Counting dark matter particles in LHC events

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.