Physics Colloquium

Searches for dark matter in the mass range for meV to GeV scale (neutrino to proton mass scale) require the development of macroscopic detectors with sensitivity to meV-eV scale energy depositions and very low background rates. Unfortunately to date, all light mass dark matter calorimeters have measured a low energy unexplained, non-ionizing background whose rate decreases with time since cooldown. These observed background characteristics strongly disfavor standard radiogenic background hypotheses, and suggest that stress relaxation processes which produce athermal phonon bursts within the calorimeter or its mechanical support are the most likely background source. We've explicitly shown that the use of glue for the mechanical support and thermal link of the calorimeter increases this background by 2 orders of magnitude at low energies. Recently, we've further characterized this unexplained background and have shown that a significant fraction of this background is consistent with stress relaxation within the Al and W metal films of our calorimeter.

Due to the similarity of materials used in these calorimeters (superconducting Al films on Si substrates), it is likely that this background source contributes to the quasi-particle excess seen in superconducting qubits as well.

Join via Zoom:
https://caltech.zoom.us/j/81866929019
Meeting ID: 818 6692 9019

The colloquium is held in Feynman Lecture Hall, 201 E. Bridge.