Probing new realms in the hunt for dark matter: low-mass detection

The ongoing efforts to directly detect dark matter have a primary focus on the search for WIMPS, or Weakly Interacting Massive Particles. Physicists have focused the dark matter search on WIMPs because the math shows they are among the most plausible candidates for the elusive missing mass that makes up a big part of the universe.   

The LUX-ZEPLIN (LZ) dark matter detector is the world’s leading experiment in the search for WIMPs. LZ is located a mile beneath the surface at the Sanford Underground Research Facility (SURF), in Lead SD. 

In the simplest sense, LZ is designed like an onion with several layers surrounding a core tank filled with 10 metric tons of liquid xenon. Researchers believe some of the particles of dark matter streaming through every square inch of the universe will interact with some of the xenon atoms. You can think of this interaction like two pool balls colliding. When this reaction happens, it will create a tiny flash of light at the center of the xenon chamber, possibly indicating dark matter. This collision liberates electrons from the xenon atoms. These electrons migrate up into the top of the chamber and as they exit the liquid into the gas a second flash of light occurs, providing more data for researchers. 

In physics, and all of science, theory must be proven experimentally. As scientists zero in on the possibilities for dark matter, the search is narrowing. Experiments, like LZ, are homing in on the possibilities for WIMPs. As the search continues, both the possible interaction strength that dark matter particles exhibit, and their potential weight, is shrinking.  

Seeing the Unseen

If dark matter falls low enough in this range of lighter particles with weaker interaction strength, eventually the pool-ball-type interaction analogy does not apply anymore. This is where different methods of searching for dark matter might be needed.

Maurice Garcia-Sciveres, a senior scientist at Lawrence Berkeley National Laboratory spoke on the subject of low-mass dark matter detection during a recent lecture hosted by the Institute for Underground Science at SURF called Deeper Talks: The End of Ionization. 

He explains, “there are particle interactions that are too weak to ionize—it’s these we're actually interested in.” 

If dark matter falls into this low-mass realm, the particles might be invisible to a detector like LZ, in a similar way that infrared light, created by a heat source, is invisible to the naked eye. Garcia-Sciveres compares lower-mass dark matter to a heater hidden in a dark room. “You would not be able to see this heat source, but if you put on a set of night vision goggles, then you’d see it bright as day. This is because our eyes can’t see the infrared wavelengths coming from this heat source without extra tools.”

Throughout the history of science, new tools have enabled new discoveries; Galileo’s telescope opened a revolution in cosmic understanding of his time. As the hunt for dark matter expands into these low-mass realms, the detection tools are pushing the boundaries of both physics and materials science. This is where physicists like Garcia-Sciveres are focusing their work. 

Supercooled superconductors expand the hunt

Garcia-Sciveres specializes in developing advanced instrumentation for discovering new particle interactions across energy and intensity extremes—including the realm of possibilities for low-mass dark matter. He has a long history in the field of physics, playing a pivotal role in the ATLAS experiment, and serving as co-founder and co-leader of the RD53 collaboration, to develop pixel readout integrated circuits for upgrades to the Large Hadron Collider at CERN. 

One aspect of Garcia-Sciveres research utilizes supercooled superconductors in various materials, this includes the use of transition edge sensors. In a nutshell, these sensors are two types of superconductors sandwiched together in a small chip and carefully kept at a specific temperature—on the transition point of superconductivity. 

Dark matter particles hitting one of these perfectly cooled chips could cause a tiny change in temperature—which could indicate their existence in this lower mass realm.   

The article “Small But Mighty: TESSERACT Joins the Hunt for Dark Matter,” explains how this technology is currently being employed in the ongoing hunt for dark matter. The TESSERACT experiment is planned to be installed inside dilution refrigerators at France’s Modane Underground Laboratory, with data taking expected to begin in 2029. 

You could compare the global hunt for dark matter to the coordinated search for a child lost in a large American corn field. If an entire small town was out looking for the child in the tall corn stalks, it would be important for search parties to report back to the local sheriff the locations where they have thoroughly scoured with no results; this way coordinators could move the resources to a new unsearched area. In this analogy, LZ could be searching in the daylight, and when the sun sets, TESSERACT would be similar to local officials bringing in night goggles to continue hunting in the dark. 

The right tool for the right job

Garcia-Sciveres notes that dilution refrigerators, which are used to super cool experiments and quantum computers to ultra-low operating temperatures, are essential for this kind of research.  He notes TESSERACT technology will be located in Japan before it comes online in France. 

“There's a new cryogenics lab at Kamioka that was recently established, so in the near term we have a collaboration with Kamioka in Japan.” 

Garcia-Sciveres said the underground laboratory in Japan will be able to start early research with TESSERACT technology this year. 

SNOLAB in Canada is among the global list of laboratories with dilution refrigerators being employed in underground research. The Cryogenic Underground TEst (CUTE) facility has supported development of experiments like SuperCDMS that is part of the global search for dark matter. Fermilab also has a laboratory dedicated to this research, the Quantum Underground Instrumentation Experimental Testbed, or QUIET is located about 300 feet underground in Illinois. Pacific Northwest National Laboratory’s superconducting qubit testbed sits inside the facility’s shallow underground laboratory in Washington state.  

SURF is actively seeking to install a cryogenics lab and a dilution refrigerator to house future research in quantum information science, including low-mass dark matter sensors, and other fields that would be empowered by this technology.

This article is based on a lecture, Deeper Talks: The End of Ionization given by Maurice Garcia-Sciveres, a senior scientist at Lawrence Berkeley National Laboratory and hosted by the Institute for Underground Science at SURF.