Physicists propose search for fourth neutrino

November 29, 2011 by Lisa Zyga, feature

In the proposed test for a fourth neutrino, a small electron antineutrino source (blue) located at the center of a large liquid scintillator detector would be used to bombard a target. The red curve represents the oscillation of the antineutrino rate as a function of the distance within the detector. If the bombardment involves sterile neutrinos, interactions of the electron antineutrinos would show a spatial modulation of a few percent over a few meters. Image credit: L. Scola (CEA)
( -- Physicists know that neutrinos (and antineutrinos) come in three flavors: electron, muon, and tau. In several experiments, researchers have detected each of the neutrino flavors and even watched them “oscillate” back and forth between flavors. But starting in the early ‘90s, some experiments have also revealed a nagging anomaly: muon antineutrinos oscillate into electron antineutrinos at a 3% higher rate than predicted. Physicists can reconcile this discrepancy by adding a fourth neutrino with a specific mass, although such a move would require modifying the Standard Model, the theory of subatomic particles that has taken decades to build. In a new study, a team of physicists thinks it’s time to put the question of the fourth neutrino’s existence to the test.

In their study published in a recent issue of Physical Review Letters, Michel Cribier, et al., have proposed an experiment that would reveal whether a fourth flavor of neutrino really exists. If it does, then it would have huge implications not only for neutrino science, but also for understanding the building blocks of matter overall.

The first hints that something was amiss came in the early ‘90s from the Liquid Scintillator Neutrino Detector (LSND) experiment at Los Alamos National Laboratory. In the experiment, an antimuon beam bombarded a target, revealing a greater number of antielectron neutrino oscillations than predicted. Or in other words, antineutrino oscillations seemed to be occurring at a faster-than-expected rate.

But Cribier and his coauthors’ main motivation for carrying out a test of a fourth neutrino rests on the results of a more recent finding, which is now known as the Reactor Antineutrino Anomaly. In a recent study, (including some from the recent paper) at the French Atomic Energy Commission (CEA) in Saclay recalculated the rate of antineutrino production in nuclear reactors that was first calculated in the 1980s. Using improved techniques, the scientists estimated that the rate of antineutrino production is about 3% more than previously predicted. Even after rechecking the new estimates, the 3% antineutrino surplus remains. As a consequence, the same physicists reanalyzed more than 20 previous reactor neutrino experiment results, finding more discrepancies.

The simplest physics explanation for this anomaly is the existence of a fourth neutrino. Physicists have estimated the mass of the fourth neutrino and also determined that it would be “sterile” because it doesn’t interact with matter through the weak nuclear force like the other neutrinos do. This property would make the fourth neutrino particularly difficult to detect; some physicists even suspect that it could be a dark matter candidate.

With so many implications riding on this hypothetical particle, Cribier and his coauthors have proposed a search that they say will unambiguously test for its existence. The experiment would involve firing a 1.85 PBq antielectron neutrino isotropic source (about 10 grams, or less than 4 cm) at a target in the center of a large liquid scintillator detector (LLSD). Possible detectors include Borexino, KamLAND, and SNO+, which contain about a thousand tons of ultrapure liquid scintillator inside a nylon or acrylic vessel. The antielectron neutrino generator would consist of a radioactive source such as cerium nuclei, a common fission product from nuclear reactors that can be extracted from spent fuel rods. In order to achieve a meaningful certainty level, the experiment would run for a full year.

If the bombardment of the target results in a sterile neutrino, the scientists could measure a unique oscillation signature to confirm the neutrino’s existence.

