Sensitivity of Proton Fixed-Target Experiments to Light Dark Matter

Abstract

Despite its remarkable success, the Standard Model of particle physics falls short of being a completely satisfactory theory. One prominent shortcoming is its inability to account for all the matter in the Universe, a discrepancy best explained by the presence of dark matter. Astrophysical and cosmological observations strongly indicate its existence, yet no non-gravitational interactions have been observed. The persistent null result may be attributed to dark matter being lighter than previously hypothesised, allowing it to have gone unnoticed in previous searches. This has driven growing interest in accelerator-based experiments, particularly fixed-target experiments. In this thesis, light dark matter (LDM) is investigated at proton fixed-target experiments, focusing on a minimal dark sector model with complex scalar dark matter and a dark vector mediator. Using the MadDump plugin to the MadGraph5_aMC@NLO framework, the sensitivity of the primary dark matter production channels is studied for the forthcoming experiments SHiP and DUNE ND, as well as the operational NOνA ND. In particular, the newly approved SHiP design and different operational modes of DUNE ND are considered. Additionally, a new secondary production channel in the form of photoproduced vector meson decay is considered, with the analysis performed largely analytically. This channel has recently been shown to enhance sensitivity in electron beam experiments. Here, no such enhancement is observed. The origin of this difference is not yet fully understood, with possible explanations including an insufficient flux of high-energy photons in the processes considered and a potential overestimation of dark photon production in the primary channel.