UsingMT2to distinguish dark matter stabilization symmetries

Abstract

We examine the potential of using colliders to distinguish models with parity (${Z}_{2}$) stabilized dark matter (DM) from models in which the DM is stabilized by other symmetries, taking the latter to be a ${Z}_{3}$ symmetry for illustration. The key observation is that a heavier mother particle charged under a ${Z}_{3}$ stabilization symmetry can decay into one or two DM particles along with standard model 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. The arXiv:1003.0899 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 ${Z}_{3}$ 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 analysis the missing energy/momentum in the event. For the ${Z}_{3}$ symmetry stabilized mothers, the resulting inclusive final state can have two, three or four DM particles. In contrast, models with ${Z}_{2}$ symmetry can have only two. We show that the shapes and edges of the distribution of ${M}_{T2}$-type variables, along with ratio of the visible momentum/energy on the two sides of the event, are powerful in distinguishing these different scenarios. Finally we conclude by outlining future work which focuses on reducing combinatoric ambiguities from reconstructing multijet events. Increasing the reconstruction efficiency can allow better reconstruction of events with two or three dark matter candidates in the final state.