“A sterile neutrino, by definition, is not able to induce an interaction allowing its direct detection,” coauthor Thierry Lasserre from the CEA told “Nevertheless, theory predicts oscillation between the three ordinary neutrinos and the sterile one. Thus the experimental signature of a sterile neutrino consists in the observation of interactions of the ordinary neutrinos with a modulation in energy and/or distance controlled by the mixing and masses of the fourth neutrino. The mass (eV scale) and coupling of the sterile neutrino able to explain the reactor antineutrino anomaly is such that interactions of neutrino/antineutrino of typical energy of 1-2 MeV would induce a spatial modulation of several percent over a few meters. Hence if an intense source of neutrino is placed at the center of a spherical liquid scintillator detector (see illustration), the radial distribution of the interaction vertex will deviate from a flat distribution with a sinusoidal modulation. The spatial period is inversely proportional to the mass of the sterile neutrino whereas the amplitude is a function of the coupling between the fourth and the usual electron neutrino.”

Lasserre explained that this proposed experiment will provide greater certainty about the existence of a fourth neutrino compared to other experiments due to the neutrino source’s smaller size.

“It is difficult to probe this oscillation using standard accelerator or reactor neutrino experiments because the oscillation length is quite small (a few meters with of a few MeV),” he said. “A compact radioactive neutrino source provides a new window to look for such oscillations. Thanks to the small spatial dimensions of the source, our proposed experiment would have the potential to actually see the oscillatory behavior of the antineutrino interaction rate as a function of the detector radius (thus inside the detector!). No need to rely on the knowledge of the source activity to the sub-percent; we are looking for a relative oscillatory behavior inside the detector.”

One of the biggest difficulties in any neutrino experiment is ruling out background noise, which could give false positives. Background noise can be induced by the environment, the detector, the antineutrino source, or the source’s shielding. Due to type of decay event the scientists would analyze (inverse beta-decay), which involves a specific delay time, the scientists explain that this experiment should have the advantage of an almost background-free detection.

The greatest technical challenges of the proposed experiment would be producing the antineutrino source itself and fabricating a thick shielding material to surround the source. Due to these challenges and the kiloton-scale detectors needed, realizing the experiment would require a large collaborative effort. The researchers have begun to talk about carrying out such an experiment.

“I'm requesting some funding to realize the source and shielding to the European Commission for the period 2012-2018,” Lasserre said. “Furthermore, we are discussing with the host detectors, especially with Borexino and KamLAND that expressed an interest in this new source project. I will be in Japan in early December for four seminars and discussion.”

Explore further: New results confirm standard neutrino theory

More information: Michel Cribier, et al. “Proposed Search for a Fourth Neutrino with a PBq Antineutrino Source.” Physical Review Letters 107, 201801 (2011). DOI: 10.1103/PhysRevLett.107201801

Journal reference: Physical Review Letters search and more info website


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1 / 5 (26) Nov 29, 2011
A sterile neutrino could explain the superluminal neutrino results. In my idea, at the brief moment, when the normal neutrino oscillates into antineutrino or back again, the particle is behaving like the uncharged superluminal gravitational wave and it makes a sudden jump through space-time. The higher speed/energy of neutrino is, the higher is the probability of this transition.
4.6 / 5 (13) Nov 29, 2011
@ rawa1

You're a huge n00b. Since when are gravitational waves superluminal?
1 / 5 (21) Nov 29, 2011
Since when are gravitational waves superluminal?
Aether Wave Theory predicts so with water surface model of space-time foam... http://aetherwave...ves.html

As Eddington pointed out already before many years, gravitational waves do not have a unique speed of propagation. The speed of the alleged waves is coordinate dependent. A different set of coordinates yields a different speed of propagation and such waves would propagate like noise.

He effectively predicted the existence of CMBR noise in this way, but he died like senile numerologist and n00b, as perceived with the rest of scientific community of his time.
4.7 / 5 (13) Nov 29, 2011
"superluminal gravitational wave"

What? Evidence?
4.1 / 5 (13) Nov 29, 2011
A sterile neutrino could explain the superluminal neutrino results. In my idea, at the brief moment, when the normal neutrino oscillates into antineutrino or back again, the particle is behaving like the uncharged superluminal gravitational wave and it makes a sudden jump through space-time. The higher speed/energy of neutrino is, the higher is the probability of this transition.

