Cryogenic & SiPM Facility

The APEX group at Carleton is at the forefront of noble-liquid 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. Our group also has a leading role in DEAP-3600 at SNOLAB, currently the world’s largest liquid argon dark matter detector.

The cryogenic facility planned for construction at Carleton in 2017-18 will facilitate, and further improve the continuation of research into noble-liquid detector technologies, and their implementation into the next generation of dark matter and neutrinoless double beta decay experiments. In particular, the facility will address challenges posed by the design of future detectors, the scales of which are many times larger than the current generation, leading to improved sensitivity to the physics of interest.
 

Concept design for a next generation EXO detector (nEXO). (Left)An 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.

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 photodetectors and readout hardware to be used in such experiments. The primary UV scintillation light from xenon will be directly detected, while that for argon will need to be wavelength shifted. Candidates for reading out the resulting photons are photomultiplier tubes (PMTs) and silicon photomultipliers (SiPMs).

PMTs have traditionally been used, and are typically most efficient in the visible 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 noble-liquid based detectors. Other objectives of the facility include:

  • Prototyping of single and dual-phase detector technologies.
  • Wavelength shifting materials for optimal background rejection.
  • Long term noble-liquid purity and stability studies.
  • Scattering and absorption of bulk noble liquids.
  • Recirculation of noble liquids.
  • Calibration and characterization of optical readout prototypes.
  • Control and characterisation of radioactive backgrounds.