Cryogenic & Silica-PM Facility

The group at Carleton is at the forefront of liquid-noble detector R&D with contributions to the world’s first hundred-kilogram scale xenon experiment, EXO-200; the first of its kind to measure the two-neutrino double beta decay of Xe-136. It also has a leading role in DEAP-3600, currently the world’s largest liquid argon dark matter detector.

The cryogenic facility planned for construction at Carleton in 2017 will facilitate, and further improve the continuation of research into liquid-noble detector technologies, and their implementation into the next generation of dark matter and neutrinoless double beta decay experiments. In particular, the goals of the facility are to address the challenges posed by the design of future detectors, the scales of which are many times larger than the current generation, but whose increased target masses are necessary in improving the overall sensitivity to physics of interest.

Shown above is a nEXO detector concept. (Left) Inner time projection chamber (TPC) showing charge readout tiles, SiPMs for light readout, and field shaping rings. (Right) Detector suspended in a water shielding tank in the SNOLAB Cryopit.

One of the primary goals of the facility is to determine the best optical read-out hardware to be used in such detectors. The primary UV scintillation light from xenon or argon will, respectively, either need to be directly detected or wavelength shifted. Candidates for reading out these produced photons are PMTs and SiPMs. PMTs have traditionally been used, and are typically most efficient in the optical regime. However, in lieu of currently unavailable ultra-low background fabrication, the radioactivity of conventional PMTs would be expected to contribute a sizeable, and overall unfeasible background rate. In addition, the operation of PMTs in close to cryogenic conditions has associated difficulties. SiPMs offer a viable alternative, with many advantages over PMTs. These include: sensitivity to both UV and optical photons, low mass, low residual natural radioactivity, insensitivity to magnetic fields, low-voltage operation, compact and flat form factor, and good performance at cryogenic temperatures. The facility at Carleton will test the scalability and versatility of SiPM technology for use in large liquid-noble based detectors. Other objectives of the facility include:

• Studies to determine an optimal wavelength shifter.
•  Prototyping of single and dual-phase detector technologies.
• Wavelength shifting materials for optimal background rejection.
• Long term liquid-noble purity and stability studies.
• Scattering and absorption of bulk noble-liquids.
• Calibration of optical read-outs.
• Recirculation of noble-liquids.
• Characterisation of alternative optical read-out methods.
• Control and characterisation of radioactive backgrounds.