Please stop.
1 / 5 (8) Nov 29, 2011

Well, one could have tachions (sp?) surfing the g waves - why not?
1 / 5 (13) Nov 29, 2011
Please stop.

Why I should do? There is whole article about it.

It's my usual game, to grab the random ArXiv article, present its idea under my name and collect the opinions from trolls, who insist, it's a BS.
4.3 / 5 (11) Nov 29, 2011
do you have to clog up every thread you visit with your aether wave theory? you are not exactly winning us over so why waste the effort?
1 / 5 (10) Nov 29, 2011
you are not exactly winning us over so why waste the effort
If nothing else, it could save us 800 billions of Euro for gravitational detectors. If the gravitational waves are well known CMBR noise and very simple logics is reaquired for such understanding, why to spend these money for their findings? Why not to use them for cold fusion research? Or is it really better to keep the world in financial crisis and risk of global nuclear war?

Does something still appear illogical with my stance?
1 / 5 (10) Nov 29, 2011
Would you protest against Hitler regime before WWW II, if you could imagine the consequences? Or would you accept it as your destiny once again?
5 / 5 (2) Nov 29, 2011
Glad to see this is being looked into, seeing as how no one responded to my question on the article about faster than light neutrinos. My question was "had it been considered that there are possibly more than 3 flavors of neutrinos". Guess I am not the only one thinking about its possibility.
not rated yet Nov 29, 2011
The water does not have to form a sphere around the emitter, It could be in the shape of a cone with emitter at the point. It would take longer to get the results though
1.8 / 5 (5) Nov 30, 2011
Why can't they wait 20 years to find a damn useless neutrino? By then their detector will cost 3 canadian dollars and run on solar power.

but seriously if a neutrino oscillates to a different flavor it must travel through a spectrum, it may be happening so fast or have other characteristics that make observing this change from flavor to flavor impossible to directly view (im pretty sure we only see the result, emit a tau detect an electron flavor or something). So why not develop the mathematics to simulate the oscillation of such a light mass particle

I would wager, foolishly perhaps, that superluminal neutrino phenomenon has to do with a fourth neutrino which is its own antiparticle. makes sense because changeless and mass less would make something very hard to find proof of.
3.5 / 5 (6) Nov 30, 2011
Please stop.

Why I should do? There is whole article about it.

It's my usual game, to grab the random ArXiv article, present its idea under my name and collect the opinions from trolls, who insist, it's a BS.

The problem is you don't understand the article nor its idea, idiot
1 / 5 (3) Nov 30, 2011
The problem is you don't understand the article nor its idea, idiot
The problem rather is, you cannot prove it, so you're resorting to personal attacks.
Need a 4th neutrino. It smells.
It's actually third neutrino and it corresponds the neutral Z particle of Standard Model. When all particle generations are taken into account, the we would need not just one new neutral neutrino, but neutral muino and tauino as well. It would mean, we wouldn't recognize six neutrinos, but nine ones. The funny part is, even the fourth generation of neutrinos may probably exists - so we could recognize twelve neutrinos after then.
5 / 5 (2) Nov 30, 2011
Vendicar Decarian, are you trolling?

The reason the Standard Model still exists is because it works. Like any scientific theory though, it can never be guaranteed to be the complete and final description of the world on the scale it refers to. But then this is true of ANY theoretical statement of ANY sort about the real world.
1 / 5 (2) Nov 30, 2011
At least one neutrino has long been known to be superluminal:

"The Neutrino as a Tachyon," Phys. Lett. B 150(6), 431-435 (1985)
1 / 5 (2) Nov 30, 2011
Certain type of Neutrinos has been long known to be superluminal
They're supposed to be superluminal, to be more specific. We didn't detected these neutrinos yet.

