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George
2008-Dec-31, 09:03 PM
Is it possible in principle to collect neutrinos and put them into a can? IOW, could something like a laser beam placed against a neutrino flow stop some in their track where we can grab them with tiny tweezers?

[I did not find a comparable thread, but apologize if this has been addressed already.]

swansont
2008-Dec-31, 09:17 PM
You'd need a container that interacts via the weak force. The reason we can trap neutral atoms is that they interact via the electromagnetic force, and we can build magneto-optic traps and magnetic traps to confine them. Charged particles are, by comparison, trivial to contain. But absent those forces, what would your interaction be that comprises the "walls" of the container, since you lack these other interactions?

Cheap Astronomy
2008-Dec-31, 09:44 PM
I recall an Astronomy Cast episode where Pamela Gay said it would take a light year of lead to stop a neutrino. So, you'll need a big can.

cosmocrazy
2008-Dec-31, 09:47 PM
I recall an Astronomy Cast episode where Pamela Gay said it would take a light year of lead to stop a neutrino. So, you'll need a big can.

Thats Superman stumped then! :lol:

George
2008-Dec-31, 10:18 PM
You'd need a container that interacts via the weak force. The reason we can trap neutral atoms is that they interact via the electromagnetic force, and we can build magneto-optic traps and magnetic traps to confine them. Charged particles are, by comparison, trivial to contain. But absent those forces, what would your interaction be that comprises the "walls" of the container, since you lack these other interactions? So they are stopable, which is the heart of my question. I suppose we could float them in a can in space if we are careful with the tweezer movement. ;)

I suppose also that at all times, stopped or on the fly, they too would see light traveling to them or away at the speed of light, right?

antoniseb
2008-Dec-31, 10:30 PM
So they are stopable...

Well they can be made to interact with something, but a light-year of lead won't slow one down.

A few notes:
- a light year of Lead is way more than enough to stop half the neutrinos from a beam of neutrinos. Take a look at the interaction cross-section for these things and calculate the mean free path yourself.
- Neutrinos can't be made to slow down at all, ever, if they are massless. Right now we THINK they have mass, but we are not sure.

swansont
2008-Dec-31, 11:03 PM
So they are stopable, which is the heart of my question. I suppose we could float them in a can in space if we are careful with the tweezer movement. ;)

I suppose also that at all times, stopped or on the fly, they too would see light traveling to them or away at the speed of light, right?

I didn't mean to give that impression I'm not aware of anything that could actually confine them. If something were able to do so, it would use the weak force.

They are stoppable but cease to be neutrinos. It's sort of like saying you stopped photons with a black surface that absorbed them. The LY of lead that would stop most of a neutrino beam would interact via a reverse-beta-decay interaction, popping an electron out after changing a neutron to a proton. No more neutrino.

George
2009-Jan-01, 12:46 AM
I didn't mean to give that impression I'm not aware of anything that could actually confine them. If something were able to do so, it would use the weak force. Yes, I see your point.

Let's assume that they do have mass, and I think this is the mainstream view due to their apparent change in flavors while in route.


They are stoppable but cease to be neutrinos. It's sort of like saying you stopped photons with a black surface that absorbed them. The LY of lead that would stop most of a neutrino beam would interact via a reverse-beta-decay interaction, popping an electron out after changing a neutron to a proton. No more neutrino. Ok, that's absorption, but what about photon pressure acting on an object of mass, could the force of on-coming photons slow some down? If so, then could they be made to slow down enough to rest in our inertial frame, assuming we are in deep space beyond much gravitational influence?

nauthiz
2009-Jan-01, 01:07 AM
Ok, that's absorption, but what about photon pressure acting on an object of mass, could the force of on-coming photons slow some down? If so, then could they be made to slow down enough to rest in our inertial frame, assuming we are in deep space beyond much gravitational influence?

If neutrinos are massless, then according to special relativity they must move at the speed of light, always. The closest thing you can do to slowing down or stopping them is to destroy them.

If neutrinos have mass, then what happens is going to depend on how the photon and neutrino interact. I don't know the details on that (and couldn't readily find any information on the Web), but it could be that the result of the interaction is the production of different particles rather than a neutrino with less momentum than it had before.

Jeff Root
2009-Jan-01, 01:15 AM
If neutrinos can slow down, then we are probably awash in neutrinos
having all different speeds. The problem in that case is that there is no
known way to detect slow neutrinos. They need to be moving with some
speed in order to collide with nuclei, be absorbed, and be detected.
Raising the question of whether dark matter consists of slow-moving
neutrinos. I forget whether the last round of thinking ruled that out.

