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Re: neutrino mass



I have a question about a finite mass neutrino. If it is so, then it takes over
as the smallest non-zero mass particle from the electron. When photons with
energies above twice the electron rest mass pass through matter, they create
electron/positron pairs. So if neutrinos of mass 0.07 eV exist why don't photons
of energy > 0.14 eV create neutrino/antineutrino pairs? (And how would optics
be different if they did?)

Tim Sullivan
sullivan@kenyon.edu

Neutrinos are uncharged, which means that they don't couple directly
to photons. The electron remains the lightest particle that the photon
does couple to. So for a photon passing through matter to produce a
pair of neutrinos, it would have to go through an e+e- pair as an
intermediate step. The e+e- pair could then exchange a W and convert
to neutrino-antineutrino. Not impossible, but very strongly suppressed
because the W is so heavy (or equivalently, because the weak interaction
is so weak).

If the W were lighter (i.e., if the weak interaction were stronger),
then I guess photon beams would be attenuated significantly as they
pass through matter. But by the same token, neutrinos would be much
easier to detect, so neutrino beams might be commonplace in optics labs.
Fun to think about!

Dan