How the neutrino could solve great cosmic mysteries and win its next Nobel Prize

October 9, 2015 by Simon Peeters, The Conversation
James Sinclair from the University of Sussex entering the SNO detector for upgrade work to transform this experiment into SNO+. Credit: The SNO+ collaboration, Author provided

The humble neutrino particle won its fourth Nobel Prize in physics this year (also in 2002, 1995 and 1988). Despite being millions of times smaller than other subatomic particles, it is of major importance in physics and could be the key to unravelling some of the universe's best-kept secrets. So where is neutrino research heading next – and what could it discover?

Matter is made of fundamental particles. Most people will have heard of electrons, neutrons and protons – and perhaps even quarks, which make up the latter two. But to me, the neutrino is the most amazing fundamental particle. They are everywhere. About 65 billion , produced by nuclear fusion in the Sun, pass through every square centimetre of area on Earth, every second (you could try and calculate that yourself), without doing anything.

Because neutrinos hardly interact with other matter, this year's Nobel prize winners for physics, Takaaki Kajita and Arthur B McDonald, had to build vast detectors, filled with thousands of tonnes of water, in order to study them. What they found out was that the neutrino is even more interesting than we thought.

While travelling through space, a neutrino apparently continuously flips between different "types" of neutrino, changing the way they interact with matter. This is called . You might imagine this as a little fellow that, while running at nearly the speed of light, continuously changes the colour of its jacket by which you are trying to identify it. Neutrinos can only do this if they have mass. So until the results from these experiments were published, they were assumed to be massless. Clearly this was ground-breaking news.

Chasing new discoveries

Since these fascinating properties of neutrinos were revealed, around the year 2000, a large number of experiments have been successfully built to investigate this in more detail. However, as always, these new insights led to further questions. Today, we have studied neutrino oscillations in great detail and understand it pretty well.

But one very important question remains: does the neutrino oscillate the same as its polar opposite: the anti-neutrino? All particles have anti-particles. For example, the common electron, with a negative electric charge, has the positron as its anti-particle, which is virtually identical but has a positive charge and has to be produced in a nuclear reaction. But as the neutrino has no charge, it is difficult to know what its anti-particle would look like. In fact it could be virtually the same, but still behave differently.

The UK is taking a big part in two experiments that will study neutrino oscillations in the future in more detail to answer this question: HyperKamiokande in Japan, and the Deep Underground Neutrino Experiment in the US.

The distribution and movement of galaxies helped scientists figure out that dark matter could must be hiding in there. Credit: wikimedia

Solving the matter-antimatter mystery

Finding out that neutrinos interact differently to anti-neutrinos could have huge consequences as it could help solve one of the greatest mysteries in physics: why is our entire universe made out of just matter? We have strong reasons to believe that in the Big Bang, matter and anti-matter were created in equal measure. So where did all the anti-matter go? We know that anti-matter and matter destroy each other in a flash of light whenever they meet, so maybe this could explain that it's not around? Not really, all the matter would be gone as well.

One of the key components in the currently favoured explanation is that matter behaves differently to anti-matter. But the difference between how neutrinos and anti-neutrinos change the colour of their jacket isn't going to provide the entire solution. The answer comes with a possible solution to a second mystery relating to neutrinos: why is the mass of a neutrino so incredibly small?

The masses of other , generated by coupling to the famous Higgs particle, vary widely – from the electron, about 2,000 times smaller than the mass of a proton, to the top quark, which weighs nearly 200 times more than the mass of a proton. The , however, is at least 10,000,000,000 times smaller than the proton mass.

So why is the neutrino so much lighter than the other particles in the Standard Model? We believe their mass is generated differently. If this is correct, we could end up with two versions of neutrinos (on top of the particle-anti-particle duality): one that has the tiny mass we observe today and an extremely heavy one, that was abundantly present when the universe was first born.

