Posted by “The saying ‘It’s not over ’til the fat lady sings’ is erroneous, because women who are fat are never listened to.” -Margaret Cho
Last year, the OPERA collaboration made worldwide headlines when they announced the results of a remarkable experiment.
Image credit: OPERA / CERN.
From over 730 kilometers away, in another country, neutrinos were created by one of the most powerful particle accelerators in the world. Protons at over 99.999% the speed of light were smashed into matter, creating a highly collimated beam of neutrinos, which was launched through the Earth at, presumably, speeds indistinguishable from the speed of light.
Underground, beneath the Italian mountain of Gran Sasso, laid the huge OPERA detector, capable of detecting these high-energy neutrinos.
Image credit: OPERA / INFN / CERN.
But what it was also able to do, so they claimed, was to measure the timing of these neutrinos so accurately as to be able to test Einstein’s theory of special relativity!
As you well-know, nothing is supposed to be able to move faster than the speed of light in a vacuum. Nothing. Which is why it was absolutely shocking when they released their first results.
Image credit: OPERA Collaboration; T. Adam et al.
60 nanoseconds early, they said, their neutrinos arrived. This wasn’t an error, either, they said, as their uncertainties were only around 10 nanoseconds. And if that was true, over the distances they were talking about, that means these neutrinos would be moving something like 7,500 m/s faster than light, which is huge!
Image credit: United Visual Artists / Tom Oldham.
As we’ve said many times, claims like these, that are extraordinary, require evidence that is also extraordinary. So I was very excited to report that, in short order, we were going to either confirm or refute OPERA’s claims!
Because two experiments — T2K in Japan, above, and MINOS in the USA, below — were all set up to measure the same exact thing to even better precision.
But another experiment, one that had come out earlier and challenged OPERA’s results, had other plans. You see, OPERA had recently announced that they had uncovered two potential problems with their experiment — the loose cable and a possible timing miscalibration — which threw their results into doubt.
What it really meant, if you look up at the image of their claimed results, is that their claimed errors, which were tiny, should have actually been much larger due to those issues.
Image credit: Matt Strassler.
This is a problem that plagues a great many experimental and observational sciences: fully accounting for your systematic errors. After all, it is difficult to account for uncertainties and / or errors due to something you were simply expecting would work properly! You account for systematics based on all the errors you can reasonably anticipate, but once those are over and done with, you stop counting. But when an unexpected error does happen, and you weren’t expecting it, it can lead you to have an undue amount of false confidence in what are actually insignificant results.
And it was the ICARUS team — another neutrino detector underneath Gran Sasso — that set out to show that OPERA had done exactly that. Intending to refute the OPERA team’s results, ICARUS has gone out to set the record straight about Einstein’s relativity.
Image credit: the ICARUS-T600 detector installed in LNGS - HallB, retrieved from neutel11.wordpress.com.
Evoking shades of Ethel Merman, ICARUS basically said to OPERA, “Anything you can do, I can do better.” And, over practically the same baseline, using the same energy neutrinos created from the same proton beam, ICARUS set out to re-test the OPERA experiment.
Image credit: the latest ICARUS paper; M. Antonello et al.
Except, you know, without the errors. And what they found should put the whole issue to rest. The OPERA neutrinos, you’ll remember, arrived around 60 nanoseconds early, with an originally claimed uncertainty of 10 ns. The ICARUS results, making the same measurements with different equipment?
Image credit: the latest ICARUS paper; M. Antonello et al.
As others have noted, this time, there can be no doubt that ICARUS has directly refuted OPERA.
It means that, combined with ICARUS’ earlier results, we can constrain that not only are neutrinos of this energy not moving at the speed OPERA concluded, but they must be moving much closer to the speed of light than OPERA’s original results would have indicated.
Image credit: Matt Strassler, edited by me.
And that’s pretty much the end of the line for these faster-than-light neutrino claims. It will be interesting to see what OPERA’s next results are, as well as what MINOS and T2K have to say, but with the ICARUS results in and the OPERA uncertainties known to be much larger than originally claimed, there’s suddenly no reason to believe that neutrinos move faster-than-light at all.
And if you were skeptical the whole time, good for you. The extraordinary evidence you were waiting for just came in, and it’s the sound of the fat lady singing!
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