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  • richardmitnick 12:21 pm on July 16, 2019 Permalink | Reply
    Tags: , being replaced by LBNL Lux Zeplin project, , ending, , Lead, Lux Zeplin project, , SD, , U Washington LUX Dark matter Experiment at SURF, ,   

    From Lawrence Berkeley National Lab: “Some Assembly Required: Scientists Piece Together the Largest U.S.-Based Dark Matter Experiment” 

    Berkeley Logo

    From Lawrence Berkeley National Lab

    July 16, 2019

    Glenn Roberts Jr.
    geroberts@lbl.gov
    (510) 486-5582

    Major deliveries in June set the stage for the next phase of work on LUX-ZEPLIN project.

    1
    Lower (left) and upper photomultiplier tube arrays are prepared for LZ at the Sanford Underground Research Facility in Lead, South Dakota. (Credit: Matt Kapust/SURF)

    Most of the remaining components needed to fully assemble an underground dark matter-search experiment called LUX-ZEPLIN (LZ) arrived at the project’s South Dakota home during a rush of deliveries in June.

    When complete, LZ will be the largest, most sensitive U.S.-based experiment yet that is designed to directly detect dark matter particles. Scientists around the world have been trying for decades to solve the mystery of dark matter, which makes up about 85 percent of all matter in the universe though we have so far only detected it indirectly through observed gravitational effects.

    The bulk of the digital components for LZ’s electronics system, which is designed to transmit and record signals from ever-slight particle interactions in LZ’s core detector vessel, were among the new arrivals at the Sanford Underground Research Facility (SURF). SURF, the site of a former gold mine now dedicated to a broad spectrum of scientific research, was also home to a predecessor search experiment called LUX.

    U Washington LUX Dark matter Experiment at SURF, Lead, SD, USA

    A final set of snugly fitting acrylic vessels, which will be filled with a special liquid designed to identify false dark matter signals in LZ’s inner detector, also arrived at SURF in June.

    3
    An intricately thin wire grid is visible (click image to view larger size) atop an array of photomultiplier tube. The components are part of the LZ inner detector. (Credit: Matt Kapust/SURF)

    Also, the last two of four intricately woven wire grids that are essential to maintain a constant electric field and extract signals from the experiment’s inner detector, also called the time projection chamber, arrived in June (see related article).

    LZ achieved major milestones in June. It was the busiest single month for delivering things to SURF — it was the peak,” said LZ Project Director Murdock Gilchriese of the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab). Berkeley Lab is the lead institution for the LZ project, which is supported by an international collaboration that has about 37 participating institutions and about 250 researchers and technical support crew members.

    “A few months from now all of the action on LZ is going to be at SURF — we are already getting close to having everything there,” Gilchriese said.

    Mike Headley, executive director at SURF, said, “We’ve been collectively preparing for these deliveries for some time and everything has gone very well. It’s been exciting to see the experiment assembly work progress and we look forward to lowering the assembled detector a mile underground for installation.”

    4
    Components for the LUX-ZEPLIN project are stored inside a water tank nearly a mile below ground. The inner detector will be installed on the central mount pictured here, and acrylic vessels (wrapped in white) will fit snugly around this inner detector. (Credit: Matt Kapust/SURF)

    All of these components will be transported down a shaft and installed in a nearly mile-deep research cavern. The rock above provides a natural shield against much of the constant bombardment of particles raining down on the planet’s surface that produce unwanted “noise.”

    LZ components have also been painstakingly tested and selected to ensure that the materials they are made of do not themselves interfere with particle signals that researchers are trying to tease out.

    LZ is particularly focused on finding a type of theoretical particle called a weakly interacting massive particle or WIMP by triggering a unique sequence of light and electrical signals in a tank filled with 10 metric tons of highly purified liquid xenon, which is among Earth’s rarest elements. The properties of xenon atoms allow them to produce light in certain particle interactions.

    Proof of dark matter particles would fundamentally change our understanding of the makeup of the universe, as our current Standard Model of Physics does not account for their existence.

    Standard Model of Particle Physics (LATHAM BOYLE AND MARDUS OF WIKIMEDIA COMMONS)

    Assembly of the liquid xenon time projection chamber for LZ is now about 80 percent complete, Gilchriese said. When fully assembled later this month this inner detector will contain about 500 photomultiplier tubes. The tubes are designed to amplify and transmit signals produced within the chamber.

    5
    An array of photomultiplier tubes that are designed to detect signals occurring within LZ’s liquid xenon tank. (Credit: Matt Kapust/SURF)

    Once assembled, the time projection chamber will be lowered carefully into a custom titanium vessel already at SURF. Before it is filled with xenon, this chamber will be lowered to a depth of about 4,850 feet. It will be carried in a frame that is specially designed to minimize vibrations, and then floated into the experimental cavern across a temporarily assembled metal runway on air-pumped pucks known as air skates.

