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11 February 1998
The "omega-minus" in detail
This diagram shows in detail the particles identified in the historic first example of the production and decay of an omega-minus particle, in the 80-inch bubble chamber at the Brookhaven National Laboratory in New York. Solid lines show tracks formed by electrically charged particles in the liquid hydrogen in the bubble chamber; dotted lines show where neutral particles have passed (being uncharged they leave no track). A magnetic field bends the tracks of negative particles to the right and positive particles to the left.
A beam of negative kaons (K-) enters the chamber from below the picture, and one of them (1) interacts with a proton (a hydrogen nucleus) in the liquid. The reaction creates an omega-minus (3), together with a positive kaon (2) and a neutral kaon (K0). The omega-minus decays into a positive pion (4) and a neutral xi or "cascade" particle. The latter leaves no track but soon decays to create a neutral lambda particle, which continues up the image, and two gamma-ray photons (7 and 9). The gamma rays are in fact the decay products of a very short-lived neutral pion. Each gamma ray converts to an electron-positron pair. Finally, the lambda particle decays to a proton (6) and a negative pion (5).
Credit: Brookhaven National Laboratory
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