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CERN team claims measurement of neutrino speed >c

by turbo
Tags: anisotropy, cern, ftl, gps, new math books
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Chronos
#55
Sep23-11, 12:19 AM
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Agreed, the OPERA team is seeking confirmation [I agree with Pallen it appears unlikely]. Neutrino detection is tricky business and correlating capture with emission is no easy task. I can't help but wonder how many of the detected neutrinos were actually emitted by CERN and how that might skew the measurement. There was a paper about 10 years ago about neutrinos as tachyons by Chodos, IIRC.
seerongo
#56
Sep23-11, 01:04 AM
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Quote Quote by Chronos View Post
Agreed, the OPERA team is seeking confirmation [I agree with Pallen it appears unlikely]. Neutrino detection is tricky business and correlating capture with emission is no easy task. I can't help but wonder how many of the detected neutrinos were actually emitted by CERN and how that might skew the measurement. There was a paper about 10 years ago about neutrinos as tachyons by Chodos, IIRC.
My background is engineering, not physics, but frankly, the method used to correlate the proton extractions with the v detections doesn't seem that bad to me so far, although at first blush, 16,111 detected events doesn't seem too great statistically. I'd like to see more expert comments on that however. Regarding potential contamination, would most contamination come from B-decay, which would be anti's? I think they accounted for anti's, counting about 2% unless I read it wrong. Could someone comment on that? I'm not sure about the potential sources of spurious neutrinos in significant numbers.

I'm more struck by the timing aspects. There seem to be so many places in this system where inaccuracies can gang up on you. This is a pretty complex system with a lot of timing points, all with tolerances. I'd be the last person to second guess this work, but I think that's where I'd look.
Gilles
#57
Sep23-11, 01:06 AM
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I think the question of clock synchronization may be tricky. In GR, there is no absolute definition of simultaneity. Due to differences in gravitational potential, as mentioned, clocks evolves differently at different points. So you must periodically resynchronize them, but how ? there is no unique choice, and the measured time of flight probably depends of how you define the timescale at each point.
Parlyne
#58
Sep23-11, 03:09 AM
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Quote Quote by edgepflow View Post
There is one remote possibility I have not seen discussed in this thread.

Is it possible in theory that a neutrino has zero mass and the test is showing tachyonic properties? This would not violate SR.

An unlikely explanation but just wanted to see what an expert has to say.
I'm afraid that's already ruled as a reasonable explanation for this by supernova 1987A. The problem is that the speed of a tachyon is given by

[tex]v = c\sqrt{1+\frac{|m^2|c^4}{E^2}}[/tex].

This means that a tachyon's speed increases as its energy decreases. As noted above, the OPERA neutrinos have higher energy than the 1987A neutrinos, meaning that, were they tachyonic, they should be slower, not faster, than the supernova neutrinos. But, in fact, the 1987A neutrinos have a discrepancy from c that is, at worst, something like 4 orders of magnitude smaller than the OPERA discrepancy.
JordanL
#59
Sep23-11, 03:46 AM
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Quote Quote by zadignose View Post
I'm sorry, but I don't quite buy a slight tweak to our definition of "c" as a complete answer.
Anyone suggesting that simply adjusting the "c" constant will fix things needs to explain how 150 years of mathematical and physics equations didn't detect the discrepancy.

Looking to an adjustment to c as the answer to this data, if correct, is... creative. It is not borne out of a dedication to science but a fear of change, as given data like this, that is certainly not the most likely cause, even within our CURRENT theories.
Dmitry67
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Sep23-11, 03:56 AM
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What if neutrinos are very high energy tachions, so we never noticed that they are moving slightly faster than c? We can't detect low energy neutrinos, so usually dont see them moving much faster than c.
JordanL
#61
Sep23-11, 03:59 AM
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Quote Quote by Dmitry67 View Post
What if neutrinos are very high energy tachions, so we never noticed that they are moving slightly faster than c? We can't detect low energy neutrinos, so usually dont see them moving much faster than c.
I believe someone else already asked this question. The answer that was given is that tachyons decrease in energy as they increase in speed. Using the neutrinos detected from the referenced supernova, were they tachyonic, the neutrinos should have been traveling even faster than the ones CERN is talking about. Instead we saw them arrive simultaneously with the photons.
Demystifier
#62
Sep23-11, 04:13 AM
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The idea that neutrinos are tachyons is not new. Many papers already exist:
http://xxx.lanl.gov/find/hep-ph/1/ti.../0/1/0/all/0/1
TrickyDicky
#63
Sep23-11, 04:25 AM
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It is reasonable that after this kind of announcements people starts getting nervous and all kind of silly things are said. Maybe it is not so normal that knowledgeable people first reaction to this apparently "FTL neutrinos" be that SR must be modified, or everything that was measured so far to a certain accuracy is now wrong. It is not. Let's listen to Vanadium 50 here.
First thing to rule out is obviously some kind of error in the measurement, and this is explicit in most posts. Even if no measurement error is found, we must first look for explanations that are compatible with the accuracy level of thousands of previous experiments that can't just be ignored.
So far little attention has been focused to the special nature of the subject particle, the neutrino and the way it is measured, I would say that this is the weakest link of the chain if no obvious claculational or silly error is found so I think the first serious theoretical searches must come from this side rather than question relativity.
Chi Meson
#64
Sep23-11, 05:06 AM
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Quote Quote by Vanadium 50 View Post
This is a systematic effect. You can take that to the bank.

