  We suggest trying to count the number of invisible particles produced in
missing energy events at the LHC, arguing that multiple production of such
particles provides evidence that they constitute stable Dark Matter and that
counting them could yield further insights into the nature of Dark Matter. We
propose a method to count invisible particles, based on fitting the shapes of
certain transverse- or invariant-mass distributions, discuss various effects
that may affect the measurement, and simulate the use of the method to count
neutrinos in Standard Model processes and Dark Matter candidates in new physics
processes.
