Number 116 (Story #1), March 3, 1993 by Phillip F. Schewe and Ben Stein|
NEW MEASUREMENTS OF CP-VIOLATION , performed in an experiment which monitors the way K-zero mesons transform into their own antiparticles (a process also called mixing), have reached a level of precision twice as good as that of previous experiments. The failure of interactions to be invariant under the combined operations of charge conjugation (C) and parity inversion (P) was first discovered in an early K-zero experiment in 1964. Since then particle physicists have sought in vain for additional manifestations of CP violation. Some scientists, suspecting that B mesons may exhibit the phenomenon, hope to build colliders dedicated to producing B mesons. But this could be years away, and so K-zero mixing remains the best physical system for studying CP violation, which continues to be of interest to theorists because it has a bearing on the asymmetry between matter and antimatter in the universe and because it has not fully been accounted for by the so-called Standard Model. The new experiment (L.K. Gibbons, 1 Mar. 1993 Physical Review Letters), carried out at Fermilab by a Chicago-Elmhurst-Fermilab-Princeton-Saclay collaboration, measured a variety of K-zero parameters. CP violation was observed to occur in the mixing of K-zeros but not in their decays. The experiment also served to further verify the invariance of CPT, the compound operation involving CP and the operation of time reversal (T).