conservation of parity

In physics, parity refers to the symmetry of a system's wave function. A parity transformation creates a mirror image of the system. If the system remains unchanged after this transformation, it has even parity; if it becomes negative, it has odd parity. For a long time, it was assumed that parity was always conserved in fundamental interactions, meaning physical laws were indifferent to mirror reflection.

However, in 1956, physicists proposed that parity is not always conserved, particularly in weak interactions. Experiments confirmed that in processes like beta decay, electrons are predominantly emitted in a "left-handed" manner, demonstrating a violation of parity conservation. While parity (P) and charge conjugation (C) are not conserved individually by the weak force, the combined CP symmetry was thought to hold. Later experiments revealed that even CP symmetry is violated in certain particle decays, a phenomenon that has significant implications for understanding the imbalance between matter and antimatter in the universe.12