Questions tagged [neutrinos]

Neutrinos are light, uncharged leptons. The neutrino tag should be applied to question relating to neutrino properties or interactions involving neutrinos.

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Why do electrons, according to my textbook, exist forever?

Does that mean that electrons are infinitely stable? The neutrinos of the three leptons are also listed as having a mean lifespan of infinity.
HyperLuminal's user avatar
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Superluminal neutrinos

I was quite surprised to read this all over the news today: Elusive, nearly massive subatomic particles called neutrinos appear to travel just faster than light, a team of physicists in Europe ...
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Where are all the slow neutrinos?

The conventional way physicists describe neutrinos is that they have a very small amount of mass which entails they are traveling close to the speed of light. Here's a Wikipedia quote which is also ...
Physics Footnotes's user avatar
56 votes
2 answers
6k views

Neutrinos vs. Photons: Who wins the race across the galaxy?

Inspired by the wording of this answer, a thought occurred to me. If a photon and a neutrino were to race along a significant stretch of our actual galaxy, which would win the race? Now, neutrinos ...
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4 answers
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How do we know Dark Matter isn't simply Neutrinos?

What evidence is there that dark matter isn't one of the known types of neutrinos? If it were, how would this be measurable?
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What is the evidence for 'billions of neutrinos pass through your body every second'?

This statement is repeated so often that it has become somewhat of a cliche: 'billions of neutrinos pass through your body every second'. For example see 1, 2, 3, 4, 5, 6. What is the evidence for it,...
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Why do the neutrinos (with mass) from a supernova arrive before the light (no mass)?

I've already read the below questions (and their answers) regarding neutrinos vs. electromagnetic waves propagating through space, but I'm still not clear on something. Neutrinos arrived before the ...
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38 votes
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Are neutrino stars theoretically possible?

Since neutrinos have a small mass and are affected by gravity, wouldn't it be theoretically possible to have such a large quantity of them so close to each other, that they would form a kind of a ...
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Why was the first discovered neutrino an anti-neutrino?

In the search for neutrinos, Cowan and Reines discovered the electron anti-neutrino and named it as such. Why is the particle they discovered the anti-variety? The reason we call electrons 'electrons'...
Joshua's user avatar
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34 votes
4 answers
486 views

Models of neutrinos consistent with OPERA's results

I guess by now most people have heard about the new paper (arXiv:1109.4897) by the OPERA collaboration which claims to have observed superluminal neutrinos with 6$\sigma$ significance. Obviously this ...
Joe Fitzsimons's user avatar
31 votes
5 answers
3k views

Why do or don't neutrinos have antiparticles?

This was inspired by this question. According to Wikipedia, a Majorana neutrino must be its own antiparticle, while a Dirac neutrino cannot be its own antiparticle. Why is this true?
Peter Shor 's user avatar
29 votes
3 answers
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What does the cosmic neutrino background look like today, given that neutrinos possess mass?

This question is inspired by (or a follow-up to) the threads Where are all the slow neutrinos? and Is it possible that all “spontaneous nuclear decay” is actually “slow neutrino” induced? The cosmic ...
Jeppe Stig Nielsen's user avatar
28 votes
2 answers
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What exactly is an anti-neutrino?

According to the the definition of anti-particles, they are particles with same mass but opposite charge. Neutrinos by definition have no charge. So, how can it have an anti-particle?
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3 answers
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Can neutrinos "hit" electrons?

I understand that particles interact via the fundamentals forces of nature. For example photons interact with matter because they carry the change in the electromagnetic field. Neutrinos, on the other ...
user's user avatar
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27 votes
2 answers
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What exactly do we see on the famous neutrino image of the sun?

An answer to the question If we could build a neutrino telescope, what would we see? contains a link to a neutrino image of the sun by the Super-Kamiokande neutrino detector. There it says that the ...
doetoe's user avatar
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The transit of Venus and solar neutrino rates

The following question was posed at the end of Maury Goodman's June 2012 long-baseline neutrino newsletter. During the Venus transit of the sun, were more solar neutrinos absorbed in Venus, or ...
dmckee --- ex-moderator kitten's user avatar
26 votes
4 answers
8k views

Are neutrinos Majorana particles?

