weak interaction

A weak interaction is a particle interaction associated with the weak force. The weak force was conceived as a force underlying beta decay, and has been considered one of four fundamental physical forces. However, a theory has since been developed that defines an electroweak force that encompasses what is known of both the weak and electromagnetic forces, reducing the number of fundamental forces to three. Despite this, the weak force and electromagnetism are generally treated as distinct force types.

Weak interactions involve a weak boson (W boson or Z boson) with quarks or with leptons, interactions that either emit or absorb a weak boson. The interactions consist of the creation or annihilation of a pair of quarks or a pair of leptons. Beta decay consists of such an interaction with a pair of quarks effectively changing their flavor, simultaneously emitting a W boson (W⁺ or W^-, indicating its electric charge), the latter decaying, i.e., interacting spontaneously, producing a neutrino and a beta particle (electron or positron). This is termed a charged current interaction as an electric charge is transferred and carried away by the beta particle.

Interactions incorporating the Z boson (i.e., Z⁰, the only type), which carries spin and momentum but no electric charge, are termed neutral current interactions. These occur in elastic scattering, such as that between like-particles (e.g., electrons) and that between neutrinos and other particles.

Note the term weak interaction is also used in astrophysics without meaning the weak force, for small interactions such as the small effects of gravity between two stars passing each other but not very close.