What is the difference between low and high energy neutrinos?

[repoman]

So, with photons E=hf, with protons, neutrons and electrons the mass is set and the total particle energy is determined is a combination of rest mass, and kinetic energy and some relativistic jiggering.

But I am confused about what determines the energy of a neutrino and how it varies. The actual rest mass of the neutrino (be it electron, muon or tau type) is not known, correct? But it does have constraints from various known facts?

I hear that the cosmic neutrino background is 1.9 K. But what does that mean as far as energy, frequency, velocity and so on?

Could a neutrino get so "cold" that it would travel at speeds well below the speed of light?

 

[barbos]

So, with photons E=hf, with protons, neutrons and electrons the mass is set and the total particle energy is determined is a combination of rest mass, and kinetic energy and some relativistic jiggering.

But I am confused about what determines the energy of a neutrino and how it varies. The actual rest mass of the neutrino (be it electron, muon or tau type) is not known, correct? But it does have constraints from various known facts?

yes, it's not known but there are different constrains on masses of neutrinos.
Energy of any particle is E^2=m^2*c^4+P^2 where m is rest mass, P is momentum which can change from 0 to infinity.

Neutrino is no different from any other particle as far as kinematics concerned.

I hear that the cosmic neutrino background is 1.9 K. But what does that mean as far as energy, frequency, velocity and so on?

it means average energy is about 1.9K which is 8.621738e-5*1.9eV = 0.000163813022 electronvolts.
Speed and wavelength would depend on mass. and frequency is the same formula as photon or any other particle - E=hf, f=E/h.

Could a neutrino get so "cold" that it would travel at speeds well below the speed of light?

if it has rest mass then yes.

 

[barbos]

As for the the original question then about difference, then there is no difference. It's just low energy neutrino are practically impossible to detect.

 

[repoman]

So,

I know that the CMB is the leftover from when protons and electrons recombined to make atomic hydrogen at roughly 3,000 K. But I couldn't find out what reaction happened when the cosmic background neutrinos were released and what type they were and the temp at the time.

So the CMB is at a density now of ~411 photons per cubic centimeter. The CNB is estimated at 56 per each 6 type (regular and anti- electron muon and tau neutrinos) from theory though none have been detected.

I would imagine that not only would a detection method have to be found but it would have to have a high level of data collection to be very useful.

Is there any good lead for a detection method yet?

Also, for cosmis rays that scream across the universe these CNB neutrinos must be very blue shifted. But so are the CMB photons. So maybe any reaction with blueshifted neutrinos would be just a blip compared to the blueshifted photons and therefore no usable signal.

 

[barbos]

So,

I know that the CMB is the leftover from when protons and electrons recombined to make atomic hydrogen at roughly 3,000 K. But I couldn't find out what reaction happened when the cosmic background neutrinos were released and what type they were and the temp at the time.

CMB is a result of universe becoming transparent (for photons) at certain temperature. Same is true for CNB, universe became neutrino transparrent at temperatures lower than scale of electroweak interaction (mass of W/Z)

So the CMB is at a density now of ~411 photons per cubic centimeter. The CNB is estimated at 56 per each 6 type (regular and anti- electron muon and tau neutrinos) from theory though none have been detected.

I would imagine that not only would a detection method have to be found but it would have to have a high level of data collection to be very useful.

Is there any good lead for a detection method yet?

There is no method to detect them currently.

Also, for cosmis rays that scream across the universe these CNB neutrinos must be very blue shifted. But so are the CMB photons. So maybe any reaction with blueshifted neutrinos would be just a blip compared to the blueshifted photons and therefore no usable signal.

I am not sure what are you getting at here.
there is no blue shifted background neutrinos, they are all red shifted.

 

[repoman]

When a cosmic ray gets emitted by an accretion disk or pulsar or whatever, it will be see the CMB blue shifted in its travel direction.

https://en.wikipedia.org/wiki/Greisen–Zatsepin–Kuzmin_limit

They predicted that cosmic rays with energies over the threshold energy of 5×1019 eV would interact with cosmic microwave background photons , relatively blueshifted by the speed of the cosmic rays...

