Jul. 7, 2022
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UMass Amherst Office of Communications
性闻联播
Chris Nedlik who received his PhD in physics at UMass, sealing liquid xenon in the UMass model of the LZ detector that he and Scott Hertel built in Hertel鈥檚 lab. Image credit: UMass Amherst
Deep below the Black Hills of South Dakota, the Sanford Underground 性闻联播 Facility (Sanford Lab) is hosting an innovative and uniquely sensitive dark matter detector鈥攖he , led by Lawrence Berkeley National Lab (Berkeley Lab) and to which physicists at UMass Amherst contributed. The LZ experiment has passed a check-out phase of startup operations and delivered first results, the very first step in helping to determine one of the fundamental mysteries of the universe.
No one has ever seen dark matter. It does not emit, absorb or scatter light, and yet it is estimated that about 85% of the total mass of the universe comes from the substance.
Dark matter is the main source of the gravity we see in astrophysics. We need dark matter. But no one has seen a dark matter particle.
Scott Hertel
Professor of Physics, UMass Amherst
鈥淭here are lots of problems in astrophysics which are solved by dark matter,鈥 says , a professor of physics at UMass Amherst and whose team designed some of the techniques and equipment to calibrate the LZ detector. 鈥淭here is more dark matter in the universe than normal matter. It tells us how galaxies form, how stars orbit and how things worked in the early universe, which was hot and dense. Dark matter is the main source of the gravity we see in astrophysics. We need dark matter. But no one has seen a dark matter particle. We have no idea what the particle is.鈥
Chris Nedlik, who received his Ph.D. in physics at UMass, works onsite and nearly a mile underground in a temporary clean-tent constructed to unwrap the LZ time projection chamber.
Image credit: UMass Amherst
That might soon change, thanks to the LZ experiment, which has just released results from its first 60 鈥渓ive days鈥 of testing, long enough to confirm that all aspects of the detector were functioning well. , LZ researchers report that with the initial run, LZ is already the world鈥檚 most sensitive dark matter detector.
LZ Spokesperson Hugh Lippincott of the University of California Santa Barbara said, 鈥淲e plan to collect about 20 times more data in the coming years, so we鈥檙e only getting started. There鈥檚 a lot of science to do and it鈥檚 very exciting!鈥
The heart of the LZ dark matter detector is buried nearly a mile underground in the Sanford Lab in Lead, S.D. The detector itself is comprised of two nested titanium tanks filled with ten metric tonnes of very pure liquid xenon and viewed by two arrays of photomultiplier tubes (PMTs) able to detect faint sources of light. LZ is designed to capture dark matter in the form of weakly interacting massive particles (WIMPs). The experiment is underground to protect it from cosmic radiation at the surface that could drown out dark matter signals.
鈥淲e鈥檙e hoping to see one atom of xenon get 鈥榢icked鈥 by one galactic WIMP particle, which will produce a brief and tiny signal: several electrons and several photons of light,鈥 says Hertel.
Particle collisions in the xenon produce visible scintillation or flashes of light, which are recorded by the PMTs, explained Aaron Manalaysay from Berkeley Lab who, as Physics Coordinator, led the collaboration鈥檚 efforts to produce these first physics results. 鈥淭he collaboration worked well together to calibrate and to understand the detector response,鈥 Manalaysay said.
The design, manufacturing, and installation phases of the LZ detector were led by Berkeley Lab project director Gil Gilchriese in conjunction with an international team of 250 scientists and engineers from over 35 institutions from the U.S., U.K., Portugal and South Korea. The LZ Operations Manager is Berkeley Lab鈥檚 Simon Fiorucci. Together, the collaboration is hoping to use the instrument to record the first direct evidence of dark matter, the so-called missing mass of the cosmos.
Mile-deep research
Chris Nedlik spent the entirety of his UMass Amherst physics Ph.D. research working with Hertel on the LZ detector鈥檚 calibration system.
鈥淚 was a graduate student at a really fortunate time,鈥 he says, 鈥渂ecause I got to see it all come together, and then got to spend a few months underground in South Dakota at the end.鈥
Nedlik readies the source injection panel for testing. This panel is part of the calibration system that the UMass team helped to design and build. Image credit: UMass Amherst
Because the LZ detector is so sensitive鈥擧ertel says that 鈥渋f one innocent object that has normal background radiation, like a banana, is around the detector, it could kill the experiment鈥濃攆iguring out how to calibrate it without destroying it was no small feat. So, the team build a scale model replica of the detector here at UMass and practiced calibrating it so that when they arrived in South Dakota, and confronted the real thing, they could perform their tasks flawlessly.
It was quite the experience for Nedlik. 鈥淚t was a huge transition working in an underground lab,鈥 he says. 鈥淵ou ride the lift down through pitch-black darkness for ten minutes and then arrive in a laboratory space that is fully finished. You wouldn鈥檛 even know you鈥檙e underground.鈥
鈥淥ne of the reasons that I chose to get my Ph.D. at UMass,鈥 Nedlik continues, 鈥渋s that I knew the department had many opportunities for world-class research. I didn鈥檛 exactly know what I wanted to do in physics, but over the course of the time working on LZ, I was constantly in disbelief that I got to contribute to a project like this and meet such incredible colleagues.鈥
The take-home message from this successful startup: 鈥淲e鈥檙e ready and everything鈥檚 looking good,鈥 said Berkeley Lab Senior Physicist and past LZ Spokesperson Kevin Lesko. 鈥淚t鈥檚 a complex detector with many parts to it and they are all functioning well within expectations,鈥 he said.
Mike Headley, executive director of Sanford Lab, said, 鈥淭he entire Sanford Lab team congratulates the LZ Collaboration in reaching this major milestone. The LZ team has been a wonderful partner and we鈥檙e proud to host them at Sanford Lab.鈥濃
One of the reasons that I chose to get my Ph.D. at UMass is that I knew the department had many opportunities for world-class research. I didn鈥檛 exactly know what I wanted to do in physics, but over the course of the time working on LZ, I was constantly in disbelief that I got to contribute to a project like this and meet such incredible colleagues."
Chris Nedlik
Physics Ph.D. Candidate, UMass Amherst
LZ is supported by the U.S. Department of Energy, Office of Science, Office of High Energy Physics and the National Energy 性闻联播 Scientific Computing Center, a DOE Office of Science user facility. LZ is also supported by the Science & Technology Facilities Council of the United Kingdom; the Portuguese Foundation for Science and Technology; and the Institute for Basic Science, Korea. Over 35 institutions of higher education and advanced research provided support to LZ. The LZ collaboration acknowledges the assistance of the Sanford Underground 性闻联播 Facility.
