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Lecture 22: Elementary Particles and Conservation Laws
April 22, 2025
Reading Assignment
- Read: Supplementary Reading Ch 9
Objectives
- (Continuing objective) Describe quantum and elementary particle theories in your own words, and discuss applications of the material.
- List the types of particles (bosons, fermions, hadrons, leptons, baryons, mesons, messengers) and their properties. Using data tables, classify and identify the properties of various fundamental particles.
- Describe what happens if a particle combines with its anti-particle.
- Name the six main conservation laws of particle physics and give the conditions under which they apply. Analyze given particle reactions or decays to test the main conservation laws, or to discover properties of a new unknown particle.
- Build various hadrons with given properties from combinations of quarks, given a quark data table for up, down, and strange quarks.
Homework
- Wednesday's Assigned Problems: Supp CH 9: 2, 6, 7, 8, 10, 11, 12, 13, 14abc, 15
- Monday's Hand-In Problems from Lecture 22:
A83; Supp CH 9: 3, 4, 14def, 16
Note: this is only the first half of the hand-in set.
Lecture Materials
- Click here for the Lecture overheads. Answers: CT1 - 2; CT2 - 5; CT3 - 1
- Table of particle properties (also inside the back cover of the Supplementary Reading.)
Videos of example problems
To see the problem statement, click on the link below. To play the video example, click on the underlined words "Video Demonstration" near the top of the page with the problem statement.- Example #1: Video example: using conservation laws to identify a particle.
- Example #2: Another video example of using conservation laws to identify a particle. Note: at the very end the units should be MeV/\(c^2\), not GeV/\(c^2\).
- Example #3: Video example: determining quark configuration for some hadrons.
Pre-Class Entertainment
- Where Do the Children Play - Cat Stevens
- Hook My Pony - The Belairs
- You Can Call Me Al - Paul Simon
- Take Five - Dave Brubek
- I Wish - Stevie Wonder
Assigned Problems Guide
- Supp 9-2: quick. Basic issue of classification.
- Supp 9-6: medium. Conserve Q to learn the charge of the unknown particle. Then conserve baryon number. Then lepton numbers, etc.
- Supp 9-7: medium-quick. Check strangeness conservation. If it's violated, then it requires the weak interaction instead of the strong interaction.
- Supp 9-8: medium. The equations refer to specific reactions. Check those reactions for all the conservation laws.
- Supp 9-10: medium-quick. Check the conservation laws.
- Supp 9-11: medium-quick. If it's going by the strong interaction, strangeness must be conserved.
- Supp 9-12: medium. Use strangeness first to figure out how many strange quarks are involved. Then use charge to figure out the rest.
- Supp 9-13: medium-quick. How many strange quarks are required? Once you sort that out, think about the implications for charge.
- Supp 9-14abc: medium. Add up Q, B, and S, and then check the tables.
- Supp 9-15: medium. Your plot won't look exactly like Fig 9.1. But you should see a pattern nonetheless. These patterns were a big clue that led us to the quark model.