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    ICARUS Refutes Opera's Superluminal Neutrinos
    By Tommaso Dorigo | October 18th 2011 04:34 AM | 105 comments | Print | E-mail | Track Comments
    About Tommaso

    I am an experimental particle physicist working with the CMS experiment at CERN. In my spare time I play chess, abuse the piano, and aim my dobson...

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    The saga of the superluminal neutrinos took a dramatic turn today, with the publication of a very simple yet definitive study by ICARUS, another neutrino experiment at the Gran Sasso Laboratories, who has looked at the neutrinos shot from CERN since 2010.

    The ICARUS team jumped on the chance to test the Opera result based on the article recently published by Cohen and Glashow. The latter argue that superluminal neutrinos should lose energy through  neutral-current weak-interaction radiation -the analogue of Cherenkov radiation for a neutral particle. Given a neutrino moving at a speed v>c as the one measured by Opera, and given the distance traveled to the Gran Sasso cavern, one can relatively easily compute the energy spectrum of observable neutrinos at the cavern, given the production energy spectrum.

    The physics is a bit more complicated than I summarized it in the paragraph above, but really, you need not squeeze your brains: there is nothing much to know. What is important is that there is a clean and simple relationship between the superluminal speed and the rate of decrease of the neutrino energy. Neutrinos at CERN are produced with an average energy of 28.2 GeV, and neutrinos at the receiving end - the LNGS where Opera and ICARUS both sit - should have an average energy of only 12.1 GeV for neutrinos detected via charged-current interaction.


    (Above: a picture of ICARUS in the LNGS cavern)

    Incidentally, a charged-current neutrino interaction occurs when the neutrino "exchanges" a unit of electric charge, along with weak quantum numbers, with a nucleus. The neutrino thus turns into a muon, while the nucleus breaks apart in a shower of light hadrons. The muon is then very easy to detect and measure.

    I can imagine the ICARUS team brainstorming all together at a meeting. Everybody brings about their favourite objections to the timing measurement of Opera. Some argue whether they can redo the Opera measurement. Others pass along the tray of donuts. Then somebody brings up the Cohen-Glashow paper: "Look, it is quite easy: we take neutrino interactions, measure their energy, and compare with various hypotheses for the superluminal speed. All based on known physics and hard facts. Can we do it ? Can we ? OMG wait... We have already those neutrino interactions!"

    So off they go, and do their homework. And a very good homework it is: in less than three weeks from the appearance of the Cohen-Glashow paper -yesterday evening-, they publish a preprint. Kudos to them for their speed and focus. True, ICARUS is not flooded with neutrino statistics these days -I could not help chuckling at their honest but a bit vintage description of why they lost this or that event, ending up with a statistics of less than 100 interactions (OPERA has 16000, although they've run for much longer so far). But those less-than-100 neutrinos do kick ass.

    In fact, what do they find ?



    (Above: the distribution of muon momenta as detected by ICARUS [black points] is compared with a simulation [in red] assuming that neutrinos retain their energy spectrum in their trip from CERN to LNGS. A much leaner distribution would be observed if neutrinos were superluminal.)

    They find that the energy spectrum of the detected neutrino interactions in ICARUS shows a very nice agreement with the expectation for well-behaved light-speed-moving neutrinos. A very dramatic distortion of that spectrum would instead be expected for the speed measured by OPERA, such that indeed ICARUS can place a very tight constraint on the superluminal speed of the CERN neutrinos: consistent with the speed of light, and not larger than that by more than four part in ten billionths. An order of magnitude looser than the limit obtained with the neutrinos from SN1987a, but still quite tight -and certainly excluding without argument the value of 50 millionths measured by OPERA.

    If you are unfamiliar with millionths and billionths, I can make it easier for you: the ICARUS result says that the difference between the speed of neutrinos and the speed of light cannot be as large as that seen by OPERA, and is certainly smaller than that by three orders of magnitude, and compatible with zero.

    So, forget superluminal neutrinos. Or maybe not: what remains to be seen is whether other experiments will find results consistent with v=c or not. That's right: regardless of the tight ICARUS bound, every nerd with a neutrino detector in his or her garage is already set up to produce an independent confirmation of the startling OPERA result... We'll soon see measurements by MINOS and Borexino, for instance. Interesting times to be a neutrino expert are these!

    As for me, I can chuckle and archive this umpteenth 6-sigma anomaly in the Zoo of wannabe new physics results. Physics is hard, folks - you can't expect to be dealt a straight flush all of the times.

    Comments

    Tommaso,

    Thanks for sharing the news. Once again, Einstein is sticking out his tongue to all his detractors.

    But I am convinced that the FTL neutrino saga will continue to unfold and it won't die soon. In fact, I wonder if people will ever stop challenging Special Relativity with erroneous measurements or fundamental misinterpretations...

    Cheers,

    Ervin

    vongehr
    I do not see how this result excludes V bigger c over small distances as indicated by the data.
    dorigo
    It doesn't, but your "indicated by the data" flies in the face of Occam's razor, since it invokes unnecessary entities in addition to the known players, to explain just one odd result.

    Cheers,
    T.
    vongehr
    So you admit it does not do anything like that, but you nevertheless claim exactly this in your headline? Great science-outreach - sure the public will love scientists like you now more than the bad media who hype so much. Well, here is the conclusion that ICARUS proves faster than light neutrinos.
    About your misuse of Occam's razor: You are aware that this is only good "philosophy" for people who barely understand science, right? Occam's razor cut the cosmological constant out, you know, that thing that got a Nobel Prize in physics recently. Occam's razor is a big no no for philosophers who understand modern science.
    Your physics may stand up but your written English is very poor. I found the article difficult to read due to poor grammar and terrible use of punctuation. Your random use of hyphens is quite puzzling.

    dorigo
    Dear Momar, thanks for your comment. I always try to improve - English is not my native language.
    Cheers,
    T.
    If I may speak as a veteran copyeditor of physics journals, your prose is fine. It would be a happy time at the office if minor matters of editorial style were the only thing to worry about.

    I don't understand why you distract attention from content to style. What you allege to be "poor grammar" of this entry has nothing to do with the subject matter.

    Really- that's all you got-you sir are an a**hole!

    Hank
    Your physics may stand up but your written English is very poor. I found the article difficult to read due to poor grammar and terrible use of punctuation. Your random use of hyphens is quite puzzling.
    Wow.  Tough crowd.  Wait until Momar reads my Italian!
    Punctuation is constantly evolving, and Tommaso's use of dashes does seem to correspond to an established convention:

    http://en.wikipedia.org/wiki/Dash#Parenthetic_and_other_uses_at_the_sent...

