Grant: Subatomic Physics Envelope - Research Tools and Instruments

Sterile neutrinos (SN) are mysterious new particles predicted by theory that offer an intriguing possibility in the quest for understanding the nature of dark matter (DM) and could have far-reaching cosmological implications as their properties might be linked to the matter-antimatter asymmetry, which is an outstanding puzzle in cosmology. Unlocking these connections could provide insights into the universe's origins and evolution including galaxy formation. Unlike the known "active" neutrinos in the Standard Model of particle physics, SN do not interact with normal matter, making them very difficult to detect. However, their presence can be indirectly inferred through their mass-generated effects from momentum conservation with SM particles. For the past few years, the BeEST (Beryllium Electron capture in Superconducting Tunnel junctions (STJs)) collaboration has taken the approach of embedding electron-capture (EC) decaying radioisotopes in thin-film STJs to precisely measure the recoiling atom that gets an eV-scale "kick" from the neutrino following EC decay. Since these recoils must conserve energy and momentum with the neutrino, they carry unique and potentially "hidden" signatures of weakly coupled beyond standard model (BSM) physics; including neutrino mass, exotic weak currents, and potential "dark" particles created within the Q-value window of the decay. Such measurements provide a complimentary and model-independent portal to the dark sector with sensitivities that push towards synergy between laboratory and cosmological probes. Recent advances in rare isotope beam (RIB) production, combined with decades of development in sensing technology have opened exciting new experimental opportunities for conducting fundamental tests of nature involving unstable nuclei. This approach is a powerful, model independent method in the search for BSM physics and is the most sensitive of its kind to date. This powerful technique triggered efforts for applications beyond the search for SN in the EC decay of 7Be, the presently only investigated science case within the collaboration. STJs need to be operated at low temperatures ~10 to 100 mK. We request funds to equip an existing dilution refrigerator at TRIUMF for STJ operation on site. Direct access to RIBs makes TRIUMF the ideal location to employ STJs for precision measurements and explore new applications for the technique. These include investigations of other EC decaying isotopes to independently verify potential evidence for SNs, increase the sensitivity of the BeEST and investigate material effects, as well as BSM physics searches in the High-Energy Physics domain with the goal to detect eV-scale dark photons (DM candidate). Lastly, the requested equipment will enable interdisciplinary research collaborations at TRIUMF and allow us to investigate applications for medical physics, i.e., spectroscopy on shorter-lived Auger emitting isotopes will become possible when operating STJs at TRIUMF.