And neutrino isn't really a tachyon, it cannot move with arbitrary speed, being attached to our space-time brane in similar way, like the Falaco soliton at the water surface. The example of true tachyons are gravitational waves/gravitons, which manifest with CMBR noise. They're traveling with speed at least ten thousand times higher, than the speed of light.
4 / 5 (4) Dec 01, 2011
Another neutrino has problems for the Standard Model. There should be ONE neutrino per lepton type. There are three types of lepton, electron, muon, and tau. Adding a new neutrino is not just adding a single particle. If there is another neutrino there should be another lepton and another pair of quarks.

So claiming a sterile neutrino exists is not just adding a single particle. It is either adding a so far undetected set of particles or a whole new model has to be built.

It smells like a hard problem.

3.7 / 5 (3) Dec 01, 2011
It does, but there are an awful lot of parameters to tune and the particles chosen are done to match observation rather than specified by theory.
I don't expect any theory to produce those parameters so I don't have a problem with it. There are no theories that do produce numbers for the various parameters. There is one that produces a few of the numbers fairly close to correct but blows it on all the others so it looks like pure coincidence.

Hence creating new theoretical ones is more theoretically arbitrary.
They do have to fit evidence so they cannot be purely arbitrary. For instance another round of particle of higher energy than the three we have now does not fit with the proposed particle.>>
0.7 / 5 (48) Dec 01, 2011
There is one that produces a few of the numbers fairly close to correct but blows it on all the others so it looks like pure coincidence.

Heim theory? If only it were true :(
3.7 / 5 (3) Dec 01, 2011
Although all present data is consistent with three generations of leptons, some particle physicists are searching for a fourth generation. The current lower limit on the mass of the fourth charged lepton is 100.8 GeV/c2,[28] while its associated neutrino has a mass of at least 45.0 GeV/c2.[29]
Even if the mass should fit the proposed 4rth neutrino there is the little problem that it should still interact via the Weak Force.

If you can now have 4 Neutrino's, how about 19?
That requires more particles of other kinds as well. However there is a way to get a set of three new neutrinos. Supersymetry requires a bunch of particles only none have been detected and the probability of their existence goes down with each new increase in accelerator energies.>>
3.7 / 5 (3) Dec 01, 2011
Charge isn't conserved? No problem. It is carried away by a massless foogiewiggle.
The name is no less silly then some in present use. However carrying charge away is a bit of a problem. The particle would interact via the electro-magnetic force. MUCH easier to detect than neutrinos are. So am afraid your foogiewiggle is even less likely to exist than Supersymmetric particles.

However it make more sense than ZephyrAWITBS' Handwave theory of instant gravity as that inherently violates any Aether theory of any kind. There can be no instantaneous action in an aether based theory. This includes any cellular automata theory.

Heim theory? If only it were true :(
I think thats the one. I agree it isn't a valid theory. The claim of it matching the measured numbers only holds for one closely and the rest in increasing amounts of error. Most aren't remotely close.

3.7 / 5 (3) Dec 02, 2011
So far it has worked out that way. Symmetry is not just handwaving since using it to think about things often produces theories that work. Symmetry is not all there is because if that was the case there would be nothing. Symmetry breaking must occur but where and how can only be found through experiment.

The catch with the

sterile neutrino

is that is just sitting there on its own.

Separate from everything else.

With no rhyme or reason except to cover a 3 percent error. And breaking everything else in the process. To put it in fairly standard terms in science. It's ugly. Which I suppose could be better expressed as appearing to be arbitrary and capricious or in Zephir's favorite, and never applied to his own idea no matter much it fits, ad hoc.

Quark theory is not ad hoc contrary the cry of many cranks. It fits together and is expected to have broken symmetry somewhere but the expectation is is that will be in the constants.

1 / 5 (4) Dec 02, 2011
"There should be ONE neutrino per lepton type." - Ethelred
Where is "there"? In your head? The Standard Model predicts both neutrino, both antineutrino and it's supported experimentally.

3.7 / 5 (3) Dec 02, 2011
Where is there a difference between what I wrote and what you linked to?

Thinking is not your strong suit.


