Charmed Baryons - Charmed Omega History and Mass

Charmed Omega History and Mass

Not surprisingly, of the 4 weakly decaying, singly charmed baryons, the Ω
c (the css quark combination), was the last to be discovered and the least-well measured. Its history is murky. Some authors claim that in 1985 a cluster of 3 events observed at CERN was a signal, but this can now be excluded on the grounds of its incorrect mass. The ARGUS experiment published a small peak as a possible signal in 1993, but this can now be excluded on cross-section grounds, as many experiments have operated in the same environment as ARGUS with many more collisions. The E-687 experiment at Fermilab published two papers, one in 1993 and the other in 1994. The former one showed a small peak of marginal significance in the decay mode Ωπ, and a larger, apparently robust signal in the decay mode Σ+K−K−π+. This latter observation is considered valid by the Particle Data Group, but increasingly seems odd in that this decay mode has not been observed by other experiments. The CLEO experiment then showed a peak of 40 events in the sum of a variety of decay modes and a mass of 2,494.6 MeV/c2. Since then, two experiments, BaBar, and Belle, have taken a great deal of data, and have shown very strong signals at a mass very similar to the CLEO value. However, neither have done the necessary studies to be able to quote a mass with an uncertainty. Therefore, though there is no doubt the that particle has been discovered, there is no definitive measurement of its mass.