The mathematics of this theory states that, if these heavy neutrinos had anti-particles that behaved differently from them, they would subsequently decay into a number of smaller particles like electrons and positrons. However, this would have happened "asymmetrically", meaning that fewer anti-particles than particles would be created in the decay – which then, in the conditions of the early universe, could result in the (relatively) small amount of leftover matter that forms our universe today.

It's no wonder then, that scientists are investing so much effort into understanding the nature of the neutrino. The only way we currently know of to determine the exact nature of these neutrinos is to look for an extremely rare nuclear decay called "neutrinoless double-beta decay". This has never been observed and would only be possible if neutrinos are different than the other matter particles. A number of experiments is getting ready to study large quantities of isotopes for which it would be possible to observe this decay. The UK has leading roles in two of those: it is involved with the science and construction of the SuperNEMO experiment in France and SNO+, a modification of Art McDonald's Sudbury Neutrino Observatory (SNO) experiment in Canada.

Could dark matter be made up of neutrinos?

Neutrinos could possibly also explain puzzling observations made by astrophysicists. They have shown that there is much more matter in the universe than we can directly observe. We call the matter we don't see dark matter. There is about five times more of this unknown dark matter than all the matter that we do know about.

Until around 2000, it was thought that the ghost-like neutrinos could be this dark matter, but we now know that they are not heavy enough. We have observed three types of neutrinos – electron, muon and tau – and there seem to be three types of all the other matter particles. Since we don't know why there are only three, the obvious questions is: are there additional neutrinos that could explain the dark matter?

Many neutrino oscillation experiments are looking for cracks in our theory of neutrino oscillations that could be explained by additional neutrinos. Also astrophysicists are hunting for signs in cosmic rays for additional neutrinos.

What constitutes and why the universe has more matter than antimatter are two of the most important questions in physics today. If we could solve either of those or even just figure out why the neutrino is so light, it would be a major breakthrough. There is a world-wide race between many experiments going on to answer them: plenty of chances for the amazing neutrino to get (at least) one more Nobel!

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Returners
1 / 5 (6) Oct 09, 2015
and there seem to be three types of all the other matter particles


I proposed something like this when trying to "unify" ordinary matter, Dark Matter, and Dark Energy using alternate combinations of attraction and repulsion between different types of particles.

As far as I can tell, the most stable configuration I came up with ends up producing filaments and sheets of dark matter and "dark energy particles" between and among galaxies, but I had to take certain liberties, such as assuming asymmetric attraction and repulsion values for the particles to get something which seems to be somewhat stable both within a galaxy and in the space intervening between two galaxies. Since I have toruble visualizing this system for more than 2 galaxies and intervening filaments I can't say much else about it. Not exactly what we observe though.

I don't know if they are referring to something similar, or another unrelated problem with ordinary elementary particles.
my2cts
not rated yet Oct 09, 2015
"Despite being millions of times smaller than other subatomic particles"
We do not have a value for the size of the neutrino.
Returners
1 / 5 (4) Oct 09, 2015
"Despite being millions of times smaller than other subatomic particles"
We do not have a value for the size of the neutrino.

Take the mass of a radio isotope which produces a neutrino upon decay.
Watch the decay.
Take the mass and kinetic energy of daughter particles.
Take the energy of any EM radiation released.

Whatever remains is likely the mass and kinetic energy of the neutrino.
ogg_ogg
not rated yet Oct 09, 2015
What if neutrinos do usually, but NOT always, travel at exactly c? Now, wouldn't that be cool? Ah, the places we'll go!
antialias_physorg
3.7 / 5 (6) Oct 09, 2015
What if neutrinos do usually, but NOT always, travel at exactly c?

You'd see a ton of radiation coming from every which way (conservation of momentum).
eachus
not rated yet Oct 09, 2015
Take the mass of a radio isotope which produces a neutrino upon decay.
Watch the decay.
Take the mass and kinetic energy of daughter particles.
Take the energy of any EM radiation released.

Whatever remains is likely the mass and kinetic energy of the neutrino.