1 / 5 (4) Dec 02, 2011
No contemporary peer-reviewed theory predicts ONE neutrino per lepton type. Therefore your sentence is wrong in every meaningful context. Period.
3.4 / 5 (5) Dec 03, 2011
Please no.

They added a 4th flavor to Fruit Loops AND Fruity Pebbles and then it was all down hill from there.
3.7 / 5 (3) Dec 03, 2011
No contemporary peer-reviewed theory predicts ONE neutrino per lepton type.
Incorrect. They all predict that. It is what the evidence shows.

Your problem is you don't understand TYPE.

There is ONE electron and ONE electron neutrino. Period.

ONE positron and electron antineutrino.

That's TWO types TWO neutrinos.

Matter and antimatter are two material manifestations of energy.

Quit thinking everyone that disagrees with you is stupid. I know there is a positron and electron. YOU don't seem to understand that is TWO leptons and not one.

1 / 5 (2) Dec 03, 2011
That was a joke, guys, a JOKE.

Sadly, nobody got it i guess.
1 / 5 (2) Dec 04, 2011
That was a joke, guys, a JOKE.

Sadly, nobody got it i guess.

What gets me is the complete and utter lack of Quisp and Quake.
1 / 5 (1) Dec 05, 2011
No particle physics theory has predicted the existence of any particle as far as I know. Implied.. Yes. But predicted? Nope.
I do agree. The existence of neutrinos has been postulated just after the anomalous dispersion of beta decay was observed. The anomalous antiparticle tracks were observed a long time in film emulsions before Dirac predicted them. Even in 1928 Dirac didn't predicted positrons, he just published time symmetric solution for electrons - he wasn't farseeing enough for it. The muon had come as complete surprise for theorists ("Who ordered that?"). The quarks were deduced from dispersive experiments, not postulated. And so on.

Despite of it, the theoretical physics of the first half of the last century was remarkable more successful with its predictions, than the later physics. The dense aether theory explains it with dependence of symmetry to the dimensions of observable scale - the symmetric, predictable phenomena appears just at the certain areas of it.
1 / 5 (1) Dec 05, 2011
If we compare the symmetry level with the size of objects, we can observe, the symmetric solutions and artefacts appear just around the dimensional scale of atom nuclei and the cosmological objects, which are composed mostly of atom nuclei.
The more distant we are from these two areas of dimensional scale, the more the observable reality appears fuzzy and unpredictable. It explains the relative success of the nuclear physics, which has been credited later with construction of nuclear bombs. From this time the success of theoretical physics suffers with gradual decline, because it's preferentially based on time symmetric formal models.
Therefore the aether model provides the geometric context even for the rise and decline of mainstream physics evolution. The physicists are good at the moment, when the character of observable reality changes from asymmetric to symmetric along time dimensions, not vice-versa.
1 / 5 (3) Dec 05, 2011
The quarks were deduced from dispersive experiments, not postulated.

For sure, not postulated. However, was the deduction correct?

3.7 / 5 (3) Dec 05, 2011
No particle physics theory has predicted the existence of any particle as far as I know.
I even mentioned the first of the particles predicted.

The positron, by Dirac, AND the neutrino, by Pauli, were both predicted.

Top and bottom quarks various bosons. If you are demanding a prediction of the mass I think we will have to stick with Dirac's positron though.

Implied.. Yes. But predicted? Nope.

Higgs particles,
More of a WAG than a prediction.

More of a Higgs than a WAG.

and poopiewoopies.
I think that is more part of fecalology not particle physics. The sort of thing Archaeologists have to deal with. The difference between an Archaeologist and a Paleontologist is whether it still stinks or not.

It is just another epicycle
At the moment I agree with that. If someone can put some real reasoning behind it that might change my mind.

3.7 / 5 (3) Dec 05, 2011
The muon had come as complete surprise for theorists
Ah but the Book of Urantia predicted the Meson. Of course it was actually published AFTER the real thing was found and named and the only thing that matches in the BOU is the name but they assure me they predicted it in unpublished notes. I think they got it from Galactic Inspector 127828.


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