CP violation
The CP violation (charge conjugation and parity) was established in the neutral kaon system in 1964. Steinberger recognized that the phenomenological parameter epsilon ("ε") which quantifies the degree of CP violation could be measured in interference phenomena (See CP violation). In collaboration with Carlo Rubbia, he performed an experiment while on sabbatical at CERN during 1965 which demonstrated robustly the expected interference effect, and also measured precisely the difference in mass of the short-lived and long-lived neutral kaon masses.