    Finally, it will be lowered into a larger outer titanium vessel, already underground, to form the final vacuum-insulated cryostat needed to house the liquid xenon.

    That daylong journey, planned in September, will be a nail-biting experience for the entire project team, noted Berkeley Lab’s Simon Fiorucci, LZ deputy project manager.

    “It will certainly be the most stressful — this is the thing that really cannot fail. Once we’re done with this, a lot of our risk disappears and a lot of our planning becomes easier,” he said, adding, “This will be the biggest milestone that’s left besides having liquid xenon in the detector.”

    Project crews will soon begin testing the xenon circulation system, already installed underground, that will continually circulate xenon through the inner detector, further purify it, and reliquify it. Fiorucci said researchers will use about 250 pounds of xenon for these early tests.

    Work is also nearing completion on LZ’s cryogenic cooling system that is required to convert xenon gas to its liquid form.

    6
    Researchers from the University of Rochester in June installed six racks of electronics hardware that will be used to process signals from the LZ experiment. (Credit: University of Rochester)

    LZ digital electronics, which will ultimately connect to the arrays of photomultiplier tubes and enable the readout of signals from particle interactions, were designed, developed, delivered, and installed by University of Rochester researchers and technical staff at SURF in June.

    “All of our electronics have been designed specifically for LZ with the goal of maximizing our sensitivity for the smallest possible signals,” said Frank Wolfs, a professor of physics and astronomy at the University of Rochester who is overseeing the university’s efforts.

    He noted that more than 28 miles of coaxial cable will connect the photomultiplier tubes and their amplifying electronics – which are undergoing tests at UC Davis – to the digitizing electronics. “The successful installation of the digital electronics and the online network and computing infrastructure in June makes us eager to see the first signals emerge from LZ,” Wolfs added.

    Also in June, LZ participants exercised high-speed data connections from the site of the experiment to the surface level at SURF and then to Berkeley Lab. Data captured by the detectors’ electronics will ultimately be transferred to LZ’s primary data center, the National Energy Research Scientific Computing Center (NERSC) at Berkeley Lab via the Energy Sciences Network (ESnet), a high-speed nationwide data network based at Berkeley Lab.

    NERSC

    NERSC Cray Cori II supercomputer at NERSC at LBNL, named after Gerty Cori, the first American woman to win a Nobel Prize in science

    NERSC Hopper Cray XE6 supercomputer


    LBL NERSC Cray XC30 Edison supercomputer


    The Genepool system is a cluster dedicated to the DOE Joint Genome Institute’s computing needs. Denovo is a smaller test system for Genepool that is primarily used by NERSC staff to test new system configurations and software.

    NERSC PDSF


    PDSF is a networked distributed computing cluster designed primarily to meet the detector simulation and data analysis requirements of physics, astrophysics and nuclear science collaborations.

    Future:

    Cray Shasta Perlmutter SC18 AMD Epyc Nvidia pre-exascale supeercomputer

    NERSC is a DOE Office of Science User Facility.

    The production of the custom acrylic tanks (see related article), which will contain a fluid known as a liquid scintillator, was overseen by LZ participants at University of California,Santa Barbara.

    5
    The top three acrylic tanks for the LUX-ZEPLIN outer detector during testing at the fabrication vendor. These tanks are now at the Sanford Underground Research Facility in Lead, South Dakota. (Credit: LZ Collaboration)

    “The partnership between LZ and SURF is tremendous, as evidenced by the success of the assembly work to date,” Headley said. “We’re proud to be a part of the LZ team and host this world-leading experiment in South Dakota.”

    NERSC and ESnet are DOE Office of Science User Facilities.

    Major support for LZ comes from the DOE Office of Science, the South Dakota Science and Technology Authority, the U.K.’s Science & Technology Facilities Council, and by collaboration members in the U.S., U.K., South Korea, and Portugal.

    More:

    For information about LZ and the LZ collaboration, visit: http://lz.lbl.gov/

    See the full article here .

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    Bringing Science Solutions to the World
    In the world of science, Lawrence Berkeley National Laboratory (Berkeley Lab) is synonymous with “excellence.” Thirteen Nobel prizes are associated with Berkeley Lab. Seventy Lab scientists are members of the National Academy of Sciences (NAS), one of the highest honors for a scientist in the United States. Thirteen of our scientists have won the National Medal of Science, our nation’s highest award for lifetime achievement in fields of scientific research. Eighteen of our engineers have been elected to the National Academy of Engineering, and three of our scientists have been elected into the Institute of Medicine. In addition, Berkeley Lab has trained thousands of university science and engineering students who are advancing technological innovations across the nation and around the world.

