Neutrinos have extremely low masses, and it's quite easy for them to reach high energies and speeds. As such, it almost always makes sense to treat a neutrino as being relativistic. I've been doing some reading on non-relativistic neutrinos, with kinetic energies of $\lesssim$ 1 meV. These would interact even less with matter than ordinary neutrinos; for example, the threshold for producing inverse beta decay is 1.8 MeV. The only non-relativistic neutrinos currently known to be produced naturally are from the cosmic neutrino background (C$\nu$B), which is redshifted enough for its neutrinos to have a temperature of $\sim$1.95 K and speeds of only several hundred kilometers per second. Therefore, I'm interested in the possibility of producing non-relativistic neutrinos on Earth. Is it possible?

I know that existing neutrino beams produce neutrinos through pion decay (see here for some general history). Proton-proton collisions produce other baryons, including pions and kaons. The charged pions can be aligned by a magnetic field, producing a beam. The pions then decay into muons and muon neutrinos: $${\pi }^{-}\to {\mu }^{-}+{\overline{\nu }}_{\mu },{\pi }^{+}\to {\mu }^{+}+{\nu }_{\mu }$$ The muons can be blocked, allowing the muon neutrinos and antineutrinos to continue on to their target.

The problem is, these neutrinos have way too much energy, and clearly continue through the Earth unimpeded until they reach a detector. This makes me think that it's not a great idea to try to create non-relativistic neutrinos in a particle accelerator: The beams need to have a lot of energy to ensure a significant number of proton-proton collisions, but this also means that the decay products have a lot of energy. Assuming my logic is correct (and it could be wrong), we would need another way. Is it possible to create some sort of beam of non-relativistic neutrinos on Earth, or, as I'm increasingly of the opinion, is this simply completely impossible?

posted almost 5 years ago

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5y ago

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