    I found Tommaso's piece easy to read.

    At some point we're likely to be faced with a next-generation physics theory in which many of our most hallowed physics concepts and conventions are liable to be overturned or downgraded, and I'm not sure how we're going to have the mental flexibility to cope with that if we're so set in our habits that we're even having trouble adjusting to modern punctuation conventions.

    I offer an apology Tommaso. My comments were out of place. Nice physics btw.

    Admittedly, Momar has to his/her credit apologised. Ervin makes an essential point because the style and detailed content is lucid and highly informative.

    Tommaso has no need to feel uneasy because English is not his first language. Infact, I would claim that his written English is better than 90% of all English speakers for whom English, and I am English myself, is their first language.

    No doubt had he written in Italian most of us would be struggling. Unbeknown to Momar, it could have been all Greek to us. How's the Greek course going Tommaso?

    As for correct punctuation English writers tend to go beserk when it is mentioned. I am not the one to lecture on punctuation. You can't , sorry cannot (can not) go wrong if you keep it simple with the use of only . , ; . Don't get too clever with colons : and never use that slash - oops hyphen, although I use it too often. A little attention to this last paragraph and you will become a sine qua non 3 sigma English science writer.

    dorigo
    Very nice indeed Graham. Yes, I do use too much that hyphen thing. And I am sensitive to the issue, since if we were discussing Italian, I would claim I can use punctuation better than most. With English... Oh well.
    Greek is going very well, since I have a wonderful personal instructor. I'm making progress by the week. In a few months I'll call it quits and turn to some other language (want to master five by the time I turn fifty).

    Cheers,
    T.
    I do not share the excitement about the 100 events energy spectrum shown by ICARUS.
    I understand is a good story for the media but, back to science, other experiments have measured neutrino energy spectra in the past and I am sure Opera has its own energy spectrum which exceed the 12.5 GeV upper limit calculated by Cohen-Glashow for superluminal neutrinos.
    As a matter of fact If superluminal neutrinos lose energy with the mechanism proposed by Cohen-Glashow, then, since the effect increases with energy and distance, the best limit comes from observation of high energy atmospheric neutrino interactions in experiments like SuperKamiokand and IceCube. The corresponding limit in the paper by Cohen-Glashow exclude the Opera observation by many orders of magnitude and is way better than the ICARUS limit.
    Incidentally, for kinematical reasons similar to the argument invoked by Cohen and Glashow, also pions decay to superluminal neutrinos should be strongly suppressed. This would also be in contrast with many observations since pion decay is precisely the major source of neutrinos produced using accelerators. The problem with these arguments is that they are a rather indirect and model dependent rebuttal of the superluminal neutrinos since they assume that Lorenz simmetry is broken and the usual energy vs momentum relations hold. If the usual energy momentum dispersion relation is modified, than these arguments would not hold against superluminal neutrinos.

    Actually in the middle of the media storm about "Einstein failure" stories is fair to say that the community is still waiting for the final version of the Opera paper which as far as I know, has not yet been submitted to a peer reviewed journal.
    When this will happen, at some point the media excitement will settle but I am afraid only others experimental measurement will be able to kill (or confirm...) faster than light neutrinos.

    "If the usual energy momentum dispersion relation is modified, than these arguments would not hold against superluminal neutrinos."

    It is worth recalling that many theories based on violation of Lorentz invariance via changing the relativistic dispersion relation have been severely constrained by recent astrophysical observations.

    Ervin

    I agree with you, although also theories with explicit breaking of Lorenz-invariance are very strongly constrained.
    Actually I find the Cohen-Glashow argument very strong and elegant and IMHO there are (yet) no compelling evidence for faster than light neutrinos. My point is simply that if the CG argument holds, than we know already that superluminal neutrinos are not here since Opera is observing neutrinos with energy well above the 12.5 GeV CG limit and even much more stronger limits are set by the observation of high energy atmospheric neutrino interactions. In addition, the kinematical suppression of the pion decay to muons and superluminal neutrinos at high energy is incompatible with the observed cosmic rays spectrum.

    At the end, if the Opera result will pass in the first place the critical analysis of the Opera collaboration and the peer review process, then the final word will be to experiments repeating this measurement in improved conditions and convincingly ruling out - well this is my personal bias here - their result.

    PS I am as well a non-native english speaker. Are the hyphens above correct ? ;-)

    "PS I am as well a non-native english speaker. Are the hyphens above correct ?"

    I've been reading English for -- umm -- about 66 years. Your use is perfectly fine with me.

    I prefer to use two hyphens because it looks more like the em dash often seen in print, which is a bit wider than a mere hyphen. In my opinion the main misuse of the hyphen character in this context is to omit bracketing spaces, which you have not failed to do. (Spaces aren't used with an em dash.)

    More at http://www.grammarbook.com/punctuation/dashes.asp
    And a caution against their overuse http://www.slate.com/articles/life/the_good_word/2011/05/the_caseplease_...

    Halliday
    Of course, with a very little knowledge of HTML, one can have true em dashes (—), and en dashes (–) within this forum.  ;)
    Sterile neutrinos don't lose energy through this Cohen-Glashow mechanism. There are theories that attempt to explain the OPERA result by having the neutrinos oscillate to superluminal sterile neutrinos for part of their trip. These theories are consistent with the ICARUS result. Thus, there is really no conflict between the OPERA and ICARUS results.

    dorigo
    Dear Lucio,

    I thank you for your very insightful comment. Indeed your points are valid, as far as I understand them. However, I still feel quite a bit fortified in my scepticism of the Opera speed measurement after this, huhm, "lack of confirmation".

    True, the paper has not been submitted yet. And whether it will is anybody's guess. If it is published, I will regain interest actually - for the moment (oops hyphen again) I feel authorized to deal with other new physics wannabe signals.

    Cheers,
    T.
    Vladimir Kalitvianski
    We can admit that "slow" neutrino belong to the Standard Model with its charged and neutral currents. But if the neutrino is superluminal, can we apply the SM to derive its energy losses? Does SM allow superluminal neutrino? ;-)
    dorigo
    The Standard Model does not in itself have a problem with that Vladimir...

