OPERA

Tying Off Loose Ends

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Reminder: New York, Saturday June 16th at 2pm, I’ll be giving a public lecture (click here for details): THE EINSTEIN OBSESSION: SCIENCE, MYTH AND PUBLIC PERCEPTION. I’ve been doing a little work on my extra dimensions articles, adding one that describes how we know experimentally that the ordinary particles we’re made of (and most of … Read more

End of the OPERA Story

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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 ICARUS already made … Read more

Guess What?! Neutrinos Travel Just Below the Speed of Light

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Five out of five experiments agree: neutrinos do not travel faster than the speed limit. Or more precisely: to within the uncertainties of current measurements, neutrino speed, for neutrinos with energies far larger than their masses, is experimentally indistinguishable from the speed of light in vacuum.  This is just as expected in standard Einsteinian special … Read more

Question to Laypersons: Your Views on the Neutrino Saga

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So, many of you have probably been following, to a greater or lesser degree, the story of the OPERA experiment.  This is the one that  found that neutrinos sent from the CERN lab near Geneva, Switzerland to the Gran Sasso lab in Italy (where OPERA is located)  arrived earlier than they expected.  Of course there were, from … Read more

Denouement: How OPERA’s Mystery Was Solved

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On Friday I learned, and reported to you, that the OPERA experiment’s investigations into its early-arriving-neutrino anomaly (widely reported as `faster-than-light neutrinos’), performed with help from the nearby LVD experiment, have basically confirmed that a combination of (1) an optical fiber within the main timing system that was incorrectly screwed in, and (2) a timing … Read more

OPERA’s Timing Issue Confirmed? Yes!

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[QUICK UPDATE April 2: I’ve now finished an article giving more details of how OPERA, with LVD’s help, solved the mystery.]

[UPDATE March 31 2 a.m.: following study of the slides from a mini-workshop recording the results of investigations by OPERA and LVD, I now have the information to remove all the guesswork from my original post; you’ll see outdated information crossed out and newer and more precise information written in orange.  I’ve also added figures from the talks.]

March 30 5:30 p.m. Two main scientists at OPERA, one leading the OPERA team as a whole and the other leading the neutrino speed measurement, resigned their leadership positions today.  The suggestion from the press is that this is due to personal and scientific conflicts within the OPERA experiment, rather than due directly to the errors made in the neutrino speed experiment; but of course the way the measurement was publicized by OPERA caused serious internal conflicts at the time and are surely part of the issue.    [Oh, and meanwhile, back over at the CERN lab, some good news: collisions at the Large Hadron Collider with 8 TeV of energy per collision were achieved this afternoon.]

The mystery surrounding OPERA, the Gran Sasso experiment which (apparently through a technical problem) measured that neutrinos sent from the CERN lab to the Gran Sasso lab in Italy arrived earlier than expected by 60 nanoseconds, seems to be on the verge of being is resolved.  Statements made by an OPERA scientist in the Italian language press, pointed out to me by commenters (Titus and A.K.), seem to imply that OPERA has more or less confirmed that the problematic fiber optic cable (along with the clock problem, to a lesser extent) was responsible for a 60 nanosecond (billionth-of-a-second) shift in the timing, creating the false result.  We do not yet have official information from OPERA about this, but talks given at a mini-workshop a couple of days ago make clear that this is the case.

The way this was done if I/we understand the Italian correctly is something like is the following  with all details still very uncertain.

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This Time, ICARUS Really DOES Refute OPERA

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Well, ICARUS flies even higher, and so far shows no sign of losing its wings.

Remember OPERA, the experiment that claimed neutrinos sent from the CERN lab in Switzerland to the Gran Sasso lab in Italy arrive earlier than they were expected to? And that a couple of weeks ago had to admit they’d found a couple of problems that were large enough to scrap their result for the moment, and that require additional investigation?

