Kollisionsquerschnitt

Kollisionsquerschnitt, often denoted by the symbol $\sigma$, is a concept primarily used in nuclear physics and particle physics to describe the probability of a particular interaction occurring between two particles. It can be visualized as the effective target area that a particle presents to another particle for a specific type of collision. The unit of cross-section is typically area, with the barn (10⁻²⁸ m²) being a common unit in nuclear physics. A larger cross-section indicates a higher probability of interaction.

The term "cross-section" arises from the idea of scattering experiments. If you imagine firing a beam of particles at a target, the total cross-sectional area of the target atoms that would lead to a specific scattering event is the macroscopic cross-section. When considering individual interactions, it's the effective "size" of the interaction, not necessarily the physical size of the particles themselves. Different types of interactions, such as elastic scattering, inelastic scattering, or reactions, will have different associated cross-sections. These cross-sections are often dependent on the energy of the colliding particles. Measuring cross-sections allows physicists to infer properties of fundamental particles and forces.