Berkeley Lab researchers record success

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– By William Schultz

Deep in the Black Hills of South Dakota in the Sanford Underground Research Facility (SURF), an innovative dark matter detector with unique sensitivity – the LUX ZEPLIN (LZ), led by Lawrence Berkeley National Lab (Berkeley Lab) – passed a phase of verification of start-up operations and delivered the first results.

The take-home message from this successful startup: “We’re ready and all is well,” said Kevin Lesko, Berkeley Lab senior physicist and former LZ spokesperson. “It’s a complex detector with many parts and they all work well within expectations,” he said.

In an article posted online today about the experience website, LZ researchers report that with the first run, LZ is already the most sensitive dark matter detector in the world. The paper will appear on the arXiv.org online preprint archive later today. LZ spokesman Hugh Lippincott of the University of California, Santa Barbara said: “We expect to collect about 20 times more data in the coming years, so we’re just getting started. There is a lot of science to do and it is very exciting!

Dark matter particles have never been detected – but perhaps not for a long time. The countdown may have begun with the results of LZ’s first 60 “live days” of testing. This data was collected over a three and a half month period of initial operations beginning in late December. This was a long enough period to confirm that all aspects of the detector were working well.

Invisible, because it does not emit, absorb or scatter light, the presence and gravitational pull of dark matter are nevertheless fundamental to our understanding of the universe. For example, the presence of dark matter, estimated at around 85% of the total mass of the universe, shapes the shape and motion of galaxies, and it is invoked by researchers to explain what is known about the structure. and large-scale expansion. of the universe.

The heart of the LZ Dark Matter Detector is made up of two interlocking titanium tanks filled with ten tons of very pure liquid xenon and visualized by two photomultiplier tube (PMT) arrays capable of detecting faint light sources. The titanium tanks reside in a larger detection system to catch particles that might mimic a dark matter signal.

“I’m excited to see this complex detector ready to solve the long-standing problem of the composition of dark matter,” said Nathalie Palanque-Delabrouille, director of the Berkeley Lab’s physics division. “The LZ team now has the most ambitious instrument in hand to achieve this!”

The design, fabrication, and installation phases of the LZ detector were led by Berkeley Lab project director Gil Gilchriese, in collaboration with an international team of 250 scientists and engineers from more than 35 institutions in the United States, UK, Portugal and South Korea. LZ’s COO is Simon Fiorucci of Berkeley Lab. Together, the collaboration hopes to use the instrument to record the first direct evidence of dark matter, the so-called missing mass of the cosmos.

Henrique Araújo of Imperial College London leads the UK groups and previously the final phase of the UK-based ZEPLIN-III programme. He worked closely with the Berkeley team and other colleagues to incorporate international contributions. “We started with two bands with different perspectives and ended up with a very tuned orchestra working together seamlessly to deliver a great experience,” Araújo said.

An underground detector

Nestled about a mile underground at SURF in Lead, SD, 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 on the surface that could drown out dark matter signals.

Particle collisions in xenon produce visible scintillation or flashes of light, which are recorded by PMTs, explained Aaron Manalaysay of Berkeley Lab who, as physics coordinator, led the collaboration’s efforts to produce these first results of physics. “The collaboration worked well to calibrate and understand the detector response,” Manalaysay said. “Given that we just activated it a few months ago and during the COVID restrictions, it’s impressive that we already have such significant results.”

The collisions will also knock off electrons from xenon atoms, sending them drifting up the chamber under an applied electric field where they will produce another flash allowing reconstruction of spatial events. Scintillation characteristics help determine the types of interacting particles in xenon.

The South Dakota Science and Technology Authority, which operates SURF under a cooperative agreement with the US Department of Energy, obtained 80% of LZ’s xenon. 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 on reaching this major milestone. The LZ team has been a great partner and we are proud to welcome them to SURF.

Fiorucci said the on-site team deserved special praise at this start-up stage, given that the detector was transported underground in late 2019, just before the COVID-19 pandemic began. He said that with travel severely restricted, only a few LZ scientists could make the trip to help on site. The South Dakota team took very good care of LZ.

“I would like to second the praise of the SURF team and would also like to express my gratitude to the large number of people who provided remote support throughout the construction, commissioning and operations of LZ, including many worked full-time from their institutions ensuring the experiment would be a success and continue to do so now,” said Tomasz Biesiadzinski of SLAC, LZ Detector Operations Manager.

“Many subsystems started coming together when we started collecting data for detector commissioning, calibrations and scientific operation. Launching a new experiment is a challenge, but we have a great LZ team who have worked closely together to help us take the first steps in understanding our detector,” said David Woodward of Pennsylvania State University. , which coordinates the scheduling of the detector run.

SLAC’s Maria Elena Monzani, Deputy Director of Operations for Computing and Software, said: “We had incredible scientists and software developers throughout the collaboration who tirelessly supported the movement of data, data processing and simulations, enabling flawless commissioning of the detector. Support from NERSC [National Energy Research Scientific Computing Center] was invaluable.

With confirmation that LZ and its systems are working successfully, Lesko said, it’s time to begin large-scale observations in hopes that a dark matter particle will collide with a xenon atom in the detector very soon. LZ.

LZ is supported by the US Department of Energy, Office of Science, Office of High Energy Physics, and the National Energy Research Scientific Computing Center, a user facility of the DOE Office of Science. LZ is also supported by the UK Science & Technology Facilities Council; the Portuguese Foundation for Science and Technology; and the Institute of Basic Sciences, Korea. More than 35 higher education and advanced research institutions have supported LZ. The LZ Collaboration acknowledges assistance from the Sanford Underground Research Facility.

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Founded in 1931 on the belief that the greatest scientific challenges are best met by teams, Lawrence Berkeley National Laboratory and its scientists have been awarded 14 Nobel Prizes. Today, Berkeley Lab researchers are developing sustainable energy and environmental solutions, creating useful new materials, pushing the boundaries of computing, and probing the mysteries of life, matter, and the universe. Scientists around the world rely on the laboratory’s facilities for their own scientific discovery. Berkeley Lab is a multi-program national laboratory, operated by the University of California for the US Department of Energy’s Office of Science.

The DOE’s Office of Science is the largest supporter of basic physical science research in the United States and works to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.

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