An antineutrino is the antimatter equivalent particle of the neutrino. It is produced in nuclear beta decay as a balance to the electron emitted by the nucleus.
Neutrinos and antineutrinos only interact with other matter particles via the weak nuclear force, and consequently their properties do not differ greatly.
There is a hypothesis that the neutrino and the antineutrino are actually the same particle. This would mean, that the neutrino field is not a Dirac spinor, as in the standard model, but a Majorana spinor. For experimental evidence on this attempts are made to find neutrinoless double beta decay.
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