble, or addendum

[hubie]

Years ago I was at a conference where the session was on results from air shower detectors. During one talk this fella was saying that you shouldn't believe anything less than 4 sigma anyway. The next guy to talk presented his 3 sigma results from a different experiment.

Whoops... swap former and latter.

[Peter T Ermit]

Neutrinos require mass assumption; g-2 requires supersymmetry or other extension.

Someone fill me in

[Old Wolf]

The poster comments that the anti-neutrinos seem to be disappearing.... dont know about you, but the first idea that occurred to me was that they would have met normal neutrinos and annihilated.

And before someone writes 'RTFA' (or 'Dont start a sentence with a conjunction'), I can't find it: the first link seems to be to the reserach centre's homepage, the second and third go to explanations of the standard model, and the fourth is broken.

Re:Someone fill me in

[helix400]

I not a neutrino guru myself, but I think I have enough information for you.

Neutrinos and anti-neutrinos don't annaliate each other simply because they have an extremely small cross section for interactions with other matter. They are incredibly small, and have next to zero mass. This means that a neutrino would roughly have to travel an average 10^18 meters before it interactes with particles. Because of this, it would then seem unlikely that a neutrino would interact with an anti-neutrino.

In fact, the way my physics teachers taught us was that billions of neutrinos are passing through your body every second. Virtually all of these neutrinos will also pass through Earth as well.

Now the reason this Japan detecter can detect neutrinos is that it has a tank of 3000 tons of water. It patiently waits until one of these zillions of neutrinos scatters an electron, and then it can be detected.

The importance of neutrinos disappearing is that it could help out other models of physics, such as Grand Unified Theries or another theory of neutrinos that involves WIMPs. Basically, these are physics models that are very deep and complicated...often not covered in detail in a physics bachelor courses. But they are exteremly important in that they help physically test our latest theories about the universe.

(Note for post nit-pickers...all the information I explained came from my Astrophysics text book. Some of it may be a bit different than what KamLand's site says.)

this link works (at the moment)

[tqft]

http://www.lbl.gov/Science-Articles/Archive/NSD-Ka mLAND-Freedman.html

a bit more info

[ErfC]

This is actually interesting for several reasons. There are basically three types of neutrino experiments: "solar neutrino" experiments like SNO, which look at the number of neutrinos of various types coming from the sun and compare that to our (pretty successful) theories on how the sun generates neutrinos; "atmospheric neutrino" experiments like Kamiokande, Super Kamiokande, and the upcoming Hyper Kamiokande (I kid you not), which look at neutrinos generated in the atmosphere from cosmic rays; and "accellerator neutrino" experiments which look at neutrino "beams" from accellerators (or reactors, in this case).

These have three basic length scales, and they're all quite different. As I understand it (and there may be more to it than what I'm saying), the neutrino oscillation theories say that there should be *some* characteristic length to the oscillations. But all three types of experiments show oscillations! That's weird!

I think that's weird, anyway. ;) But they are all independent measurements of things, in any case. For one thing, they all look at neutrinos coming from different processes, so they're less sensitive to our understanding of how they're produced. They're also all looking at different types of neutrinos. Solar neutrinos are mostly associated with electrons. Atmospheric neutrinos are mostly muon neutrinos (and I *think* they get a lot of muon antineutrinos, too). Accellerator/reactor neutrinos would be either electron or muon neutrinos/antineutrinos, according to the design of the experiment.