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Essential idea: 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).
Nature of science:
Predictions: Our present understanding of matter is called the Standard Model, consisting of six quarks and six leptons. Quarks were postulated on a completely mathematical basis in order to explain patterns in properties of particles. (1.9)
Collaboration: It was much later that large-scale collaborative experimentation led to the discovery of the predicted fundamental particles. (4.3)
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
Guidance:
A qualitative description of the standard model is required
Data booklet reference:
International-mindedness:
Research into particle physics requires ever-increasing funding, leading to debates in governments and international research organizations on the fair allocation of precious financial resources
Theory of knowledge:
Does the belief in the existence of fundamental particles mean that it is justifiable to see physics as being more important than other areas of knowledge?
Utilization:
An understanding of particle physics is needed to determine the final fate of the universe (see Physics option sub-topics D.3 and D.4)
Aims:
Aim 1: the research that deals with the fundamental structure of matter is international in nature and is a challenging and stimulating adventure for those who take part
Aim 4: particle physics involves the analysis and evaluation of very large amounts of data
Aim 6: students could investigate the scattering angle of alpha particles as a function of the aiming error, or the minimum distance of approach as a function of the initial kinetic energy of the alpha particle
Aim 8: scientific and government organizations are asked if the funding for particle physics research could be spent on other research or social needs
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