# Why is the mass of a particle different from its antiparticle?

Like, for example, the neutrinos and the $B_0$ and the $\overline{B}^0$ mesons?

• Are you sure? In the case of neutrinos noone have really measured their mass, but in the case of B mesons, I'll check on PDG, they should be the same. Where did you read that they are different? – Hydro Guy Nov 6 '14 at 1:28
• Relevant context: Particle oscillation occurs only if the states between which oscillation occurs have different energy eigenvalues, which one might also phrase as a mass difference. However, it is not clear to me the particles $B$ and $\bar B$ actually are the eigenstates that are oscillating, since CPT invariance would naively imply that particles and antiparticle have the same mass. However, there are arguments that show that CPT does not necessarily impose equal masses. – ACuriousMind Nov 6 '14 at 1:37
• To the extent that it has been tested (which is neither comprehensive nor to very high precision) the neutrino mass differences and the anti-neutrino mass differences are the same. (Note that the MINOS results from 2010 have not held up to increased statistics.) – dmckee --- ex-moderator kitten Nov 6 '14 at 3:02