They don't see a velocity dispersion. By itself, that's a huge problem. If you want to argue that not only are neutrinos faster than light, but they all travel at the same speed regardless of energy, you have to explain why the neutrinos from SN1987A arrived on the same day as the light did, instead of (as the Opera data would indicate) four years earlier.
Thank you for posting this! I was pouring through all this info, with this same obvious fact in mind, wondering what I missed. The neutrino burst is part of the standard method for studying Type 2 supernovae in other galaxies, and they all arrive, exactly according to precise calculations, after the light gets here. So granted there's plenty I don't know or understand about the data, but place me in the camp that thinks a systematic error is to blame, rather than derailment of SR.

But hey, I'm a good little scientist--I'll leave the door open.
MarcoD
#65
Sep23-11, 05:22 AM
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Quote Quote by TrickyDicky View Post
Yes, it would be a big problem.
The problem here theoreticians don't seem to make up their mind what speed neutrinos should travel at, when they were supposed to be massless they were expected to have light speed, and supernovae detections so seemed to verify, when agreement was reached that they had mass they obviously should be slower than c, but as Demystifier pointed out there were several people that hypothesized that they should be FTL.
One has to wonder what they really are all measuring, is it really neutrinos? Is there a serious agreement about what its speed should be?
The fact that particles arrive at the same moment from supernovae is a compelling argument it is a fluke, unfortunately. Success to you all.
suprised
#66
Sep23-11, 06:15 AM
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To be sure: it is not CERN who is claiming this, but a team outside of CERN, and all what CERN does is to provide a platform for today's press conference. Unfortunately so, and many colleagues strongly object this. Of course this is being mixed up all over in the media, as usual. Incidentally neither the General Director nor the research director will be present.
xts
#67
Sep23-11, 06:22 AM
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Seems that I am only one here who bothered to read OPERA preprint: http://arxiv.org/ftp/arxiv/papers/1109/1109.4897.pdf

Just some points after reading:

1. There is no information what reference frame they use for analysis and how they covered relativistic effects in their analysis:
CERN? Gran-Sasso? Centre-of-Earth? Solar System?
Please note, that SR time dilation between CERN and Gran-Sasso frames is 10 times stronger than the effect they report. How the clocks were corrected for dilation?
There is also no information if GR effects were taken into account.

2. There is no discussion about systematic errors which may be caused by delays in readout electronics and scintillators itself (except of light propagation, which is the only one discussed). The systematic error caused by DAQ and detectors is estimated as for few ns each, which seems to be too optimistic.

3. Detailed experimental setup is delegated to other paper not available online.
dgwsoft
#68
Sep23-11, 06:36 AM
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Quote Quote by PAllen View Post
There would be a race to determine the mass of the photon. It would be a huge surprise, but I think it would be a bigger hit for QED than SR or GR - the latter rely only on the fact that there is a spacetime structure speed limit. Whether a particular particle reaches it is irrelevant.

I would definitely take the bet against this being confirmed.
My first thought was perhaps photons do no travel at "the speed of light", ie photons have (rest) mass.

According to wikipedia http://en.wikipedia.org/wiki/Photon#...on_photon_mass the experimental limit is at least as good as m < 1e-14 eV/c^2

I could not find a formula to convert photon mass into speed, but I think I have worked it out:

(v/c) = SQRT( (1+d^2)/(1+2d^2) ) where d = Lmc/h (L = wavelength, m = photon rest mass, c = "cosmic speed limit for which we need to find a new name", h = Planks constant).

