Leptons as a Window to Dark Matter
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Date
2024-12-19
Authors
Radick, Aria
Journal Title
Journal ISSN
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Publisher
University of Oregon
Abstract
There is a huge amount of evidence the dark matter exists, however we still do not know what kind of particle it is. Many experiments have been performed to test different models for dark matter, but its nature still remains elusive. In this work we study two different ways of looking for dark matter by using leptons.
First, we look at low threshold experiments in the form of dark matter-electron scattering. We know that the rate of dark matter-electron scattering depends on the underlying velocity distribution of the dark matter halo. In particular, dark matter electron scattering is more sensitive to the high velocity tail which can be significantly different depending on the dark matter halo model. This work quantifies the effects of different dark matter halo models and parameter choices on these rates, finding an $\mathcal{O}(0.01\%)$ to $\mathcal{O}(100\%)$ change in the rate predictions in silicon targets.
Secondly, we use a different lepton, the muon, to search for dark matter at colliders. In particular, we simulate a particular class of dark matter model, known as flavored dark matter, at a theoretical future muon collider to predict the capability of such a machine to detect or place bounds on this model, if it were to be built. We focus on the less-explored regime of feeble dark matter interactions, which suppresses the dangerous lepton-flavor violating processes, gives rise to dark matter freeze-in production, and leads to long-lived particle signatures at colliders. We find that the interplay of dark matter freeze-in and its mediator freeze-out gives rise to an upper bound of around TeV scales on the dark matter mass. The signatures of this model depend on the lifetime of the mediator, and can range from generic prompt decays to more exotic long-lived particle signals. In the prompt region, we calculate the signal yield, study useful kinematics cuts, and report tolerable systematics that would allow for a $5\sigma$ discovery. In the long-lived region, we calculate the number of charged tracks and displaced lepton signals of our model in different parts of the detector, and uncover kinematic features that can be used for background rejection. We show that, unlike in hadron colliders, multiple production channels contribute significantly which leads to sharply distinct kinematics for electroweakly-charged long-lived particle signals.
This dissertation includes previously published co-authored material.