That is, are they identical to their anti-particles? (Any results of double beta decay experiments?)
Gordon 's user avatar
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26 votes
1 answer
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Neutrino Oscillations and Conservation of Momentum

I would like to better understand how neutrino oscillations are consistent with conservation of momentum because I'm encountering some conceptual difficulties when thinking about it. I do have a ...
armin's user avatar
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22 votes
2 answers
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Can neutrino detectors tell what direction the neutrinos came from?

I was reading this question and got to thinking. Can neutrino detectors give us any clue where the neutrinos came from or when a supernova may occur?
Dale's user avatar
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2 answers
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Why are neutrinos ruled out as a major (or even sole) component of dark matter?

A number of times I have encountered in text-books and articles that neutrinos might contribute only a small fraction to dark matter. The reason has to do with the fact that if all of the dark matter ...
ThisGuy's user avatar
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21 votes
6 answers
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Why was the neutrino thought to be massless?

Wolfgang Pauli once said (regarding the neutrino): I have done a terrible thing. I have postulated a particle that cannot be detected. Why did he figure it couldn't be detected? Was this because he ...
David Callanan's user avatar
21 votes
3 answers
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Should Beta Minus decay put an upper limit on the mass of a neutrino?

Beta minus decay emits an electron with a range of energies. Within the nucleus, the following is happening: $n\rightarrow p+e^-+\bar{v}_e$. For this reaction to be possible, by lepton number ...
Noah P's user avatar
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Why does matter/antimatter only produce gamma rays?

According to wikipedia, all antimatter annihilation produces gamma rays (along with potentially other elements). Why specifically Gamma rays? Why not electromagnetic waves of other wavelength?
Charles Shiller's user avatar
21 votes
2 answers
2k views

Could Hawking radiation have a lot of neutrinos and dark matter?

Up till now I have thought that Hawking radiation would be mostly photons, since the temperatures are typically small. However, a comment on another question (thanks to John Doty) suggested that we ...
Andrew Steane's user avatar
21 votes
5 answers
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What would be the effects on theoretical physics if neutrinos go faster than light?

Earlier today, I saw this link on Facebook about neutrinos going faster than the speed of light, and of course, re-posted. Since then, a couple of my friends have gotten into a discussion about what ...
El'endia Starman's user avatar
21 votes
2 answers
4k views

Neutrino oscillations versus CKM quark mixing

I wish to describe in simple but correct terms the analogy between the Cabibbo–Kobayashi–Maskawa (CKM) and Pontecorvo–Maki–Nakagawa–Sakata (PMNS) matrices. The CKM matrix describes the rotation ...
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What is chirality?

I actually wanted to make the title as "What is the difference between chirality and helicity"? But I didn't do that because I don't understand properly what chirality is. I have gone through this ...
user22180's user avatar
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21 votes
1 answer
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What happened to the idea of tachyonic or other superluminal neutrinos?

While hunting around for information about the recent OPERA measurement that hints at superluminal neutrinos, I discovered that this idea was actually considered back in the 1980s. Wikipedia lists as ...
David Z's user avatar
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20 votes
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Why do neutrino oscillations imply nonzero neutrino masses?

Neutrinos can pass from one family to another (that is, change in flavor) in a process known as neutrino oscillation. The oscillation between the different families occurs randomly, and the likelihood ...
jormansandoval's user avatar
20 votes
2 answers
6k views

Sun light takes 1,000/30,000/100,000/170,000/1,000,000 years bouncing around inside to then reach the Earth

When light (photon particle) is generated inside the Sun, it takes a long time to bounce around inside to later escape and travel outwards. Neutrinos escape immediately. The numbers for the years ...
Prem's user avatar
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2 answers
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How can neutrinos be solely left-handed if they have mass?

Helicity: projection of spin onto motion. Since neutrinos are massive, I can always move to a reference frame where their motion is towards the opposite direction, meaning I should reverse their ...
TrentKent6's user avatar
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3 answers
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A thought experiment about neutrinos

I don't understand all the details of Dirac mass, Majorana mass, and many other "deep" notions. I have in mind a very simple thought experiment. Because of neutrino oscillations we know ...
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Do neutrinos not couple to the Higgs field?

I was reading the CernCourier, my favorite source of message on Higgs and friends. I was rather shocked, when I saw this: "The mechanism by which neutrino mass is generated is not known." What? ...
draks ...'s user avatar
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3 answers
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How can neutrinos oscillate though the lepton flavors have differing masses?

