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Lecture 24: Diagrams, Decays, and Lifetimes
April 28, 2026
Reading Assignment
- Read: Supplementary Reading Ch 11
Objectives
- (Continuing objective) Describe quantum and elementary particle theories in your own words, and discuss applications of the material.
- Construct correct interaction diagrams for given strong and weak interactions among particles, showing the underlying quark structure.
- Given a particle's mass and quark constituents, list possible decay schemes and estimate decay times, using particle tables and the conservation laws.
- Describe in words and diagrams a possible proton decay and explain why such an occurrence must be very rare.
Homework
- Wednesday's Assigned Problems:
X14 (below); Supp CH 11: 1, 3, 4, 5, 7, 8, 9, 11
Problem X14 Draw a complete reaction diagram for the following interaction: $$ e^+ + \Lambda \to \Sigma^+ +\overline\nu_e $$ In the diagram, be sure to label all messengers, and label all particles with color/anti-color, where relevant.
- Monday's Hand-In Problems:
Supp CH 11: 2, 6, 10, 12
Note: this is only the first half of the hand-in set.
Lecture Materials
- Click here for the Lecture overheads. Answers: CT1 - 1&6; CT2 - 6; CT3 - 2; CT4 - 3; CT5 - 4
- Step-by-step method for Interaction Diagrams
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 with interaction diagram involving a W particle.
- Video example: interaction Diagram involving a gluon
- Video example: particle Lifetimes
Pre-Class Entertainment
- My Babe - Little Walter
- Unsquare Dance - Dave Brubeck
- I'm Gonna Be (500 Miles) - The Proclaimers
- Message of Love - The Pretenders
- I Love Rock'n Roll - Joan Jett
- Ramble On - Led Zeppelin