    Cheers,
    T.
    Vladimir Kalitvianski
    Neutrino in SM are massless but not superluminal, as far as I know. I think Cohen and Glashow used the standard model neutrinos to estimate the losses of a specific (Cherenkov-like) character. Indeed, they mention W-boson in v -> v+gamma channel. They assume that some "radiation" losses, as soon as V > c, are allowed - a purely imaginary supposition. Such losses have never been discovered, to tell the truth. The authors suppose that such losses are uniformly distributed along the trajectory - a thing impossible to imagine for the regular neutrinos. Maybe Cohen and Glashow are right but they propose loss channels basing on common sense and analogy with the long-range Coulomb interaction, not on observed phenomena. For such a short-range force as the weak force we cannot expect to have collective medium effects like "refraction" or "Cherenkov radiation" of any kind.

    For some reason they think that the "Cherenkov channel" v -> v + e^- + e^+ is much more probable than the same standard channel (which is also kinematically permitted).

    I wonder whether anybody observed a Cherenkov radiation due to relativistic neutrons (n) in media? I mean a short-range interacting and neutral particle as a superluminal projectile in a medium?
    dorigo
    Neutrons do not travel far in a medium Vladimir!
    Cheers,
    T.
    Vladimir Kalitvianski
    Yes, relativistic neutrons travel far, they are rather penetrating. Also, in order to observe the searched Cherenkov radiation like n -> n + gamma, n -> n + e^- + e^+, etc., it is not necessary to have long trajectories for neutrons.
    hello what looks strange to me is the claim it is well known a superluminal particle would loose energy even in vacuum. It is not known by me, who has got some references? As no superluminal particles have never been observed before it is not a fact, so why do they use it? Finally, maybe it is because OPERA measurements were stronger than we thought.

    Correct me if I am wrong, but don't you use SO(3,1) symmetry to determine which terms are allowed in the SM Lagrangian? That naively seems to give the SM a pretty strong reason to dislike neutrinos moving faster than c.

    Halliday
    No, SO(3,1) (or any SO(d,1)) does not provide "a pretty strong reason to dislike neutrinos moving faster than c."  In fact, the whole raison d'etre for "tachyons" is the allowance for space-like (faster than the speed of light) curves within SO(d,1).
    I am not a physicist, so please, forgive my ignorance. I heard that charged particles that go faster than light in water, for example, emit radiation because they go faster than c/n (n= refractive index). But what is the speed of light in the rock? Should not neutrinos going at c emit radiation, because in any case, the speed of light in the rock is different from c (refractive index different from 1)? My question is: why don't we see any Cherenkov radiation at all?

    Cheers,

    p

    The conclusion of the original post here seems greatly overstated. Neutrinos in the ICARUS paper are behaving like Lorentz invariant particles with respect to some universal speed limit "c", but nothing in the paper tells us if that "c" is the experimentally measured speed of light, or some other slightly different c' that is higher by one part per 10^-5 than the accepted measurement of "c".

    All it does is rule out the hypothesis, that was a long shot even among the "new physics" proponents, that high energy neutrinos behave like a certain hypothetical set of speed limit violating particles called tachyons. But, another way, the value of the ICARUS result is highly theory dependent, while the OPERA methodology is highly theory independent.

    "...while the OPERA methodology is highly theory independent."

    How can this be? For instance, the protocols for clock syncronization (as well as the GPS technology itself) are strongly rooted on Relativity. Estimating the start time for neutrino beams relies on the physics of pions/kaons decay...and so on.

    OPERA tested whether one theory (high energy neutrinos travel at (1-10^-19)*c) is supported by experiment or not. It doesn't discuss why the experimental result might differ and OPERA specifically refrained from speculating on that point. There could be many reasons that the OPERA results differ from the predicted value. Disproving one possible reason that the OPERA result is different doesn't logically rule out any other reason that the OPERA result could differ. The result at OPERA is independent of the theory one uses to explain it. It is a classic speed measurement - measure distance, measure time, divided, compare to the theoretical prediction, analyze potential sources of experimental error that are known. Assuming that nobody screwed up experimentally or in conceptualizing the theoretical prediction its result is very simpe: the theoretical prediction and the measured result differ by a six sigma margin.

    OPERA also interesting because it is not an "agenda driven" result. The neutrino speed check was a side project that wasn't expected to discover anything and wouldn't have gotten funding as a stand alone project. Call it a routine check up with the doctor for special relativity that came up with an unexpected yellow flag that requires further tests.

    But even a "classic speed measurement" is necessarily based on some underlying theoretical principles. In particular, protocols used for timing neutrinos and signal transfer via GPS satellites are strongly dependent on both Relativity, aside from detailed knowledge of the physics involved in proton-proton collisions and pion decays. This is why I don't subscribe to your view that "..the result at OPERA is independent of the theory one uses to explain it".

    Tommaso,

    Nothing is more succinct than ICARUS's 'Reductio ad absurdum'. Next .. find OPERA's error...

    Liked your TEDx talk....

    Best,

    Paul

    Very nice, thanks a lot for the heads-up. I check out every day the hep-ph arxiv, but honestly would be hardly able to pick an interesting article in the hep-ex (unless the title is "Higgs Discovery at LHC").

    Cheers,
    Stefano

    It is amazing how beeing somebody who works in HEP you can write so misleading considerations and by stressing them so much. It is very well known by everybody that the energy spectrum of neutrinos in Gran Sasso agrees with the predicted beam flux. This was shown in tens of OPERA presentations at conferences, even in the neutrino velocity seminar given at CERN on September 23rd and for instance published with much higher accuracy than ICARUS in this OPERA paper:
    http://arxiv.org/PS_cache/arxiv/pdf/1102/1102.1882v1.pdf
    So ICARUS does not really add anything new to this discussion. The problem is only related to the "universal validity" of the argument by Glashow, which, if assumed as correct, was already self supporting without this ICARUS result, or if there are any other theoretical arguments to get around Glashow's point. This is a purely theoretical discussion. Sorry for ICARUS which just reinvented the wheel in a smaller size ...

    dorigo
    Dear Anon,

    the fact that you let yourself go with anonymous comments against the blog owner would be enough to ignore you. In addition, you raise points that others, with a name attached, have also raised with less strong words.

    Nevertheless I do answer you here. What you fail to realize is that articles such as the one above, which is certainly correct in the physics it explains although admittedly strong in the conclusions (but those reflect my personal bias about the measurement), have a positive effect, namely they bring attention to experiments and fundamental physics from a pool of interest readers. I see nothing wrong with that. Being potentially misleading is a necessary, but mild, evil in some circumstances when one wants to popularize science.

