Neutrinos

[The Code]

I found this fascinating...

Astrophysicists have predicted that a supernova explosion would produce a sharp pulse of neutrinos, the elusive uncharged particles that move at or near the speed of light. Neutrinos interact with matter hardly at all and are therefore extremely difficult to detect. In 1987 two big detectors were up and running, part of the field of experimental neutrino physics, and they observed neutrinos from supernova 1987A.

Neutrinos carry nearly all of the energy of a supernova explosion. After the explosion of 1987A, the two detectors observed an increase of 19 neutrino counts, the first ever observation of neutrinos produced by a supernova. Moreover, the neutrinos arrived in a pulse about three hours before the visible light from the supernova, just as astrophysicists had predicted.

TC: The fact that Neutrinos Hardly interact with matter and left the star, at the time the Explosion was moving outwards from within... And they saw this three hours before they saw the Super Nova's light... Just Inspires me to say... Just what else can't we see ?

http://www.physicscentral.com/explore/a ... utrino.cfm

[Chris Peterson]

TC: The fact that Neutrinos Hardly interact with matter and left the star, at the time the Explosion was moving outwards from within... And they saw this three hours before they saw the Super Nova's light... Just Inspires me to say... Just what else can't we see ?

Depends what you mean by "see". In this case, I think we're talking about not seeing by EM radiation, because we do "see" neutrinos by other means. The obvious answer to your question is dark matter, which is probably made up of particles similar to neutrinos in many respects. We can't see dark matter by EM radiation, but we can see it in other ways (by its gravitational effects).

[Beyond]

So how come the neutrinos got here 3-hours faster than the visible light?

[The Code]

Because They can pass through matter.... and photons can't...

[Chris Peterson]

So how come the neutrinos got here 3-hours faster than the visible light?

They don't get here faster than light. They are emitted very early in the core collapse (before the major release of photons), and I think that there is a delay in release of photons because the initial dense expanding cloud absorbs most of them. If we were looking in exactly the right spot, we might see some increase in the light nearly coincident with the neutrino pulse, but it takes a few hours after the supernova for the major light burst to be seen.

[The Code]

So how come the neutrinos got here 3-hours faster than the visible light?

They don't get here faster than light. They are emitted very early in the core collapse (before the major release of photons), and I think that there is a delay in release of photons because the initial dense expanding cloud absorbs most of them.

Now There's A Thought ! Dark Matter ?

[Ann]

So how come the neutrinos got here 3-hours faster than the visible light?

They don't get here faster than light. They are emitted very early in the core collapse (before the major release of photons), and I think that there is a delay in release of photons because the initial dense expanding cloud absorbs most of them. If we were looking in exactly the right spot, we might see some increase in the light nearly coincident with the neutrino pulse, but it takes a few hours after the supernova for the major light burst to be seen.

Chris, I thought that light might move "slower than light" due to "obstacles" (for example, when light is moving through a medium like liquid water), even though it isn't possible for light to move "faster than light".

Isn't it possible for light to be very slightly slowed by, say, dense matter right next to the supernova, whereas neutrinos aren't slowed down by matter? (Yes, individual neutrinos might possibly be slowed down - I think - but it is so extremely rare for a neutrino to hit, say, an atom, that for all intents and purposes, neutrinos in general aren't slowed down by matter.)

Ann

[The Code]

So how come the neutrinos got here 3-hours faster than the visible light?

They don't get here faster than light. They are emitted very early in the core collapse (before the major release of photons), and I think that there is a delay in release of photons because the initial dense expanding cloud absorbs most of them. If we were looking in exactly the right spot, we might see some increase in the light nearly coincident with the neutrino pulse, but it takes a few hours after the supernova for the major light burst to be seen.

Chris, I thought that light might move "slower than light" due to "obstacles" (for example, when light is moving through a medium like liquid water), even though it isn't possible for light to move "faster than light".
Ann

Neutrinos Can Pass through A Light year of solid steal without their speed being impeded... Which is why we saw them three hours before the Super Nova's Photons...

