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Identification of particles from a collision by their decays

We have seen how an unstable neutral particle can be identified via its decay into two oppositely charged particles, a vee.

An unstable charged particle may also decay - usually into a charged particle of the same sign and one or more neutral particles. This shows up in the bubble chamber as a kink - a sudden change into a more curved track (active area A).

Notice that one of the positive tracks kinks twice (active area B), ending up with a positive spiralling track (produced by an anti-electron - only and ordinary electrons spiral).

The number of unstable particles that travel far enough to decay in the bubble chamber is limited. They leave characteristic decay signatures that enable the parents to be identified. As we will see in the next step, in bubble chambers this is a comparatively simple matter of visual pattern recognition.

(At the LHC, where the events will have hundreds of particles in the final state, imaginative systems of electronic detectors and software have been designed to do the same job at incredibly high data-acquisition rates.)


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