    Berkeley Lab is a member of the national laboratory system supported by the U.S. Department of Energy through its Office of Science. It is managed by the University of California (UC) and is charged with conducting unclassified research across a wide range of scientific disciplines. Located on a 202-acre site in the hills above the UC Berkeley campus that offers spectacular views of the San Francisco Bay, Berkeley Lab employs approximately 3,232 scientists, engineers and support staff. The Lab’s total costs for FY 2014 were $785 million. A recent study estimates the Laboratory’s overall economic impact through direct, indirect and induced spending on the nine counties that make up the San Francisco Bay Area to be nearly $700 million annually. The Lab was also responsible for creating 5,600 jobs locally and 12,000 nationally. The overall economic impact on the national economy is estimated at $1.6 billion a year. Technologies developed at Berkeley Lab have generated billions of dollars in revenues, and thousands of jobs. Savings as a result of Berkeley Lab developments in lighting and windows, and other energy-efficient technologies, have also been in the billions of dollars.

    Berkeley Lab was founded in 1931 by Ernest Orlando Lawrence, a UC Berkeley physicist who won the 1939 Nobel Prize in physics for his invention of the cyclotron, a circular particle accelerator that opened the door to high-energy physics. It was Lawrence’s belief that scientific research is best done through teams of individuals with different fields of expertise, working together. His teamwork concept is a Berkeley Lab legacy that continues today.

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  • richardmitnick 1:45 pm on December 17, 2018 Permalink | Reply
    Tags: , , , Lux Zeplin project, PMT's-photomultiplier tubes, ,   

    From Brown University: “Massive new dark matter detector gets its ‘eyes’” 

    Brown University
    From Brown University

    1
    The detector’s “eyes”
    Powerful light sensors assembled at Brown into two large arrays will keep watch on the LUX-ZEPLIN dark matter detector, looking for the tell-tale flashes of light that indicate interaction of a dark matter particle inside the detector. Credit: Nick Dentamaro

    LBNL Lux Zeplin project at SURF

    December 17, 2018
    Kevin Stacey

    Brown University researchers have assembled two massive arrays of photomultiplier tubes, powerful light sensors that will serve as the “eyes” for the LUX-ZEPLIN dark matter detector, which will start its search for dark matter particles in 2020.

    The LUX-ZEPLIN (LZ) dark matter detector, which will soon start its search for the elusive particles thought to account for a majority of matter in the universe, had the first of its “eyes” delivered late last week.

    The first of two large arrays of photomultiplier tubes (PMTs) — powerful light sensors that can detect the faintest of flashes — arrived last Thursday at the Sanford Underground Research Facility (SURF) in Lead, South Dakota, where LZ is scheduled to begin its dark matter search in 2020. The second array will arrive in January. When the detector is completed and switched on, the PMT arrays will keep careful watch on LZ’s 10-ton tank of liquid xenon, looking for the telltale twin flashes of light produced if a dark matter particle bumps into a xenon atom inside the tank.

    The two arrays, each about 5 feet in diameter and holding a total of 494 PMTs, were shipped to South Dakota via truck from Providence, Rhode Island, where a team of researchers and technicians from Brown University spent the past six months painstakingly assembling them.

    “The delivery of these arrays is the pinnacle of an enormous assembly effort that we’ve executed here in our cleanroom at the Brown Department of Physics,” said Rick Gaitskell, a professor of physics at Brown University who oversaw the construction of the arrays. “For the last two years, we’ve been making sure that every piece that’s going into the devices is working as expected. Only by doing that can we be confident that everything will perform the way we want when the detector is switched on.”

    The Brown team has worked with researchers and engineers from the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) and from Imperial College London to design, procure, test, and assemble all of the components of the array. Testing of the PMTs, which are manufactured by the Hamamatsu Corporation in Japan, was performed at Brown and at Imperial College “The PMTs have already qualified for significant air miles, even before they started their 2,000-mile journey by road from Rhode Island to South Dakota,” Gaitskell said.

    “The PMTs have already qualified for significant air miles, even before they started their 2,000-mile journey by road from Rhode Island to South Dakota,” Gaitskell said.

    Catching a WIMP

    Nobody knows exactly what dark matter is. Scientists can see the effects of its gravity in the rotation of galaxies and in the way light bends as it travels across the universe, but no one has directly detected a dark matter particle. The leading theoretical candidate for a dark matter particle is the WIMP, or weakly interacting massive particle. WIMPs can’t be seen because they don’t absorb, emit or reflect light. And they interact with normal matter only on very rare occasions, which is why they’re so hard to detect even when millions of them may be traveling through the Earth and everything on it each second.

    The LZ experiment, a collaboration of more than 250 scientists worldwide, aims to capture one of those fleetingly rare WIMP interactions, and thereby characterize the particles thought to make up more than 80 percent of the matter in the universe. The detector will be the most sensitive ever built, 50 times more sensitive than the LUX detector, which wrapped up its dark matter search at SURF in 2016.