[geckzilla]

Neutrinos Can Pass through A Light year of solid steal without their speed being impeded... Which is why we saw them three hours before the Super Nova's Photons...

And yet they managed to hit a detector here on Earth significantly smaller than a light year. You have never made much sense and I don't think you ever will.

[The Code]

And yet they managed to hit a detector here on Earth significantly smaller than a light year. You have never made much sense and I don't think you ever will.

19 of them... out of several trillions.... look it up !

[geckzilla]

Look what up? That doesn't sound to me like an equivalent argument to a neutrino passing through an entire light year of steel. In conclusion, you still make no sense and the stupid things you constantly try to vaguely infer here are tired and boring. Just go away.

[Chris Peterson]

Neutrinos Can Pass through A Light year of solid steal without their speed being impeded... Which is why we saw them three hours before the Super Nova's Photons...

No, we saw them first because they were produced first. The neutrino pulse is produced in the first seconds; the photon intensity rises over several hours.

Neither neutrinos nor photons have their velocity significantly altered by any of the mediums they pass through. It's a question of absorption. Certainly, fewer neutrinos are absorbed than photons during the first phases of a core collapse supernova. But many neutrinos are absorbed, which is the energy transfer mechanism that actually drives the explosion.

[The Code]

Look what up? That doesn't sound to me like an equivalent argument to a neutrino passing through an entire light year of steel. In conclusion, you still make no sense and the stupid things you constantly try to vaguely infer here are tired and boring. Just go away.

Ok And I will leave you with this... Just to show everybody who has NO ClUE about this subject !

https://www.youtube.com/watch?v=yfUBkkuxoF0

BYE !

[geckzilla]

Yeah, neutrinos are confusing and hard to understand. It's even harder when you come along to make them even more confusing with an extra layer of vagueness and insinuation about alternative theories.

[The Code]

Yeah, neutrinos are confusing and hard to understand. It's even harder when you come along to make them even more confusing with an extra layer of vagueness and insinuation about alternative theories.

The Universe is Mind blowing mate.. You need all your tools in the box to understand it and Many tools out of the box...

[Qev]

Neutrinos Can Pass through A Light year of solid steal without their speed being impeded... Which is why we saw them three hours before the Super Nova's Photons...

And yet they managed to hit a detector here on Earth significantly smaller than a light year. You have never made much sense and I don't think you ever will.

The Code is basically referring to the fact that neutrinos have a very long "mean free path"; ie. a typical neutrino will travel a huge distance, even through very dense materials, without interacting with even a single particle of that material. Usually I hear it quoted as "passing through a light-year of solid lead without interacting".

That isn't to say that no neutrinos will interact over that distance, or even shorter ones (like the relatively tiny detectors here on Earth); only that the vast majority of them will not. A supernova produces truly stupendous quantities of neutrinos. Going by the information about SN1987A on Wikipedia, around three hundred trillion neutrinos from the supernova passed through each square meter of Earth's disc... and we detected a total of 24 of them.

They're elusive little devils.

[geckzilla]

And very interesting, too, unless they are wrapped in various, vague allusions that the mainstream is totally wrong. Do you really think that they could pass through a light year of solid lead without interacting or is that hyperbole? A light year is significantly longer than an Earth width.

[Chris Peterson]

And very interesting, too, unless they are wrapped in various, vague allusions that the mainstream is totally wrong. Do you really think that they could pass through a light year of solid lead without interacting or is that hyperbole? A light year is significantly longer than an Earth width.

Just a quick back-of-the-envelope calculation looking at the neutrino cross section suggests that a neutrino has a 50% chance of interacting with a nucleus for every 10 light years it travels through a solid medium (I don't think the nature of the medium matters all that much). So I think the assessment that most of a neutrino source will pass unaffected through a light year of lead is accurate.

