Just my two cents about neutrinos and how they're seen in modern (experimental) physics.
Basic stuff about neutrinos are nicely presented on cassiopaedia and there is also this one C's session.
But there is no mention of neutrino oscillation, so I'll be addressing that and related issues.
[quote author=wikipedia http://en.wikipedia.org/wiki/Neutrino_oscillation]
Neutrino oscillation is a quantum mechanical phenomenon predicted by Bruno Pontecorvo whereby a neutrino created with a specific lepton flavor (electron, muon or tau) can later be measured to have a different flavor. The probability of measuring a particular flavor for a neutrino varies periodically as it propagates. Neutrino oscillation is of theoretical and experimental interest since observation of the phenomenon implies that the neutrino has a non-zero mass, which is not part of the original Standard Model of particle physics.
[/quote]
This phenomenon, as mathematically described today, connects the energy of neutrinos, their distance travelled from "origin" to observational point and difference between squared masses of two (or more) different neutrino types. These neutrino types are usually called mass eigenstates, while the "normal" one that can be identified through weak interaction processes are called weak eigenstates (lepton flavor).
The mass term in neutrino probability function (probability to change flavor) gives that there is no oscillation possible if mass eigenstates have identical masses (meaning that they all can't be 0 either).
There is evidence that neutrinos do oscillate (_http://www.phys.hawaii.edu/~jgl/nuosc_story.html) but, until now, all that's been measured (in whatever experiment you pick) is a deficit in neutrino flux (from expected one) in one way or another; so called disappearance experiments; and no measurement of neutrinos appearing with previously nonexistent lepton flavor have been done so far. First of these appearances experiments is OPERA. They, at the highest nominal beam intensity and 5 years of full running, expect to maybe collect 10-15 events of tau neutrino appearing in muon neutrino beam. Until now, no such thing has been observed (officially it's stated that OPERA started in 2008, but I was working there and the first data was already collected in 2006).
Fwiw, it could easily be that these observed deficits are due to neutrino interaction with consciousness and not oscillation at all. ;D
Ok, back to oscillations and mass.
All observed neutrinos so far are left ones but if they have some finite mass then some system could exceed them in speed and by outrunning them look back and see that these neutrinos have now become right-handed.
Btw, right-handed (massive) neutrinos are unfailing spring for numerous theories, especially about the origin of baryon asymmetry of the Universe (matter-antimatter asymmetry, the reason why our physical world exists as it is; the observed ratio between matter and antimatter is very very small so it presents a so called fine-tuning problem in physics)
_http://en.wikipedia.org/wiki/Antimatter.
Also, if neutrino has some finite mass then the question arises is it Dirac or Majorana particle?
[quote author=wikipedia http://en.wikipedia.org/wiki/Neutral_heavy_lepton]
Dirac and Majorana neutrinos
Two types of neutrinos originate from the following question: Is a particle really different from its antiparticle?" While the answer is obvious for charged particles, since the positive are distinct from negative particles by their electromagnetic properties, it is not clear in the case of neutral particles. Depending on the answer, the neutral particles will be either Majorana or Dirac types. If the answer to the above question is "yes", then the particle is a Dirac particle. If the answer is "no" and the particle is identical to its antiparticle, then it is a Majorana particle. The concept of the Majorana particle was first introduced by Majorana in 1937. Examples of the Dirac-Majorana particles are the neutral pion, which is identical to its antiparticle and according to the definition belongs to the Majorana type, and the neutral kaon, which is different from its antiparticle and belongs to the Dirac type. To put this in mathematical terms, we have to make use of the transformation properties of particles. We define a Majorana field as an eigenstate of charge conjugation. This definition is only for free fields. We have to generalize it to the interacting field. Neutrinos interact only via the weak interactions, which are not invariant to charge conjugation C. An interacting Majorana neutrino cannot be an eigenstate of C. The generalized definition is: "a Majorana neutrino field is an eigenstate of the CP transformation".
Consequently Majorana and Dirac neutrinos behave differently under CP transformations (actually Lorentz and CPT transformations). The distinction between Majorana and Dirac neutrinos is not only theoretical. A massive Dirac neutrino has nonzero magnetic and electric dipole moments, that could be observed experimentally, whereas a Majorana neutrino does not.
The Majorana and Dirac particles are different only if the neutrino rest mass is not zero. If the neutrino has no mass and travels at the speed of light, then the Lorentz transformation to a faster moving frame is not possible. The difference between the types disappears smoothly. For Dirac neutrinos, the dipole moments are proportional to mass and vanish for a massless particle. Both Majorana and Dirac mass terms however will appear in mass lagrangian if neutrino is to have a mass (which as we know it does).
[/quote]
The process that could resolve this dilemma is called neutrinoless double beta decay.
Some years ago, when I was extensively pondering on these matters, the analogy between neutrinos (sort of mix the mass) and quarks (sort of mix the electric charge) came to my mind, and I played for quite some time with these (and some other as well) concepts, but as my mathematical skills have not been good enough it remained in geometrical sketches and word explanations, i.e. scientifically said "in diapers". :/
Ok, this were my two cents... off to smoke now...
