Example of charged pi+  mu+  e+ decay in rich K- interaction

This picture was taken in the CERN 2-metre hydrogen bubble chamber, filled with liquid hydrogen and exposed to an incoming parallel beam of negative kaons with an energy of 8.2 GeV, entering from bottom of the picture.

The magnetic field will curve the trajectory of charged particles; negatively charged particles are curved in one direction, positively charged in the opposite direction. The knock-on electrons in the top right-hand part of the picture tell us that negative particles are turning to the right.

A major feature of this picture is the track which leaves the interaction near the bottom of the picture and makes a large curve to the left. It then kinks about 90 degrees into a short  track, which then kinks again into a spiralling track.

In a bit more detail, the stops before decaying characteristically to a muon , which, having a momentum of only about 30 MeV/c (click here for more details), can only travel a short distance before stopping. The other decay product is a muon-neutrino , which travels in the opposite direction, but leaves no track.. The muon then decays into an anti-electron (positron) , which spirals in a characteristic way (click here for more details).

The full decay scheme for this process: