Abstract
We introduce a Minimal Simplified Dark Matter (MSDM) framework to quantitatively characterise dark matter (DM) searches at the LHC. We study two MSDM models where the DM is a Dirac fermion which interacts with a vector and axial-vector mediator. The models are characterised by four parameters: m DM , M med , g DM and g q, the DM and mediator masses, and the mediator couplings to DM and quarks respectively. The MSDM models accurately capture the full event kinematics, and the dependence on all masses and couplings can be systematically studied. The interpretation of mono-jet searches in this framework can be used to establish an equal-footing comparison with direct detection experiments. For theories with a vector mediator, LHC mono-jet searches possess better sensitivity than direct detection searches for light DM masses (≲5 GeV). For axial-vector mediators, LHC and direct detection searches generally probe orthogonal directions in the parameter space. We explore the projected limits of these searches from the ultimate reach of the LHC and multi-ton xenon direct detection experiments, and find that the complementarity of the searches remains. Finally, we provide a comparison of limits in the MSDM and effective field theory (EFT) frameworks to highlight the deficiencies of the EFT framework, particularly when exploring the complementarity of mono-jet and direct detection searches.
Highlights
As in [12], a more appropriate approach to characterise dark matter (DM) searches at colliders is the use of simplified models [23]
This is another advantage of implementing this process in the POWHEG BOX since it is capable of simulating both the effective field theory (EFT) case and the Minimal Simplified Dark Matter (MSDM) case
We show a comparison of the current MSDM mono-jet limit with the naive limit obtained in the EFT framework for each of the four parameter planes shown in figures 5 to 8
Summary
The use of simplified models to characterise new physics searches at the LHC has become a standard procedure in both the experimental and theoretical communities. We consider the case when the dark matter is a Dirac fermion χ and assume that the quark-mediator coupling gq is equal for all quarks In this case, as shown schematically, the model is completely characterised by the four parameters discussed above. A treatment of the loop-induced contribution is beyond the scope of this work so we do not consider the case of mixed vector and axial-vector couplings further As both hadron collider and direct detection searches for dark matter primarily probe the interactions of dark matter with quarks, we set the mediator interactions with leptons to zero; the lepton couplings play no role (at tree-level) in the phenomenology in either hadron collider and direct detection searches [58, 59]. Variations of the assumptions which we have made in this paper should be explored in the future to fully map out the MSDM landscape; the approach should be extended to include, for instance, other spins for the mediator and dark matter particle, different coupling structures and additional experimental constraints
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