For small d this approximates to v/c = 1 - d^2/2

Using the mass given above and for a green photon of wavelength 500nm that comes out as one part in about 10^30, much smaller than the 20 parts in a million quoted for the neutrinos.

To look at it the other way, for a photon to be travelling 6000m/s slower then true "c" would require it to have a rest mass of about 1.5e-2 ev/c^2 which would have been noticed.

However my SR is a bit rusty so if anyone wants to check this I would be grateful.

(AIUI it is not significant that light is observed to travel "at c" because since there is no evidence (as yet) that photons have mass, we have just taken "c" to be the speed of light).
Vanadium 50
#69
Sep23-11, 07:27 AM
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Quote Quote by PeterDonis View Post
The paper mentions SN1987A, and notes that the energies of those neutrinos were several orders of magnitude smaller than those of the CERN neutrinos in this experiment. So one could try to account for the SN1987A results and these consistently by postulating a really wacky dispersion relation for neutrinos, that caused virtually no dispersion at energies around the SN1987A energies, but yet caused significant dispersion at the CERN neutrino energies.
It's even wackier than that. You have to argue that you have no velocity dispersion at the 10-10 level or so for MeV neutrinos that vary by a factor of ~3 in energy, and no velocity dispersion at the 10-6 level or so for GeV neutrinos that vary by a factor of ~3 in energy, but between those two energies the velocity changes by 25 x 10-6.

Quote Quote by xts View Post
There is no information what reference frame they use for analysis and how they covered relativistic effects in their analysis:
It's not relevant. Essentially what they are doing is measuring the Lorentz-invariant interval between the production and detection of the neutrinos, and comparing that to a null interval. Since interval is a Lorentz invariant quantity, it doesn't matter what frame they worked it in.

Quote Quote by xts View Post
2. There is no discussion about systematic errors which may be caused by delays in readout electronics and scintillators itself (except of light propagation, which is the only one discussed). The systematic error caused by DAQ and detectors is estimated as for few ns each, which seems to be too optimistic.
If the experimenters are competent, this is easy to do, and as such not worth much space. You get the electronics timing by checking the time difference between input and output on a scope. The detector timing is a little trickier, but signal formation time for plastic scintillator and even a slow phototube is a few nanoseconds. Timing in the detector relative to itself to 1-2 ns is commonplace.
TrickyDicky
#70
Sep23-11, 07:34 AM
P: 3,004
Quote Quote by Vanadium 50 View Post
It's even wackier than that. You have to argue that you have no velocity dispersion at the 10-10 level or so for MeV neutrinos that vary by a factor of ~3 in energy, and no velocity dispersion at the 10-6 level or so for GeV neutrinos that vary by a factor of ~3 in energy, but between those two energies the velocity changes by 25 x 10-6.
Exactly. So I would agree with the cautious Susan Cartwright, senior lecturer in particle astrophysics at Sheffield University when she says "Neutrino experimental results are not historically all that reliable, so the words 'don't hold your breath' do spring to mind when you hear very counter-intuitive results like this."
Most likely they didn't measure what they thought they were measuring.
rhody
#71
Sep23-11, 07:45 AM
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Quote Quote by TrickyDicky View Post
What happened to the last posts by ???? and rodhy?
Were they erased?
TrickyDicky,

Rhody here, yes, mine was, I was in a hurry this morning and in the interest of accuracy could have provided the link, which I will again, here, the Guardian article. Normally, I would only paraphrase part of the article, but because I was in a hurry and names, experiment name, dates, etc... were sprinkled through the article, I posted the whole thing, that is a copyright violation. It was pulled by a mentor. I should have known better. The paper referred to in the article has already been posted in post #71 by atty. The experts will examine this paper with a fine tooth comb, and any weaknesses, errors will be found, if any. If there are none, results will need to be independently verified, and those results bounced against this one. Let's see what transpires at press conference at CERN today. It should prove interesting to say the least.

Rhody...
PAllen
#72
Sep23-11, 07:52 AM
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Quote Quote by Vanadium 50 View Post

It's not relevant. Essentially what they are doing is measuring the Lorentz-invariant interval between the production and detection of the neutrinos, and comparing that to a null interval. Since interval is a Lorentz invariant quantity, it doesn't matter what frame they worked it in.
Can you explain this more? If they are moving faster than c (the spacetime c), this would make the interval spacelike, and taken as particle worldline, would represent travel back in time. Also, while it doesn't matter what frame you compute it in, you must make measurements in some frame or frames to compute the interval, no?


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