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Merged Puzzling results from CERN

Pixel42

Schrödinger's cat
Pixel42
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http://www.bbc.co.uk/news/science-environment-15017484

Speed-of-light experiments yield baffling result at LHC

Puzzling results from Cern, home of the LHC, have confounded physicists - because it appears subatomic particles have exceeded the speed of light.

Neutrinos sent through the ground from Cern toward the Gran Sasso laboratory 732km away seemed to show up a few billionths of a second early.

The results will soon be online to draw closer scrutiny to a result that, if true, would upend a century of physics.

The lab's research director called it "an apparently unbelievable result".
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Well that's pretty cool. The article does a really good job of acknowledging that the most likely explanation is that an error was made somewhere, and the scientists involved are publishing their work so someone else can either reproduce their results or find the error. It's nice to see some science reporting that doesn't immediately scream "Scientists were wrong!" and instead focuses on the self-correcting nature of science. While also noting that this would be a pretty shocking result if true, of course.

But the group understands that what are known as "systematic errors" could easily make an erroneous result look like a breaking of the ultimate speed limit, and that has motivated them to publish their measurements.

"My dream would be that another, independent experiment finds the same thing - then I would be relieved," Dr Ereditato said.

But for now, he explained, "we are not claiming things, we want just to be helped by the community in understanding our crazy result - because it is crazy".
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There's a lot of buzz about this; I'm looking forward to the paper.

One of the confusing points is that there are already very good limits on the speeds of low-energy neutrinos; if the OPERA beam (what, 100 GeV?) travels at a similar speed to the Supernova 1987a beam (10 MeV), then the timing-offset can't be larger than a few picoseconds (which I won't find it hard to imagine might be due to an unforeseen systematic error.) The MINOS beam (3 GeV) was timed only at the 100-nanosecond level, which certainly allows room for a Lorentz-violating speed that OPERA might detect confidently.

If it's true, it's the biggest physics discovery since GR. But give it time (Years! Seriously!) to get sorted out confidently. A "six sigma" result means that it's unlikely to be a statistical fluctuation, but systematic errors are under no such constraint.
 
How exactly to you measure a distance of 732km through the earth to an accuracy of a few meters.... other than by the travel time of neutrinos?
 
sol invictus said:
How exactly to you measure a distance of 732km through the earth to an accuracy of a few meters.... other than by the travel time of neutrinos?
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The fact it goes through the earth makes me wonder if it's some sort of time dilation effect related to GR. I think Zig is probably right about the GPS.
 
Ziggurat said:
GPS?
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That's all I could think of too - but inside a mountain?

And they say a few billionths of a second, so for five sigma they need .5m accuracy or better. That's pushing the limits of GPS (might be beyond them, I'm not sure) even apart from the fact that they're under a lot of rock. Considering that earth tides can be a few cm, not to mention earthquakes, thermal expansion, etc., it sounds very hard to me. And the detector itself is probably meters across, and there's also uncertainty in the size of the source.

Color me skeptical.
 
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Backwards travel in time has been proposed in some quantum models and I believe the concept of a particle having a complex or an imaginary mass (in the mathematical sense) has also been proposed. Either model might be supported by this result, with a big, fat caveat: maybe. It's too early to say.

Warp 1.0000000000000001, Mr. Sulu!
 
I would think issues of thermal expansion etc would show up differently in repeated tests, and apparently they've done some 15,000 measurements of this phenomenon. So we've got something new (very exciting!) or a fundamental flaw somewhere in the test protocol.

eta: the latter is probably termed a bit harshly, since the study wasn't initially designed to test speed. On the other hand, how many great discoveries have been made while looking for something else?
 
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This seems akin to the same thing that was found with quantum tunneling. I'll have to look for the link.
 
sol invictus said:
How exactly to you measure a distance of 732km through the earth to an accuracy of a few meters.... other than by the travel time of neutrinos?
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It's done with extremely careful traditional surveying. In some cases, that means literally standing at the mine entrance and aiming a theodolite (or the modern, laser-y equivalent) down the tunnel as far as it will go. You find the position of the experiment relative to the lab, the lab relative to the entrance, the entrance relative to the Earth, etc.
 
ben m said:
It's done with extremely careful traditional surveying. In some cases, that means literally standing at the mine entrance and aiming a theodolite (or the modern, laser-y equivalent) down the tunnel as far as it will go. You find the position of the experiment relative to the lab, the lab relative to the entrance, the entrance relative to the Earth, etc.
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To 50cm accuracy, over 700km of Alps?
 
Checkmite said:
Like what - a fine??
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More like time travel, the unravelling of causality, quantum feedback loops, and the consequent instantaneous annihilation of the universe. :eye-poppi

Or, maybe they're just off by a meter or so on the distance.
 
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ben m said:
if the OPERA beam (what, 100 GeV?) travels at a similar speed to the Supernova 1987a beam (10 MeV), then the timing-offset can't be larger than a few picoseconds
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The article says 'few billionths of a second', which I presume means few nanoseconds (unless they're using the deprecated British 'billions' of course). And if it really was picoseconds, that'd need a distance accuracy of around 1mm, wouldn't it?
 
sol invictus said:
To 50cm accuracy, over 700km of Alps?
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Measuring time is almost trivial these days. In my humble ham shack I can easily measure to better than 10e-9 with my GPS disciplined Rubidium oscillator.
Measuring distances is much harder. I would have a hard time working out how far it is from my front door to the mailbox, to the nearest inch or so.

I presume they are referring to chordal rather than great circle distances?

V.
 
There must also be some uncertainty in when and where the neutrinos originate - presumably they're from the decay of some relativistic particle (muons perhaps) at LHC, which can't be pinpointed exactly.

But I suspect it's systematics in the distance measurement.
 
Verde said:
Measuring time is almost trivial these days. In my humble ham shack I can easily measure to better than 10e-9 with my GPS disciplined Rubidium oscillator.
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It's easy if you can mark precisely when both events occurred, yes. But you can't know exactly when (or where) the neutrino was produced.

I presume they are referring to chordal rather than great circle distances?
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Yes - neutrinos should travel in a nearly perfectly straight line.
 
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