Helicity

Helicity is a property of particles related to the direction of their spin relative to their movement. Imagine a particle moving forward; if its spin (a kind of intrinsic angular momentum) is aligned with its direction of travel, it has positive helicity. If the spin points opposite, it has negative helicity. Helicity helps physicists understand particle behavior, especially in high-energy physics, by describing how their internal angular momentum relates to their motion. For massless particles like photons, helicity remains constant, making it an important concept in understanding their interactions and fundamental properties.