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A very rich 'typical' bubble chamber picture
This is a bubble chamber picture from the CERN 2 metre-long bubble chamber that is filled with liquid hydrogen—a clean source of proton targets (no neutrons). The chamber is exposed to an incoming parallel beam of negative kaons (к-) with energy of 8.2 GeV, entering from the bottom of the picture.
The picture contains examples of many characteristic features that need to be recognized if one is to be able to interpret such pictures. In particular:
- Collisions between beam particle and a target proton (the initial state)
- Identification of as many final state particles as possible, usually by analyzing their decays
- A neutral particle usually decays into a positive particle and a negative particle, giving a characteristic letter vee (V)-shaped vertex
- A charged particle usually decays into another particle of the same charge, but lower momentum, and at least one neutral particle; the sudden change in curvature is called a ‘kink’.
- Dark tracks are often protons
- Spiralling tracks are electrons
(or antielectrons
)
During this tutorial, a cleaned-up version of this picture will be used. (Click on picture, then move cursor over A or B to activate.)
All tracks that are not associated with the parallel beam are background and will be removed from subsequent pictures. (Move cursor to active area B)