MRI: Track 1 Development of DarkQuest: A Dark Sector Upgrade to SpinQuest at the 120 GeV Fermilab Main Injector

The search and understanding of dark matter is one of the great problems of 21st-century particle physics. Expanding the mass range and techniques by which we search for dark matter is an integral part of the worldwide particle physics program. This award will upgrade the SpinQuest spectrometer, creating the DarkQuest Experiment and enabling the search for dark matter. The DarkQuest experiment will be a proton fixed-target experiment with leading sensitivity to an array of visible dark sector signatures in the mega-electron volt to giga-electron volt mass range. These signatures include dark photons, strongly interacting massive particles (SIMPs), and models that can explain the muon anomalous magnetic moment. DarkQuest provides a unique opportunity to bring hands-on particle physics experience, from assembly to commissioning to operation, to a new generation of undergraduate and graduate students, including members of a historically black university. The SpinQuest experiment is a beam dump experiment that currently runs on the Fermilab Main Injector with an incoming proton beam of 120 GeV. The experiment is designed to measure the total spin contribution of the sea quarks within the proton. The upgrade of SpinQuest with an electromagnetic calorimeter from the decommissioned PHENIX experiment will allow for particle identification leading to the observation of new signatures, including displaced di-electron final states. An upgrade to the DAQ and trigger systems will further improve the ability to detect dark sector signatures. Additionally, an upgrade to the polarized target will enable new, unique measurements of nuclear properties. DarkQuest can search for a wide range of new particles, such as long-lived dark photons, dark scalars, axion-like particles, and DM excited states, leading to a broad physics program. For light dark matter searches with displaced signatures, searches will be enhanced by a factor of 100 over SpinQuest, allowing it to be the world’s most sensitive displaced light dark matter experiment in the near future. Moreover, DarkQuest will explore novel dark sector models in regions of interest that have never been explored before. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.