    Cheers,
    T.
    I am just glad that projects still get funded or I would be bored to tears. Thanks to all for inspiring comments. We all want to know what's going on with this preliminary result. And Tomasso, don't worry about your English skills. They are superior to most.

    Dear Tomasso,
    thanks for this interesting news about the superluminal neutrino research.
    ive noticed that you got a lot of criticism these days and i wanted to point out that i think you are doing a very good job trying to keep us all "up to date" and explain the newest results and successes of physics to your readers.
    As many other students at my university I follow your blog every day.
    So keep going!

    Greetings from a physics student who is just getting started to contribute to cms analyses.

    dorigo
    Thanks Student, this is the kind of feedback that keeps me motivated!
    Cheers,
    T.
    How about to consider the paper of Ronald A.J. van Elburg "Time-of-flight between a Source and a Detector observed from a Satellite" at http://arxiv.org/PS_cache/arxiv/pdf/1110/1110.2685v3.pdf
    Everything is relative ?

    dorigo
    Hi Pedro, thanks for the link. Unfortunately I am swamped today due to my course, so I cannot look at the material in the short term.
    Cheers,
    T.
    @Pedro: Elburg seems to think that the clocks used were moving, which they weren't. GPS is only used to synchronize the clocks. There seem to be all sorts of other problems with his analysis; for example, to measure time with GPS you need to acquire 4 or more satellites. The time is then calculated from the data and, importantly, the relative motion of all of these satellites. I also don't understand his doubling of 32ns - that looks like double accounting to me.

    OPERA already had measured its energy spectrum. This ICARUS paper adds almost nothing.

    I wonder whether the water detectors of neutrinos, or the ice cube, have seen such coincidences : when they find the direction of a neutrino from the Cerenkov of the neutrino interaction products, there should be a ring of light around that direction, coming from putative light emitted from neutrino Cerenkov, since the geometry should be similar to the usual Cerenkov..

    Also does anybody have a reference to the energy spectrum of the 16000 Opera neutrinos?

    dorigo
    Hi Anna,

    even admitting all the admissible (superluminal neutrinos, detection late in the detector such that one can both see the interaction and the results of prior radiation, ectetera), I doubt one could detect such a tiny emission. Don't forget that this "cherenkov" radiation is a weak process.

    Cheers,
    T.
    Don't get intimidated Tommaso. Can't talk for others, but I, as a physics student, appreciate very much your efforts.

    what you are saying is using standard model, well known to be false, we can prove Opera didn't find anything??? There are thousands of paper claiming they found a fail. If it is superluminal, it is unexpected, and thus known physics doesn't apply in these regime, especially a physics known to be false. Standard model predict a 0 mass for neutrinos, this at least wrong. This is a theoretical argument against an experimental one, so the theory can say what is real to the experiment??? Very strange conception of science. I also think it's an error, but it will take time to find why.

    The OPERA results, if valid, only demonstrated that the _group_ speed of the neutrino pulses were faster that the fastest possible _signal_ (i.e., transfer of information), e.g., if sent by light. They do not even _attempt_ to demonstrate that any neutrino _signal_ travelled faster than the well-established relativistic signal speed limit, which can only be negligibly, if anything, faster than light (since, experimentally, photons have negligible, probably and presumed zero, rest mass). Although groups speed is _usually_ pretty well synonymous with signal speed (and used to be thought absolutely so!), it has been shown, theoretically and experimentally, that they can vary - either way!

    So the 60 ns is interesting, but not amazing! Ideally, we need to time the leading or trailing edges of a square wave - assuming no dispersion! Failing that, we should surely note the speed at the limit as the likelihood that a signal was present (or the associated information rate) approaches zero.

    As far as I can see, from the graphs, 60 ns would be lost in the noise, as far as a signal is concerned, e.g., comparing when source and destination intensities rose to (or fell from) significantly above background level. No significant evidence of violation of relativity, as far as I can see!

    My stance is, for chargeless neutrinos the analogy with charged particles cannot be applied - on the contrary, these neutrinos are moving with superluminal speed in brief moments of their life just because they're losing their charge during this (while changing into sterile Majorana neutrinos in this way). No charge means no radiation into outside.

    Hello to everybody,
    it is interesting to note how most people in the scientific community refuse to accept the possibility of superluminal particles, to my opinion because of lack of theoretical working ideas to account for them: even in the quantum gravity schemes, the discrepancy between light and neutrino speed is not that big, as measured by OPERA. In the Glashow-Cohen paper there's some confusion between Cherenkov effect (where the atoms of the traversed medium radiate) and bremsstrahlung (where the particle itself radiates), but the worst is that they assume without any experimental proof that weak interactions behave as e.m. interactions.
    Relativity was born to solve incompatibility between classical physics and electromagnetism, for which it retains its validity, because of huge amount of exp. verification; but for nuclear forces, we've taken it for granted.
    Perhaps it is not such an universal theory as we have believed so far.

    dorigo
    Thank you for visiting Sergio. What you say is true (and indeed I too was confused by G and C's paper when they talk about Cherenkov radiation -I reported it as such, unwilling to stand against a giant.

    I continue to believe that superluminal motion is a rather steep claim to interpret the Opera measurement. I like more the interpretation that Laveder and Tamburini are giving of the effect -a spreading of the wave form of neutrinos in matter. Anyway, we'll soon see more light on these issues.

    Cheers,
    T.
    Hi Sergio, you say:
    "but for nuclear forces, we've taken it for granted."

    That statement is not true. From the binding energy curve to the periodic table of elements to the plethora of elementary particles that have been organized in the Standard Model the special theory of relativity has been vindicated over and over and over.

    If you had labored during your studies to fit elementary particle interactions you would know that they only make sense if special relativity holds.

    "Relativity was born to solve incompatibility between classical physics and electromagnetism, for which it retains its validity, because of huge amount of exp. verification; but for nuclear forces, we've taken it for granted.
    Perhaps it is not such an universal theory as we have believed so far."

    Your statement is utterly false. SM is entirely based on relativistic QFT whose internal consistency relies heavily on Lorentz Invariance. This symmetry principle is on solid grounds and has been experimentally verified countless times. Without it, relativistic QM and the EW model would simply fail to describe particle physics.