    3
    This rendering shows a cutaway view of the LZ xenon tank (center), with PMT arrays at the top and bottom of the tank. (Credit: Greg Stewart/SLAC National Accelerator Laboratory)

    The PMT arrays are a critical part of the experiment. Each PMT is a six-inch-long cylinder that is roughly the diameter of a soda can. To form arrays large enough to monitor the entire LZ xenon target, hundreds of PMTs are assembled together within a circular titanium matrix. The array that will sit on top of the xenon target has 253 PMTs, while the lower array has 241.

    PMTs are designed to amplify weak light signals. When individual photons (particles of light) enter a PMT, they strike a photocathode. If the photon has sufficient energy, it causes the photocathode to eject one or more electrons. Those electrons strike then an electrode, which ejects more electrons. By cascading through a series of electrodes the original signal is amplified by over a factor of a million to create a detectable signal.

    LZ’s PMT arrays will need every bit of that sensitivity to catch the flashes associated with a WIMP interaction.

    “We could be looking for events emitting as few as 20 photons in a huge tank containing 10 tons of xenon, which is something that the human visual system wouldn’t be able to do,” Gaitskell said. “But it’s something these arrays can do, and we’ll need them to do it in order to see the signal from rare particle events.”

    The photons are produced by what’s known as a nuclear recoil event, which produces two distinct flashes. The first comes at the moment a WIMP bumps into a xenon nucleus. The second, which comes a few hundred microseconds afterward, is produced by the ricochet of the xenon atom that was struck. It bounces into the atoms surrounding it, which knocks a few electrons free. The electrons are then drifted by an electric field to the top of the tank, where they reach a thin layer of xenon gas that converts them into light.

    In order for those tiny flashes to be distinguishable from unwanted background events, the detector needs to be protected from cosmic rays and other kinds of radiation, which also cause liquid xenon to light up. That’s why the experiment takes place underground at SURF, a former gold mine, where the detector will be shielded by about a mile of rock to limit interference.

    A clean start

    The need to limit interference is also the reason that the Brown University team was obsessed with cleanliness while they assembled the arrays. The team’s main enemy was plain old dust.

    “When you’re dealing with an instrument that’s as sensitive as LZ, suddenly things you wouldn’t normally care about become very serious,” said Casey Rhyne, a Brown graduate student who had a leading role in building the arrays. “One of the biggest challenges we had to confront was minimizing ambient dust levels during assembly.”

    Each dust particle carries a minuscule amount of radioactive uranium and thorium decay products. The radiation is vanishingly small and poses no threat to people, but too many of those specks inside the LZ detector could be enough to interfere with a WIMP signal.

    4
    Much of the assembly work was done while the arrays sat inside PALACE, an ultraclean enclosure designed to keep the arrays dust-free. Nick Detamaro

    In fact, the dust budget for the LZ experiment calls for no more than one gram of dust in the entire 10-ton instrument. Because of all their nooks and crannies, the PMT arrays could be significant dust contributors if pains were not taken to keep them clean throughout construction.

    The Brown team performed most of its work in a “class 1,000” cleanroom, which allows no more than 1,000 microscopic dust particles per cubic foot of space. And within that cleanroom was an even more pristine space that the team dubbed “PALACE (PMT Array Lifting And Commissioning Enclosure).” PALACE was essentially an ultraclean exoskeleton where much of the actual array assembly took place. PALACE was a “class 10” space — no more than 10 dust particles bigger than one hundredth the width of a human hair per cubic foot.

    But the radiation concerns didn’t stop at dust. Before assembly of the arrays began, the team prescreened every part of every PMT tube to assess radiation levels.

    “We had Hamamatsu send us all of the materials that they were going to use for the PMT construction, and we put them in an underground germanium detector,” said Samuel Chan, a graduate student and PMT system team leader. “This detector is very good at detecting the radiation that the construction materials are emitting. If the intrinsic radiation levels were low enough in these materials, then we told Hamamatsu to go ahead and use them in the manufacture of these PMTs.”

    7
    A PMT is carefully inserted into the array inside PALACE. Nick Dentamaro

    The team is hopeful that all the work contributed over the past six months will pay dividends when LZ starts its WIMP search.

    “Getting everything right now will have a huge impact less than two years from now when we switch on the completed detector and we’re taking data,” Gaitskell said. “We’ll be able to see directly from that data how good of a job we and other people have done.”

    Given the major increase in dark matter search sensitivity that the LUX-ZEPLIN detector can deliver compared to previous experiments, the team hopes that this detector will finally identify and characterize the vast sea of stuff that surrounds us all. So far, the dark stuff has remained maddeningly elusive.

    See the full article here .

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