At Last We Have an Undisputed Observation of ‘Direct’ CP Violation in Kaon Decay

A long‐awaited experimental result, recently announced by the KTeV collaboration at the Fermilab Tevatron, does much to clarify the mechanism by which the decay of the neutral K mesons violates CP symmetry. Despite 35 years of painstaking investigation since the discovery of CP‐violating ${\mathrm{K}}^0$ decay by James Cronin, Val Fitch, James Christenson, and René Turlay, the important issue of what causes this asymmetry in nature had remained disturbingly unsettled. CP denotes the combined operation of charge conjugation (C), that is to say, the replacement of particles by their antiparticles, and parity inversion (P). After the rude overthrow of parity conservation in 1957, CP offered a refuge for believers in mirror symmetry, but only until the next rude overthrow, by Fitch, Cronin and company, in 1964.

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