Basic stuff about neutrinos are nicely presented on cassiopaedia and there is also this one C's session.
But there is no mention of neutrino oscillation, so I'll be addressing that and related issues.
[quote author=wikipedia http://en.wikipedia.org/wiki/Neutrino_oscillation]
Neutrino oscillation is a quantum mechanical phenomenon predicted by Bruno Pontecorvo whereby a neutrino created with a specific lepton flavor (electron, muon or tau) can later be measured to have a different flavor. The probability of measuring a particular flavor for a neutrino varies periodically as it propagates. Neutrino oscillation is of theoretical and experimental interest since observation of the phenomenon implies that the neutrino has a non-zero mass, which is not part of the original Standard Model of particle physics.
[/quote]
This phenomenon, as mathematically described today, connects the energy of neutrinos, their distance travelled from "origin" to observational point and difference between squared masses of two (or more) different neutrino types. These neutrino types are usually called mass eigenstates, while the "normal" one that can be identified through weak interaction processes are called weak eigenstates (lepton flavor).
The mass term in neutrino probability function (probability to change flavor) gives that there is no oscillation possible if mass eigenstates have identical masses (meaning that they all can't be 0 either).
There is evidence that neutrinos do oscillate (_http://www.phys.hawaii.edu/~jgl/nuosc_story.html) but, until now, all that's been measured (in whatever experiment you pick) is a deficit in neutrino flux (from expected one) in one way or another; so called disappearance experiments; and no measurement of neutrinos appearing with previously nonexistent lepton flavor have been done so far. First of these appearances experiments is OPERA. They, at the highest nominal beam intensity and 5 years of full running, expect to maybe collect 10-15 events of tau neutrino appearing in muon neutrino beam. Until now, no such thing has been observed (officially it's stated that OPERA started in 2008, but I was working there and the first data was already collected in 2006).
Fwiw, it could easily be that these observed deficits are due to neutrino interaction with consciousness and not oscillation at all. ;D
Ok, back to oscillations and mass.
All observed neutrinos so far are left ones but if they have some finite mass then some system could exceed them in speed and by outrunning them look back and see that these neutrinos have now become right-handed.
Btw, right-handed (massive) neutrinos are unfailing spring for numerous theories, especially about the origin of baryon asymmetry of the Universe (matter-antimatter asymmetry, the reason why our physical world exists as it is; the observed ratio between matter and antimatter is very very small so it presents a so called fine-tuning problem in physics)
_http://en.wikipedia.org/wiki/Antimatter.
Also, if neutrino has some finite mass then the question arises is it Dirac or Majorana particle?
[quote author=wikipedia http://en.wikipedia.org/wiki/Neutral_heavy_lepton]
Dirac and Majorana neutrinos
Two types of neutrinos originate from the following question: Is a particle really different from its antiparticle?" While the answer is obvious for charged particles, since the positive are distinct from negative particles by their electromagnetic properties, it is not clear in the case of neutral particles. Depending on the answer, the neutral particles will be either Majorana or Dirac types. If the answer to the above question is "yes", then the particle is a Dirac particle. If the answer is "no" and the particle is identical to its antiparticle, then it is a Majorana particle. The concept of the Majorana particle was first introduced by Majorana in 1937. Examples of the Dirac-Majorana particles are the neutral pion, which is identical to its antiparticle and according to the definition belongs to the Majorana type, and the neutral kaon, which is different from its antiparticle and belongs to the Dirac type. To put this in mathematical terms, we have to make use of the transformation properties of particles. We define a Majorana field as an eigenstate of charge conjugation. This definition is only for free fields. We have to generalize it to the interacting field. Neutrinos interact only via the weak interactions, which are not invariant to charge conjugation C. An interacting Majorana neutrino cannot be an eigenstate of C. The generalized definition is: "a Majorana neutrino field is an eigenstate of the CP transformation".
Consequently Majorana and Dirac neutrinos behave differently under CP transformations (actually Lorentz and CPT transformations). The distinction between Majorana and Dirac neutrinos is not only theoretical. A massive Dirac neutrino has nonzero magnetic and electric dipole moments, that could be observed experimentally, whereas a Majorana neutrino does not.
The Majorana and Dirac particles are different only if the neutrino rest mass is not zero. If the neutrino has no mass and travels at the speed of light, then the Lorentz transformation to a faster moving frame is not possible. The difference between the types disappears smoothly. For Dirac neutrinos, the dipole moments are proportional to mass and vanish for a massless particle. Both Majorana and Dirac mass terms however will appear in mass lagrangian if neutrino is to have a mass (which as we know it does).
[/quote]
The process that could resolve this dilemma is called neutrinoless double beta decay.
Some years ago, when I was extensively pondering on these matters, the analogy between neutrinos (sort of mix the mass) and quarks (sort of mix the electric charge) came to my mind, and I played for quite some time with these (and some other as well) concepts, but as my mathematical skills have not been good enough it remained in geometrical sketches and word explanations, i.e. scientifically said "in diapers". :/
Ok, this were my two cents... off to smoke now...



