Neutrinos are created in beta decays like 60Co—›60Ni+e-+n, bringing with them the "missing" energy and momentum. Neutrionos another, apart from their invisibility, problem to the physics: they are exclusively left-handed (or rather left-rotating*). For contrary anti-neutrinos n are right rotating. In that sense neutrinos are extraordinary particles, because other, like electrons can rotate in both directions.
This "one-handed" rotation of neutrinos is the very first reason of breaking the parity symmetry: only left-rotating elementary particles are subject to weak interactions, in which a charge change takes place, like beta decays; right-rotating particles do not decay in this way.
Experimental
confirmation of the beta decays assymetry was done in 1958: cobalt
nuclei oriented in the up direction in the magnetic field emit
electrons always to the down direction and -neutrinos always up.