[neufer]

And very interesting, too, unless they are wrapped in various, vague allusions that the mainstream is totally wrong. Do you really think that they could pass through a light year of solid lead without interacting or is that hyperbole? A light year is significantly longer than an Earth width.

Just a quick back-of-the-envelope calculation looking at the neutrino cross section suggests that a neutrino has a 50% chance of interacting with a nucleus for every 10 light years it travels through a solid medium (I don't think the nature of the medium matters all that much). So I think the assessment that most of a neutrino source will pass unaffected through a light year of lead is accurate.

[url=http://hyperphysics.phy-astr.gsu.edu/hbase/particles/neutrino3.html][size=150]neutrino interaction cross section[/size][/url]

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The neutrino mean free path ~ a light year of solid lead
(corresponding to a neutrino interaction cross section ~ 10^-47 m² )
is, indeed, somewhat misleading:

The mean free path of very low energy (i.e., beta decay type) neutrinos
(cross section ~ 10^-47 m² ) is, in fact, ~1.6 light years (~100,000 AU) of lead.

The mean free path of 15 Gev neutrinos (cross section ~ 10^-41 m²) is ~ 0.1 AU of lead.

The mean free path of PeV neutrinos is only ~ 250 km of lead (~ 2800 km of water)
and hence struggle even to make it through the Earth

[BDanielMayfield]

And very interesting, too, unless they are wrapped in various, vague allusions that the mainstream is totally wrong. Do you really think that they could pass through a light year of solid lead without interacting or is that hyperbole? A light year is significantly longer than an Earth width.

Just a quick back-of-the-envelope calculation looking at the neutrino cross section suggests that a neutrino has a 50% chance of interacting with a nucleus for every 10 light years it travels through a solid medium (I don't think the nature of the medium matters all that much). So I think the assessment that most of a neutrino source will pass unaffected through a light year of lead is accurate.

[url=http://hyperphysics.phy-astr.gsu.edu/hbase/particles/neutrino3.html][size=150]neutrino interaction cross section[/size][/url]

---

The neutrino mean free path ~ a light year of solid lead
(corresponding to a neutrino interaction cross section ~ 10^-47 m² )
is, indeed, somewhat misleading:

The mean free path of very low energy (i.e., beta decay type) neutrinos
(cross section ~ 10^-47 m² ) is, in fact, ~1.6 light years (~100,000 AU) of lead.

The mean free path of 15 Gev neutrinos (cross section ~ 10^-41 m²) is ~ 0.1 AU of lead.

The mean free path of PeV neutrinos is only ~ 250 km of lead (~ 2800 km of water)
and hence struggle even to make it through the Earth

So the more energetic a neutrino, the shorter it's mean free path? That seems counter-intuitive. Why would that be the case?

[Chris Peterson]

So the more energetic a neutrino, the shorter it's mean free path? That seems counter-intuitive. Why would that be the case?

Because as it gets more energetic, its interaction cross section gets larger. It's as if the particle gets bigger. It should be somewhat intuitive that a more energetic particle has a larger zone of interaction.

[BDanielMayfield]

So the more energetic a neutrino, the shorter it's mean free path? That seems counter-intuitive. Why would that be the case?

Because as it gets more energetic, its interaction cross section gets larger. It's as if the particle gets bigger. It should be somewhat intuitive that a more energetic particle has a larger zone of interaction.

Ok. I was thinking that a more energetic particle would zip through stuff easier, but remembering the wavelike nature of sub-atomic particles I'm picturing a more energetic neutrino with an increased vibrational amplitude, thereby increasing the likelihood of interaction.

For those having trouble with the notion of neutrinos being able to pass through so much solid material it's important to realize how much empty space is inside ordinary atoms. I read recently that if you scaled an atom up to the size of a fourteen story building the nucleus would be the size of a grain of sand located on the seventh floor.

