Quarks, antiquarks and hadron charges

Last time

Before we start: last time, in Mesons, baryons and leptons, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.

The building blocks of the nucleus

Protons and neutrons seemed like the smallest parts of matter, until experiments in the 1960s fired electrons at them at high energy. The electrons bounced off hard, small centres inside, as if the proton had parts. Those parts are quarks, and the rules for combining them explain a whole zoo of particles.

Quarks

Quarks are fundamental particles. They come in six flavours: up, down, strange, charm, bottom and top. Up, charm and top quarks have charge plus two thirds of e. Down, strange and bottom quarks have charge minus one third of e. Quarks are never found alone. They are always in groups inside particles called hadrons.

Antiquarks

Every quark has an antiquark. It has the same mass, but opposite charge. An anti-up quark has charge minus two thirds of e. An anti-down quark has charge plus one third. An up quark and an up antiquark are alike in mass, in the size of their charge, and both are fundamental. They differ in the sign of their charge, and one is matter, the other antimatter.