L1.5 Fermions, Bosons, and Fields: Reactions  Summary and Q&A
TL;DR
This video explains how reactions are related to crosssections in particle physics.
Key Insights
 ☠️ Experimentally measured properties in particle physics, such as reaction rates, can be related to the forces involved by considering the number of particles and target material density.
 😵 The likelihood of a collision occurring is quantified by the concept of a crosssection, which can be seen as a geometrical area.
 ☠️ The thickness of the target material influences reaction rates by increasing the probability of collisions.
 😵 Angular distributions of reactions can be described using the differential distribution of the crosssection as a function of sine theta.
 😵 An isotropic reaction is one where the crosssection per solid angle is independent of theta and phi.
 😵 The mapping between sine theta and theta is not trivial, resulting in the specific shape of the crosssection distribution.
 ☠️ Quantum field theory or Feynman rules are used to calculate crosssections and decay rates in more advanced analyses.
Transcript
MARKUS KLUTE: Hello. Welcome back to 8.701. In this lecture, this little video, we're going to look at reactions and how they relate to crosssections. So we start or continue the discussion of how we can relate experimentally measured determined properties to the forces involved. The last lecture, we looked at decay rates and the rates of unstable... Read More
Questions & Answers
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 crosssection in particle physics?
In particle physics, a crosssection 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 crosssection, 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 crosssection in terms of angular distributions?
The crosssection differential distribution is given as a function of sine theta, which represents the angular distribution of reactions. Additionally, the crosssection 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 crosssections as a measure of the likelihood of collisions occurring is introduced, with a classical model of billiard balls used as an example.