| Understandings |
|---|
| Quarks, leptons and their antiparticles |
| Hadrons, baryons and mesons |
| The conservation laws of charge, baryon |
| number, lepton number and strangeness |
| The nature and range of the strong nuclear |
| force, weak nuclear force and electromagnetic |
| force |
| Exchange particles |
| Feynman diagrams |
| Confinement |
| The Higgs boson |
| Applications and Skills |
|---|
| Describing the Rutherford-Geiger-Marsden experiment |
| that led to the discovery of the nucleus |
| Applying conservation laws in particle reactions |
| Describing protons and neutrons in terms of quarks |
| Comparing the interaction strengths of the fundamental |
| forces, including gravity |
| Describing the mediation of the fundamental forces |
| through exchange particles |
| Sketching and interpreting simple Feynman diagrams |
| Describing why free quarks are not observed |
| Charge | Quarks | Baryon Number |
|---|---|---|
| (2/3)e | u, c, t | 1/3 |
| (-1/3)e | d, s, b | (-1/3) |
All quarks have a strangeness number of $0$ except the strange quark that has a strangeness number of $-1$.
| Charge | Leptons |
|---|---|
| -1 | e, µ, T |
| 0 | U_e, U_µ, U_T |
All leptons have a lepton number of $1$ and antileptons have a lepton number of $-1$.
| Gravitational | Weak | Electromagnetic | Strong | |
|---|---|---|---|---|
| Particles experiencing | All | Quarks, leptons | Charged | Quarks, Gluons |
| Particles mediating | Graviton | W+, W-, Z0 | γ | Gluons |
It is believed that all the matter around us is made up of fundamental particles called quarks and leptons. It is known that matter has a hierarchical structure with quarks making up nucleons, nucleons making up nuclei, nuclei and electrons making up atoms and atoms making up molecules. In this hierarchical structure, the smallest scale is seen for quarks and leptons ($10^{–18}m$).
At the end of the nineteenth century, physicists experimented with electrical discharges through gases at low pressure.
If a gas sample is introduced into the region between two charged plates, a current flow can be observed, suggesting that the atoms have been broken down into charged constituents. The source of these charged particles is a cathode ray.
In 1897, J.J. Thomson set out to prove that the cathode rays produced from the cathode were actually a stream of negatively charged particles called electrons.
A high voltage is applied across two electrodes at one end of the tube which causes a beam of particle to flow from the cathode to the anode.