Clarification about the question of whether neutrinos are their own antineutrinos

Question

There are various pages that say we can distinguish between neutrinos and antineutrinos.

• Why do we not know whether or not neutrinos are their own antiparticles?
• Why are neutrino and antineutrino cross sections different?

However, other (not too old) sources claim that we still don't know whether neutrinos and antineutrinos are the same particle (as of 2022).

• Neutrinos from beta decay
• Is the neutrino its own antiparticle?

If we can distinguish between neutrinos and antineutrinos, then how is it still possible that neutrinos and antineutrinos might be the same?

Answer 1

Up until now, every experimental result involving neutrinos can be explained simply by helicity - left-handed neutrinos couple to leptons and right-handed neutrinos couple to anti-leptons. These right-handed neutrinos are currently referred to as antineutrinos, but we don't actually have any evidence that neutrinos/antineutrinos have a definite lepton number that is conserved in their interactions independently of helicity. If not, the only thing distinguishing neutrinos from "anti-"neutrinos is their helicity, which isn't used to differentiate particles from antiparticles, so the neutrino would be its own anti-particle. This is somewhat analogous to photons, which are also their own anti-particle but which have two helicity (circular polarization) states.

Here are a couple of the many questions on Majorana neutrinos whose answers may also help:

• Majorana neutrinos
• If a neutrino and his antineutrino has different helicity how can it be a possibility that it is a Majorana particle?

One process that could happen if neutrinos have a Majorana nature is neutrinoless double beta decays, but this has not yet been observed.