A Six-Sigma Signal Of Superluminal Neutrinos From Opera!
By Tommaso Dorigo | September 19th 2011 05:17 AM | 41 comments | Print | E-mail | Track Comments

I am an experimental particle physicist working with the CMS experiment at CERN. In my spare time I play chess, abuse the piano, and aim my dobson...

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[Introduction: I published the text below last Monday, when the news of this controversial new measurement had spread in the corridors of physics departments, as well as in the threads of popular HEP blogs. I felt I was not doing anything wrong, since all I was reporting were facts, with a cautious opinion on my part. I was however forced to take it down only a few hours afterwards, due to a kind of pressure I could not ignore, my own job being at stake. I understand that the experiment who did this measurement was not too happy to see the news in print before they wanted to, but then again the fault is theirs. And in retrospect, what damage did I cause with the post below ?

I believe I should have the right to exercise science popularization here when I have a chance, as I believe it should be the duty of every researcher. Unfortunately, this is not easy to do, and with time and repeated incidents such as this one the risk becomes that of self-censoring oneself. I will try to avoid changing my style, but I will need to learn to be more cautious.

As for the result: it is now public, and yesterday it already circulated in dozens of newspapers throughout the world. There is a preprint out here (see link below), and a CERN press release which explains some details that were unknown to me a few days ago:

The OPERA result is based on the observation of over 15000 neutrino events measured at Gran Sasso, and appears to indicate that the neutrinos travel at a velocity 20 parts per million above the speed of light, nature’s cosmic speed limit. Given the potential far-reaching consequences of such a result, independent measurements are needed before the effect can either be refuted or firmly established. This is why the OPERA collaboration has decided to open the result to broader scrutiny. The collaboration’s result is available on the preprint server arxiv.orghttp://arxiv.org/abs/1109.4897.

In order to perform this study, the OPERA Collaboration teamed up with experts in metrology from CERN and other institutions to perform a series of high precision measurements of the distance between the source and the detector, and of the neutrinos’ time of flight. The distance between the origin of the neutrino beam and OPERA was measured with an uncertainty of 20 cm over the 730 km travel path. The neutrinos’ time of flight was determined with an accuracy of less than 10 nanoseconds by using sophisticated instruments including advanced GPS systems and atomic clocks. The time response of all elements of the CNGS beam line and of the OPERA detector has also been measured with great precision.

So now below is my original post, amended where obsolete.]

The news is all in the title. A unconfirmed rumor from the Opera experiment (see picture below), the neutrino underground detector in the Gran Sasso cavern in central Italy, tells that a measurement has been performed on the time that muon neutrinos take to travel from their production point at CERN to the Opera detector, finding that neutrinos take a handful of nanoseconds less than if they were traveling at light speed.

This, apparently, is a very significant effect, since the experimental resolution on the timing is six times less than the observed time deficit.

Before I comment on the result, let me give you a little background on the whole thing. Opera is a very innovative concept in neutrino detection. Its aim is to detect tau neutrino appearance in a beam of muon neutrinos.

Combining the strength of photographic emulsions with the most advanced electronic scanning capabilities of modern-day computers and with charged particle tracking, the heart of Opera is a set of "bricks" containing a wafer of emulsions and lead plates.

When neutrinos hit the lead nuclei, sometimes they materialize into charged leptons, leaving a trail of hadronic debris which allows the precise identification of the interaction point, with micrometric accuracy. The charged particles that emerge from the brick can be identified and tracked back to the brick which contains the interaction among the 150,000 making up the detector target material. In order to find out precisely what happened in the interaction, the brick is dislodged from the detector and the photographic emulsions scanned.

If a tau-neutrino hits a nucleus, the tau lepton may travel some tens of microns before decaying back into neutrino and charged tracks; this may allow its identification, proving that muon neutrinos sent in by CERN oscillated into tau neutrinos on their 3 millisecond trip to the Gran Sasso.

So let us go back to the superluminal neutrinos now. Apparently, the analysis was performed by a group of physicists from Lyon, who belong to the Opera collaboration. And apparently, the result is controversial within the collaboration -a CERN seminar had been scheduled for last week but has been withheld until this coming Friday. It appears that it is hard to produce independent checks of the result. A result which, if confirmed, would be a magnitudo X earthquake for fundamental physics!