    Ervin

    Tommaso, What would your reaction be if OPERA's statistical error in δt was 15 ns instead of 10ns, i.e, the 60 ns faster than light was 4 standard deviations instead of 6?

    dorigo
    The same... I would still believe there is a unknown systematics making the total error larger. A true 4-sigma result is something serious otherwise.

    Cheers,
    T.
    I will tell you my guess - there will be no one single big error that will explain the OPERA result, it will be the accumulation of a lot of small problems.

    To anna v and Ervin Goldfain

    Your faith in the validity of SM and QFT is nice but very naive.
    As you know, there are a lot of open questions, from the quantization of the electric charge to the quark family structure, the origin of CP violation, the smallness of neutrino mass...not to mention the mass of elementary particles (CERN has now a very low probability of finding the Higgs and if it doesn't, what happens?) So the failure of SM is behind the corner.
    The exp. verifications that you mention cannot prove that the IVB of weak interaction or the gluon (provided it exists) move exactly at the speed of light: are the experiments sensitive to differences of, say, 1.E-5? I don't think so. The internal consistency of the theory is not a sufficient reason for proving its universal validity, there could be another explanation.
    Someone used the term 'HEP paradox' to describe the present situation, where the need for new theoretical developments doesn't come from disagrrement of exp. results with SM, but from internal insufficiencies and inconsistencies of the theory, which substantially agrees with experiments. Now, if the OPERA measurement were confirmed, this scenario would change completely.

    "Your faith in the validity of SM and QFT is nice but very naive."

    It is well known that are many open questions in both QFT and SM and almost nobody will argue that SM is an "effective" framework that is likely to be amended by TeV physics at one point or another.

    But this has nothing to do with your previous point on the validity of Lorentz Invariance for electroweak interactions, which turns out to be wrong.

    Vladimir Kalitvianski
    Does that mean SM is OK if one does not speak of TeV phenomena? I am afraid not. It may need not only "amendement" with higher excitations but rebuild quite differently, without Higgs, for example, to say the least.
    Sergio B.
    You said:
    "Your faith in the validity of SM " ???

    The sure thing of the Standard Model is that it organizes the data, in families , so that one need not remember individual particles and resonances, in the same way that one can describe a crystal lattice and not have to list all the individual molecules sitting in it. The only faith I talked about is in the data, and that within their errors. All the elementary particles discovered, all the resonances, are within the reference system of special relativity and a resounding verification of its validity for nuclear and particle physics.

    The final theory will have to accommodate the Standard Model as far as the groups and symmetries go, because it is a beautiful shorthand for a lot of data. Any modification to special relativity will be just that, a modification, because special relativity has been validated in all particle reactions studied, bar this neutrino speed measurement, if it holds up.

    dorigo
    Hi Sergio,

    what does it mean "CERN has now a very low probability of finding the Higgs" ? This is not true, and if I interpret your "now" with "since it has been excluded in most of the parameter space already", it is specifically totally false. The exclusion of wrong Higgs mass hypotheses has nothing to do with the likelihood that the Higgs exists, with the god-chosen mass it has.

    Cheers,
    T.
    Hello Ervin, Hello Tommaso,
    I did not say that Lorentz invariance necessarily doesn't hold true for EW interactions, but only simply that we don't have the required exp. verification of that, so it means that relativity may be able to describe only a portion of the physical reality (i.e. electromagnetism), but not everything. And, I insist, this possibility is not excluded in our present knowledge! Otherwise why should there be exptl. proposals to check Lorentz and CPT invariance? Expts will tell us.
    About the Higgs: unfortunately, the Higgs and his mass are not god-chosen but man-conceived, so their robustness is quite more questionable! As you may know, there are some upper-limit (I think < 1.4 TeV, I should retrieve the papers, I am not a theorist myself) beyond which inconsistency between SM and SSB occurs. As a general statement, Higgs mass cannot be too high, and, according CERN people at Mumbai conference, there's little space left for finding it. Or...?

    dorigo
    Hi Sergio,

    indeed the Higgs mass in the SM can't be too high. But if the SM is consistent, we actually know that most of the probability density function, given indirect fits to electroweak observables, is lying in the 115-130 GeV mass range. The rest of the mass range is basically adding little. So having excluded the regions of mass where the Higgs is not consistent with the SM (140-600 GeV), what is left is the region which is most likely to contain it. It is with this in mind that I am saying that the probability to find the Higgs at the LHC has not decreased by a bit.

    Cheers,
    T.
    "I did not say that Lorentz invariance necessarily doesn't hold true for EW interactions, but only simply that we don't have the required exp. verification of that, so it means that relativity may be able to describe only a portion of the physical reality (i.e. electromagnetism), but not everything."

    If this statement were true, one would not be able to include Dirac currents in EW Lagrangian simply because antifermions would lack any physical content. This is absurd because no computations and experimental validation of electroweak theory would be then possible. Sorry, but this is simply nonsense to me.

    Ervin

    What do you mean? that the existence of antiparticles is a proof of the validity of relativity everywhere?

    The real limits of Lorentz symmetry and SM are indeed uncertain. Both may continue to hold far in the TeV sector as we understand them today or fail at some intermediate energy scale. There are some hints from astrophysics that Lorentz symmetry is going to stay unbroken in the deep ultraviolet region but these hints are not cast in stone. The same remains true for neutrino physics that is likely to reveal a lot of surprises in the upcoming years.

    But, again, these facts have nothing to do with your contention that Special Relativity is unsupported by evidence at the subatomic level. Special Relativity is deeply ingrained in the structure of SM whose predictions have been brilliantly confirmed countless times. This is precisely why it remains true at the subatomic level.

    Hello Tommaso,
    thanks for your clarifying answer about the Higgs. I don't want to be uselessly controversial, but now, since the interesting mass region has shrunk to < 140 GeV, the prob. of finding Higgs is also lower, isn't it? Otherwise it is difficult to explain the attitude of CERN Management, which, during recent press conferences, started to speak about the possibility of not finding the Higgs: "If it does not (exist), its absence will point the way to new physics." said Bertolucci.
    Which kind of NP is wrapped in mystery.
    To come back to neutrino speed, hopefully the OPERA measurement will be refuted: if not, the absence of a valid theoretical framework to account for it will put the SM in serious trouble. In addition, missing the Higgs will make our hope of finding an universal model of particle physics fade away definitely, leaving us with a piecewise approximation of the truth.
    What's your feeling?

