This uses the concept of the nucleus developed in Stage 1, Subtopics 6.1: The Nucleus, and 6.2: Radioactive decay.
The Standard Model suggests that there are three fundamental types of particles: gauge bosons, leptons, and quarks.
The Standard Model identifies four fundamental forces: electromagnetic, weak nuclear, strong nuclear, and gravitational.
Gauge bosons are particles which mediate the four fundamental forces.
Photons are the gauge bosons for electromagnetic forces; W or Z particles are the gauge bosons for weak nuclear forces; and gluons are the gauge bosons for strong nuclear forces.
The gauge boson for gravitational forces, the graviton, is still to be discovered.
- Describe the electromagnetic, weak nuclear, and strong nuclear forces in terms of gauge bosons.
- Solve problems involving the fundamental forces and gauge bosons.
Leptons are particles that are not affected by the strong nuclear force. There are six types of leptons – electron, electron-neutrino, muon, muon-neutrino, tau, and tau-neutrino.
The electron, muon and tau are negatively charged. Neutrinos do not have charge.
Quarks are fractionally charged particles that are affected by all of the fundamental forces.
Quarks combine to form composite particles and are never directly observed or found in isolation.
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SHE example: W bosons from photon collision
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Video: The Standard Model (Fermilab)
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There are six types of quark, with different properties, such as mass and charge. Each quark has a charge of either +2/3e or -1/3e.
| Quark | Symbol | Charge (e) |
| Up | u | 2/3 |
| Down | d | -1/3 |
| Strange | s | -1/3 |
| Charm | c | 2/3 |
| Top | t | 2/3 |
| Bottom | b | -1/3 |
- Identify which types of fundamental particles are affected by each type of fundamental force.
- Identify the charges of each type of fundamental particle.
- Describe the properties of a specified antimatter particle.
- Determine the charge of a specified antimatter particle.
All composite matter particles, such as atoms, are thought to be combinations of quarks, antiquarks and leptons.
Baryons are composite particles that consist of a combination of three quarks.
Mesons are composite particles that consist of a combination of one quark and one antiquark.
- Describe how protons, neutrons, and other baryons consist of different combinations of quarks.
- Determine the charge of a baryon, given its quark composition.
- Describe how pions and other mesons consist of different combinations of quarks and antiquarks.
- Determine the charge of a meson, given its quark-antiquark composition.
Each particle is assigned a lepton number and a baryon number.
Lepton numbers can be one of three types:
- electronic lepton number,
- muonic lepton number,
- tauonic lepton number,
The lepton number, regardless of type, for a lepton is 1. Antileptons have a lepton number of -1. All other particles have a lepton number of 0.
The baryon number of a quark is 13. Baryons have a baryon number of 1. Antiquarks have a baryon number of -13. Antibaryons have a baryon number of -1.
All other fundamental particles have a baryon number of 0.
The laws of the conservation of baryon number, charge, and lepton number determine the types of reactions that can occur between particles.
- Use the conservation laws to determine the baryon number, lepton number, and charge of particles in reactions.
- Given a reaction between particles, demonstrate that baryon number, lepton number, and charge are conserved.
When a particle and its antiparticle collide, they annihilate, releasing energy according to the mass–energy equivalence formula:
- Use the mass–energy equivalence relation to determine the energy released when a particle and antiparticle annihilate.
Practice program: Conservation laws
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Video: Annihilation and conservation of momentum
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