Underground Dark Matter Search Experiment Reaches Major Milestone

The LUX-ZEPLIN time projection chamber, the experiment’s main detector, is pictured here in a clean room at the Sanford Underground Research Facility before it was wrapped up and delivered underground. Credit: Matthew Kapust/Sanford Underground Research Facility

LUX-ZEPLIN crews overcome COVID-19 obstacles to reach major milestone en route to startup.

Crews working on the largest U.S. experiment designed to directly detect dark matter completed a major milestone last month, and are now turning their sights toward startup after experiencing some delays due to global pandemic precautions.

U.S. Department of Energy officials on September 21 formally signed off on project completion for LUX-ZEPLIN, or LZ: an ultrasensitive experiment that will use 10 metric tons of liquid xenon to hunt for signals of interactions with theorized dark matter particles called WIMPs, or weakly interacting massive particles. DOE’s project completion milestone is called Critical Decision 4, or CD-4.

LZ’s central detector, pictured here during assembly, is located inside a large water tank on the 4850 Level of Sanford Lab. LZ will search for theorized dark matter particles known as WIMPs. Credit: Nick Hubbard/Sanford Lab

Dark matter makes up an estimated 85 percent of all matter in the universe. We know it’s there because of its observed gravitational effects on normal matter, but we don’t yet know what it is. LZ is designed to detect the two flashes of light that occur if a WIMP interacts with the nucleus of a xenon atom.

“We are completing commissioning of the detector – the testing phase – and will be looking at LZ data next year,” said Simon Fiorucci, LZ operations manager and a physicist at the DOE’s Lawrence Berkeley National Laboratory (Berkeley Lab), which is the lead institution for the LZ collaboration.

LZ is installed nearly a mile below ground at the Sanford Underground Research Facility (Sanford Lab) in Lead, South Dakota. Its depth provides natural shielding against the constant shower of cosmic rays at the Earth’s surface, which are a source of background particle “noise” that could drown out the WIMP interaction signals scientists are searching for. LZ is also built from components that have been individually selected and tested to be low in naturally occurring radiation that could also complicate the search.

Mike Headley, executive director of Sanford Lab, said, “The entire Sanford Lab team congratulates the LZ Collaboration in reaching this major milestone. The LZ team has been a wonderful partner and we’re proud to host them at Sanford Lab. We’re looking forward to LZ data collection next year.”

The response to the COVID-19 pandemic led Sanford Lab to reduce its operations to only those deemed essential on March 25, and the site began a transition back toward increased operations on May 6. Berkeley Lab and other institutions in the LZ collaboration had also reduced their operations in response to the coronavirus. Sanford Lab, and LZ project workers, were fortunate in being able to resume work quickly, Fiorucci noted.

An array of photomultiplier tubes that are designed to detect signals occurring within LZ’s liquid xenon tank. Credit: Matt Kapust/Sanford Lab

He noted that xenon-purifying activities at SLAC National Accelerator Laboratory had been temporarily delayed due to COVID-19-related reductions. Xenon purified at SLAC will be shipped to Sanford Lab and converted to liquid xenon for the LZ experiment.

“We’ve made decent progress despite all of these complications,” he said. “We’d managed to maintain a workforce at Sanford Lab and at SLAC, and to keep things going at least at 80 percent speed. By June we were back at nominal speed, and have been back in that mode since.”

Even so, COVID-19 risks persist, and Fiorucci noted that workers continue to adhere to safety protocols to reduce these risks. During this commissioning phase, there are about 15-20 LZ workers split into two shifts at Sanford Lab, Fiorucci said, and he expects that level of staffing to hold through the end of this year.

Now that CD-4 has been achieved, Fiorucci said it’s exciting to have the finish line in sight.

“We are getting a lot less engineering – and a lot more science – in the mix,” he said. “It’s certainly exciting and thrilling.” He noted that members of the collaboration have been in this position before: LZ’s predecessor, the LUX experiment, was also installed and operated in the same underground research cavern at Sanford Lab.

But this time it’s different.

Dark MatterDOELawrence Berkeley National LaboratoryLUX-ZEPLINParticle Physics
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  • The 10th Man

    What an outrageous waste of wealth. Dark matter is simply mass bleeding through dimensional walls. Mass rules in this universe and all others. Wake up.

  • Howard Jeffrey Bender

    Well, I certainly wish them luck, especially since LUX didn’t find anything.

    Another possibility, from a view of String Theory, is that Dark Matter appears to us as an effect of string/anti-string annihilations. As you may know, quantum mechanics requires that strings must be formed as pairs in the quantum foam – a string and an anti-string – that immediately annihilate each other. Quantum mechanics also requires both the string and anti-string to be surrounded by “jitters” that reduce their monstrous vibrating energies. What if this jitter remains for a fraction of an instant after their string/anti-string annihilations? This temporary jitter would be seen by us as matter for that instant before it too returns to the foam. That’s why we never see it – the “mass” lasts only for that instant but is repeated over and over and over, all over. Specifics on this can be found in my YouTube at https://www.youtube.com/watch?v=N84yISQvGCk

  • Julian Rosenman

    It is hard to judge which of the two above ideas is more nonsensical. Yet, in a way, they touch on two reasonable possibilities; 1) dark matter is the residual effect of ordinary mass from “nearby” extra-dimensional universes — perhaps containing our missing antimatter or 2) it has something to do with the mysterious, incalculable zero-point energy of the vacuum of our universe.

    If the LUX-ZEPLIN experiment fails to show dark matter then we need to expand our thinking on what might cause galaxies to spin too fast or what appears to be gravitational lensing.

    In the play “Hamlet” by Shakespeare Hamlet suggests, “There are more things in heaven and Earth, Horatio, / Than are dreamt of in your philosophy.”

  • xABBAAA

    … business as usual, … it goes till it fails…