    The answer to the OPERA anomaly might be simpler and more straightforward than what a lot of people think, albeit rather counter-intuitive. It will not "put the SM in serious trouble", as so many theorists are inclined to believe nowadays. It reminds me of the days of neutrino's discovery and the genius of Pauli's intuition.

    dorigo
    Hi Sergio,

    we are mixing up two very different things here. One is not finding the Higgs where it is not. The other is knowing we will soon have the sensitivity to see it or exclude it anywhere it hides, which opens the possibility to be soon facing the absence of a SM Higgs altogether. It "opens the possibility", but it does not decrease the chance of its existence, until we have investigated the low mass range at the cross sections predicted by the SM. As I said before, the SM implicitly indicates that the Higgs, if it exists, must be in the 115-135 GeV range -other masses being much less likely. Now excluding the less likely values is not yet an indication of the Higgs being not anywhere, especially since the CMS and ATLAS experiments are now seeing an excess exactly of the right size at the most probable mass.

    Cheers,
    T.
    "the CMS and ATLAS experiments are now seeing an excess exactly of the right size at the most probable mass."

    Really T.?. Do tell us more. I was aware that CMS has seen a 2 sigma excess c.120 GeV but had heard that Atlas were not seeing the same. And how is 2 sigma "exactly" of the right size?
    And is it reasonable to describe 120GeV as "the most probable mass" when the global fit of precision electroweak data gives the Higgs mass = 87 (+35/-26) GeV (cf RPP 2010 Higgs Bosons: Theory and Searches, p12)?
    Surely it is only "most probable" in the sense that LEP2 ruled out any Higgs below 114 GeV. i.e. wouldn't it be more objective to admit that LEP2 had ruled out much of the "most probable mass" range for the Higgs in the first place?

    dorigo
    Hi DB,

    starting from the bottom: I do not see what is more objective -putting in the latest values of Mw and Mt in the electroweak fits and then comparing with a 9-year-old limit, or starting from the experimental limits and adding in the indirect fits from the latest set of measurements... I prefer the latter, though, and I think I'm not the only one, as you can see from gFitter (they have this plot in their header page):



    In any case "most probable" does include, in my mind, all the information we so far have.

    Now, 2-sigma is of the right size because that is the ballpark of our sensitivity to a 120 GeV Higgs with the Summer 2011 data.

    Finally, let's say I am eyeballing the separate results of Atlas and CMS on Summer 2011 data, which both show mild excesses, compatible with expectations, in the 115-125 GeV range. See the plot below for CMS, for instance:

    As you see from the bottom part of the figure, the best fit xs is right where it should be.

    Cheers,
    T.
    Fair enough, and a robust defence as expected. Personally I find the chart provided by the CERN Electroweak group to be more "objective", as it shows more clearly how "improbable" the remaining unexcluded regions are for the Higgs, while not constantly recreating a "most probable mass" on the basis of prior exclusions:

    http://lepewwg.web.cern.ch/LEPEWWG/icons/s11_blueband.jpg

    I am intrigued that CMS and Atlas both independently appear to see the excess, given the differences in detectors and background estimation. If correct, that's quite interesting.

    (Note: the Electroweak chart, although dated July 2011 doesn't yet appear to include the latest LHC exclusions but I mention it for comparison purposes)

    dorigo
    Yes, I am familiar with your perspective and many indeed still prefer the original blue band plot to the gFitter one. As for the mild excesses, I think I already made my prediction: 119 GeV, give or take 3 GeV. I believe a 2-sigma excess when it is a believable signal, and I am willing to bet on this one. I should be given odds of 3:1, since the high-prob region is about 20 GeV wide... Any takers ? I would put 333$ on it.

    Cheers,
    T.
    Vladimir Kalitvianski
    I am too poor to bet but I think there will not be Higgs anywhere.
    Hi T,

    As always great to read your blog. Isn't Atlas less sensitive for a 117-119 GeV std model Higgs and would need 9-10/fb for a 3 sigma signal ... while CMS would need only 5/fb for 3 sigma? In which case evidence for such a Higgs would be found by CMS before Atlas -- maybe we are in this situation?

    --Ravi

    dorigo
    Hi Ravi,

    no, at present the sensitivity of ATLAS and CMS are quite similar in the low-mass region. I believe that once the gamma-gamma mass resolution is fixed, CMS will obtain a small lead, but I do not recall it as being as important as the number you quote would imply.

    Cheers,
    T.
    Hi T,
    I am looking at page 776 in this paper that has the graphs for Atlas (Fig 9a) and CMS (Fig 9b) giving the sensitives I mentioned: http://www.ias.ac.in/pramana/v76/p767/fulltext.pdf
    Ravi

    The same sensitivity graph on the Atlas site is at: https://twiki.cern.ch/twiki/pub/AtlasPublic/PublicHGPlotsAtlPhysPub20110...

    dorigo
    Hi,

    those are simulation studies, but then real data came... What I make out from the results is that the sensitivity is a tad better in CMS, but not so much to grant a different conclusion with 2011 data if Mh=120 GeV, I don't think.

    Cheers,
    T.
    ok cool thanks.

    Here is another theory about "superluminal" neutrinos:

    http://vixra.org/pdf/1110.0052v2.pdf

    Briefly: neutrino's speed does not exceed the speed of light, so the Cohen-Glashow-ICARUS objection does not apply. Neutrinos arrive in OPERA by 60 ns too early, because their travel distance is 18 meters shorted than everybody thinks. When mu-neutrino is created in a meson decay it emerges not from the decay vertex but 18 meters away from it in the forward direction. This weird property can be understood if one takes into account mu-tau neutrino oscillations. The neutrinos can oscillate not only between different flavors, but also between different positions in space (even if these positions are separated by several meters).

    This theory does violate the special-relativistic ban on superluminal propagation of signals. However, it is not obvious that causality is violated in moving frames. We are dealing here with an interacting system, so transformation to the moving frame should be performed with an interaction-dependent boost operator. This means that boost transformations are different from usual linear and universal Lorentz formulas, and usual arguments proving "superluminality=noncausality" do not work.

    Cheers.
    Eugene.

    Vladimir Kalitvianski
    Eugene, how is your "18 m away picture"  compatible with particle treks like the rightest one?

    dorigo
    Eugene, I find your claim puzzling to say the least. Why does the decay of a pion to a muon and nothing for 18 meters not violate four-momentum conservation ? I can see the pion and the muon track, and the latter makes a kink, so something must be carrying away that momentum at the pion decay vertex.