Bruce

[neufer]

I was thinking that a more energetic particle would zip through stuff easier, but remembering the wavelike nature of sub-atomic particles I'm picturing a more energetic neutrino with an increased vibrational amplitude, thereby increasing the likelihood of interaction.

Think of a bull in a china shop.

For those having trouble with the notion of neutrinos being able to pass through so much solid material it's important to realize how much empty space is inside ordinary atoms. I read recently that if you scaled an atom up to the size of a fourteen story building the nucleus would be the size of a grain of sand located on the seventh floor.

It's important here to realize how much empty space is inside ordinary protons & neutrons (i.e., the china shops).

Neutrino interactions are mostly with the individual point particles: quarks (i.e., the demitasse cups):

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Fundamental Physics at the Intensity Frontier - Hewett, J.L. et al. arXiv:1205.2671 [hep-ex] ANL-HEP-TR-12-25, SLAC-R-991, FERMILAB-CONF-12-879-PPD

Existing muon neutrino charged-current cross section measurements as a function of neutrino energy. The contributing processes in this energy region include quasi-elastic (QE) scattering, resonance production (RES), and deep inelastic scattering (DIS). The error bars in the intermediate energy range reflect the uncertainties in these cross sections (typically 10−40%, depending on the channel).

Low energy (< 0.003 GeV = 3 MeV ~ up/dn quark mass) neutrinos are virtually undetectable.

Neutrinos detected from SN1987A ranged in energy from 6 to 39 MeV.

[BDanielMayfield]

Think of a bull in a china shop.

It's important here to realize how much empty space is inside ordinary protons & neutrons (i.e., the china shops).

Neutrino interactions are mostly with the individual point particles: quarks (i.e., the demitasse cups):

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Fundamental Physics at the Intensity Frontier - Hewett, J.L. et al. arXiv:1205.2671 [hep-ex] ANL-HEP-TR-12-25, SLAC-R-991, FERMILAB-CONF-12-879-PPD

Existing muon neutrino charged-current cross section measurements as a function of neutrino energy. The contributing processes in this energy region include quasi-elastic (QE) scattering, resonance production (RES), and deep inelastic scattering (DIS). The error bars in the intermediate energy range reflect the uncertainties in these cross sections (typically 10−40%, depending on the channel).

Low energy (< 0.003 GeV = 3 MeV ~ up/dn quark mass) neutrinos are virtually undetectable.

Neutrinos detected from SN1987A ranged in energy from 6 to 39 MeV.

Thanks. That is, I believe, not a lot of bull. I can't detect even a quanta of b.c.

To put it in more understandable terms though, how much smaller are quarks than protons and neutrons?

[neufer]

To put it in more understandable terms though, how much smaller are quarks than protons and neutrons?

[b][color=#0000FF][size=150]Presumed elementary (point/string?) particles[/size][/color][/b]

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<<An elementary particle or fundamental particle is a particle whose substructure is unknown, thus it is unknown whether it is composed of other particles. Known elementary particles include the fundamental fermions (quarks, leptons, antiquarks, and antileptons), which generally are "matter particles" and "antimatter particles", as well as the fundamental bosons (gauge bosons and Higgs boson), which generally are "force particles" that mediate interactions among fermions. A particle containing two or more elementary particles is a composite particle.

When probed at energies available in experiments, particles exhibit spherical sizes. In operating particle physics' Standard Model, elementary particles are usually represented for predictive utility as point particles, which, as zero-dimensional, lack spatial extension. Though extremely successful, the Standard Model is limited to the microcosm by its omission of gravitation, and has some parameters arbitrarily added but unexplained. Seeking to resolve those shortcomings, string theory posits that elementary particles are ultimately composed of one-dimensional energy strings whose absolute minimum size is the Planck length:

>>

• Proton ~ 1.755 x 10⁻¹⁵ m
  
  Amalthea ~ 1.67 x 10⁵ m