# Difference between a neutrino and an antineutrino

#### Ed Aboud

Hi all.
What is the difference between a neutrino and an antineutrino if they both have no charge and aren't made up of quarks?
Thanks.

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#### malawi_glenn

Homework Helper
How they interact with other weak interacting particles.

They "carry" lepton familiy number, which is something that must be conserved in an interaction.

for example:

allowed:
$$\overline{\nu} _{\mu} + u \rightarrow \mu ^+ + d$$

Not allowed:
$$\nu _{\mu} + u \rightarrow \mu ^ + + d$$

where u and d are up- and down- quarks.

in the first reaction, initial muon-family number is -1, and final muon-family number is -1 (since antiparticles has -1, and particles has +1, postive charged leptons are defined to be antiparticles, and negative charged leptons is then particles.)

in the secon reaction, initial muon-family number is +1, and final muon-family number is -1

#### blechman

Hi all.
What is the difference between a neutrino and an antineutrino if they both have no charge and aren't made up of quarks?
Thanks.
It is interesting to note that IF the neutrinos have MAJORANA masses rather than DIRAC masses, then there is NO difference between a neutrino and an antineutrino! This is an open question in the particle physics community. Malawi-Glenn rightfully points out a potential experiment to test and see if the neutrino is Majorana or Dirac - if it's Majorana it would necessarily violate lepton number as his "forbidden" interaction would now be allowed. People are looking...

#### malawi_glenn

Homework Helper
but the basis of what I wrote was used when determine the quark charges of the nucleons, in inelastic neutrino scattering, right?

#### blechman

but the basis of what I wrote was used when determine the quark charges of the nucleons, in inelastic neutrino scattering, right?
Yes. The thing to keep in mind is that if the neutrino masses are majorana and thus you can have lepton number violation, the mass is quite small, and hence the violation is also VERY small (hence why we haven't seen it yet). so it does not invalidate the old DIS experiments and their results. the error would be substantially below background, I believe. if there's anyone out there reading this with a better understanding of these experiments, I invite you to comment on this...

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