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edpell
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Now that Neutrinos have mass is it true the only zero mass particle is the photon?
bcrowell said:We only know for sure that there are differences in mass between types of neutrinos are nonzero. It's still possible that one type of neutrino is massless.
All oscillation formula involve mass differences. The absolute measurements are even more challenging than the oscillation measurements. There is a dedicated chapter 14 in "Fundamentals of Neutrino Physics and Astrophysics" by C. Giunti and C. W. Kim (Oxford University Press 2007) which begins withblechman said:If any neutrino is massless, then it cannot oscillate. And that would show up in measurements of the mixing angles.
Look for instance at the effect of neutrino masses on the end point of electron energy spectrum in beta decay of tritium. For a mass of 10 eV the end point will be shifted by ... 10 eV out of about 20 keV. This is so challenging that systematic uncertainties give us negative estimates. So at present, the best we get is that the electron neutrino mass is less than about 2 eV.[...] the results of neutrino oscillation experiments have recently proved that neutrinos are massive. Since these experiments give only information on the neutrino squared-mass differences, we currently know that there are at least two massive neutrinos [...]
humanino said:All oscillation formula involve mass differences. The absolute measurements are even more challenging than the oscillation measurements. There is a dedicated chapter 14 in "Fundamentals of Neutrino Physics and Astrophysics" by C. Giunti and C. W. Kim (Oxford University Press 2007) which begins with
Look for instance at the effect of neutrino masses on the end point of electron energy spectrum in beta decay of tritium. For a mass of 10 eV the end point will be shifted by ... 10 eV out of about 20 keV. This is so challenging that systematic uncertainties give us negative estimates. So at present, the best we get is that the electron neutrino mass is less than about 2 eV.
Neither pion and tau decays or neutrinoless double beta decay are more sensitive. It remains a major challenge to provide an absolute scale (declare lightest non-zero) in the neutrino mass spectrum.
blechman said:My logic is simply that a massless state cannot oscillate.
bcrowell said:But isn't the physical state a superposition of the electron-, mu-, and tau-neutrino states? So isn't the physical state not an eigenstate of mass?
hamster143 said:I don't see how it follows from special relativity that massless states can't oscillate. If it's something to do with bad behavior of energy and momentum (E=p for a massless state, but E>p for a massive state), four-momentum is already non-conserved (at least on the face of it) even in normal oscillations.
hamster143 said:four-momentum is already non-conserved (at least on the face of it) even in normal oscillations.
Vanadium 50 said:Why do you say that? In normal oscillations the particle propagates in a mass eigenstate, so 4-momentum is still conserved.
A simple way to see it is that a massless particle travels at c, so it is infinitely time dilated, so never has time to oscillate.
Vanadium 50 said:Why do you say that? In normal oscillations the particle propagates in a mass eigenstate, so 4-momentum is still conserved.
A simple way to see it is that a massless particle travels at c, so it is infinitely time dilated, so never has time to oscillate.
blechman said:It's a subtle question. It might be that because we are measuring FLAVOR states and not mass states, nothing rules out a massless [itex]\nu_1[/itex].
Vanadium 50 said:What it does not mean is that a freely propagating rho will turn into a photon and back again.
Vanadium 50 said:I'm not so sure. I'd want to repeat the derivation separately for the two helicity states and see what happens. The problem with a massless [itex]\nu_1[/itex] is that it has only one helicity state, but the particles it is oscillating into have two.
edpell said:Now that Neutrinos have mass is it true the only zero mass particle is the photon?
It seems, if you really have an argument against one massless neutrino, Glashow would support publicationMost of what is known about neutrino masses and mixings results from studies of oscillation phenomena. We focus on those neutrino properties that are not amenable to such studies: [itex]\Sigma[/itex], the sum of the absolute values of the neutrino masses; [itex]m_\beta [/itex], the effective mass of the electron neutrino; and [itex]m_{\beta\beta} [/itex], the parameter governing neutrinoless double beta decay. Each of these is the subject of ongoing experimental or observational studies. Here we deduce constraints on these observables resulting from anyone of six ad hoc hypotheses that involve the three complex mass parameters [itex]m_i[/itex]:
- ([itex]1[/itex]) Their product or
- ([itex]2[/itex]) sum vanishes;
- ([itex]3[/itex]) Their absolute values, like those of charged leptons or quarks of either charge, do not form a triangle;
- ([itex]4[/itex]) The [itex]e[/itex]-[itex]e[/itex] entry of the neutrino mass matrix vanishes;
- ([itex]5[/itex]) Both the [itex]\mu[/itex]-[itex]\mu[/itex] and [itex]\tau[/itex]-[itex]\tau[/itex] entries vanish;
- ([itex]6[/itex]) All three diagonal entries are equal in magnitude. The title of this note reflects the lack of any theoretical basis for any of these simple assertions.
Zero mass particles are subatomic particles that have no rest mass, meaning they do not have any measurable mass when at rest. These particles travel at the speed of light and are therefore always in motion.
Neutrinos and photons are both examples of zero mass particles. Neutrinos are electrically neutral particles that interact weakly with matter, while photons are particles of light that have no electric charge and travel in waves.
Neutrinos are detected using large underground detectors that can capture the rare interactions between neutrinos and other particles. Photons, on the other hand, can be detected using detectors such as telescopes or cameras that can detect light and other electromagnetic radiation.
Zero mass particles are important in physics because they behave differently than particles with mass. They are able to travel at the speed of light, have no electric charge, and can pass through matter without interacting with it. This allows them to provide valuable insights into the nature of the universe and its fundamental laws.
While the study of zero mass particles is primarily a theoretical pursuit, there are some practical applications. For example, neutrinos are used to study the core of the sun and other stars, and photons are used in technologies such as solar panels and fiber optic communications.