    Cheers,
    T.
    meopemuk
    Tommaso, Vladimir,

    Tommaso wrote: " Why does the decay of a pion to a muon and nothing for 18 meters not violate four-momentum conservation ? I can see the pion and the muon track, and the latter makes a kink, so something must be carrying away that momentum at the pion decay vertex."

    Yes, there is a kink, which marks the disappearance of the pion and the creation of the muon and the muon neutrino. However, the energy-momentum conservation law does not require the latter two particles' trajectories to start exactly at the point where the pion has disappeared. In principle, these two trajectories can start instantaneously at any point in space, and the energy-momentum conservation law will still hold.

    There is, however, a different conservation law, which imposes further restrictions on trajectories. This law says that the center of mass (or, better to say, center of energy) of any isolated physical system always moves with a constant velocity along a straight line. This requirement is independent on any internal changes (e.g., decays), which may occur in the system. Before the pion decay, the center of energy trajectory coincides with the pion. After the decay, we should expect that the center of energy of the muon+neutrino system will continue uninterrupted. If the muon and neutrino were "ordinary" particles, then this law would demand that their trajectories start exactly at the point of pion's disappearance. Muon is an "ordinary" particle, so it behaves, as expected. However, neutrino is not that simple. My major point is that neutrino can oscillate between mu-neutrino and tau-neutrino states (I ignore the other electron-neutrino state, for simplicity). It appears, that these oscillations can involve not only changes of flavor, but also changes of particle locations: The mu-neutrino and tau-neutrino components may have different (but parallel) trajectories, and the system may switch back and forth between these trajectories in the course of flavor-changing oscillations. Then the neutrino center-of-energy (imaginary) trajectory stays between the (real) mu-neutrino and tau-neutrino trajectories. The total center-of-energy continuity law requires that the (imaginary) center-of-energy neutrino trajectory must be attached to the pion-muon kink. But the (real) mu- and tau-neutrino trajectories are allowed to start far from this point. This is shown in Fig. 2 in the paper.

    My explanation of the OPERA effect is that the distance between oscillating mu- and tau-neutrinos is macroscopic (=36 meters). Then, after the pion decay, the mu-neutrino emerges 18 meters ahead of the decay point, so it arrives in the OPERA detector 60 ns earlier than expected. The tau-neutrino is 18 meters behind the center-of-energy, so its arrival is 60 ns late. (Only one tau-neutrino event has been seen at the OPERA detector so far. So, this prediction is not easy to verify.)

    The macroscopic "size" of the neutrino system seems weird, but, as far as I can tell, it doesn't contradict any experimental data or conservation laws. One can say that this "nonlocal" behavior of neutrinos contradicts postulates of local quantum field theory. And I can reply that the orthodox Standard Model assumes massless neutrinos and misses the whole oscillation phenomenon. Perhaps one can enhance the Standard Model, so that it takes into account neutrino masses and oscillations of both neutrino flavors and spatial locations.

    Vladimir wrote: "You want to say that the wave function of neutrino is a wave-train of 36 m long and overlapping the vertex?"

    No, this is not what I want to say. In my approximation the description has been simplified to the classical trajectories level. The only feature left from quantum mechanics is the possibility of the mu-tau neutrino oscillations. So, the total wave function of the neutrino system in the position space is a superposition of two delta functions. One delta function describes the mu-neutrino component, and the other describes the tau-neutrino component. Both of them move with the speed of light on parallel tracks. The distance between them is kept at 36 meters. The coefficients in front of the two delta functions oscillate with time in a sinusoidal fashion. This is eq. (21) in the paper. http://vixra.org/pdf/1110.0052v2.pdf

    Eugene Stefanovich.
    Vladimir Kalitvianski
    Eugene, the weak force is rather short-range and cannot act at or create a 18 m distant neutrino. Also, the particles interact with each other, not with the Center of Inertia (which is an imaginary point). The only possibility is to create a long wave train overlapping the decay point (decay of the initially localized wave packet into one localized and another delocalized. The kink may indicate that the neutrino wave-train has a quite certain classical energy-momentum, but to be quantum-mechanically "long", a much longer transition in time is necessary. In OPERA the pion and Kaon decays occur indeed in a 1 km long vacuum tunnel, but still a very monochromatic wave-train is improbable, in my opinion.
    meopemuk
    the weak force is rather short-range and cannot act at or create a 18 m distant neutrino. Also, the particles interact with each other, not with the Center of Inertia (which is an imaginary point).

    Vladimir, as I said, nobody has ever seen neutrino tracks and their attachment to decay vertices. So, the "locality" of the weak force is no more than a theoretical assumption. I hope you would agree that superluminal neutrinos do not fit into existing paradigm, and they require that one or two previous theoretical assumptions should be replaced. The big question is which assumptions must go? The least reliable assumptions are those, which do not follow from direct experimental measurements. So, in my opinion, the weak force "locality" is a legitimate suspect. Eugene.
    Vladimir Kalitvianski
    Yes, but we have to stay in the realm of QM anyway. So the only possibility is the quantum mechanical uncertainty for which the long wave trains are the only plausible explanation.
    meopemuk
    Vladimir, if the neutrino wave function had the position uncertainty of 18 meters (as you seem to suggest), then the arrival time uncertainty would be no less than 60 nanosecond. However, the full experimental uncertainty is only about 10 ns. This is consistent with the idea that neutrinos are well localized, i.e., there are no "long wave trains".

    Eugene.
    Vladimir Kalitvianski
    I just suggest that a good monochromaticity can cause time arrival uncertainty but I do not believe it is the case for those neutrinos.

    You, on the other hand, propose a distant particle creation/interaction. Note, those pions are relativistic and the corresponding distance is Lorentz contracted, so in a slow pion decay the neutrino must be born even farther. May be such a distant creation/interaction is responsible for not observing the neutrino track?
    Do The Observations of Superluminal Neutrinos Lead to The Model Where Light Speed Increases Over Time?

    Here are my thoughts and explanation of OPERA experiment.

    a. The OPERA experiment shows that speed of neutrinos is greater than 299,792,458 m/s (light speed in the SI system).
    b. The research A.G. Cohen and S. L.Glashow showed that neutrinos can not travel faster than light, because "most of the neutrinos would have suffered several pair emissions en route".
    c. The ICARUS paper shows that speed of neutrinos is equal to speed of light.