I am reminded of a series of thought-provoking questions and answers by Maury Goodman I posted a week ago on the issue of the significance of physics discoveries, explicitly in the field of neutrino physics. Some 2-sigma results can be fully believed, some 8-sigma ones should be frowned upon. Would you believe in one six-sigma evidence that neutrinos are superluminal ? I would argue you'd be a fool if you did.

Neutrinos seen by the Opera detector are produced when a high-intensity spill of protons from the SpS hits a target in the CERN laboratories. The large flow of pions and kaons results downstream of the collisions; these particles are then focused and allowed to decay to muons and muon neutrinos, and the latter travel underground to the Gran Sasso, where -once in a while- one of them is detected.

Now, measuring with great accuracy the timing of the whole process is not so hard, since the protons hit the target at very precise times and the Opera detectors can indeed record these interactions with nanosecond accuracy. What is impossible to know with precision, IMHO, is the fine structure of the proton spill. The protons arrive at the target with a time-bunched structure, but the details of the spill structure are not known in great detail -the "bunches" might be very sharp peaks of intensity or have straggling tails, for instance.

Furthermore, neutrino interactions are rare, and it takes many spills at CERN to see a single charged-current interaction at the Gran Sasso. Opera has by now collected a large statistics of neutrino charged-current interactions (of the order of 10k events) such as the one shown in the picture on the right, and the analysis is presumably using this large statistics of these data.

But if so, then one would need to know the nanosecond details of hundreds of thousands of spills occurred in the last few years... I wonder if this is the case and thus the six-sigma effect is statistically dominated, or if instead (let me guess that this is instead what is happening) there are unknown systematics on the spills structure which have been estimated with a bit too much optimism.

In any case, this is for sure a very exciting result to scrutinize. Next Friday, hopefully, we will get to know more about the details, since a preprint is expected to appear, in conjunction with a talk at CERN. Stay tuned for more information!

but the observation of neutrinos from supernovae has not provided any evidence for superluminal neutrinos as far as i know...

Wolfgang--

What about the Mont Blanc signal, which arrived in advance of the Kamiokande II + IMB signal by 4.7 hours? Kamiokande II reported their pulses as electron only (when they had the capability to distinguish between the two flavours, electron and muon), while Mont Blanc seemingly did not distinguish between flavours. Hence, it is not ruled out that the signal which Mont Blanc received could have been (tachyonic) muonic neutrinos with a tachyonic mass parameter greater than that of the nu-e. A back-of-the-envelope calculation would then give a value of under 1 keV for this value for m_{nu_ mu}. Otherwise, the Mont Blanc signal seems to have been forgotten as a "highly improbable spurious burst". It is interesting to read M. Koshiba's Phys. Rep. in 1992 entitled "Observational Neutrino Astrophysics", which gives an account of the details of the events, especially concerning the various neutrino observatories, after SN1987A was first reported through visual observation. The report says that Kamiokande searched long after their observation of the electron events, and saw no comparable muon neutrino pulse. Note that the threshold of the Mont Blanc LSD detector was lower than KKII's, and that lower energy events were detected by Mont Blanc at its time, while KKII didn't see anything then, while Mont Blanc saw only two events (possibly electron) at the KKII time, but it was not far from the expected number for Mont Blanc, whose detector had much less volume than KKII. So this might be why one group didn't see anything significant at the other group's time.

Best regards,
Marek

Right. But those were electron neutrinos traveling in vacuum, while these are muon neutrinos traveling in a dense medium. Scientifically, we must keep an open mind...

Cheers,
T.
Italian rocks are dense for a mountain climber who wants to climb through them, and even for electromagnetic waves, which want to penetrate. But as far as known science goes, they can't be  a "dense medium" for the propagation of the neutrinos: the latter are basically non-interacting with the rocks. More comments of mine:
http://motls.blogspot.com/2011/09/italian-out-of-tune-superluminal.html

So you should better try to open your mind when it comes to the theory that what you're promoting is in direct contradiction with more accurate previous experiments and your readers are much more knowledgeable than you.

and would this be compatible with the similar measurement performed by the MINOS experiment some years ago:
http://arxiv.org/abs/0706.0437

Quite nostalgic to have such tasty rumors at large.

