Weird Results from Neutrino Experiments

[sanman]

Recently, the MINOS detector has shown results that call into question the symmetrical properties of anti-neutrinos with respect to neutrinos:

http://arstechnica.com/science/news/2010/06/antineutrino-masses-throw-physics-a-curve.ars

More strange results came from MiniBooNE:

http://blogs.nature.com/news/thegreatbeyond/2010/06/post_59.html

http://www.symmetrymagazine.org/bre...esults-suggest-antineutrinos-act-differently/


If these results are not yet enough to question the Standard Model for neutrinos, then what further experiments will shed light on the issue?

What possible explanations are available to account for the anomalous results?

 

[Parlyne]

Very weird, indeed. I won't be totally shocked if the ultimate consensus is that the differences have more to do with the material the neutrinos propagate through to get to the detectors. But, if that isn't the case, this looks like there must be some pretty serious CP violation involved.

It's worth noting that the existence of neutrino oscillations already means that the standard model fails to describe neutrinos correctly, as standard model neutrinos have no mass. There isn't really a "standard model" of neutrino masses at the moment. In fact, there are something like four different mechanisms to give neutrinos mass. It will be interesting to see what these results have to say about them.

 

[jtbell]

Recently, the MINOS detector has shown results that call into question the symmetrical properties of anti-neutrinos with respect to neutrinos:

http://arstechnica.com/science/news/2010/06/antineutrino-masses-throw-physics-a-curve.ars

The release announcing them cautions that the data is only just approaching statistical significance, and will require extensive confirmation work, not to mention a trip through peer review before publication.

(emphasis added by me) In other words, the result isn't statistically significant yet. Lots of time, interesting things pop up in a preliminary data set which disappear after more data comes in.

More strange results came from MiniBooNE:

http://blogs.nature.com/news/thegreatbeyond/2010/06/post_59.html

MiniBooNE has now confirmed the LSND anomaly with a confidence of 99.4% -- or just under a 3 sigma significance. In the physics world, that's not nearly enough evidence to claim a discovery.

(again, emphasis added) Again, not statistically significant enough. Five sigma is the minimum required for people to take such things seriously. Physicists have learned this from painful experience in the past.

 

[sanman]

If these latest results are eventually borne out by statistical validity, then I'm wondering if this symmetry-breaking between neutrinos and anti-neutrinos is correlated with the fact that the Weak force's small scale is much closer to the Planck Length as compared to other forces.

After all, the dynamic vacuum is supposed to be frothing with particle-antiparticle pairs separating/emerging from nothingness and then merging/disappearing again. But neutrinos and anti-neutrinos are very weakly interacting particles, so it seems likely that they would escape each others' grasp more easily.

So I'm not saying that the neutrino-antineutrino symmetry breaking is caused by the fact that they can escape each other more easily. I'm saying that this ability for their virtual pair partners to more easily escape each other makes them the "canary in the coalmine" (ie. a tell-tale indicator) for CP-violation.

 

[Count Iblis]

Note that recently it been shown that ignoring subtleties of quantum measurement theory has caused problems in the interpretation of the results of neutrino oscillation experiments:

http://arxiv.org/abs/1005.4307

 

[Parlyne]

I think I need to amend my previous statement. Thinking about it, if this effect comes from new physics (which I still highly doubt it does), it would have to involve CPT violation, not just CP violation. And, CPT violation, as I understand it, necessarily means local Lorentz violation. In other words, if this is borne out as an effect of new physics, that new physics would have to involve the violation of relativity.

 

[Prathyush]

Why is it CPT? To me it seems that anti neutrinos behaving differently to neutrinos involves only a CP violation.

 

[Parlyne]

Why is it CPT? To me it seems that anti neutrinos behaving differently to neutrinos involves only a CP violation.

CPT requires that the anti-neutrino mass matrix be the complex conjugate of the neutrino mass matrix. That means that the anti-neutrino mass matrix can be Takagi diagonalized by the complex conjugate of the unitary matrix that Takagi diagonalizes the neutrino mass matrix. Ergo, neutrinos and anti-neutrinos should have the same mass eigenstates and mixing parameters. If they don't, the assumption of CPT symmetry must be bad.

 

[Salman2]

There was also recently a report of asymmetry in oscillations between matter & antimatter B meson, in violation of Standard Model.

http://www.nytimes.com/2010/05/18/science/space/18cosmos.html

The pre-published Fermi Lab results of the reported B Meson experiment (see link below) indicate 50 X more matter than antimatter than predicted by the current Standard Model.

http://arxiv.org/PS_cache/arxiv/pdf/1005/1005.2757v1.pdf

I note that this report uses a limit between 3-4 standard deviations to suggest statistical significance from the Standard Model. Another post indicated 5 SD was needed, but perhaps not given the vast number of physicists that signed their name.

==

Would there be any significance to the observation that both neutrinos and B mesons have property of oscillations between matter and antimatter--is this perhaps the reason (CPT) assumptions of the Standard Model may be violated ? I am new here, not a physicist, but have interest in the topic.

 

[JustinLevy]

Wait, I thought one could derive CPT as a requirement Lorentz symmetry. So if neutrinos and anti-neutrinos don't have the same mass eigenstates or mixing parameters, is that equivalent to measuring a Lorentz violation?

I'm definitely confused here.

 

[Haelfix]

CPT is more than just a statement about lorentz invariance. Its a statement about the theory of quantum fields.

No known formulation of quantum field theory exists that also includes CPT violation. There is some work in the algebraic approach where you can begin to kinda sort of start playing around with it, but that is very tentative and a difficult research direction.

