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In the early 2020s, an experiment on dark matter to be put online by the Canadian SNOLAB underground laboratory will carry out one of the most sensitive research on hypothetical particles called low interaction solid particles, or WIMP.
Scientists consider WIMPs to be candidates for dark matter. But what if dark matter turns out to be something else? After all, despite intense hunting with increasingly sophisticated detectors, scientists still need to directly detect dark matter.
That's why researchers at SNOLAB's SuperCDMS dark matter experiment are looking for ways to expand their research. And they found one: they tested a prototype detector that would allow their experience to also search for much lighter dark matter candidates.
"This development is exciting because it gives us access to a new particle sector, where alternatives to WIMP might be hiding," says Priscilla Cushman of the University of Minnesota, spokesperson for the SuperCDMS collaboration. "It also demonstrates the flexibility of our sensing technology, now reaching the energy thresholds and resolutions that were not possible a few years ago."
The collaboration released the results of the first research on low mass dark matter with new technology Letters of physical examination. Some scientists on the team also described the prototype in a previous article Applied Physics Letters.
An ultrasensitive microphone for dark matter
The heart of the SuperCDMS experiment is made up of highly sensitive detectors on the top and bottom silicon-germanium crystals in the shape of hockey pucks. The detectors are able to observe very small vibrations caused by dark matter particles passing through the crystals. The challenge in using this technology to find dark matter particles is that the lighter the particle, the smaller the vibrations.
"To pick up these vibrations, you need an extraordinary microphone," says Matt Pyle, of the University of California, who contributed to both articles. "Our goal is to create microphones – detectors – that are sensitive enough to detect very light particle signals. Our technology is at the forefront of what is currently possible. "
Vibrations caused by a dark matter interaction can also dislodge negatively charged electrons in the crystal. This leaves positively charged spots or holes where the electrons are. If an electric field is applied, the electron pairs and the holes pass through the crystal in opposite directions, and the detector can measure their charge.
One way to make the experience more sensitive is to increase the efficiency with which it measures the charge of electron-hole pairs. This approach has been the main factor in improving sensitivity up to now. The predecessor of SuperCDMS SNOLAB – Sudan's SuperCDMS experiment, located in the Sudan mine in Minnesota – needed the charge of 70 pairs of electron-holes to perform a detection. SuperCDMS SNOLAB will only ask for half.
"But that's not the kind of improvement we've done here," says Roger Romani, an undergraduate student at Blas Cabrera's group at Stanford University and lead author of Applied Physics Letters paper. The team found a different way to make the experience even more sensitive.
"In our approach, we counted the number of electron-hole pairs by observing the vibrations they caused when crossing our detector crystal," he explains.
To do this, Cabrera's team, joined by Pyle and Betty Young of Santa Clara University, applied a high voltage that pushed the electron-hole pairs through the crystal. The acceleration led to the production of more vibrations, in addition to those created without tension.
"As a result, our prototype is sensitive to a single electron-hole pair," says Francisco Ponce, a postdoctoral researcher on the Cabrera team. "The ability to measure a smaller charge gives us a higher resolution in our experience and allows us to detect lower mass particles."
First search for dark matter
The SuperCDMS collaboration used the prototype detector for a first dark matter search, and the result is promising.
"Experience shows that we are sensitive to a mass range in which we had no sensibility before," says Cabrera, former director of the SuperCDMS SNOLAB project at the Kavli Institute for Particle Astrophysics and Cosmology, an institute Department of Energy. SLAC National Accelerator Laboratory and Stanford.
Noah Kurinsky, a recent PhD student from the Cabrera group, says, "Although technology is in the early stages of development, we are able to set dark dark-matter properties and are already competitive with others. same mass range. "
The result is even more convincing given the experimental circumstances: Located in Cabrera's laboratory in a basement at Stanford, the experiment was not immune to the undesirable cosmic background (SuperCDMS SNOLAB will operate at 6,800 feet underground); he used a very small prototype crystal, limiting the size of the signal (Sudan's SuperCDMS crystals were 1500 times heavier); and this lasted relatively short time, limiting the amount of data for analysis (XENON10 had 20,000 times more exposure).
Eventually, researchers want to increase the size of their crystal and use it in a future SNOLAB SuperCDMS generation. However, much more R & D work needs to be done before this can happen.
Currently, they are working to improve the quality of the crystal and better understand its fundamental physics: for example, how to handle a quantum mechanical effect that randomly creates electron-hole pairs for no apparent reason and can create a signal background that looks exactly like a dark matter signal.
The team hopes their efforts will lead to new detector models that will continue to make SuperCDMS SNOLAB more powerful, says Pyle:
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