You don't mention, but a larger, less uncertain effect is folded into the
spill structure - the decay time for the pions produced on the target. If
there is a stop at the end of the decay volume, it may be hard to calculate
the number of neutrinos produced there.

Or possibly, (and I apologize in advance for the gratuitous pun, but in
this case it seems compulsory) are they -
YOU CAN STILL LOOK AWAY
setting "see tau" equal to one?

Ryan Rohm

The SN neutrinos from 1987A did precede the optical emission (as expected, on boring grounds), so they limit (v-c)/c < 10^{-9} or so, but don't strictly exclude superluminal motion. Of course we already know from DAMA that either the laws of physics, or the laws of statistics, are screwed up in the Gran Sasso lab, so that seems a more likely explanation.

On the one hand, this looks so exciting, on the other, “there’s probably a very simple explanation”.  (Sorry, can’t include the tone of voice to that second bit.)

However, if it is genuine, then I find myself wondering how fast they would travel through a neutron star ...
Robert H. Olley / Quondam Physics Department / University of Reading / England
It is interesting that you ran the risk of losing your job for doing your honest, transparent part of reporting about science news, while to me Sergio Bertolucci, research director of CERN, said that he was all for transparency and openness. See http://www.youtube.com/watch?v=cBxlEGYxocc at minute 6:50.

Hi David,
thank you for your note. I do not think Sergio was involved, but the management of INFN was evidently not happy about this, partly due to pressure from Opera -all this I am just speculating about.
Cheers,
T.
The physics behind this result on superluminal neutrinos is best explained by this graph. Plus, of course, the physics of axe-wielding as applied to science budgets.

This has got me pondering.

(1) Would the rest mass of a superluminal object be negative or even imaginary?

(2) Neutrinos are the first things to arrive after a supernova explosion.  Or should that (allowing for time of light travel) be before?  Lots of star stuff to get through before they reach open space.
Robert H. Olley / Quondam Physics Department / University of Reading / England
True, but these are muon neutrinos, and their energy is much higher Robert. So in principle one could say the SN neutrino measurements do not apply here.
Cheers,
T.
It seemed a little silly to ask you to pull this so Reuters could look like they were breaking this first - Reuters doesn't have any physicists so they simultaneously know less and can't be pressured by CERN, so it is doing a disservice to the public to let big media cover this first.
If the light velocity c is not a limit, then why the neutrino fly so close to c? ;-)
(v-c)/c=2.5 10-5

By the way, how long is the wave packet of neutrino?
"If the light velocity c is not a limit, then why the neutrino fly so close to c? ;-)"
... very good point indeed.

Hi--
Approaching this from the point of view of a tachyonic neutrino, yes, c is still a limit for both bradyons (slower-than-light particles) and tachyons. The reason that neutrinos travelling closer to the speed of light may be "seen" more frequently could be that, according to the usual Lorentz transformation laws (applied to spacelike 4-momenta), the higher the energy, the lower the speed (but still above c). Higher energy neutrinos are expected to be more easily detected (a full quantum field theory calculation might be needed to verify this). Hence that might be a reason for the observed fact you mentioned (within the context of the tachyonic neutrino hypothesis). Best regards,
Marek

Hi Marek,
thank you for this explanation. Indeed it may be due to a detection bias in this case.
Cheers,
T.
No, frankly, if a neutrino is very monochromatic, it is created instantly as a long wave train that induces immediately uncertainty in time of subsequent interactions (reactions).
I wonder how "wrong" the packet model needs to be to see this effect. If one thinks the packets are nice Gaussian shapes, but may have more particles in front of what gets labelled as average, then that would appear as happening too soon.

Since neutrinos are so detector unfriendly, one needs to worry about effects we cannot know. For example, perhaps the neutrinos at the front of the packet happen to be 50.5% more likely to interact than the ones at the tail of the packet at 49.5%. That would be an explanation that would be difficult to confirm or deny. Blackjack teams can make money on that kind of difference. [Additional question: is the packet at least 9m in length?]
Moessbauer photons have a wave train of 30 m long, for example.