It's been done. The neutrino that leaves carries energy with it. So look at cases where the neutrino carries very little energy. There should be a cutoff, which shows the neutrino mass/ Unfortunately, when you do that experimental error is much greater than the combined energy of the neutrinos. In other words, the experiment can't separate the neutrino mass from zero.

Actually what I said above is a bit misleading. None of the experiments involving neutrino mass actually look for mass, they look for momentum squared. IF (very big if) neutrinos have a negative momentum squared, they will have an imaginary mass. In other words they would be tachyons that cannot travel slower than the speed of light.
Returners
1.8 / 5 (5) Oct 09, 2015
Actually what I said above is a bit misleading. None of the experiments involving neutrino mass actually look for mass, they look for momentum squared. IF (very big if) neutrinos have a negative momentum squared, they will have an imaginary mass. In other words they would be tachyons that cannot travel slower than the speed of light.


Then maybe Neutrinos are imaginary.

Maybe they are "packets of uncertainty", the Uncertainty Principle and all, maybe we need a quantum unit of "uncertainty" to make the universe make sense.
docile
Oct 09, 2015
This comment has been removed by a moderator.
Hyperfuzzy
not rated yet Oct 09, 2015
nonsense
docile
Oct 09, 2015
This comment has been removed by a moderator.
Graeme
not rated yet Oct 09, 2015
Does the mass of the neutrino come from the weak force? If so it may be able to be calculated. After all the mass of the electron comes from the electromagnetic field around it. But can its mass be predicted from other physical constants?
Urgelt
1 / 5 (2) Oct 09, 2015
The article attributes quark masses to coupling with the Higgs Field.

However, most of mass of protons and neutrons doesn't come directly from quark masses. It comes from the gluons' binding energies. Einstein hasn't been banished entirely from subatomic particles; E=MC^2 still holds.

As a consequence, there are two terms for quark masses: with and without binding energies associated with the quarks. Only for one of those terms, quarks stripped of binding energies, does it make sense to attribute their masses to the Higgs Field. Stripped quarks are wee little guys, hardly any mass at all.

In other words, for visible matter, most of the mass comes from binding energies, not the Higg's mechanism. The article really should have said this, rather than declaring that quarks get their mass from the Higgs mechanism, which is only conditionally true and possibly misleading.
Urgelt
2 / 5 (4) Oct 09, 2015
Graeme wrote, "...the mass of the electron comes from the electromagnetic field around it."

No. Contemporary theory is that mass is produced by binding energies and by interaction of particles with the Higgs Field. The electron is thought to lack binding energies (it's a fundamental particle, indivisible). So it gets its mass from the Higgs mechanism.

The only direct evidence for electrons being elementary is our inability to break any with particle smashers. There are, of course, higher energies we can't plumb with accelerators. But if electrons possessed such enormous binding energies, then they should have much larger masses than they do. Theory predicts electrons can't be busted into component particles and binding energies.

"Does the mass of the neutrino come from the weak force?"

No. The neutrino is another elementary particle lacking binding energies, under current theory. The weak force operates in atoms, not neutrinos.
Urgelt
2.3 / 5 (3) Oct 09, 2015
But if it makes you feel any better, atoms were once regarded as indivisible and elementary. Now there's an entire zoo of subatomic particles to track.

So, who knows. We're still a long way from the end game in physics, and there are still surprises in store for us. Maybe electrons are not elementary, have enormous binding energies but somehow manage to avoid E=MC^2 to keep their masses down - some sort of reverse Higgs mechanism, perhaps. It doesn't seem likely, but then not long ago, oscillating neutrinos didn't seem likely, and there they are, by gosh.

