Of Particular Significance

End of the OPERA Story

POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON 06/08/2012

In case you haven’t yet heard (check my previous post from this morning), neutrinos traveling 730 kilometers from the CERN laboratory to the Gran Sasso laboratory do arrive at the time Einstein’s special relativity predicts they would.

Of course (as the press mostly seems to forget) we knew that.  We knew it because

So the news from the Neutrino 2012 conference in Kyoto, on new data from May 2012 taken by OPERA and three nearby experiments, is no surprise to anyone who was paying attention back in March and early April; it’s exactly what we were expecting.

One thing that almost no one is reporting, as far as I can tell, is that CERN’s research director Sergio Bertolucci did not give the first talk on neutrino speeds in Kyoto.  That talk was given by Marcos Dracos, of OPERA.  Dracos presented both OPERA’s corrected 2011 results (with corrections based on the detailed investigation shown in March of the problems reported back in February) and also the new 2012 results, which were taken with a kind of short-pulse beams similar to that used in OPERA-2.  (A short pulse beam allows for a neutrino speed measurement to be made rather easily and quickly, at the expense of OPERA’s neutrino oscillation studies, which were the main purpose of building the OPERA experiment.)

Following Dracos’ talk, Bertolucci spoke next, and reported the results of the neighboring Borexino, LVD and ICARUS experiments on the May 2012 data, which along with OPERA are all bathed in the same CERN-to-Gran Sasso neutrino beam, and collected their data simultaneously.  All of the results are preliminary so the numbers below will change in detail.  But they are not going to change very much.  Here they are: neutrinos arrive at a time that differs from expectation by:

  • Borexino: δt = 2.7 ± 1.2 (stat) ± 3 (sys) ns
  • ICARUS: δt = 5.1 ± 1.1 (stat) ± 5.5 (sys) ns
  • LVD: δt = 2.9 ± 0.6 (stat) ± 3 (sys) ns
  • OPERA: δt = 1.6 ± 1.1 (stat) [+ 6.1, -3.7] (sys) ns

(Here “ns” means nanoseconds, and “stat” and “sys” mean statistical and systematic uncertainty.)  The original OPERA result was an early arrival of about 60 nanoseconds, about six standard deviations away from expectations.  You see that all the experiments are consistent with zero early/late arrival to about 1 standard deviation — almost too consistent, in fact, for four experiments.

So there is no longer any hint of any evidence whatsoever of a problem with the predictions of special relativity, and in particular with the existence of a universal speed limit.

A summing up is called for, but I want to write that carefully.  So unless something else comes up, that’s all for today.

Share via:


29 Responses

  1. Hi Professor,
    Not unexpected news! however, as the BBC reported on March 30th, professor Ereditato resigned…a story that leaves me with a bitter aftertaste. The OPERA findings were carefully documented and well-aired to the scientific community; why did he have to go? peer-pressure, politics, shame? Any of these choices sadden me. But of course, it could have been any number of reasons.
    Still, I have always considered the scientists as our world’s “true bastions” of knightly characteristics with the strength to step aside of modern vices in the pursuit of truth (to know the how and when if you will).
    As an astrophysicist-to-be I have been encouraged by my professors to hold the practicing of my profession to the highest standards recognized in the scientific community. We could all agree I am not singular to these expectations.
    Then, to see somebody in the position of having to resign -as the mentioned article insinuated as a possible reason- perceptibly earthquaked these “romantic” views of mine, maybe because it wouldn’t be uncommon or unheard of but on the contrary.

    Orem, UT, US.

    1. I wrote about this in a few places (if you search on my posts on OPERA from March, you’ll see some discussion.)

      Ereditato resigned from his position as head of the OPERA experiment — not from the experiment himself, which he remains a member of (as far as I know.) His resignation from the leadership was brought about by the members of the OPERA experiment themselves, many of whom felt, it would appear, that he had led the OPERA experiment into disrepute (possibly endangering its future) by the way the presenting and characterization of the results was handled. More precisely, many of his collaborators voted against him in a no-confidence vote, and he decided that with so many opposed, it was best that he step down.

      Were his collaborators right to be upset with him? Well, I have seen other scientists handle somewhat similar situations much better than the OPERA leadership did. And people who lead experiments are expected to handle external politics well; that’s part of their job, as leaders. If they fail to do so, maybe they should step down and let others take the reins.

      But note: Ereditato did not lose his scientific position, nor was he asked to leave the experiment.

      So I think your “romantic” views are still intact. And somewhat justified.