-- Jeff, in Minneapolis

swansont
2009-Jan-01, 01:33 AM
If neutrinos are massless, then according to special relativity they must move at the speed of light, always. The closest thing you can do to slowing down or stopping them is to destroy them.


I don't know anywhere near enough particle physics to know the answer, but perhaps there is an equivalent to an index of refraction for neutrinos for slowing and/or reflection.

nauthiz
2009-Jan-01, 01:40 AM
I believe it's been shown that neutrinos do refract when they pass through materials, but not identically to the way photons do. I think it's that they refract less because they interact more weakly, so the speed of a neutrino in a non-vacuum can actually be quite a lot higher than the speed of light in the same medium.

George
2009-Jan-01, 02:40 AM
I believe it's been shown that neutrinos do refract when they pass through materials, but not identically to the way photons do. I think it's that they refract less because they interact more weakly, so the speed of a neutrino in a non-vacuum can actually be quite a lot higher than the speed of light in the same medium. That's interesting.

Is this refraction due to a weak-force field, like the EM field is to the photon, or can the EM field interact for a neutrino with mass? This is getting back to whether or not photons can impart some force upon a neutrino, I suppose.

nauthiz
2009-Jan-01, 09:19 AM
I believe neutrinos only interact via the weak force, so they would not be affected by the electromagnetic field.

Van Rijn
2009-Jan-01, 11:05 AM
A black hole certainly would keep neutrinos from leaving again, so could be a can of sorts. In principle, if you could manipulate extremely dense matter (and therefore create intense local gravity fields), you could put neutrinos on something like a racetrack.

George
2009-Jan-01, 11:30 PM
A black hole certainly would keep neutrinos from leaving again, so could be a can of sorts. In principle, if you could manipulate extremely dense matter (and therefore create intense local gravity fields), you could put neutrinos on something like a racetrack. I suppose this racetrack would be a two-way track with no center striping. :) Can they collide with each other?

Hmmm... what happens when one neutrino nudges up to another neutrino on their way to Earth, which should happen since their origins are from different locations within the Solar core, right? Is this a flavorable moment for us and them? :)

Gsquare
2009-Jan-02, 01:17 AM
I suppose this racetrack would be a two-way track with no center striping. :) Can they collide with each other?

Hmmm... what happens when one neutrino nudges up to another neutrino on their way to Earth, which should happen since their origins are from different locations within the Solar core, right? Is this a flavorable moment for us and them? :)


Interesting Question, George and Van Rijn;
There have been some attempts to identify neutrino oscillations with gravitational fields...IOW, inertial effects from gravity.

See here for ex. http://arxiv.org/PS_cache/gr-qc/pdf/9910/9910016v1.pdf

G^2

Ilya
2009-Jan-02, 02:08 PM
I believe neutrinos only interact via the weak force, so they would not be affected by the electromagnetic field.

Which means they do not interact with photons either.

However, if neutrinos have mass, they can be affected/slowed down by gravity. Every star should have some concentration of neutrinos in its center.

trinitree88
2009-Jan-02, 04:23 PM
Which means they do not interact with photons either.

However, if neutrinos have mass, they can be affected/slowed down by gravity. Every star should have some concentration of neutrinos in its center.

Ilya. I believe the weak force, like gravity, is universal in it's interactions, and includes all the particles in the Standard Model, including the photon...No? pete

Argos
2009-Jan-02, 05:17 PM
A black hole certainly would keep neutrinos from leaving again, so could be a can of sorts. In principle, if you could manipulate extremely dense matter (and therefore create intense local gravity fields), you could put neutrinos on something like a racetrack.

Yeah. Since gravity warps spacetime, the trajectories of neutrinos will be affected by gravity, like photons [which are also massless particles]. So neutrinos can be affected by concentration of matter. For photons, the bending of their trajectories due to G effetcs translates into frequency change. I wonder what would be the analogue of frequency change for neutrinos [a type changing, maybe?]

trinitree88
2009-Jan-02, 05:45 PM
Yeah. Since gravity warps spacetime, the trajectories of neutrinos will be affected by gravity, like photons [which are also massless particles]. So neutrinos can be affected by concentration of matter. For photons, the bending of their trajectories due to G effetcs translates into frequency change. I wonder what would be the analogue of frequency change for neutrinos [a type changing, maybe?]