In short CPT is about as fundamental a symmetry or principle as we know off in physics, and it would be a major disaster if it turned out to be incorrect.

Hence the enormous skepticism about these results (and its far from the first time that such things have occurred and promptly gone away).

 

[nismaratwork]

CPT is more than just a statement about lorentz invariance. Its a statement about the theory of quantum fields.

No known formulation of quantum field theory exists that also includes CPT violation. There is some work in the algebraic approach where you can begin to kinda sort of start playing around with it, but that is very tentative and a difficult research direction.

In short CPT is about as fundamental a symmetry or principle as we know off in physics, and it would be a major disaster if it turned out to be incorrect.

Hence the enormous skepticism about these results (and its far from the first time that such things have occurred and promptly gone away).

I really cannot imagine CPT symmetry breaking given how wonderfully predictive GR has been. I think JTbell really said it all here, this is probably a 'blip' destined to fade, as Haelfix says.

 

[Salman2]

A Majorana fermion is its own antiparticle. For a Dirac fermion--the particle and antiparticle are different. If the MINOS results hold, would this mean that the Majorana fermion concept would be falsified as opposed to the Dirac concept ?

 

[Haelfix]

I don't know what a Majorana, Weyl or Dirac fermion even is, without the formalism of quantum field theory to make sense of it.

 

[Parlyne]

A Majorana fermion is its own antiparticle. For a Dirac fermion--the particle and antiparticle are different. If the MINOS results hold, would this mean that the Majorana fermion concept would be falsified as opposed to the Dirac concept ?

Neither possibility allows the neutrino and antineutrino mass eigenstates to differ.

 

[Salman2]

This paper discusses CPT violation and neutrinos:

http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TVN-45XTSWD-S&_user=10&_coverDate=06%2F20%2F2002&_rdoc=1&_fmt=high&_orig=search&_sort=d&_docanchor=&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=60dc409a9eb48e6608da0a2e1747240d

Here is the Abstract:

In order to accommodate the neutrino oscillation signals from the solar, atmospheric, and LSND data, a sterile fourth neutrino is generally invoked, though the fits to the data are becoming more and more constrained. However, it has recently been shown that the data can be explained with only three neutrinos, if one invokes CPT violation to allow different masses and mixing angles for neutrinos and antineutrinos. We explore the nature of neutrinos in such CPT-violating scenarios. Majorana neutrino masses are allowed, but in general, there are no longer Majorana neutrinos in the conventional sense. However, CPT-violating models still have interesting consequences for neutrinoless double beta decay. Compared to the usual case, while the larger mass scale (from LSND) may appear, a greater degree of suppression can also occur.

 

[Demystifier]

Salman2, do these CPT-violating models violate Lorentz invariance? If not, then how do they avoid the CPT theorem? What assumptions of the CPT theorem are rejected?

 

[Salman2]

Demystifier--I only have access to the abstract that I posted--it was fyi--for those with interest in the subject. You would need to read the publication to get answers to your questions and contact the authors.

 

[Parlyne]

That paper is available, in full, on the ArXiV at http://arxiv.org/pdf/hep-ph/0203261v1. And, the model discussed therein does violate Lorentz invariance, as any CPT violating theory must.

 

[nismaratwork]

That paper is available, in full, on the ArXiV at http://arxiv.org/pdf/hep-ph/0203261v1. And, the model discussed therein does violate Lorentz invariance, as any CPT violating theory must.

...Which means I'd like to see about a thousand times more evidence than this statistical blip to start throwing GR out of the window.

 

[Demystifier]

And, the model discussed therein does violate Lorentz invariance, as any CPT violating theory must.

You mean, any CPT violating theory THAT SATISFIES ALL OTHER AXIOMS OF THE CPT THEOREM. CPT theorem follows from a set of axioms, and it is certainly conceivable that some other axiom, rather than Lorentz invariance, is violated.

 

[Vanadium 50]

Let's be careful. Yes, in these models there is Lorentz violation, but it is at a distance scale far, far smaller than has ever been probed. It is not experimentally excluded that the universe looks "smooth" (i.e. Lorentz symmetry is a good symmetry) at one scale and "bumpy" at another. These models are not a priori crazy.

That said, I would like to see much stronger evidence than we have now: the MINOS hints and the LSND/MiniBoone hints.

 

[Demystifier]

Vanadium, good point!

 

[Vanadium 50]

Demystifyer, I agree with you, but of the three requirements, breaking Lorentz violation does much less damage to our existing theoretical framework than the other two, locality and causality. Making either an a-causal or non-local (in the sense that a local theory is expressible with a finite number of derivatives) theory work is not for the faint at heart.

 

[Prathyush]

http://arxiv.org/abs/hep-ph/0201258

The abstract says
"An interacting theory that violates CP T invariance necessarily violates
Lorentz invariance. On the other hand, CP T invariance is not sufficient for
out-of-cone Lorentz invariance. Theories that violate CP T by having different
particle and antiparticle masses must be nonlocal."

 

[Demystifier]

http://arxiv.org/abs/hep-ph/0201258

The abstract says
"An interacting theory that violates CP T invariance necessarily violates
Lorentz invariance. On the other hand, CP T invariance is not sufficient for
out-of-cone Lorentz invariance. Theories that violate CP T by having different
particle and antiparticle masses must be nonlocal."

Very interesting!

 

[Prathyush]

a recent paper on the topic
http://arxiv.org/abs/1007.1150
If i understood it right this search is better and agrees with what the previous experiments suggested.