Development of Cryogenic Scintillation Detectors for the Search of New Physics

TL;DR

This paper presents the development and characterization of CryoCsI, a cryogenic scintillation detector with low energy threshold aimed at detecting new physics phenomena like CEvNS, dark matter, and non-standard neutrino interactions.

Contribution

It introduces CryoCsI, a novel cryogenic undoped CsI detector with enhanced sensitivity and discusses its construction, light yield improvements, and strategies to address cryogenic SiPM challenges.

Findings

Achieved light yield of 50 photoelectrons per keV$_{ee}$

Measured alpha and neutron quenching factors (~15%)

Identified challenges with cryogenic SiPMs and PMT overshoot effects

Abstract

CryoCsI, the proposed prototype, is a cryogenic undoped CsI scintillating detector, which has a much lower energy threshold potentially down to 0.5 keV$_{nr}$ compared to the doped CsI. This enhanced sensitivity of CryoCsI allows for the observation of more Coherent elastic neutrino-nucleus scattering events. Precise measurements of CEvNS can not only validate the predictions of the Standard Model but also explore new physics. In conjunction with other COHERENT detectors, CryoCsI has the potential to achieve world-leading sensitivities in a broad range of physics topics within and beyond the SM. The sensitivities of CryoCsI to hidden-sector dark matter, non-standard neutrino interactions, and neutron radius are explored. This thesis delves into the construction of CryoCsI and efforts to enhance its light yield from 20 to $50 \pm 2$ photoelectrons per keV electron-equivalent (keV$_{ee}$). It will address challenges with cryogenic SiPMs, including inferior energy resolution, optical cross-talk, and potential limitations on detecting rare events. Understanding the light yield of scintillating detectors for nuclear recoils is crucial, as explored through alpha-particle and neutron quenching factor measurements. A QF of approximately 15\% was measured using a neutron beam at the Triangle Universities Nuclear Lab. Proposed solutions to challenges like the overshoot effect observed in PMTs will be discussed. Additionally, the thesis will explore design considerations for minimizing background noise and optimizing the CsI crystal's shape through optical simulations.