  2. I think 30 years ago someone (J. C. Cooper?) noticed that the original antiproton discovery of Segre, Chamberlain, Ypsilantis, Weigand, etc indicated that negative pions traveled faster than the speed of light. They used a combination of Cherenkov and time of flight to pull out the antiprotons from the negative pion background. But they weren’t careful in making the absolute measurement of the distance between their scintillator paddles, and the numbers in the discovery paper indicated superluminal negative pions. All that really mattered for the antiproton discovery was the difference in time between pions and antiprotons… the absolute value of the time of arrival for pions was not the point. And so superluminal pions sat since the 1950’s in the literature… but in all probability due to a systematic error that the experimenters didn’t really care about.

  3. Prof. Strassler: Undoubtedly, Prof. Milgrom is much in my thoughts — I think that he should have won the Nobel prize 20 years ago. You seem to think highly of Arkani-Hamed. Would you please name 5 or 6 of the best particle physicists who are under the age of 45? (No doubt such a short list would have to leave out many.)

  4. “…it’s exactly what we were expecting.” Physics in fact could not exclude “nicht einmal falsch.” arxiv:1205.5998, 1204.0484, 1203.5008, 1203.4052, 1202.5560, 1202.3319, 1201.4374, 1201.4147, 1112.5793, 1112.4714, 1112.3050, 1110.6577, 1110.6571, 1110.5866, 1110.3540, 1110.2170, 1110.0882, 1110.0783, 1110.0424, 1110.0245, 1110.0243, etc.

  5. Prof. Strassler: Consider the MILGROM DENIAL HYPOTHESIS: The main problem with M-theory is that M-theorists fail to realize that Milgrom is the Kepler of contemporary cosmology.
    In your opinion what is the probability that the preceding hypothesis is correct? (Presumably you think that the preceding question is irrelevant to the OPERA neutrino experiment, but I am in 100% disagreement if that is what you think.)

    1. It’s 100% irrelevant. You can disagree with me all you want; that’s also irrelevant. M theory (and Milgrom/Kepler) have never made a prediction for neutrino masses or for any violations of Einstein’s special relativity. Honestly, if you showed other readers a real understanding of what was and wasn’t relevant, and didn’t talk about M theory and Milgrom in almost every single comment you make, people would be a lot more likely to take what you say a bit more seriously.

  6. Dear Professor, someday would you comment on why neutrino mass is not zero? Thanks for sharing wonders with us.

    1. Ok, will try to do that at some point, I don’t think I really have yet. It is not so easy to give a coherent answer to this, because you can answer this in various ways. For instance, there’s no reason neutrino masses had to be zero in the first place. Some would argue the real question is not “why are the masses not zero?” but “why are they so small?” And others would point out that you might as well as why the electron mass is not zero — this is just as much in question. It all has to do both with the Higgs mechanism — the non-zero Higgs field http://profmattstrassler.com/articles-and-posts/the-higgs-particle/360-2/ which is needed for neutrinos, electrons, quarks, etc. to have mass, and with the structure of the Standard Model’s particles and forces, http://profmattstrassler.com/articles-and-posts/particle-physics-basics/the-known-apparently-elementary-particles/the-known-particles-if-the-higgs-field-were-zero/

      1. Matt, how gains Higg’s mechanism mass to neutrinos? AFAIK neutrinos do not interact directly with Higg’s field. Are the neutrinos masses loop corrections (like neutrino emits virtual Z, it desays in virtual elektron/positron pair and these particles interact with Higgs)?

        1. It is probably a second-order effect:

          in the notation of http://profmattstrassler.com/articles-and-posts/particle-physics-basics/the-known-apparently-elementary-particles/the-known-particles-if-the-higgs-field-were-zero/ ,

          the electron mass arises from an interaction of the form electron-right–Higgs field — electron-left

          the neutrino mass MAY arise in a similar way if neutrino-right fields exist, OR

          it MAY arise from an interaction of the form neutrino-left* — (Higgs field)2 — neutrino-left

          The latter interaction would be induced by some as yet unknown higher-energy phenomenon (there are many possibilities and the mere existence of the interaction doesn’t tell you which possibility is right.)

          Here’s a short technical review: http://www.physics.upenn.edu/neutrino/jhu/node2.html

  7. Has OPERA had any results on neutrino oscillations yet, or have they been too distracted by all this superluminality business?

    1. Hopefully, Project X in FermiLab will soon have answers to neutrino oscillations. I hope the Government fully funds this very important project. The future of our energy needs will rely on the questions and answers that come out of this research.

    2. Yes. Last year, the OPERA detected the second tau mesone, so they detected two cases of mu to tau neutrino oscilation in five years.

