# CP Violation & Antimatter

Meir Achuz
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Gold Member
I think most physicists would agree that, by definition, "charge conjugation" turns matter into antimatter. In 1956, when both P and C were found to be violated in muon decay, this gave Landau a great idea. If changing particles to antiparticles also included P, then the world would still be symmetric. This idea agreed with all known P and C violation, and was popular until CP was found to be violated. The blog is probably using this Landau idea which, except for CP violation, does make things more symmetric.

Gold Member
Just trying to get this straight: suppose we found two particles with equal mass but opposite spins and opposite charges. Would they necessarily be a matter-antimatter pair?
Thanks.

fzero
Homework Helper
Gold Member
Just trying to get this straight: suppose we found two particles with equal mass but opposite spins and opposite charges. Would they necessarily be a matter-antimatter pair?
Thanks.

An antiparticle will have the same spin as the corresponding particle, so we can rephrase your question as "suppose we found two particles with equal mass and spins but opposite charges. Would they necessarily be a matter-antimatter pair?" The answer still depends on finding experimental signatures that all of the interactions of these particles were also charge symmetric. For example, if these particles have nonzero EM charge, there should be quantum processes where an intermediate photon creates a particle-antiparticle pair. If the proper interactions occur, we can decide if they're a particle-antiparticle pair.

If the particles are electrically neutral, there can be additional complications, since it's possible that either each particle is its own antiparticle or that the particle-antiparticle eigenstates are mixed states. There's some discussion here: http://en.wikipedia.org/wiki/Neutral_particle_oscillations

Gold Member
Thank you, fzero. That is very helpful.

The relevance of CP for flipping particles ino their antiparticles is dictated by the neutrinos:

http://en.wikipedia.org/wiki/Antineutrino#Antineutrinos

The antineutrinos observed so far all have right-handed helicity (i.e. only one of the two possible spin states has ever been seen), while the neutrinos are left-handed.

Helicity is the projection of spin on the direction of momentum.
Thus, in order to create an antineutrino out of its neutrino, you woul have to apply the CP-operation. So, the physics of antiparticles is created via CP out of the physics of particles (except for the tiny CP violation).

Meir Achuz