# L1.5 Fermions, Bosons, and Fields: Reactions | Summary and Q&A

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June 24, 2021
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L1.5 Fermions, Bosons, and Fields: Reactions

## TL;DR

This video explains how reactions are related to cross-sections in particle physics.

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### Q: How are experimentally measured properties related to the forces involved in reactions?

Experimentally measured properties, such as reaction rates, can be related to the forces involved by considering the number of particles available for interactions and the density of the target material. These factors determine the likelihood of collisions occurring.

### Q: What is a cross-section in particle physics?

In particle physics, a cross-section is a measure of the likelihood of a collision occurring. It can be thought of as a geometrical area that represents the probability of an interaction between particles. The larger the cross-section, the higher the probability of a collision.

### Q: How is the thickness of the target material related to reaction rates?

The thickness of the target material affects reaction rates because the more particles in the target, the more likely it is for reactions to occur. The thickness of the material increases the chance of collisions between particles, leading to higher reaction rates.

### Q: What is the differential distribution of a cross-section in terms of angular distributions?

The cross-section differential distribution is given as a function of sine theta, which represents the angular distribution of reactions. Additionally, the cross-section can also be expressed in terms of solid angle theta, which is equal to sine theta times the infinitesimal angular width d theta times the infinitesimal azimuth angle d phi.

## Summary & Key Takeaways

• The video discusses how experimentally measured properties can be related to the forces involved in reactions.

• It explains that reaction rates are dependent on the number of particles available for interactions and the density of the target material.

• The concept of cross-sections as a measure of the likelihood of collisions occurring is introduced, with a classical model of billiard balls used as an example.