And remember ICARUS, OPERA’s neighbor in the same Gran Sasso lab in Italy, which measured the energies of neutrinos from the CERN neutrino beam, and showed they were not altered in flight? And thus proved that if the neutrinos really were traveling faster than light, they did not exhibit anything like the variant of Cerenkov radiation that was suggested by and calculated by Cohen and Glashow?

Now, ICARUS’s result from the fall didn’t directly refute the OPERA experiment (despite some claims, even by them) but it certainly added to the aura of extreme implausibility that surrounded the whole story.

Well, this time ICARUS refutes OPERA. Essentially, they did the same measurement as OPERA-2, as I called the short-pulse variant of OPERA’s original experiment.  They took data at the same time as OPERA-2, in the same neutrino beam, in the same laboratory.  It took them a while to do all the distance and timing calibrations that OPERA had done many months ago, but they’re finished now. And whereas OPERA-2 gets the same result as OPERA-1— an early arrival of 60 nanoseconds (billionths of a second) — ICARUS finds a result consistent with an on-time arrival. Same measurement, different answer. At least one experiment made a mistake; and one result is vastly more plausible than the other, so I think the consensus is pretty clear in the matter.

ICARUS's 7 neutrinos (dark blue histogram), measured in October and November, arrived as expected to within 10 nanoseconds (billionths of a second). OPERA's result (but not its neutrinos) is shown at right, at approximately 58 nanoseconds early arrival.

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Why the Curtain Has Not Fallen on OPERA

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For those of you who read the news reports about OPERA, and its potentially (not) superluminal neutrinos, on Thursday or on Friday morning, and stopped following after that, I have news for you: almost everything that appeared in the press up to that point was wrong in some important details.  Thanks to my readers and their comments and detective work, we’ve collectively managed to figure out much more clearly what’s actually going on.  I put up a relevant post Thursday morning and another Thursday afternoon, but I especially recommend Friday morning’s post (and comments) and Friday afternoon’s post (and comments).  I really emphasize the value of the comments; I have some very well-informed and insightful readers who contributed a great deal.  You can read this summary post first, and then go back to the older posts and read through the earlier viewpoints and the detailed commentary.  [The science press has caught up, though; here’s an accurate article from 2/27 in Nature.]

Most press reports on Wednesday, Thursday and Friday boiled down to this statement: “The OPERA folks found a loose wire, and when they fixed it their timing shifted by 60 nanoseconds [billionths of a second], bringing neutrino speeds right back to where they were supposed to be.”  That’s certainly what the original Science Insider article implied, from which many articles took their cue.  This is illustrated in the Figure below (labeled (b) to be consistent with a figure from an earlier post. )  The original OPERA result — that neutrinos arrived 60 nanoseconds before they were expected to — is shown as (a).

But this statement is completely wrong.

(a) OPERA originally claimed neutrinos arrived early by 60 nanoseconds (ns), with an uncertainty of about 10 nanoseconds, shown by the black vertical bar. (b) Incorrect press reports widely suggested that OPERA had found a mistake (a "loose wire") that caused a 60 nanosecond shift and brought the measurement back into agreement with expectations. (d/e) But in fact the two problems identified so far by OPERA, a sensitivity to an optical fiber's exact orientation and a miscalibrated timing oscillator, are both large compared to the original measurement, are both imprecisely known, and point in opposite directions. This makes the situation entirely unclear for the moment.

In fact the OPERA press release made clear that there were two problems (a problematic fiber-optic cable and a miscalibrated oscillator), causing shifts in opposite directions, and mentioned that a re-run of the experiment would be necessary.  Still, most press articles seemed to give this lip service, and assume the correct reading of the situation was that the fiber was the main source of the problem, and that a re-run of the experiment was just pro forma.  They mostly stuck with the simplistic idea that the OPERA people found a mistake and now everything agrees nicely with Einstein.  A few, such as the New York Times, did a somewhat better job.  But they still missed key points.

So what is the real story?  

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