You Gotta Know These Classes of Particles

The mass of particles is usually given in mega-electronvolts (MeV), where an electronvolt is the energy acquired by an electron when it crosses a potential difference of one volt. The energies are converted to masses by Einstein’s equation E = mc2, where c is the speed of light in a vacuum. Charges are given in terms of the fundamental electric charge (the absolute value of the charge on an electron).

Every kind of particle also has a corresponding anti-particle made of anti-matter; when it is said that there are (for instance) six leptons, anti-particles are not counted, so in some sense there are twelve. Anti-particles have the same mass, but the opposite charge, of the original. There are no particles with negative mass. Note that in some rare situations, a particle can be its own anti-particle.

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