The completion of the detector towers for the SuperCDMS SNOLAB dark matter detection experiment marks a significant milestone achieved by researchers at the Department of Energy's SLAC National Accelerator Laboratory. The towers were finished in September of last year, and two of them have already been sent to SNOLAB in Ontario, Canada.
SuperCDMS SNOLAB aims to detect relatively light dark matter particles, ranging from half the mass of a proton to about 10 proton masses. In this mass range, it will be the most sensitive direct-detection experiment in the world. Richard Partridge, a senior staff scientist at SLAC and a long-time SuperCDMS researcher, attributes this achievement to advancements in detector design and the strategic location of the experiment at SNOLAB.
The project has involved the development of innovative technologies such as flexible superconducting cables, electronics systems capable of functioning in extreme cold, improved cryogenics systems, and enhanced detector shielding. These advancements have greatly improved the ability to detect passing dark matter particles.
The experiment's underground location at SNOLAB, situated 1.25 miles below the surface, offers the advantage of reduced interference from cosmic ray background, further enhancing the prospects of detecting a dark matter signal.
Jodi Cooley, Executive Director of SNOLAB, expresses excitement about the potential of SuperCDMS to directly detect dark matter and deepen our understanding of the universe's nature.
Vitaly Yakimenko, SLAC's Deputy Director for Projects and Infrastructure and SuperCDMS Project Director, emphasizes the technological development spanning a decade to create these state-of-the-art detectors. Regardless of the outcome, the experiment sets the stage for more sensitive experiments in the future.
JoAnne Hewett, head of SLAC's Fundamental Physics Directorate, underscores the significance of understanding dark matter and expresses satisfaction with the experiment's progress. She looks forward to collaborating with partners to construct this cutting-edge experiment.
Searching deep underground
Scientists have determined that the visible matter we can observe in the universe, such as planets, stars, and dust, only constitutes about 15% of the total matter present. The remaining portion is known as dark matter, the nature of which remains a mystery. Although its gravitational effects on ordinary matter confirm its existence, detecting dark matter directly is extremely challenging.
This is where experiments like SuperCDMS SNOLAB come into play. The project represents the latest advancement in a series of experiments utilizing silicon and germanium crystals to search for dark matter particles. These crystals are cooled to temperatures just above absolute zero, earning the experiment its name: Cryogenic Dark Matter Search or CDMS. The idea is that by achieving such low temperatures, researchers can identify the vibrations generated by dark matter particles colliding with the crystals.
These collisions generate pairs of electrons and electron deficiencies, known as holes, which traverse the crystals, leading to further vibrations and amplifying the dark matter signal. Advanced superconducting electronics are employed to detect these signals.
To facilitate this endeavor, the experiment will be constructed and operated at SNOLAB, located 6,800 feet underground within a nickel mine near Sudbury, Ontario. This underground location shields the SLAC-built detectors from cosmic radiation, high-energy particles that could produce unwanted background signals.
A long journey
After completing the construction of the detectors, the SLAC team faced the challenge of transporting them to SNOLAB while minimizing exposure to cosmic rays. The team had to consider the tradeoff between a direct route over the Rocky Mountains or a flight to Ontario for quicker delivery versus the thinner atmosphere at higher altitudes, which provides less protection from cosmic rays.
Tarek Saab, SuperCDMS spokesperson and physicist from the University of Florida, explained the decision-making process: “In principle, we want to keep things as low as possible, but there's also a cost to the total number of days you're on the surface. So, we want a route that gives you the least overall exposure to cosmic rays.”
Ultimately, the team opted for an eastern route, traveling through Texas before heading north to SNOLAB.
Meanwhile, SNOLAB has been diligently preparing the SuperCDMS facility to accommodate the detectors. The first two detectors arrived on May 12 and were transported 6,800 feet underground the following day. The remaining towers will arrive later this year, and initial preparations for the experiment are expected to be finalized by 2024. At that point, the experimental team can commence data collection, working through any remaining system adjustments. Researchers anticipate running the experiment for three to four years until they gather enough data to push the boundaries of our knowledge about dark matter.
Saab expressed the excitement surrounding the delivery of the detectors, stating that having them at SNOLAB will be a significant milestone for the project.
Source: SLAC National Accelerator Laboratory