Collaborative Research: Construction and Deployment of a Cryogenic, Undoped CsI Scintillator at the Spallation Neutron Source within the COHERENT Experiment

Despite being the most numerous massive particle, neutrinos remain the least understood known fundamental particle. The undetermined properties of the neutrino likely connects to some of the largest open questions in modern physics such as the origin of neutrino mass, nature of dark matter, and whether there are undiscovered forces of nature. Progress resolving these open questions is slow primarily because neutrinos interact very feebly with matter. Thus, neutrino experiments are typically massive, often measured in the thousands of tons. We will build and operate a detector that will test the unknown properties of neutrinos with a small, 10-kg detector by searching for very low energy signals. A small-scale detector enables full engagement in neutrino science by students from design to data analysis. The PIs will leverage this opportunity to involve young scientists at Florida State University, North Carolina Central University, and the University of South Dakota and nurture their identities as early career neutrino physicists. The detector constructed under this project will measure coherent, elastic neutrino-nucleus scattering (CEvNS) in which a low-energy (< 50 MeV) neutrino transfers a small kinetic energy to a nucleus (< 100 keV). Low-threshold detectors are critical for CEvNS measurements. We will design, construct, and deploy a cryogenic, undoped CsI scintillation detector at the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory (ORNL) as part of the COHERENT experiment. This technology has demonstrated impressive light output with potential for detection thresholds twenty times lower than the first detection of CEvNS, made by COHERENT in 2017. In the detector's baseline design, scintillation activity in a 10-kg CsI crystal will be monitored by an array of silicon photomultiplier light detectors. The detector will be housed in a low-activity copper support structure in a cryostat cooled to 40 K. The detector will be surrounded with a composite shielding to mitigate environmental gamma and neutron backgrounds along with scintillator panels to veto cosmic activity. The detector will be operating at the SNS by the end of this award. This project is co-funded by the Historically Black Colleges and Universities Undergraduate Program (HBCU-UP), which provides awards to strengthen STEM undergraduate education and research at HBCUs. 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.