Super Cryogenic Dark Matter Search (Super CDMS)

Observations of galaxies, galaxy clusters, distant supernovae, and cosmic microwave background radiation tell us that about 85% of the matter in the universe is made up of one or more species of dark matter. With the continuing success of the Standard Model of particle physics, the existence of dark matter provides one of the few tangible sign posts as we seek to understand what lies beyond the Standard Model. Deciphering the nature of this dark matter would be of fundamental importance to cosmology, astrophysics, and high-energy particle physics.

A leading hypothesis is that dark matter consists of particles produced moments after the Big Bang. SuperCDMS is one of several experiments underway to directly detect these particles and begin an era of dark matter science that we hope will enable us to understand the nature of dark matter.

The SuperCDMS Experiment

The SuperCDMS experiment is designed to detect dark matter particles with masses in the range of about 0.5 GeV/c2 to 10 GeV/c2, equivalent to the mass of about 0.5 to 10 protons. The SuperCDMS SNOLAB experiment is currently (as of 2020) being installed underground in SNOLAB facility in Sudbury, Ontario, Canada. SuperCDMS SNOLAB follows on from previous versions of the experiment located underground at Stanford University and then underground at the Soudan Mine, a former iron mine in Minnesota.

SuperCDMS uses ~1 kg crystals of silicon and germanium, that are cooled to fraction of a degree Kelvin. These ultra-cold crystals are designed to detect dark matter particles colliding with silicon and germanium nucleons, and measure the collision energy deposited into phonons in the crystals. The experiment at SNOLAB will have a total of 24 detector crystals—18 germanium and six silicon—arranged in four towers, with each tower housing a stack of six detector crystals.

SuperCDMS SNOLAB Germanium crystal detector within its protective copper housing. The electrical readout cable wraps around the exterior and mates to the superconducting flex cable visible to the left. (Credit: Andy Freeberg / SLAC.)
SuperCDMS SNOLAB Germanium crystal detector within its protective copper housing. The electrical readout cable wraps around the exterior and mates to the superconducting flex cable visible to the left. (Credit: Andy Freeberg / SLAC.)

 

Two types of detector operation and readout will be used, to help discriminate between nuclear recoils from dark matter particle interactions and electron recoils. The energy deposited in a detector by an interacting dark matter particle may be as low as a few tens of electron volts (eV). The SuperCDMS SNOLAB experiment is scheduled to begin a three-year period of science data collection in 2022, following construction of the experiment at SNOLAB during 2020–2021 and a one-year commissioning period.

The SuperCDMS Collaboration

The SuperCDMS SNOLAB experiment is being built by the member institutions of the SuperCDMS Collaboration, in a project funded by the Department of Energy (DOE) and the National Science Foundation (NSF) in the U.S., and by the Canada Foundation for Innovation (CFI) in Canada. SLAC National Accelerator Laboratory (SLAC) is hosting the the management of the project and other major collaborators include Fermi National Accelerator Laboratory (Fermilab), Pacific Northwest National Laboratory (PNNL), SNOLAB, and a consortium of U.S. and Canadian universities. KIPAC professor Blas Cabrera was the first Project Director, and the current Project Director is KIPAC professor David MacFarlane. Stanford and SLAC scientists and engineers are responsible for detector fabrication, and the design, assembly, and cold-testing of the final detector towers, managed by KIPAC senior staff scientist Richard Partridge.

The SuperCDMS Collaboration consists of about 100 members from 26 institutions, of which 16 institutions are in the U.S., six are in Canada, and one each can be found in the UK, France, Germany, and India. Of the US institutions, three are DOE national laboratories (Fermilab, PNNL and SLAC), while seven university groups have research support from DOE (Caltech, Florida, Minnesota, South Dakota Mines, South Dakota, Stanford, and Texas A&M), and six university groups have research support from NSF (Berkeley, U. Colorado Denver, Florida, Northwestern, Santa Clara, and Southern Methodist U). The six Canadian institutions are British Columbia, Montreal, Queen’s, SNOLAB, Toronto, and TRIUMF.

SuperCDMS Operations

Operations of the SuperCDMS SNOLAB experiment will be managed at SLAC. The Operations Manager is SLAC staff scientist and KIPAC member Dr. Robert Cameron, with Deputy Operations Managers supported by NSF and Canada.

The operations team will be responsible for installing and integrating the experiment at SNOLAB, and then commissioning the experiment to bring it to a science-ready level of performance. Following three years of science data-taking, the operations team will then be responsible for the decommissioning and disposition of the experiment. SuperCDMS operations scope also includes testing of detectors at the Cryogenic Underground TEst (CUTE) facility located underground at SNOLAB, and calibration and response measurement of detectors at the Northwestern EXperimental Underground Site (NEXUS) facility at Fermilab. SuperCDMS Operations makes use of the computing facility at SLAC, with SuperCDMS data being processed, archived and managed at SLAC, and with secondary data storage at Fermilab.

For more information, see SLAC's SuperCDMS webpage.