The wave train amplitude grows equally in all points within the wave train, like this:

Is it possible that neutrinos only travel faster than the speed of light when they are under the influence of a gravitational field and maybe taking shortcuts off the brane through large extra dimensions?
My latest forum article 'Australian Researchers Discover Potential Blue Green Algae Cause & Treatment of Motor Neuron Disease (MND)&(ALS)' Parkinsons's and Alzheimer's can be found at http://www.science20.com/forums/medicine
I can see this.  General relativity and possibly some other theory could explain this observation.  Simply treating the geometry as Euclidian as they seem to have done would not be valid.
They conducted a large scale experiment, on a spinning, massive ball of solid rock.  The reference frames aren't even inertial.

Let's just say that whatever the theory used this would not be easy to explain away.
Science advances as much by mistakes as by plans.
When making a complete measurement of a wave, I would think we would do 3 types of measurements: the speed, the wavelength and the frequency. These require different detectors. According to special relativity, different inertial observers will see the speed of light in a vacuum as exactly the same, but both the wavelength and frequency will change in ways we understand. As a nice consistency check, the wavelength times frequency measurement must equal the speed.$\lambda \times \nu = c$

I don't understand the details of what is going on in those Italian mountains by the French. It sounds like a speed measurement, and only a speed measurement. It could be there is an energy component, I don't know. I understand neutrinos are no detectors best friend. Still, if at all possible in concept, I would like to get measurements of a frequency and wavelength to see they all point to the same greater than c value. Nature has always been consistent.
I think you do great outreach on physics, Tommaso! Just keep it up (and keep your job, of course :-))

Hank has created this space for a reason...
Bente Lilja Bye is the author of Lilja - A bouquet of stories about the Earth
I think the emission and absorption of photons take some time (possibly 0.1nanosecond) , whereas the neutrino emission and absorption may be instantaneous. So the distance between the emission point and the detection point, if measured using photons, will be slightly less, and this may be the reason for that significant difference observed.

Has anybody tried to put a neutrino detector upstream rather than downstream? It would give an idea where neutrinos are born.
I noticed that the paper made no mention of the Earth's motion. During the 2.4ms time of flight, the detector at Gran Sasso moves about 71m due to the Earth's rotation about the sun. Depending on the direction of motion relative to the vector between CERN and Gran Sasso, that could create as much as +/- 238ns change in flight time. It seems pretty sloppy that this wasn't at least discussed in the paper.

Consider an inertial coordinate system A that is comoving with CERN at the instant the proton beam hits its target. After the 2.4 ms of flight time (t), a reference frame tied to the earth that coincided with A will differ it, the question is by how much in terms of distance?

The two relevant accelerations are due to the earth's rotation, and earth's revolution around the sun. In each case, neglecting small integers, factors of Pi, and various angle sins and cosines, the deviation in distance is of the order of (t/T)^2 * R, where T is the period of rotation and R is the relevant radius. Now the annual revolution is 365.25 times the daily revolution, while the annual radius is some 23,500 times the daily radius so the daily revolution is more relevant, about 5.6 times the acceleration due to the annual revolution. And the daily rotation produces a deviation of the order of
6.4*10^6 meters * ( 2.4 x 10^-3 / 86400)^2 ~ 10^-10 meters, just counting orders of magnitude.

So for this experiment, a reference frame tied to the earth's crust is inertial enough.

To get the two local clocks between Cern and Gran Sasso in sync at the accuracy in ns range, Time Transfer Device (TTD), a loaner from PTB in Braunschweig, was used.

The argument about "reference frame tied to the earth's crust is inertial enough" may hold for the neutrinos' travel. However it does not hold for the travel TTD had to make (by plane? car? in a day or a week? by what route?) to port the time from CERN to Gran Sasso - note it was a one-.way ticket.

see The OPERA neutrino velocity result and the synchronisation of clocks at http://arxiv.org/abs/1109.6160

Regards

smo

Sorry about being unattentive about the messages in this thread and others. I am in Antwerp for a TEDx event, will resume regular blogging and answers in a couple of days.

Best,
T.
Tommaso,

Just wanted to give my support and say I feel absolutely outraged by the attempts to silence you from "high up above". Are we in the f. inquisition time or what?? Keep up the good work.

