CAREER: R&D for Future Noble-Liquid-Based Dark Matter Searches: Hybrid Photosensors and Intrinsic Background Rejection

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Multiple astronomical observations have established that about 85% of the matter in the universe is not made of known particles. Deciphering the nature of this so-called Dark Matter (DM) is of fundamental importance to cosmology, astrophysics, and high-energy particle physics. Our knowledge about DM existence has grown significantly over the past decade, mainly through observation of its gravitational influence. However, fundamental questions still remain unsolved: Is DM a particle? Is there more than one type of DM? Does it interact via non-gravitational force? We are systematically searching for DM and scrutinizing the claims of its detection, but to date, no one has reported a conclusive DM signal. This forces us to broaden our search, as well as to develop technologies capable of making measurements orders of magnitude more sensitive than what is currently available. Direct DM detection experiments aim to measure the energy deposited by DM as it scatters off the atoms in a detector. Among them, noble-liquid-based experiments are presently leading the field and are expected to improve the sensitivity of DM searches by two orders of magnitude by the end of this decade. To achieve this, the experiments rely heavily on increasing target mass and achieving a very low background environment. The current generation of noble-liquid DM detectors is limited by the radioactivity in the detector materials, the photomultipliers (PMTs), and the target itself. This award will support the development of radio-pure hybrid photosensors with a simpler internal structure, much lower intrinsic sensor radioactivity, and significantly better charge resolution than a PMT. The UC Davis team will also design and construct a noble liquid test cell that will precisely tailor the effects of detector design parameters on the charge-to-light ratio background rejection. This effort will be combined with a related analysis in the liquid-argon-based DarkSide-50 DM search program. Employing the charge-to-light ratio rejection can extend the sensitivity of the DarkSide-50 detector in the energy region of importance for low mass DM searches.The main focus of the broader impacts is hands-on experience for students, ranging from high school to graduate school, combined with providing mentorship on how to successfully develop a STEM career. The PI will coordinate these efforts with two summer school programs: Nuclear Analytical Techniques (NAT) and the California State Summer School for Mathematics and Science (COSMOS). This award also aims to increase participation in the NAT School of students of underrepresented groups who will be selected through the application process of the Research Experiences for Undergraduates (REU) Physics program at UC Davis.