Big News in Tiny Physics

A couple of significant news items from the world of particle physics:

  • There was a conference on neutrino physics recently, and the big news from there is that two experiments measure something funny with neutrino oscillations, namely that the oscillations seem to proceed at different rates for neutrinos and antineutrinos. This is a really surprising sort of asymmetry, and would be awfully hard to explain. These are, however, preliminary results that are being released now because there was a conference on neutrino physics, not because the people doing the experiments have rock-solid proof that these measurements are right. Physics Buzz has more, and the Knight Science Journalism Tracker entry for this story has more links, and some good material on the difficulty of interpreting what physicists say about this stuff.
  • Ed Witten, string theory demigod, has won the Newton medal awarded by the Institute of Physics. Also, to judge from that story, he was last photographed in about 1988. The prize honors “his many profound contributions that have transformed areas of particle theory, quantum field theory and general relativity.” Witten is a name to conjure with in string theory and related areas, so this seems well justified, but as I’m reminded every time I try to say something about this field, I’m not qualified to say anything about this field, so I leave it at that. I can confidently predict some sort of reaction from Peter Woit in the near-ish future, though.

And that’s the news from particle physics. If you want further explanation, ask a particle physicist. If you are a particle physicist, please feel free to provide further explanation (or a link to further explanation) in the comments.

Comments

  1. #1 Peter Woit
    June 29, 2010

    Thanks for pointing out the Witten story I hadn’t seen it. Not sure if I’ll write anything on my blog about this though, since yet another well-deserved honor for him isn’t all that newsworthy. The citation for the medal is very good, it’s here:

    http://www.iop.org/about/awards/international/page_43947.html

    Will be interesting to see what sort of public lecture he gives on Friday.

    About the neutrinos: it seems that if you believe these experimental results, we’re seeing a violation of CPT invariance, one of the fundamental principles you get by putting together quantum theory and Lorentz invariance. Such extraordinary claims require extraordinary evidence, and these results don’t yet rise to that level.

  2. #2 Andrew Foland
    June 29, 2010

    As a former particle physicist, I’ll say this–the results tend to suggest CPT violation, not just CP violation. CP violation by now is old news, we know how to accommodate it, SUSY gives you a million ways to generate it.

    CPT violation is “all hell breaks loose”. Field theory, spin-statistics, Lorentz-invariance–say goodbye.

    These are both 2-3 sigma results, which often have a habit of fading away.

  3. #3 Andrew Foland
    June 29, 2010

    As a former particle physicist, I’ll say this–the results tend to suggest CPT violation, not just CP violation. CP violation by now is old news, we know how to accommodate it, SUSY gives you a million ways to generate it.

    CPT violation is “all hell breaks loose”. Field theory, spin-statistics, Lorentz-invariance–say goodbye.

    These are both 2-3 sigma results, which often have a habit of fading away.

  4. #4 Steven Colyer
    June 29, 2010

    Isn’t the neutrino result(s) an example of “three sigma but no cigar” sort of thing? Don’t we need five sigma to achieve indisputability?

  5. #5 Hamish Johnston
    June 29, 2010

    …Also, to judge from that story, he was last photographed in about 1988…

    I thought he just never ages!

    Hamish

  6. #6 Stephen
    June 29, 2010

    I’m on one of these experiments. I’m not really sure what to say, except that publications will follow, of course. I agree it’s not a smoking gun, but it’s certainly an argument for taking more data. Due to the nature of statistics, though, it takes 4 times as much data to cut the error bars in half, and antineutrinos are harder anyway due to their production rates and cross-section.

  7. #7 onymous
    June 29, 2010

    CPT violation is extremely hard to swallow, because CPT is known to be a consequence of Lorentz symmetry, which is pretty much the most well-tested thing in all of science. I haven’t followed this closely, but I don’t think there’s any other good explanation except that you shouldn’t believe the experimental results. (It’s not very statistically significant in the first place.)