I just want to say that the word "misleading" in my own headline did not refer to your article or any article here at science 20.  Since when I wrote it, I wasn't aware of any articles here at science20.  We all seemed strangely silent on the matter.   I now know why.
Science advances as much by mistakes as by plans.

Many physicists now believe in the existence of a lower limit for distance measurements. A lower distance than this limit has no physical meaning. This lower limit is believed to be of the order of the Planck length. Besides of that, a Planck time duration lower limit exists. The ratio of these limits is exactly the well-known factor c, which is the speed of a freely moving photon. Thus in this sub-femto environment the photon takes a Planck length sized space step at every Planck time sized progression step. Now suppose that there are more versions of the Planck length. For example let us suppose that the existence of the Planck length has to do with the ground state of the probability amplitude distributions that characterize the elementary particles. Now let there be different categories of elementary particles, where each category is characterized by a typical ground state. This would assign a different Planck length and a different maximum speed  to each category. If the neutrinos belong to a category for which the ground state is slightly wider than the ground state of the category to which photons belong, then the outcome of the Cern Opera experiment is explained without a fundamental change of physics.
Neutrinos just have a longer Planck length than photons. They take longer steps and win the race.

If you think, think twice
Interesting idea Hans, but I think it still sits wrong with the rest of known fundamental physics. I am not fresh enough with my theory studies though, so I will leave it to others to comment.
Best,
T.
Parent decays are those of $\inline \pi$- and K-mesons who have short lifetimes (>10-8 s) but relativistic effects may increase the neutrino wave train length. Has anybody made the corresponding estimations?
Not old in this subject but quick question: are neutrinos easily blocked or scattered? Are they easily formed? Did this experiment "label" the kind of neurinos being detected after transmission from cern or could they be detecting neurinos emitted from other sources or processes? So these neurinos were not losing energy as they travel at the speed close to that of light?

Hi Jamigori,

neutrinos are the things that are hardest to block or scatter. They can travel millions of kilometers inside matter without undergoing a single scatter. But Opera definitely saw the neutrinos produced at CERN, because the background from other sources is totally non-existent (there are neutrinos from the cosmos impinging on us, but they do so at all angles and not in the milliradian subtended by CERN as seen from 700 km away; plus they arrive with smaller rates and at random times, while those from CERN arrive in the time window of a few nanoseconds after the pulse of protons is shot.

Cheers,
T.
Late Last Question:
Meanwhile the whole FTL neutrino measurement has grown to a big enough scandal for Antonio Ereditato to resign. Before silence falls over the whole affair I want to know two things:
1) is it technical scandal, ie. were the engineers stupid or the measurers not looking right, or a PR scandal, ie were the spokes people unsincere, sensation seeking or elusive?
2) it is not very clear to me what exactly was the measurement error, I surely miss some transparency here. but some sources say it was a loose connection between a optical cable and an electronic circuit. But if you have a LOOSE connection, how can you get a six sigma deviation? I wouldn't call that particularly LOOSE.

Dear Paulvs,

I think it was no scandal. It was just a little bit of excess confidence on the part of Ereditato. This is what a part of his collaboration seems to have told him with their vote. Opera had to come out once the result was publicized, but of course it was someone within Opera who leaked it in the first place.

A loose connection may cause anything. In this case it caused a delay of 60 nanoseconds, such that the timing measurement erred the opposite direction. Not sure what you mean with the comment about standard deviations and being loose.

Cheers,
T.
Late Last Question:
Meanwhile the whole FTL neutrino measurement has grown to a big enough scandal for Antonio Ereditato to resign. Before silence falls over the whole affair I want to know two things:
1) is it technical scandal, ie. were the engineers stupid or the measurers not looking right, or a PR scandal, ie were the spokes people unsincere, sensation seeking or elusive?
2) it is not very clear to me what exactly was the measurement error, I surely miss some transparency here. but some sources say it was a loose connection between a optical cable and an electronic circuit. But if you have a LOOSE connection, how can you get a six sigma deviation? I wouldn't call that particularly LOOSE.

I would like to close this comment by Hontas' bottom line, but i'm insure about the spelling and i'm sure she will go piss about her copyright.