We can play what-ifs all day long. But no evidence means we're just venting hot air for fun.
theon
1 / 5 (2) Oct 09, 2015
"We know that neutrinos do not make up the dark matter" only because we believe in linear structure formation. But we should be open minded. Many observations (like AGN and GRB structures at Gpc scales) fare better with nonlinear structure formation. From another angle, lensing by the cluster A1689 is explained well by neutrinos with mass between 1.5 and 2 eV, while NFW approaches suffer. The KATRIN experiment will settle the case, not LCDM.
Protoplasmix
3 / 5 (4) Oct 09, 2015
"Despite being millions of times smaller than other subatomic particles"
We do not have a value for the size of the neutrino.
We have values for their cross sections — http://cupp.oulu....oss.html
docile
Oct 10, 2015
This comment has been removed by a moderator.
swordsman
1 / 5 (2) Oct 10, 2015
"But as the neutrino has no charge..."

??????? How do they know this to be true, when they know so little about it and cannot measure it? It may have internal electrical charges.
docile
Oct 10, 2015
This comment has been removed by a moderator.
antialias_physorg
4.1 / 5 (9) Oct 10, 2015
"But as the neutrino has no charge..."

??????? How do they know this to be true, when they know so little about it and cannot measure it? It may have internal electrical charges.

Conservation of charge.
If the other products already account for all the charge - as they always do according to all experiments currently performed - then the neutrinos can't have one.
foolspoo
4.1 / 5 (9) Oct 10, 2015
Ren, life appears to be getting lonelier in your choice of existence.
jsdarkdestruction
4 / 5 (8) Oct 10, 2015
The sellers of false hopes.

What hopes? That we understand the universe more fully?
How is this a threat to your god and peoples belief in him?
antialias_physorg
4.6 / 5 (10) Oct 11, 2015
Are you sure that we understand universe more fully?

I'm not sure we understand the universe more fully - but I am 100% sure we understand the universe more fully than you do.
The basic profesional activity of modern physicists and astrophysicists is guesing

Educated guessing. You guess and then you check your guess against experiment. If experiment disagrees your guess is wrong (if experiment agrees then it isn't necessarily right - but its confidence value increases). It's that simple.

This is in contrast to religion where you just guess ("gods exist") and then leave it at that. The confidence value of such a guess is exactly zero (and it's unscientific to boot).

This task is technicaly impasible if you are undestanding me.

You need some basic introduction into statistical analysis. Because you couldn't be more wrong about...anything/everything.
jsdarkdestruction
4.3 / 5 (6) Oct 12, 2015
Ren,
1. Yes. Our understanding is increasing.
2. Guessing? How many scientific papers on physics and astrophysics have you read? Since you are so quick to dismiss these fields I assume you've read them all? (Sarcasm)
3. How many papers on neutrinos have you read?
4. What evidence do you have to disprove they exist?
5. Do you know why they were proposed and what experiments detected them?
6. It is near impossible to know everything in our universe at this point, yes. That doesn't mean we should just give up and stop trying to learn more.
7. Are you aware neutrinos are created in some radioactive processs?
8. We have much evidence and observations and are learning and collecting more all the time.
9. Didn't your god say we are supposed to try to understand and appreciate his creation?
10. I understand what you were trying to say. As you can tell by me picking apart your argument I don't agree with you and don't find your comments arguments have much merit.
my2cts
5 / 5 (2) Oct 12, 2015
"Despite being millions of times smaller than other subatomic particles"
We do not have a value for the size of the neutrino.

Take the mass of a radio isotope which produces a neutrino upon decay.
Watch the decay.
Take the mass and kinetic energy of daughter particles.
Take the energy of any EM radiation released.

Whatever remains is likely the mass and kinetic energy of the neutrino.

The mass of the neutrino would have been known since its discovery in 1956 if that would work.
my2cts
5 / 5 (5) Oct 12, 2015
How not existing elusive particles can solve anything? The searching for non existant objects has become a lucrative business.

Not as lucrative as the business of your non-existent god(s).
Neptune, wasn't it ?
my2cts
5 / 5 (6) Oct 12, 2015
The sellers of false hopes.

