Next-to-minimal dark matter at the LHC

TL;DR

This paper investigates collider signatures of minimal dark matter models involving singlet and n-plet fermions at the LHC, focusing on long-lived particles, displaced vertices, and constraints from various searches.

Contribution

It provides a detailed analysis of collider signatures for n=3 and n=5 minimal dark matter models, including constraints from displaced lepton and disappearing track searches.

Findings

5-plet masses below ~280 GeV are ruled out by displaced lepton searches.

Long-lived particles lead to distinctive collider signatures such as displaced vertices.

Parameter space exists where models match relic density but are constrained by disappearing track searches.

Abstract

We examine the collider signatures of a WIMP dark matter scenario comprising a singlet fermion and an SU(2) n-plet fermion, with a focus on n=3 and n=5. The singlet and n-plet masses are of the order of the electroweak scale. The n-plet contains new charged particles which will be copiously pair-produced at the LHC. Small mixing angles and near-degenerate masses, both of which feature naturally in these models, give rise to long-lived particles and their characteristic collider signatures. In particular, the n=5 model can be constrained by displaced lepton searches independently of the mixing angle, generically ruling out 5-plet masses below about 280 GeV. For small mixing angles, we show that there is a parameter range for which the model reproduces the observed thermal relic density but is severely constrained by disappearing track searches in both the n=3 and the n=5 cases. The n=3 model is further constrained by soft di-lepton searches irrespectively of whether any new particles are long-lived.