Using MT2 to Distinguish Dark Matter Stabilization Symmetries
Abstract
We examine the potential of using colliders to distinguish models with parity (Z2) stabilized dark matter (DM) from models in which the DM is stabilized by other symmetries, taking the latter to be a Z3 symmetry for illustration. The key observation is that a heavier mother particle charged under a Z3 stabilization symmetry can decay into one or two DM particles along with Standard Model (SM) particles. This can be contrasted with the decay of a mother particle charged under a parity symmetry; typically, only one DM particle appears in the decay chain. In arXiv:1003.0899, some of us studied the distributions of visible invariant mass from the decay of a single such mother particle in order to highlight the resulting distinctive signatures of Z3 symmetry versus parity symmetry stabilized dark matter candidates. We now describe a complementary study which focuses on decay chains of the two mother particles which are necessarily present in these events. We also include in our analyss the missing energy/momentum in the event. For the Z3 symmetry stabilized mothers, the resulting inclusive final state can have two, three or four DM particles. In contrast, models with Z2 symmetry can have only two. We show that the shapes and edges of the distribution of MT2-type variables, along with ratio of the visible momentum/energy on the two sides of the event, are powerful in distinguishing these different scenarios.