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Lecture 24: Diagrams, Decays, and Lifetimes
April 29, 2025
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 from Lecture 24:
Supp CH 11: 2, 6, 10, 12
Note: this is only the first half of the hand-in set.
Lecture Materials
- Here are some videos from Fermilab about particle physics. This is NOT required material. If you're interested in hearing a bit more about these
topics, you might find them interesting. One warning: when they show
Feynman diagrams, time is flowing left to right, instead of from bottom to
top.
- Quantum Electrodynamics (the electromagnetic force)
- Quantum Chromodynamics (the strong force)
- The Weak Force (Note: when he talks about the range of possible masses for the particles, he's talking about virtual particles. Real particles have a precise mass.)