Particle Physics and the Standard Model
The Fundamental Constituents of Matter
Quarks, Leptons, and Force Carriers
The Standard Model has 3 generations of quarks (each in 3 colours, bound by gluons) and leptons (electron, muon, tau + their neutrinos). All forces are mediated by spin-1 gauge bosons:
- Strong force: 8 gluons (QCD)
- Weak force: (range m)
- Electromagnetic: photon ()
The Higgs boson (, spin-0) gives mass via the Higgs mechanism.
Standard Model Generations
| Gen | Quarks | Lepton | Neutrino |
|---|---|---|---|
| 1st | up, down | electron | |
| 2nd | charm, strange | muon | |
| 3rd | top, bottom | tau |
Colour Confinement
Free quarks are never observed (confinement). They are always bound into hadrons: mesons (quark-antiquark) and baryons (three quarks). The proton consists of , the neutron of .
Which fundamental force is responsible for beta decay?
Beta decay: , mediated by the boson (weak force).
Correct answer: The weak nuclear force
The Higgs boson's role in the Standard Model is to:
The Higgs field's non-zero vacuum expectation value breaks electroweak symmetry, giving masses.
Correct answer: Give mass to , , and fermions via the Higgs mechanism
What is the difference between a hadron and a lepton? Give one example of each.
Protons are hadrons; electrons are leptons.
Correct answer: Hadrons are composite particles made of quarks and interact via the strong force (e.g., proton). Leptons are fundamental, do not experience the strong force (e.g., electron).