    You might think that because the Earth is made of matter, it shouldn’t be surprising that neutrinos and antineutrinos moving through it would behave differently, and you would be right, but as I understand it this mostly affects electron neutrinos, whereas the experimental result is about muon neutrinos, for which the effect is too small to explain the observed discrepancy. Ann Nelson and collaborators have a model of how you can get apparent CPT violation from such matter effects, but it requires postulating a new light particle that is extremely weakly interacting; if it’s true, it’s a real “who ordered that?” kind of moment.

    Most likely, though, this result will go away, like all the other 2- and 3-sigma effects in particle physics in the last decade.

  8. #8 Neil B
    June 29, 2010

    Pardon if I reveal some naivety about particle physics by asking, but @7: it seems to me that whatever makes particles and antiparticles different depends to some extent on the “put in by hand” properties of the universe that we don’t fathom a priori. So seemingly, not all facts about the comparison could be necessitated by basic “legal” symmetries about laws per se. After all, if APs were merely, utterly, nothing but particles of opposite charge – then there’d be no other differences at all. But there are.

    BTW there is never “indisputability” since probability is a continuum. There’s no logical place to draw the “line”, it’s a gradated judgment call. Not only that, but given enough of them: in other worlds or regions of the universe the rarest of misleading runs actually prevail. So the phil-sci question is: are the laws there “really different” (or do they change, if the runs break); or do we say there is a matter of principle of what the ought to be, and the results are misleading? Hard for a strict positivist to handle, no?

  9. #9 Alex
    June 29, 2010

    If tantalizing effects at the 2-3 sigma level keep going nowhere, maybe the profession should institute a rule that anybody who goes around making a big deal about 2-3 sigma effects has to wear a dunce hat at the next conference.

  10. #10 Stephen
    June 29, 2010

    Neil B: a priori, could you state your argument a little more clearly? e.g. what “other differences” are you talking about per se?

    Alex: Sure, but MINOS in particular has been very cautious about the claims they are making with a 2-3 sigma result. Same with CDMS. It’s everybody else outside of the experiment that get excited and make a big deal.

  11. #11 Steven Colyer
    June 29, 2010

    Lol, Alex good one. That’s my 2nd favorite suggestion for conferences after Alain Connes’ “Every time ‘The Universe’ is mentioned, everyone rise.”

    The Neutrino 2010 Conference was held this month in Athens, Greece. What’s the good word about this from the world’s experts?

    A question for the experts: Say we do find evidence that Charge-Parity-Time symmetry is broken. Does that necessarily mean that those fields mentioned by Andrew Foland in #2 above are trashed, or could there be another symmetry we haven’t thought of, say “X”, such that CPTX invariance is not violated?

    (for this probably-Mythical symmetry I was tempted to use “M”, but that letter has already been absconded by another probably-Mythical theory. I’ll say no more.)

  12. #12 Neil B
    June 29, 2010

    Differences … Well there’s a recent result about decay times of B mesons:
    Science News. Earlier, Kaon decays were found to differ on that account. It’s “a CP violation” and shows the particles are “inherently” different (otherwise how could they have different lifetimes?) From what I’ve read, the CP violation by Kaons is not enough to account for all the matter left in the universe so some further distinction must apply. I’m saying, if there’s such a difference and it’s based on “just the way things are” it wouldn’t be logically blocked by features of e.g. relativity theory.

  13. #13 Kea
    June 29, 2010

    I am an unemployed particle physicist. The mass differences can be explained by two Brannen type Koide triplets. The eigenvalue triplets (for a 1-circulant Hermitian 3×3 matrix) give three sqrt(m) values, given up to a scale by (1 + sqrt(2) cos(theta)) where theta = delta + omega and the three omega are the cubed roots of unity. A value of delta = 2/9 + pi/12 gives the neutrino masses, and a value of delta = 2/9 – pi/12 gives the antineutrino masses. The resulting mass squared values are in good agreement with the two MINOS results. These eigenvalue sets have the same mass sum, m1 + m2 + m3 = 0.06 eV.

    Needless to say, these formula have been studied for some years in the context of a QG approach that does NOT take classical symmetries as a fundamental starting point.