    3. So far, they’ve detected two neutrinos that underwent a muon-neutrino to tau-neutrino transition…. not enough yet for significant results, but they’re getting there.

  8. Do you have an FAQ which would help me understand something about the bremsstralung predicted for supraluminal neutrinos by Glashow (I think) which should have created a spread of energies for the OPERA neutrinos which, of course, was not there.

    1. Pretty good, but I note a few things you might want to adjust. First, I think your use of the word “proper time” for L/c isn’t standard. Proper time would be “time as evaluated by an observer who is at rest with respect to the traveling particle.” Second, your statement about supernovas, neutrinos and light doesn’t look right to me. The neutrinos and the initial light are emitted simultaneously in the supernova explosion. However, the initial light is blocked by the huge density of the supernova and by the preexisting star; it is a couple of hours before the light is able to make it out of the star. The neutrinos come out almost immediately (within a second). I don’t remember the details of the light emission at the moment, but you might want to look them up and fix what is otherwise potentially misleading.

      1. L/c would be the proper time seen by an observer travelling on the beam of light, the shortest time to travel a distance L. I do know the standard “proper time” definition…But for all practical purposes, my use is not bad there.
        By the other hand, I agree with about your critics on the other side. I read my Master thesis on neutrinos last October, but I did not focus on Supernova neutrinos (just reading on it in the last days), I was more general and I did a general review on neutrino Physics. Yeah, it is the density during the collapse and the increasingly high density what somehow ties photons with a block-out, … Perhaps I should have not gone deeper on the Supernova issue, but indeed I remember that the time of flight calculation I did was suggested in some of my books on neutrinos. I will fix it ( I had other two mistakes I had to fix too…I was doing and I am yet a crash course on SR in order to pave the path into a more ambitious plan for my blog: discuss Physics and Mathematics at higher level). Thank you for your polite comments Matt.

        PS: In some weeks, I will decide and know if I can dream with make a Ph.D here or I have to move…Bank rescue today 2000 euros/hab National tragedy …And most of the people are thinking yet in nonsense…I think my future is likely abroad…Let’s see if I can find something/someone interested in the next months…

        PS(II): If Betelgeuse goes Supernova, it would be a wonderful spectacle!

        1. I really don’t think that’s the standard use of the term “proper time”. If an observer sees two events as occurring at the same spatial point — i.e., if the observer is at rest with respect to those two events — the time between those events is the “proper time”, and satisfies tau^2 = t^2 – x^2 where t and x are the time-separation and position-separation from the point of view of any other inertial observer. (I’m setting c to 1.) That means that for an observer traveling with a light beam — for which t and x are always equal, from the point of view of any inertial observer — tau = 0.

          Good luck on the financial side.

      2. The spacetime separation from CERN-GRANSASSO, in t=0, setting c=1, is given by S²=-\tau^2=(\Delta x)²-(\Delta t)². The events don’t happen at the same spacetime point. CERN = A, Gran Sasso =B. Firstly, to measure the length (distance) bewteen A and B,an so we have to measure simultaneously two events at CERN and Gran Sasso. t_A=t_B implies X_B-X_A=L from the above formula for the spacetime separation. A beam of light satisfies obviously S²=0, but it does not mean that the time from A to B is zero. You correctly say that \tau, the “proper time” usual definition is that…I agree…But please, see that two space-like separated events, imposing s²=0 imply that

        s²=0=(X_B-X_A)²-(t_B-t_A)²=0 or equivalently (X_B-X_A)=(t_B-t_A)

        This is also your remark, I believe, your x=t stuff. So the “proper time”, or proper time v.2.0 ( if you like, I think is a question of words/agreement) for light to travel L, reintroducing c, is \t_B =L/c = \tau (not of course the \tau in s²=0 = \tau ^2). Note I was also meaning that the time separation between to events is generally:


        So, for lightbeams, with standard proper time \tau = 0 the time separation is the minimum possible AND, in our case, it is t=L/c (perhaps I should have not use \tau for that time as well, I think, it is also confusing I recognize, if you are not familiarized with spacetime concepts both my notation and proper time word). I will change it…It can disorient as well…Thanks again…

Leave a Reply


Buy The Book

A decay of a Higgs boson, as reconstructed by the CMS experiment at the LHC


The particle physics community is mourning the passing of Peter Higgs, the influential theoretical physicist and 2013 Nobel Prize laureate. Higgs actually wrote very few

POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON 04/12/2024

I recently pointed out that there are unfamiliar types of standing waves that violate the rules of the standing waves that we most often encounter

POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON 03/25/2024