 

[barbos]

When a cosmic ray gets emitted by an accretion disk or pulsar or whatever, it will be see the CMB blue shifted in its travel direction.

https://en.wikipedia.org/wiki/Greisen–Zatsepin–Kuzmin_limit

They predicted that cosmic rays with energies over the threshold energy of 5×1019 eV would interact with cosmic microwave background photons , relatively blueshifted by the speed of the cosmic rays...

That's an awkward explanation of the effect. so no, it's not blue-shifted, it's relatively blue shifted and as I said weird way to explain effect.

 

[repoman]

Ok, let's say that the 1.95 K CRN (Cosmic Relic Neutrinos) become detectable by an advance in technology. How would a map of the CNB (Cosmic Neutrino Background) and its slight variations be made?

IIRC, supernova neutrinos are located because of timing differences between the different detectors which are far apart from each other.

The CNB is everywhere and on all the time. Also how can a detector only detect neutrinos from a certain direction?

 

[barbos]

Ok, let's say that the 1.95 K CRN (Cosmic Relic Neutrinos) become detectable by an advance in technology. How would a map of the CNB (Cosmic Neutrino Background) and its slight variations be made?

IIRC, supernova neutrinos are located because of timing differences between the different detectors which are far apart from each other.

The CNB is everywhere and on all the time. Also how can a detector only detect neutrinos from a certain direction?

I don't quite understand where are you going with this.
There are currently no such detectors. But in case of high energy neutrinos you can get direction with fair precision.

 

[repoman]

A single high energy neutrino can give its origin direction fairly well? Or one detector alone is all that is needed to find the direction?

 

[Bomb#20]

A single high energy neutrino can give its origin direction fairly well? Or one detector alone is all that is needed to find the direction?

The detectors don't detect neutrinos directly -- the neutrino hits something in the working medium and the collision produces a cascade of photons or other particles, and then an array of detectors get hit by the debris. From the various arrival times at the detectors you can work out the location and momentum of the original neutrino.

 

[barbos]

A single high energy neutrino can give its origin direction fairly well? Or one detector alone is all that is needed to find the direction?

I don't understand your question.

 

[repoman]

Ok, I looked over the wiki article on neutrino detection and it looks like it is Cherenkov radiation from the energetic and charged byproducts of the neutrino-water reactions can give a reasonable indication of direction even for one reaction. From browsing I didn't find another method for determining direction that would work for anything other than high energy neutrinos.

It seems like the CRNs reacting with whatever substance the 1.95K neutrino detector would be make of would NOT make charged byproducts moving fast enough to produce Cherenkov radiation.

 

[barbos]

It seems like the CRNs reacting with whatever substance the 1.95K neutrino detector would be make of would NOT make charged byproducts moving fast enough to produce Cherenkov radiation.

1.95K neutrino would not react with any current detector at all.
You need neutrino with energy above certain threshold for reaction to occur.

 

[repoman]

Well, I found one article on Arxiv about detecting 2K neutrinos. I think that Arxiv is open to anyone...

Anyway, it is way out of my depth, but it may be of interest to others.

http://arxiv.org/pdf/hep-ph/0703028.pdf

So, I guess I would need to find out what "zero threshold reaction" means in this context to be in the game as a layman/fanboy.

 

[Underseer]

[...]
E^2=m^2*c^4+P^2
[...]

Where did you get this equation? The dimensional analysis doesn't line up.

E² = [M]²[L]⁴ / [T]⁴

m²c⁴ = [M]²[L]⁴ / [T]⁴

p² = [M]²[L]² / [T]²

 

[repoman]

E^{2}=p^{2} c^{2} + m^{2} c^{4}.

E=pc for a photon. Can't remember how it works for massive particles/objects.

 

[barbos]

[...]
E^2=m^2*c^4+P^2
[...]

Where did you get this equation? The dimensional analysis doesn't line up.

E² = [M]²[L]⁴ / [T]⁴

m²c⁴ = [M]²[L]⁴ / [T]⁴

p² = [M]²[L]² / [T]²

LOL, true. It should be E^2=m^2*c^4+P^2*c^2
But usually c is set to be equal to 1 so it is E^2=m^2+p^2