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Accelerators & Detectors Reactors Life Sciences Other |
Discovery of the Charmed BaryonThe photograph of the event in the Brookhaven 7-foot bubble chamber which led to the discovery of the charmed baryon (a three-quark particle) is shown at left. A neutrino enters the picture from below (dashed line) and collides with a proton in the chamber's liquid. The collision produces five charged particles--a negative muon, three positive pions, and a negative pion--and a neutral lambda. (The spiraling pattern on the left is from electrons moving in the chamber's magnetic field after being knocked out by a muon and one of the pions.) The lambda produces a characteristic 'V' when it decays into a proton and a pi-minus. The momenta and angles of the tracks together imply that the lambda and the four pions produced with it have come from the decay of a charmed sigma particle, with a mass of about 2.4 billion electron volts (GeV). The decay happened too quickly (within 1 billionth of a second) for the original charmed particle to leave an observable track in the chamber. However, it's existence could be inferred from the other observable events shown here. The discovery of this particle was an important step in establishing a new member of the quark family.*
* Portions of this text adapted from "The Particle Explosion", Oxford University Press, New York, 1987. |
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