CERN team claims measurement of neutrino speed >c

Borek

GPS can be used to measure distance with very high accuracy (up to centimeters if memory serves me well). This is routinely used to measure displacements of ground in seismically active places. This type of measurement is very slow (unless you have a military device that can decrypt coded part of the signal), but that doesn't matter here - they had plenty of time. And as 1 feet is a 1 ns errors in distance measurements should be not a problem.

ZapperZ

This is incorrect. The neutrinos DO NOT TUNNEL through the earth. They interact only via weak interactions (and very, very weakly with gravity). "Tunneling" is a different physics entirely!

Zz.

turbo

Noted. Please chalk this up as a poor choice of words. Neutrinos interact so weakly with matter that they can zip through (not tunnel through) impressive amounts of matter without leaving a trace of interaction. Thus, you need a big sensitive detector, and LOTS of neutrinos to get statistically-significant detection-signal. Apparently, Opera was designed with this in mind, and successfully so. Are the results reliable, and are they repeatable with other instrumentation? Time will tell.

PeterDonis

I'll be interested to see exactly how they calculated what the light travel time should have been. Did they properly account for the fact that the direct path goes through the Earth's interior, and therefore the actual path length will be different than the path length that would be inferred if you just took the differential, in Euclidean geometry, between the two GPS locations, because of GR effects (the difference in spacetime curvature)? My initial guess is that the corrected "through the Earth" path length will be slightly *shorter* than the uncorrected path length you would infer from the differential in GPS locations, which would explain the results. But I haven't done a calculation to see for sure.

atyy

Newly posted by MTd2 on marcus's quantum gravity bibliography:

http://arxiv.org/abs/1109.4897
Measurement of the neutrino velocity with the OPERA detector in the CNGS beam
OPERA
(Submitted on 22 Sep 2011)
The OPERA neutrino experiment at the underground Gran Sasso Laboratory has measured the velocity of neutrinos from the CERN CNGS beam over a baseline of about 730 km with much higher accuracy than previous studies conducted with accelerator neutrinos. The measurement is based on high-statistics data taken by OPERA in the years 2009, 2010 and 2011. Dedicated upgrades of the CNGS timing system and of the OPERA detector, as well as a high precision geodesy campaign for the measurement of the neutrino baseline, allowed reaching comparable systematic and statistical accuracies. An early arrival time of CNGS muon neutrinos with respect to the one computed assuming the speed of light in vacuum of (60.7 \pm 6.9 (stat.) \pm 7.4 (sys.)) ns was measured. This anomaly corresponds to a relative difference of the muon neutrino velocity with respect to the speed of light (v-c)/c = (2.48 \pm 0.28 (stat.) \pm 0.30 (sys.)) \times 10-5.

DrGreg

Note the final paragraph:

Despite the large significance of the measurement reported here and the stability of the analysis, the potentially great impact of the result motivates the continuation of our studies in order to investigate possible still unknown systematic effects that could explain the observed anomaly. We deliberately do not attempt any theoretical or phenomenological interpretation of the results.

Jack21222

I'm kinda hoping that there is some sort of compact extra dimension explanation to come out of this (because my research advisor would do a literal jump for joy), but I recognize that this is far far FAR more likely to be just some experimental error.

Runner 1

Well one thing is for certain:

When the paper is released, we'll see a bunch of internet physics experts discover the obvious flaw that multitudes of particle physicists just happened to overlook during 3 years ;)

seerongo

Whether this is an error in methodology/measurement or it is verified that neutrinos are faster than photons and photons are slower than c and massive, etc., the outcome should be very interesting in any case. This group is not stupid and have had 4 years to figure this out. It seems to me that any outcome is bound to have important implications, even an experimental anomaly, since so many experiments are based on similar methodologies. Anyone here care to speculate on that end of it (since speculation is all we have today)? Comments here so far seem too focus on errors in measuring source/detector separation, equipment latencies, etc, but certainly they have gone over that ground ad nauseum.

For purposes of this discussion if nothing else, can we agree to differentiate the terms "speed of light" and "c", with "c" being the zero-mass SR speed limit? Using them interchangeably can be confusing in a discussion like this.

DaleSpam

Newton's laws were used for about twice as long before anyone noticed any inaccuracies.

Vanadium 50

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.

Vanadium 50

A massive photon won't explain this. All photons travel at the same speed. If the limiting speed were 1.000025c, we would see more energetic photons move faster, and we don't.

DaleSpam

Yeah, I have to agree here. I just looked at the paper, the effect is too large to have hidden in the noise for all previous experiments.

Jack21222

One can both dismiss and investigate a claim at the same time. I'd be very interested in seeing where the error is. For what it's worth, the CERN team is "dismissing" their own results here. It's still fun trying to pinpoint what could have went wrong.

The point about the SN1987A neutrinos is a big one. I just did the calculations myself... the neutrinos would have arrived 4 years earlier than they did, as V50 says.

PeterDonis

As I read it, the clocks are synchronized using GPS. Just having them identical doesn't account for time dilation if they are at different altitudes (i.e., different levels of gravitational potential), which I believe they are. There has to be some mechanism for correcting their rates to a common standard of simultaneity. That's what the GPS part is for (and it looks like it requires pretty hefty GPS equipment to get that kind of accuracy for the corrections).

Also, I see very precise measurements of distance, but they are all based on GPS location fixes, as far as I can tell. I see a reference to a "common analysis in the ETRF2000 reference frame", but there are no details, just a pointer to a reference at the end of the paper that isn't online. So I can't see if the reference frame they used for their computation of the distance, based on all the measurements, took into account that distance, as well as time, gets distorted when the altitude (i.e., gravitational potential) changes. I would think it would, since they talk about a geodetic survey, which is all about accurate measurements of equipotential surfaces. But it would be nice to have more details.

PeterDonis

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. I don't know if any reasonable physical models for neutrinos would imply such a dispersion relation.

DaleSpam

Correct, they are claiming the the neutrinos travel at 299 799 893 m/s compared to the speed of light 299 792 458 m/s. So the massive-photon resolution would require that the invariant speed be something greater than 299 799 893 m/s, but that would have been detectable in other experiments.