Success! First results from the world’s most sensitive dark matter detector

LZ team members in the LZ water tank after installing the external detector. Credit: Matthew Capost, Sanford Underground Research Facility

Berkeley Lab researchers record successful start-up of the LUX-ZEPLIN dark matter detector at Sanford Underground Research Facility

Innovative and uniquely sensitive dark matter detector Lux Zeppelin Experiment (LZ) – Passed the startup logout phase and provided the first results. LZ is located deep in the Black Hills of South Dakota in Sanford Underground Research Facility (SURF) and is led by the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Laboratory).

“We’re ready and everything looks good,” said Berkeley Lab chief physicist and former LZ spokesperson Kevin Lesko. “It is a complex detector with many parts and they all work well within expectations,” he said.

In a paper published on July 7 on the experiment websiteLZ scientists report that with initial operation, LZ has already become the world’s most sensitive dark matter detector. The paper will appear in the online preprint archive arXiv.org at a later date. LZ spokesperson Hugh Lippincott of the University of California, Santa Barbara, said: “We plan to collect about 20 times as much data in the coming years, so we’re just beginning. There’s a lot of science to be done which is very exciting!”

Research the LZ Outer Detector, which is used to reject radioactivity that could mimic a dark matter signal. Credit: Matthew Capost/Sanford Underground Research Facility

While dark matter The particles are not actually detected, they may not be true for much longer. The countdown may already have begun with results from the first 60 “live” days of testing for LZ. This data was collected over three and a half months of initial operations beginning at the end of December. This was long enough to make sure all sides of the detector were working properly.

Although it is invisible, because it does not emit, absorb, or scatter light, the existence of dark matter and the gravitational pull are nonetheless fundamental to our understanding of the universe. For example, the presence of dark matter, which is estimated to be about 85 percent of the universe’s total mass, shapes the shape and motion of galaxies, and researchers cite it to explain what is known about the large-scale structure. and expanding the universe.

Two nested titanium tanks filled with ten tons of ultra-pure liquid xenon can be viewed by two arrays of photomultiplier tubes (PMTs) capable of detecting dim light sources from the core of the LZ dark matter detector. Titanium tanks are located in a larger detector system to capture particles that may mimic a dark matter signal.

Schematic of the LZ detector. Credit: LZ تعاون Collaboration

“I am delighted to see this complex detector ready to address the long-standing issue of what dark matter is made of,” said Natalie Palanque Delabruille, director of the Department of Physics at Berkeley Lab. “Team LZ now has the most ambitious tool to do this!”

The LUX-ZEPLIN detector design, manufacture and installation phases were led by Berkeley Lab Project Manager Gil Gilchriese in conjunction with an international team of 250 scientists and engineers from more than 35 institutions in the US, UK, Portugal and South Korea. LZ’s Director of Operations is Simon Fiorucci of Berkeley Lab. Together, they hope to use the instrument to record the first direct evidence of dark matter, or the so-called missing mass in the universe.

Henrique Araujo, from[{” attribute=””>Imperial College London, leads the UK groups and previously the last phase of the UK-based ZEPLIN-III program. He worked very closely with the Berkeley team and other colleagues to integrate the international contributions. “We started out with two groups with different outlooks and ended up with a highly tuned orchestra working seamlessly together to deliver a great experiment,” Araújo said.

An underground detector

Tucked away about a mile underground at SURF in Lead, South Dakota, LUX-ZEPLIN 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.

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’s efforts to produce these first physics results. “The collaboration worked well together to calibrate and to understand the detector response,” Manalaysay said. “Considering we just turned it on a few months ago and during COVID restrictions, it is impressive we have such significant results already.”

When a WIMP – a hypothetical dark matter particle – collides with a xenon atom, the xenon atom emits a flash of light (gold) and electrons. The flash of light is detected at the top and bottom of the liquid xenon chamber. An electric field pushes the electrons to the top of the chamber, where they generate a second flash of light (red). LZ will be searching for a particular sequence of flashes that cannot be due to anything other than WIMPs. Credit: LZ/SLAC

The collisions will also knock electrons off xenon atoms, sending them to drift to the top of the chamber under an applied electric field where they produce another flash permitting spatial event reconstruction. The characteristics of the scintillation help determine the types of particles interacting in the xenon.

The South Dakota Science and Technology Authority, which manages SURF through a cooperative agreement with the U.S. Department of Energy, secured 80 percent of the xenon in LZ. Funding came from the South Dakota Governor’s office, the South Dakota Community Foundation, the South Dakota State University Foundation, and the University of South Dakota Foundation.

Mike Headley, executive director of SURF Lab, said, “The entire SURF 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 SURF.”

Chemists at Brookhaven Lab used this custom-made vacuum distillation system to purify linear alkyl benzene needed to produce liquid scintillator for the LZ dark matter experiment. Credit: Brookhaven Lab

Fiorucci said the onsite team deserves special praise at this startup milestone, given that the detector was transported underground late in 2019, just before the onset of the COVID-19 pandemic. He said with travel severely restricted, only a few LZ scientists could make the trip to help on site. The team in South Dakota took excellent care of LZ.

“I’d like to second the praise for the team at SURF and would also like to express gratitude to the large number of people who provided remote support throughout the construction, commissioning and operations of LZ, many of whom worked full time from their home institutions making sure the experiment would be a success and continue to do so now,” said Tomasz Biesiadzinski of SLAC, the LZ detector operations manager.

“Lots of subsystems started to come together as we started taking data for detector commissioning, calibrations and science running. Turning on a new experiment is challenging, but we have a great LZ team that worked closely together to get us through the early stages of understanding our detector,” said David Woodward from Pennsylvania State University who coordinates the detector run planning.

The LZ central detector in the clean room at Sanford Underground Research Facility after assembly, before beginning its journey underground. Credit: Matthew Kapust, Sanford Underground Research Facility

Maria Elena Monzani of SLAC, the Deputy Operations Manager for Computing and Software, said “We had amazing scientists and software developers throughout the collaboration, who tirelessly supported data movement, data processing, and simulations, allowing for a flawless commissioning of the detector. The support of NERSC [National Energy Research Scientific Computing Center] It was invaluable.”

With confirmation that the LZ and its systems are working successfully, Lisko said, it’s time to begin large-scale observations in the hope that a dark matter particle collides with xenon.[{” attribute=””>atom in the LZ detector very soon.

LZ is supported by the U.S. Department of Energy, Office of Science, Office of High Energy Physics and the National Energy Research 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 Research Facility.