The Naked Scientists

The Naked Scientists Forum

Author Topic: Why do neutrinos have to have mass to oscillate and how is energy conserved?  (Read 5020 times)

Offline JMLCarter

  • Sr. Member
  • ****
  • Posts: 143
    • View Profile
It has been shown that neutrinos do spontaneously oscillate from one flavour into another, which has overcome the solar neutrino problem.
This is quoted as implying that they must have non-zero mass. Why does it imply that?

Secondly, when a neutrino does oscillate it changes from a particle with one mass to one with another. Where is the energy due to mass difference supposed to go?


 

Offline Soul Surfer

  • Neilep Level Member
  • ******
  • Posts: 3345
  • keep banging the rocks together
    • View Profile
    • ian kimber's web workspace
The reasons for this are not well described in popular articles.  The wikipeadia article here  http://en.wikipedia.org/wiki/Neutrino_oscillations  is probably quite good and the article also addresses the problem of neutrino masses

This is the way I understand it at the moment.  Remember everything is both particles and waves. With photons the shorter their wavelength the more they are like particles for example gamma rays,  the longer they are it is easier to understand them as waves for example radio waves.  A similar thing is true about particles and their mass. The wavelength of a particle is dependant on its mass and low mass particles are more like waves  we see this with electrons because their wavelike nature stops them collapsing onto the nucleus.  neutrinos are very difficult to detect as particles and are much more wavelike.  So much so that they can resonate with each other in the quantum mechanical vacuum.  This allows their identities to be indeterminate and oscillate.  This effect is also seen with other particles that are extremely closely related.

This mass difference is very small indeed.  Remember even ordinary chemical reactions involve minute mass differences so mass is quite a flexible thing.
« Last Edit: 02/04/2011 23:20:45 by Soul Surfer »
 

Offline JMLCarter

  • Sr. Member
  • ****
  • Posts: 143
    • View Profile
That still does not seem to explain where the energy is supposed to have come from when an initial electron neutrino is observed as a Tau neutrino, which has maybe 5,000,000 times the mass.

Surely the need to conserve energy exists regardless of the transformation mechanism.

The wikipedia page says something about different mass eigenstates travelling at different speeds (it's a bit tricky for me to interpret).


 

Offline Pikaia

  • Full Member
  • ***
  • Posts: 81
    • View Profile
If a particle travels at the speed of light then from its point of view no time elapses as it travels from the Sun to Earth, so it cannot change from one kind to another. So if it does change then it must be travelling slower than light, and since its relativistic mass is non-zero its rest mass must also be non-zero.
 

Offline Soul Surfer

  • Neilep Level Member
  • ******
  • Posts: 3345
  • keep banging the rocks together
    • View Profile
    • ian kimber's web workspace
Nice explanation Pikaia!  I have never seen that clearly explained before.  Maybe the experts just think that it is too obvious.

Energy and momentum are conserved within the limits set by the uncertainty principle. the three neutrinos are in effect three "generations" of the same particle.  It is not fully understood precisely what distinguishes these three generations from each other except their mass and the precise origin of mass is not yet fully proved.

No doubt the string theories have something to say about it what is needed is some understandable analogy from normal life.   The article I quoted above suggests they are a bit like coupled spring resonators with the energy moving between three possible modes of vibrations.  Another way of thinking about it may be like one of those magnetically affected pendulums which swings in several different modes and switches suddenly between them.  The total energy is the same but the vibrations are different and so the "shape" (Which is what defines the properties we see) is different.
 

Offline yor_on

  • Naked Science Forum GOD!
  • *******
  • Posts: 11987
  • Thanked: 4 times
  • (Ah, yes:) *a table is always good to hide under*
    • View Profile
This is rewriting the standard model it seems, not so much invalidating it as subtly shading it in another color. And also lifting up HUP to a new and truly elevated level. It seems that the standard model expects all particles of mass to be 'right handed' but the neutrinos are 'left handed' and there has been no sightings of any 'right handed' neutrinos, ever. Which there should have to be, as you when overtaking them, traveling at light speed, then would see them as 'right handed'. That as they have to move slower than light if having a invariant mass, as Pikaia so rightly pointed out. As that one is a slightly questionable proof you can instead, looking at the Higgs mechanism whereby physics expect the invariant mass to 'distributed', see that there should exist 'right handed' neutrinos. That as quantum theory, and Lorentz invariance, expect the 'handedness' of particles to change when 'interacting' with the Higgs Boson. And as we know, there have been no such sightings.

It's all theory off course but it's also a certain kind of logic following a mathematical model of 'reality' from experimental facts. The reason why there is no right handed neutrinos can be solved using HUP. The Heisenberg uncertainty principle allows the left handed neutrino that we can see and measure, to seesaw between right handedness and left handedness. When it meets a Higgs particle (Higgs Boson) it gets this mass at the same time as it change its handedness to a right-handed one. But as it is there inside a immeasurably short period of time and then turns back to what we measure we don't notice it, it's also allowed a mass under that 'instant' that's larger than it ever would be allowed inside SpaceTime. In a way one can see this as a 'trick' for explaining what we can't see but need to make the standard model to work, or it can be the absolute truth. I think it is, but I've always liked HUP so I'm prejudiced there I guess. If it is correct we have a new way of describing particles it seems to me, and also of describing interactions. It 'fits' right in with how electrons can be super-positioned in two 'places', and also with the other kind of superposition, in where all 'states' are expected to exist, simultaneously, before a interaction/measurement/detector.