You mean false hopes like "eternal life", "resurrection", "divine intervention" ?
Tell us about it. You are the snake oil expert.
my2cts
5 / 5 (5) Oct 12, 2015

Then maybe Neutrinos are imaginary.

It was shown in 1956 that they are real.
Maybe the earth is flat ?
my2cts
5 / 5 (5) Oct 12, 2015
a useless speculative philosophy.

You are talking about your religion there.
jsdarkdestruction
5 / 5 (1) Oct 12, 2015
Answer my questions please ren. Monitoring science news sites all the time is much different than what I asked about.
jsdarkdestruction
5 / 5 (3) Oct 12, 2015
The chaos can not create order in which you beleive in fact. The increasing of order (information) in the system can be done only by intelligent being intervention. There is no other way. So the order in the universe is cretated by God who have control over the fundamental forces of nature inside and outside of our physical reality.

Ok. Sure. Let's for argument sake assume that's true. Where does that dispute neutrinos existing? Don't you think you are selling your gods creation short because of your own lack of understanding? Show the scientific arguments are wrong.
JustAnotherGuy
4.3 / 5 (6) Oct 12, 2015
The chaos can not create order in which you beleive in fact. The increasing of order (information) in the system can be done only by intelligent being intervention. There is no other way. So the order in the universe is cretated by God who have control over the fundamental forces of nature inside and outside of our physical reality. - @Ren82

This is a mere reasoning. An attempt to interpret facts by deduction (sort of) without intervention of research, evidence and data: philosophy (sort of). Your philosophy. Aren't you against this approach to reality?
Where is the science you used to probe any of this? Current scientists are closer to do that, than you. Learn.
RayInLv
not rated yet Oct 12, 2015
As anything with mass moves at speeds closer to the speed of light the mass is supposed to get larger until speed can not increase because the mass approaches infinity. How can neutrinos have mass and travel at the speed of light?
antialias_physorg
5 / 5 (2) Oct 13, 2015
How can neutrinos have mass and travel at the speed of light?

Read the article. They don't

While travelling through space, a neutrino apparently continuously flips between different "types" of neutrino, changing the way they interact with matter. This is called neutrino oscillations. You might imagine this as a little fellow that, while running at nearly the speed of light,...

Note the 'nearly'.

jane_ezernack
2.6 / 5 (5) Oct 13, 2015
I know this will annoy some people but why is the world studying subatomic particles when there are children starving around the world why don't we deal with what is in front of use before heading into the unknown
Urgelt
1 / 5 (1) Oct 13, 2015
Jane: it does not shock me that there are people like you who cannot see the big picture.

It does shock me that there are people like you who worry about starving children but not starving adults. That is a seriously twisted point of view from which to consider the world.

I can't force you to value adult humans who suffer. But I can try to open your eyes to the big picture.

Science underpins our technological civilization. Understanding nature has enabled us to feed billions more people at once than we ever could have managed without that understanding.

There is still a shortfall between food production and distribution and people's welfare. Mainly, that's because we can't curb our appetite for reproduction, but it's also due to imperfections in our understanding of nature and ourselves and to political priorities driven by people who empathize with suffering children, but not suffering adults - or who empathize with no-one but people in their own in-groups.
Urgelt
1 / 5 (1) Oct 13, 2015
Our understanding of subatomic physics is far from complete. But what we've learned in the last century plus has directly led to the rise of the information age. That advance hasn't stopped because science is still finding answers which - many of them - turn out to be useful to advancing technology.

If there is any hope at all of avoiding a Malthusian die-back in response to overpopulation, it's advancing technology. Success in science translates directly into better chances for our descendants.

That is the answer to your larger question. I can't help you find reasons to give a damn about children after they've matured into adults. For that, you're on your own.
antialias_physorg
4 / 5 (4) Oct 14, 2015
I know this will annoy some people but why is the world studying subatomic particles when there are children starving around the world

Why in the world are you sitting at a keyboard typing when you could be out there doing something against children starving in the world?

When you answer yourself this then you have answered your earlier question, too.

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