Since the total mass-energy for the neutrino presumably does not change when a neutrino changes lepton flavor, though the mass is different, what compensates for the gain or loss of mass? Does the ...
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20 votes
3 answers
3k views

Why do people say that neutrinos are either Dirac or Majorana fermions?

The question of whether a given particle "is" a Dirac or Majorana fermion is more subtle than is sometimes presented. For example, if we just consider the "old" Standard Model with massless neutrinos, ...
tparker's user avatar
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19 votes
1 answer
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Physics behind this neutrino-related joke

In the comment section of a newspaper article reporting on the 2015 Nobel Prize for Physics, which was awarded for work on neutrino oscillation, I found the following joke: "I'm sorry, we do not ...
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18 votes
4 answers
6k views

Neutrinos passing through black hole

I have read this: https://en.wikipedia.org/wiki/Neutrino The weak force has a very short range, gravity is extremely weak on the subatomic scale, and neutrinos, as leptons, do not participate in ...
Árpád Szendrei's user avatar
18 votes
6 answers
1k views

Speed of neutrinos

Everyone knows it is close to $c$, but how close? What are the recent results?
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18 votes
4 answers
3k views

Why are neutrino oscillations considered to be "beyond the Standard Model"?

Is this just a historical artifact - that the particle physics community decided at some point to call all of the pre-oscillation physics by the name the "Standard Model"? The reason I ask is because ...
dbrane's user avatar
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18 votes
3 answers
3k views

Why, precisely, is argon used in neutrino experiments?

Why is argon used in neutrino detectors? Other than liquid argon being denser than water or oil, what are its advantages?
Kurt Hikes's user avatar
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18 votes
2 answers
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Do neutrinos travel faster than light in air?

I read in wiki that the speed of light is 88km/s slower in air than it is in a vacuum. Do neutrinos travel faster than light in air?
Jitter's user avatar
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17 votes
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Why are neutrinos more weakly interacting than light?

When people describe neutrino interactions they describe them as rare/infrequent due to the fact that the neutrinos are electrically neutral and have little mass, if any. Well why then is the photon ...
Display Name's user avatar
17 votes
2 answers
3k views

Why do neutrinos propagate in a mass eigenstate?

I am aware that flavor $\neq$ mass eigenstate, which is how mixing happens, but whenever someone talks about neutrino oscillations they tend to state without motivation that when neutrinos are ...
wczwe's user avatar
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16 votes
3 answers
3k views

Mass of All the Neutrinos

I have read that the Sun produces $2 \times 10^{38}$ Neutrinos per second weighing in at approximately 8 MeV. I have 2 questions. Is there any way to calculate how many neutrinos have been produced ...
Rick's user avatar
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16 votes
1 answer
581 views

Where do high-energy neutrinos come from?

Last week the IceCube South Pole Neutrino Observatory published a press release reporting the possible discovery of two neutrinos with energies of over 1 PeV. Would anyone here be willing to help me ...
Mark Rovetta's user avatar
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16 votes
1 answer
505 views

Do primordial background neutrinos orbit in dark matter halos?

According to Wikipedia, neutrinos separated from other matter seconds after the Big Bang and formed a separate background radiation field which now fills space at a temperature ~2 K. Supposing ...
Blackbody Blacklight's user avatar
15 votes
3 answers
5k views

Why do Neutrinos pass through us but photons can't pass through us? [duplicate]

Neutrinos have no mass and no charge. Therefore, they are not deflected by the other particles in our body and pass through us. Photons too have no mass and no charge, but why are they being deflected ...
Darth Ewok's user avatar
15 votes
2 answers
3k views

If the mass of neutrino is not zero, why we cannot find right-handed neutrinos and left-handed anti-neutrinos?

I am learning P&S's Introduction of quantum field theory. My teacher said that if the mass of neutrino is exactly 0, then we should not observe any right-handed neutrinos and left-handed anti-...
ZHANG Juenjie 's user avatar
15 votes
1 answer
2k views

Do electrons oscillate into muons just like electron-neutrinos into muon-neutrinos?

And if not, why? What is the difference to neutrinos oscillations?
Tim's user avatar
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14 votes
3 answers
3k views

Why do we not know whether or not neutrinos are their own antiparticles?

Plan an experiment as follows: A neutrino source provides only neutrinos, and a detector is sensitive only to antineutrinos. If you get a signal, that proves that neutrinos are their own antiparticles....
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