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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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?
ripper234's user avatar
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90 votes
14 answers
10k views

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 ...
Sklivvz's user avatar
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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
73 votes
2 answers
4k views

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
26 votes
1 answer
2k views

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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21 votes
5 answers
5k views

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
22 votes
2 answers
3k views

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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20 votes
3 answers
3k views

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
8k views

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
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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14 votes
1 answer
554 views

How are neutrino beams emitted at CERN?

As far I know they come from accelerator collisions, but I have read confusing things like magnetically focused. How could neutrinos be guided magnetically if they aren't affected by the ...
HDE's user avatar
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20 votes
3 answers
5k views

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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12 votes
4 answers
5k views

Neutrino annihilation and bosons

Would it be theoretically possible for a high energy neutrino and another high energy anti-neutrino to annihilate into a boson? Which boson(s) would be possible theoretically? one or more photons? ...
Gerard's user avatar
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7 votes
2 answers
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"Dear radioactive ladies and gentlemen" - Letter by Wolfgang Pauli

In 1930, Wolfgang Pauli wrote a letter to Lise Meitner for a convention in Tübingen, considering the problem of beta decay. Does anybody know, where to find the original letter online ?
mate64's user avatar
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27 votes
1 answer
525 views

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
27 votes
2 answers
6k views

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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22 votes
2 answers
1k views

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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3 votes
3 answers
797 views

Neutron decay and electron anti neutrino $n\to p + e + \bar{\nu}_e$

Why do we need neutrino to explain neutron decay? Is there any evidence regarding existence neutrinos in the context of $n\to p + e + \bar{\nu}_e$?
neutrino's user avatar
2 votes
2 answers
335 views

Alternatives to the neutrino in the beta spectrum?

It is well known that the neutrino appeared to explain the power distribution in the beta decay spectrum. (see PSE) What other explanations candidates were available? It is stated that the ...
Helder Velez's user avatar
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1 vote
1 answer
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Measurement of Solar and other neutrino Mixing angles

According to the neutrino flavour oscillation formula $$ P_{\alpha\beta}=4\sum\limits_{i<j}U_{\alpha i}U_{\beta i}^*U_{\alpha j}U_{\beta j}^* \sin^2\frac{(m_i^2-m_j^2)L}{4E}.$$ Hence, there can be ...
SRS's user avatar
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116 votes
4 answers
16k views

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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18 votes
4 answers
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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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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
14 votes
3 answers
685 views

Strange modulation of radioactive decay rates with solar activity

Recently I found out this strange article about nuclear decay rates somehow showing seasonal variations with a high correlation with sun activity. Has this been experimentally confirmed/disproved? An ...
lurscher's user avatar
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6 votes
2 answers
303 views

Cosmic rays and neutrinos

I'm reading Gaggero's Cosmic Ray Diffusion in the Galaxy and Diffuse Gamma Emission and he makes the claim, ...the definitive proof of [Cosmic Ray proton acceleration in supernova remnants] would ...
Kyle Kanos's user avatar
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28 votes
2 answers
24k views

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?
Yashbhatt's user avatar
  • 1,804
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 ...
Slaviks's user avatar
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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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9 votes
2 answers
8k views

What is difference between the different 'flavours' of neutrinos?

Moreover, how-come scientist know that muon-neutrino are different from electron-neutrino when they didn't even know what the difference was? Did they interact differently with other particles?
UpandUp's user avatar
  • 91
5 votes
1 answer
5k views

Neutrinos arrived before the photons (supernova)

A while back I read about the super Kamiokande detector detected a large neutrino flux and then several hours later a supernova was seen. Anyone know of this with sources? I don't recall the source at ...
Physics_maths's user avatar
4 votes
6 answers
788 views

When has the speed of light been measured, recently?

Yes, it is weird, absurd, but I can't stop thinking that the would-be superluminal neutrino speed has been computed by an arithmetic operation (space/time) and not by direct comparison with a ...
user6090's user avatar
  • 1,436
3 votes
1 answer
337 views

What distinguishes the behaviour of particle from its antiparticle: C violation or CP violation?

It is said that a CP violation would mean that the behaviour of the particle is different from the behaviour of antiparticle. Why is C violation not good/enough?
SRS's user avatar
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2 votes
1 answer
241 views

How to observe neutrinos?

I know that neutrinos are the weakly interacting particles[possibly zero mass] that can pass through matter without any effect which makes them very difficult to detect. But I have heard that they ...
user avatar
2 votes
3 answers
673 views

If it turns out that neutrinos do travel at faster than lightspeed, how will the success of special relativity be explained?

As per in the title. If it turns out that neutrinos do travel faster than the speed of light, how will the success of special relativity be explained? My apologies if this has been asked before; I've ...
Charmed Quark's user avatar
2 votes
2 answers
2k views

The magnetic moment of a particle (and a neutrino)

Is the magnetic moment of a particle an intrinsic property or is there a formula to find it? What is its source? Is there a formula or a general explanation that can account for the $\mu$ of known ...
user avatar
1 vote
4 answers
8k views

$\beta^-$ decay: expression for maximum electron energy

I'm having some trouble finding an expression for the maximum electron energy in $\beta^-$ decay. In the frame where the neutron is initially at rest, conservation of momentum reads: $$\vec{p}_p+\vec{...
user76386'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 ...
user avatar
36 votes
1 answer
3k views

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
  • 1,373
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
1 answer
2k views

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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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
  • 171
17 votes
3 answers
3k views

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
16 votes
1 answer
582 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
  • 3,905
14 votes
1 answer
1k views

The delay between neutrinos and gammas in a supernova, and the absolute mass scale of neutrinos

In a supernova explosion (of some type), there is a huge amount of neutrinos and gamma rays produced by a runaway nuclear reaction at the stellar core. In a recent comment, dmckee noted that the ...
Emilio Pisanty's user avatar
12 votes
2 answers
888 views

If we could build a telescope to view the cosmic neutrino background, what would we see?

If we could build a neutrino telescope capable of viewing relic neutrinos that decoupled after the big bang, with a similar angular and spectral resolution that is possible now for the CMB (e.g. with ...
ProfRob's user avatar
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11 votes
2 answers
8k views

What are mass eigenstates?

According to Wikipedia Neutrino oscillation arises from a mixture between the flavor and mass eigenstates of neutrinos. That is, the three neutrino states that interact with the charged leptons in ...
Virender Ranga's user avatar
10 votes
2 answers
511 views

If neutrinos are disfavoured as DM candidates why aren't axions?

Numerical simulations of observed large-scale structure formation work best with Cold Dark Matter (CDM; see the answer here). Neutrinos are candidates for Hot Dark Matter (HDM), and hence they cannot ...
SRS's user avatar
  • 26.4k
10 votes
1 answer
338 views

Seeing beyond the CMBR with neutrinos?

As I understand it, you can't see beyond the Cosmic Microwave Background Radiation because the plasma of the early universe was opaque to electromagnetic radiation. What if you had a "neutrino ...
John's user avatar
  • 2,808
9 votes
3 answers
2k views

Does the Standard Model require neutrinos to be massless?

I am an undergraduate student in Physics, I have a basic understanding of Particle Physics and Quantum Mechanics but none whatsoever of Quantum Field Theory. I know that Neutrino mixing requires ...
SuperCiocia's user avatar
  • 24.7k
8 votes
4 answers
6k views

How do neutrinos pass through the sun so quickly?

If it takes thousands of years for light to escape our sun then how can neutrinos generated in the very center of the sun reach earth in just 8 minutes? Why is their speed so great that they can ...
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