This event shows an interaction of an 8.2 GeV/c particle with a proton in the CERN 2 metre hydrogen bubble chamber.
A neutral particle is produced which decays into one positive and one negative particle with a characteristic 'vee’ pattern. Measurements are required to show that this is a .
For a visualisation of the time development of the main tracks click
Each step corresponds to about 0.2 ns.
All the particles move with the speed of light, except the proton which moves at 0.55c.
For another example of neutral kaon click on the picture below.