There is compelling evidence for the existence of dark matter, an exotic substance which contributes most of the matter in the universe. While the identity and properties of dark matter particles are unknown, there is excellent reason to suspect that dark matter has a mass which lies at the TeV scale.

The most well studied dark matter candidates are weakly interactive massive particles (WIMPs), which were in thermal equilibrium with ordinary matter in the early universe. If the dark matter interacts with ordinary matter with an electroweak strength coupling, the early universe freeze-out process can naturally produce the correct dark matter relic abundance. Importantly, this type of dark matter could be created in collisions at the Large Hadron Collider.

The interaction of WIMPs with Standard Model particles can be described in a model independent way using an effective field theory approach. This is useful, because it allows bounds from collider searches, direct detection, indirect detection and relic density considerations to be easily compared. However, an effective field theory approach is not always valid, for example, it breaks down if the interactions are mediated by light particles.

Uncovering dark matter at the LHC is a nontrivial task, because it will not interact with the detectors at all. Instead, we can hope to infer the presence of dark matter particles created at the LHC by ascertaining that something is missing. A spectacular signal is that of the mono-X (where 'X' can signify γ, Z or jets).

In this process, a single Standard Model particle recoils against missing momentum attributed to dark matter particles which escape the detector unseen. CoEPP researchers have performed some preliminary work on mono-Z signals. This work will continue, with a focus on going beyond the effective field theory description by instead looking at simple UV complete models.


Dark matter is an invisible and unknown substance that makes up the bulk of the universe's mass.
Photo: NASA