Detector R&D with SiPMs
We develop and exploit low-threshold silicon detectors to extend the dark matter search into the sub-GeV mass regime, where conventional noble liquid detectors lose sensitivity.
Why silicon photomultipliers
Noble-liquid detectors see the world through light. A particle interaction in liquid argon or xenon produces a faint flash of ultraviolet scintillation, and the performance of the experiment — its energy threshold, its energy resolution, its ability to tell signal from background — depends on how many of those photons are detected.
Silicon photomultipliers (SiPMs) have become the photosensor of choice for the next generation of experiments. Compared with traditional photomultiplier tubes they offer single-photon sensitivity at cryogenic temperatures, lower intrinsic radioactivity, compact geometry that allows nearly full coverage of large detector surfaces, and low operating voltage.
Using them at the scale of tens of square meters raises its own questions, which have been a thread through our work:
- Photon detection efficiency at the vacuum-ultraviolet wavelengths of xenon (175 nm) and argon (128 nm) scintillation.
- Correlated noise and dark counts, which set the effective threshold and energy resolution of a large-area detector.
- Reflectivity of the sensor surface, which determines how light propagates in a detector whose walls are covered in silicon.
- Operation in real detector conditions — at cryogenic temperature, immersed in the noble liquid, and in strong electric fields.
- Large-scale production, from wafer-level cryogenic testing to assembly into tiles and photodetector units with reliable quality control.
Toward lower thresholds
The lightest dark matter candidates deposit so little energy that only a handful of photons or electrons are produced. Reaching these signals requires sensors with single-quantum sensitivity and extremely low noise. We are interested in pushing silicon-based detectors in this direction to open up the sub-GeV dark matter mass range.