A Design Study for an Experiment to Search for Dark Photons at ELSA

This thesis presents a design study for proposed dark photon search experiment at the Electron Stretcher Accelerator ELSA in Bonn, called Lohengrin.<br> Different proposed extensions to the Standard Model of particle physics exist to explain the true nature of dark matter. One class of such models introduces a dark sector and a new gauge boson, the dark photon, coupling feebly to the dark sector. The dark photon thereby acts as a portal between the Standard Model and dark sector.<br> A missing momentum based technique is employed in the proposed experiment to look for the characteristic signal process of dark Bremsstrahlung. Electrons are shot onto a thin tungsten target with an energy of about 3200 MeV to produce mainly Standard Model Bremsstrahlung. In rare occasions however dark photons could be produced. The process is characterised by the electron losing most of the initial energy and no other detectable particles behind the target. This necessitates the existence of a precise track reconstruction with trackers in a magnetic field and calorimeters as veto detectors.<br> This thesis presents an overview and review of all of the proposed detector components and their requirements. It puts special emphasis on simulation studies for two key detector components of the proposed design: the electromagnetic calorimeter and trackers.<br> For the electromagnetic calorimeter, a simulation is set up using the ExPlORA framework. Hit and energy distributions on the surface of the electromagnetic calorimeter are studied in detail and their influence on the design of Lohengrin is discussed. A clustering algorithm is implemented and a subsequent energy calibration is performed to estimate the energy resolution of the calorimeter.<br> The momentum reconstruction of electrons poses a special challenge due to the non-Gaussian nature of their energy loss when traversing material. A Gaussian sum filter implementation based on ACTS was used to track and reconstruct simulated electron tracks traversing the Lohengrin tracker geometry. This provides a first estimate on the possible reconstruction capabilities of the proposed tracker for Lohengrin.<br> A sensitivity estimate based on the capabilities of the individual detector components is given. Lohengrin is estimated to reach sensitivity to couplings small enough to explain the relic abundance of dark matter in various models for dark photon masses between ~ 1 MeV and ~ 100 MeV.