Liquid-noble Bubble Chambers for Dark Matter and CEvNS Detection

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The identity of dark matter, which makes up nearly 85% of the matter in the Universe, and the origin of the matter/anti-matter asymmetry are two of the current fundamental unknowns in modern physics. Novel instrumentation is under development aimed at resolving both challenges via searches for GeV-scale dark matter and precision measurements of neutrino properties via coherent elastic scattering (CEvNS) of reactor neutrinos. Scalable background-discriminating techniques, like Scintillating Bubble Chambers (SBC), hold the potential to revolutionize the sensitivity in these searches. This award supports personnel at Northwestern University and Northeastern Illinois University in operating, and analyzing the data from, a 10kg liquid-argon SBC located at the Fermi National Accelerator Laboratory located near Batavia IL USA. The team will characterize response of the SBC to determine the low-threshold reach of this technology to distinguish electron and nuclear recoils below approximately 1 keV. The award provides unique opportunities for hands-on instrumentation experiences for undergraduate researchers, with a directed effort to broaden access to, and participation within, the physics community for local low-income and first-generation students. Nuclear recoils in liquid-noble gas bubble chambers simultaneously create a flash of scintillation light and nucleate a single bubble in a superheated liquid target. By combining the electron-recoil insensitivity of the instrument and the position reconstruction of a bubble chamber with the event-by-event energy resolution of a scintillator, the SBC technique holds the potential to eliminate all known backgrounds to dark matter and CEvNS signals. In addition, superheated noble liquids maintain electron-recoil insensitivity at far higher degrees of superheat than can be achieved in existing molecular-fluid bubble chamber, potentially extending the quasi-background-free operation of the SBC to thresholds as low as 100 eV. The SBC ability to discriminate the electron- and nuclear-recoils at low-energy may suppress background event levels to that needed to reach the solar neutrino coherent scattering flow in a dark matter search, and to achieve signal-to-noise of better than 1 in reactor CEvNS studies.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.