Chapter 3 – Elementary particles

Other properties

There are other properties of particles that we will not be discussing but I will mention for completeness.

The total baryon and lepton numbers are conserved in particle interactions.

Antiparticles

In 1928, Paul Dirac found the equations had two solutions for each particle. This showed that every charged particle should have an antiparticle.

In 1932, the antiparticle of the electron was discovered: the positron.

Antiparticles have opposite all properties except mass and spin. When a particle and antiparticle collide, they annihilate each other and convert the combined mass into energy, usually a photon.

This is the Standard Model extended to show the antiparticle of each particle.

Interesting fact: the antiparticle of a particle behaves like the particle going backwards in time!