Fluctuations of rare particles as a measure of chemical equilibration

We calculate the time evolution of fluctuations for rare particles such as e.g. kaons in 1 AGeV or charmonium in 200 AGeV heavy ion collisions. We find that these fluctuations are a very sensitive probe of the degree of chemical equilibration reached in these collisions. Furthermore, measuring the second factorial moment the size of the initial population can be determined.