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Classifying collisions - number of neutral particles

Neutral particles do NOT leave trails of bubbles (because bubble formation is initiated by the ionisation of the hydrogen atoms by the Coulomb interaction). However, an unstable neutral particle may decay in the bubble chamber into a pair of lighter particles - one positive and one negative - leaving an easily recognisable letter V (or vee) shape. (Click on picture and move cursor over active area A).

If the tracks from the vee happen to cross again, downstream, the line joining the crossing position to the decay position (the V) points back to the origin of the neutral particle. (For details, click here.)

So our neutral decay vee can be seen to be coming from the collision and not from the kink.

(Many such decaying neutral partciles leave the bubble chamber before decaying - more in step 8.)


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