FSI (Final State Interactions)

Final State Interactions (FSI) refer to the interactions that particles experience after an initial high-energy event, such as a collision or decay. When particles are produced or scattered, they don't simply move straight to detectors; instead, they can interact with each other or the surrounding environment. These interactions can alter their trajectories, energies, or identities before measurements are made. Understanding FSI is essential in particle physics because they influence the interpretation of experimental results, helping scientists accurately reconstruct the original processes that occurred during the event.