Chapter 3 – Elementary particles

Mass and charge

Each particle in the standard model diagram is shows with its values for mass, charge and spin. We will look at each of these.

Particle mass

This shows the mass of the up and down quarks.

The first three columns of matter particles are families I, II and III. The families are identical other than the mass increasing as you move to the right. The heavier particles are less stable which is why most of the matter in the universe is made of the left column.

Two particles have zero mass: photon and gluon. Constraints of relativity mean that particles with zero mass can only exist if they travel at the speed of light. That explains why photons (which is light) goes at that speed.

Particle charge

The second value for each particle is its electric charge. You are probably used to protons having change +1 and electrons having charge -1 so may be surprised to see quarks with charge 2/3 and -1/3.

A proton is two up quarks and a down quark. That is 2/3 + 2/3 – 1/3 = +1

A neutron is one up quark and two down quarks. That is 2/3 – 1/3 – 1/3 = 0

Electrons have charge -1 as expected.