Argos. Happy New Year from the Frigid Northlands.
1.Neutrinos obey identical equations to photons. They both obey E=hv, where the energy is equal to Planck's constant times the frequency..v, pronounced "new"...nu.
2.They both carry momentum E/c =hv/c, where c is the speed of light.
So, a neutrino can redshift, or blueshift, because of it's interaction with a local gravitational gradient, or because of it's emission from a source that is in motion with respect to your reference frame.
3. There is no need for the flavor to shift for this frequency-shifting to occur.
4. The trickiness involves the walls of your container. Neutrinos and antineutrinos of the same flavor...say, electron -type, are of opposite handedness...they can be viewed as twisting away from you like right- handed and left-handed wood screws. One, as you turn it clockwise, bites into the wood...the other, as you turn it clockwise, backs towards you, out of the wood. So, if it maintains it's helicity..(clockwise), and it bounces off the wall back towards you, it converts from a neutrino to it's antiparticle partner, the antineutrino of the same flavor. That violates Conservation of Lepton Number, something never seen in a particle physics experiment..(and until we do, forbidden as a transition). Therefor, the massless neutrino is born at c, travels always at c, until absorbed, but can forward-scatter as long as it doesn't backscatter, or reflect...(hence no mirror for them, or the walls of the neutrino can).
5. The other thing neutrinos can do is emit W+'s W-'s and Z0's...which is how they operate weak interactions. It takes very energetic neutrinos, near 100 Gev/c2 to make the W's, but the Z is allowed variable energies down to virtually nil.
6. Somewhere in my old posts I did a neutrino mirror for massive neutrinos in a relativistic thought experiment. If neutrinos are massive (which is not definitive yet, see:Particle Data Group....then all this physics washes out..(and I have wasted twenty years of my life chasing trolls, Bigfoot, Champ, Ogopogo,leprechauns, Nessie, and neutrinos...:shifty::doh::lol: pete

Argos
2009-Jan-02, 05:55 PM
Argos. Happy New Year from the Frigid Northlands.

Trinitree, Happy new year from the land of endless summer. :)

Thanks for the reply. I get ya.

trinitree88
2009-Jan-02, 06:07 PM
Trinitree, Happy new year from the land of endless summer. :)

Thanks for the reply. I get ya.

You're welcome. pete

Ilya
2009-Jan-02, 06:25 PM
Ilya. I believe the weak force, like gravity, is universal in it's interactions, and includes all the particles in the Standard Model, including the photon...No? pete

Apparently not:

Fundamental weak interactions occur for all fundamental particles except gluons and photons (http://www2.slac.stanford.edu/vvc/theory/weakinteract.html)

George
2009-Jan-02, 06:35 PM
Ilya. I believe the weak force, like gravity, is universal in it's interactions, and includes all the particles in the Standard Model, including the photon...No? pete
Are you saying neutrinos can interact with photons? Could an on comming laser beam slow them down?

trinitree88
2009-Jan-02, 06:43 PM
Are you saying neutrinos can interact with photons? Could an on comming laser beam slow them down?

George. These guys say yes, neutrinos can interact with photons. 1. see:http://prola.aps.org/abstract/PRL/v79/i4/p569_1

2. see:http://arxiv.org/abs/hep-ph/0209236


3. see:http://www.iop.org/EJ/article/1538-4357/664/2/L67/21786.web.pdf?request-id=1be3051e-9031-48a8-80ea-3de81eb21415

I don't think anybody is saying you can slow them down, though, like the optical tweezers used on protists. pete

George
2009-Jan-02, 07:20 PM
George. These guys say yes, neutrinos can interact with photons. 1. see:http://prola.aps.org/abstract/PRL/v79/i4/p569_1 So, using my little knowledge of these things, a neutrino has a cross section equivalent to an x-ray. When I read "cross section" is it implied that it is an interactive cross section or one of the em field?


2. see:http://arxiv.org/abs/hep-ph/0209236 Using my typical cranal neurinos, this reads to me as if the neutrino interacts more in a wake form rather than a more direct interactioin; the weak force interacting with the electroweak.



3. see:http://www.iop.org/EJ/article/1538-4357/664/2/L67/21786.web.pdf?request-id=1be3051e-9031-48a8-80ea-3de81eb21415 That's something. My neurinos are fast but they don't interact favorably with such large intellectual cross sections. ;)


I don't think anybody is saying you can slow them down, though, like the optical tweezers used on protists. pete Perhaps that will be only a technology issue. If they can be slowed some, then they can be slowed more and more. Detecting and holding them is another matter (pun, sorry).