    This obvious paradox between experiment and theory can easily be resolved if the speed of light is slowly increasing and is now (or at least was during the experiment) higher than in 1970-1980 when it was measured and included into SI system. In this case the speed of neutrinos in the OPERA experiment can be higher than 299,792,458 m/s, but at the same time be less or equal to current c. The full paper can be downloaded here:
    http://www.smartalerter.com/Is_Speed_Of_Light_Increasing.pdf

    The Robertson test theory of the Lorentz transformation should be taken into account when analyzing Opera. I am please to inform that my paper on this subject is now available at arxiv physics gen-ph 1111.2271.
    Thanks.
    Jose G. Vargas

    On the neutrinos track, there might be some particles (atoms? any parts of atoms?) which might absorb a neutrino at one side, while on the other side, in the same time emitting a similar neutrino. Thus we get an illusion of a faster-than-light movement of a neutrino which seemingly "jumped over" another particle with no time...
    If so, could the neutrinos run even faster in heavier materials (?like Earth's core)?
    I wrote about this in Physics Forum, too, trying to make it a little bit funny (link added).

    Tommaso, What would your reaction be if OPERA's statistical error in δt was 15 ns instead of 10ns, i.e, the 60 ns faster than light was 4 standard deviations instead of 6?

    dorigo
    No difference - the delta t they measure is of systematic origin, and so the fact it is 4 sigma away from zero or 6 sigma away from zero, when sigma is measured with only a part of the effective systematics in play, does not change the picture by an inch...

    Cheers,
    T.
    "disproving" experimental observation of superluminal neutrinos via appeals to "known" physics is not very
    inspiring of confidence - - by analogy, I'm confident that after Columbus claimed to have reached America there were a number of flat earth theorists who "proved" he could not have done so

    "disproving" experimental observation of superluminal neutrinos via appeals to "known" physics is not very
    inspiring of confidence - - by analogy, I'm confident that after Magellan claimed to have circumnavigated the Earth there were a number of flat earth theorists who "proved" he could not have done so

    Immediately after its publication the Glashow & Cohen (G-C) paper has been acclaimed by many as something it definitely is not - - a knockout for the possibility of superluminal neutrinos. Even if their argument proves logically consistent its significance is minor. We were already well aware from standard sophomore physics theory, and the weight of cumulative experimental evidence that any such production and observation of superluminal particles would be extremely unlikely and needed to be exhaustively reproduced.

    If I am not mistaken, if you were to calculate the cross section for obtaining a superluminal velocity muon neutrino from a finite energy electron - positron annihilation in the presence of a subluminal velocity muon neutrino using the standard model it would be zero - - otherwise energy conservation would be violated since obviously if you attribute any mass to the neutrino its energy becomes infinite as it somehow obtains light velocity during the process. Since quantum mechanics is time reverse invariant this means the reversed sequence reaction is also impossible in currently understood quantum mechanics.

    G-C principal conclusions depend upon decay rates regarding the same time reversed reaction I discuss above which they purport to be in accordance with the standard model, so my simple analysis means their proposed decay mechanism is not a possible candidate for decay of a superluminal netrino according to our current understanding of quantum mechanics. I would argue they are sweeping a lot of uncertainty about quantum mechanical superluminal particles under the rug. And how can that not be obvious on simpler grounds? After all, before G-C all the talk was about how problematical and murky physics would become should v>c neutrinos pan out, so how is it not contradictory to now essentially argue, as many are, that firstly we don't believe v > c neutrinos have actually been observed but if they did exist, we understand them, and just a few days later, no less. If you don't sense that position is suspect, something is wrong with your perspective!

    A very recommendable articles you have. Its good for everyone who reads especially to the kids because its about science. Thanks for posting it.

    ICARUS objection is not required if it is considered a possibility indicated in the following article:
    http://vixra.org/abs/1201.0086 [1]

    The article offers a simple explanation of this phenomenon. In section 2 indicates the hypothesis that there are two areas of events, an electroweak and other gravitational, both independent and governed by two different time coordinates. It comes to the expression of velocity of a particle as the sum of the two speeds in each area. In terms of kinetic energy is:
    (1 / 2) m v2 = (1 / 2) m v22 + (1 / 2) m v12
    The subscript 2 refers to the electroweak field and the subscript 1 to the gravitational field. These speeds can be decomposed into a spherical reference system for radial and tangential components:
    (1 / 2) m (vr2 + vζ2) = (1 / 2) m (V2r2 + v2) + (1 / 2) m (V1r2 + v2)
    So far always been assumed that the speed v (tangential due to the gravitational field) was 0, the gravitational field concept so implicitly indicates the strength of the field is directed radially to the center of gravity field. However, the hypothesis proposes that site says there is a gravitational field itself but a different area of ​​events governed by a wave function differently and what we see as a gravitational field is simply the flow of the probability current at the area from zones of lower probability to areas of higher probability. Nothing prevents this current therefore for certain particle has a component normal to the rest of particles toward the center of "gravity field". In this case, the observed speed of the neutrinos have a tangential component for the electroweak field and therefore subject to the upper limit c (speed of light) and one for the gravitational field independent of the previous one and may be subject to a limit (speed of elementary oscillators according to [1]). The observed speed, sum of the two, may well be higher than that of light without breaking any fundamental pillar of physics.
    A separate issue is the reason why the experiment neutrinos have the tangential component in the gravitational field. It could be another peculiar feature of the neutrinos.
    The fact that neutrinos arriving from supernova explosions have not faster than the speed of light is explained by those who were detected were emitted in a radial direction. The rest were issued initially but with greater speed of light, the tangential component in the gravitational field was less than the escape velocity (as in the OPERA experiment) and were stopped in their path, ie, these neutrinos were only faster than light for a negligible fraction of its length.

    i don't understand 99% of this conversation but find it fascinating. so light's pretty fast but neutrinos are faster. sweet. where can we catch the next race? while not related to the question of whether or not neutrinos are faster than light, if they *were* to race, if neutrinos can move through things, then they'd always travel a shorter distance, no?

    Radhakrishna
    Excellent article on super luminal neutrinos. Theory of relativity again and again tested and came out with flying colours. Once again I think in ICARUS experiment. But still there will be another experiment to be held in the month of May. Do you have any idea about that? Are these neutrino move higher velocity in the detector medium - such as liquid argon - to produce Cerenkov radiation? Some where I read, the group failed to observe cerenkov radiation and that only a proof that neutrino are not travelling with superluminal speed. 
    dorigo
    Hi Radha,

    no, I do not recall having heard of what you mention. But I am not a neutrino physicist, so I am relatively ignorant of the new developments.

    Best,
    T.