There is another incredible thing it might explain. The question of what happened with the 'anti matter' we expect to be here, but isn't. In the first short moments of our universe those right-handed neutrinos existed, extremely massive and made out of the excess of concentrated 'energy' existing then. But as the universe cooled off that possibility of creating those neutrinos disappeared, and those existing started to decay into left handed neutrinos, interacting with the the Higgs bosons which then decayed into heavy quarks. And it's enough with a slight variation in the decay between particles and anti particles to explain why we're left with this very slight excess of 'invariant mass' aka particles.

This is very weird, and exciting, on so many planes :) but cool. And it leaves us a very interesting universe to play in. So many possibilities.
« Last Edit: 06/04/2011 10:55:04 by yor_on »
 

Offline JMLCarter

  • Sr. Member
  • ****
  • Posts: 143
    • View Profile
It's great to be able to understand why neutrinos have must have non-zero mass, many thanks Pikaia.

In terms of energy conservation during an oscillation, several possibilities;
1) The neutrino masses will turn out to be very similar
2) The neutrino slows down or speeds up when it oscillates... which make Newton's 1st look pretty bad
3) Energy is stored in some other (hidden) form... but what?
4) Energy is lost, presumably at the time of observation when the oscillation is resolved
5) Energy is not conserved... (eek! too scary to think about)

The oscillating spring analogy suggests 3) or 5). But according to the wikipedia article it is not the particles that oscillate it is the relative probability of their observation. I am liking explanation 4)?

I would also like to know in respect of Yor_On's post what defines the handedness of a particle, must be spin vector relative to something else? 
 

Offline yor_on

  • Naked Science Forum GOD!
  • *******
  • Posts: 11987
  • Thanked: 4 times
  • (Ah, yes:) *a table is always good to hide under*
    • View Profile
I've seen it explained this way. If you make a fist with your right hand, the thumb pointing out, the way your other fingers curl will tell you the way the particle 'spin' (or 'chirality' and 'helicity' as it also seem to be known as depending on what you describe, particles or molecules). Your thumb will be the 'axis' pointing to the direction which the particle propagates. And in this case you will find a 'right handed' spin, looking at your fingers. "The handedness of a particle describes the direction of its spin along the direction of motion the spin of a left-handed particle, for example, always points in the opposite direction to its momentum." 

Right hand rule

Take a look here for more conventions used. Circular polarization

"Until the 1950s, it was believed that fundamental physics was left-right symmetric; i.e., that interactions were invariant under parity. Although parity is conserved in electromagnetism, strong interactions and gravity, it turns out to be violated in weak interactions. The Standard Model incorporates parity violation by expressing the weak interaction as a chiral gauge interaction. Only the left-handed components of particles and right-handed components of antiparticles participate in weak interactions in the Standard Model. A consequence of parity violation in particle physics is that neutrinos have only been observed as left-handed particles (and antineutrinos as right-handed particles)"

When it comes to how you measure a spin, or a polarization, you can use filters or you can deduct it from the interactions happening. In the Brookhaven experiment I wrote about above before "Goldhaber and co-workers studied what happened when a europium-152 nucleus captured an atomic electron. The europium-152 underwent inverse beta decay to produce an unstable samarium-152 nucleus and a neutrino. The samarium-152 nucleus then decayed by emitting a gamma ray. When the neutrino and the gamma ray were emitted back-to-back, the handedness of the two particles had to be the same in order to conserve angular momentum. By measuring the handedness of the gamma ray using a polarized filter made of iron, the Brookhaven team showed that neutrinos are always left-handed." So there they used a clever indirect confirmation.

But one has to remember that, as I understands it, a 'spin' is no ordinary thing. That they express itself this way is due to the measurement, and 'spin' as such is just a property of the object, describing a function, not a real spin like spinning a football. If it was, that spin would be faster than light, and that shouldn't be possible. Integer spin particles are bosons like our photon, following Bose-Einstein statistics (taking no place), while half integer spins are called Fermions like electrons, following Fermi-Dirac statistics (they take a 'place').

Spin.
« Last Edit: 06/04/2011 22:12:00 by yor_on »
 

Offline yor_on

  • Naked Science Forum GOD!
  • *******
  • Posts: 11987
  • Thanked: 4 times
  • (Ah, yes:) *a table is always good to hide under*
    • View Profile
Spin is so very strange. I'm not even sure if this is right, the only thing I'm sure of is that this is what our detections tells us, as we interpret it now :) But as spin is something 'intrinsic'? "With particles the spin has a fixed value that depends only on the type of particle. Spin can also have direction, up or down and the particle carrying the spin can have a handedness, left or right. This gives four possible combinations shown below."
==

From. Ah, spin and stuff :)
=

 

The Naked Scientists Forum


 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums