Particles that are smaller than an atom. They may be elementary or composite. Elementary particles cannot be broken into smaller particles, and consist of quarks, leptons, gauge bosons, and the Higgs boson. Quarks come in six ‘flavours’: up, down, bottom, top, strange, and charm. There are six leptons: electron, electron neutrino, muon, muon neutrino, tau, and tau neutrino. There are 12 gauge bosons: photon, three W and Z bosons, and eight gluons. Composite particles are composed of smaller particles, e.g. a proton consists of two up quarks and one down quark, a neutron of one up quark and two down quarks.