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  • richardmitnick 12:48 pm on January 22, 2019 Permalink | Reply
    Tags: , LZ- LUX-ZEPLIN experiment,   

    From Sanford Underground Research Facility: “LZ gets an eye exam” 

    SURF logo
    Sanford Underground levels

    From Sanford Underground Research Facility

    January 18, 2019
    Erin Broberg

    1
    Brown University graduate student Will Taylor attaches data collection cables to a section of the PMT array. Matthew Kapust

    Lights out, windows darkened, doors closed. It’s not after hours at the Surface Assembly Lab (SAL), it’s just time for the first of LUX-ZEPLIN (LZ) dark matter detector’s on-site eye exam.

    LZ’s “eyes” are two massive arrays of photomultiplier tubes (PMTs), powerful light sensors that will detect any faint signals produced by dark matter particles when the experiment begins in 2020. The first of these arrays, which holds 241 PMTs, arrived at Sanford Underground Research Facility (Sanford Lab) in December. Now, researchers are testing the PMTs for the bottom array to make sure they are still in working condition after being transported from Brown University, where they were assembled.

    “These PMTs have already undergone rigorous testing, down to their individual components and this is the final test after transport to the site,” said Will Taylor, a graduate student at Brown University who has been working with the LZ collaboration since 2014.

    Once testing is completed, the bottom PMT array will be placed in the inner cryostat. The same process will be followed for the top array. The inner cryostat will be filled with xenon, both gaseous and liquid, and placed in the outer cryostat. Then, the entire detector will be submerged in the 72,000-gallon water tank in the Davis Campus on the 4850 Level of Sanford Lab.

    “As you can imagine,” Taylor said. “It will be impossible to change out a faulty PMT after the experiment is completely assembled. This is our last chance to ensure each PMT is working perfectly.”

    While researchers do expect a few PMTs to “blink out” over LZ’s five to six year lifetime, only the best of the best will make it into the detector. So, just how do researchers transform the SAL into an optometrist’s office?

    Royal treatment

    First, the array is placed in a special enclosure called the PALACE (PMT Array Lifting And Cleanliness Enclosure). There, the PMTs are shielded from light and dust. This enclosure also allows researchers access to the PMTs through a rotating window and to connect data collection systems to different sections of PMTs at a time.

    “We test by section, collecting data from 30 PMTs per day,” said Taylor. “Each individual PMT has a serial number and is tagged to its own data, so we know exactly what each PMT is ‘seeing.’”

    Going dark

    For the first test, researchers look at what is called the “dark rate” of each PMT. To perform this test, researchers seal up the PALACE, turn off the lights in the cleanroom and black out the windows. In this utter darkness, PMTs are monitored for “thermal noise.”

    “At a normal temperature, particles vibrate around inside the PMTs. When this happens, it is possible for electrons to ‘jump off’ and produce a signal that PMTs will detect,” Taylor explained. While most of this “thermal noise” will vanish once the experiment is cooled to liquid xenon temperature (-148 °F), researchers want to ensure the PMT’s dark rate is at the lowest threshold possible before being installed in LZ.

    “Typically, these false signals come from a single photoelectron,” Taylor said. “With the dark test, we can measure how many photoelectrons signals occur every second.”

    How much is too much noise? While a bit of noise (100-1000 events per second) is tolerable; rates closer to 10,000 events per second would be far too high, resulting in too many random signals that could overshadow WIMP signals during the experiment.

    “That’s why it is incredibly important to make sure each PMT has a low dark rate,” said Taylor.

    Lighting it up

    For the second test, called an “after-pulsing” test, researchers will flash a light, imperceptible to the human eye, at the PMTs. This test determines the health of each PMT’s internal vacuum. Why is this important?

    When light from a reaction inside the detector hits a photocathode of a PMT, an electron will be emitted. This single electron will be pulled through the PMT, hitting dynodes. Each time the electron hits an electrode, more electrons are emitted. This process continues, amplifying the original signal, turning the original electron into many, many, many electrons.

    “That’s how we get an electron signal strong enough to read out,” Taylor said. “For that to work, however, those electrons have to be able to bounce between those dynodes without interruption.”

    To decrease particle “traffic,” each PMT has a vacuum. The vacuum ensures there are no gas particles present to interfere with the amplification process. If a vacuum is faulty, gas particles may get in the way and hit an electron. This would cause the gas particle to bounce away and set off a second pulse of electrons, amplifying a signal of its own.

    “This is called an ‘after-pulse,’” Taylor said. “The after-pulse is indicative of how good the vacuum, and thus the PMT, really is.”

    Rather than depriving the PMTs of light as they did during the dark test, researchers now createa signal of their own to measure the after-pulse. To do this, an LED is affixed to the inside of the PALACE.

    “We flash the LED at a rate of 1 kilohertz for 30 seconds. That’s a total of 30,000 flashes of the LED,” Taylor said. While that might sound like a lot of light, it’s actually not even perceptible to the human eye. “Each flash lasts 10 nanoseconds and produces only 50-100 photons—so the human eye can’t detect it.”

    It is enough, however, for the PMT to detect it with a sizable initial pulse. Because researchers know exactly when the initial pulse was created, they can align their data to see when after-pulses occur and measure their strength.

    “This helps us see how healthy the vacuum is and determine if the PMT is fit for LZ,” Taylor said.

    20/20 vision

    After a week of testing, researchers have announced the bottom array has 20/20 vision.

    “Accepting the first of the two PMT arrays onsite, is one of many milestones toward the assembly and installation of the LZ experiment,” said Markus Horn, research support scientist at Sanford Lab and a member of the LZ collaboration. “While the detector assembly progresses at the Surface Lab, underground the installation of the xenon gas and Liquid Nitrogen cooling system begins. That would be the heart and the lung of LZ. But that’s another story!”

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings
    Please help promote STEM in your local schools.

    Stem Education Coalition

    About us.
    The Sanford Underground Research Facility in Lead, South Dakota, advances our understanding of the universe by providing laboratory space deep underground, where sensitive physics experiments can be shielded from cosmic radiation. Researchers at the Sanford Lab explore some of the most challenging questions facing 21st century physics, such as the origin of matter, the nature of dark matter and the properties of neutrinos. The facility also hosts experiments in other disciplines—including geology, biology and engineering.

    The Sanford Lab is located at the former Homestake gold mine, which was a physics landmark long before being converted into a dedicated science facility. Nuclear chemist Ray Davis earned a share of the Nobel Prize for Physics in 2002 for a solar neutrino experiment he installed 4,850 feet underground in the mine.

    Homestake closed in 2003, but the company donated the property to South Dakota in 2006 for use as an underground laboratory. That same year, philanthropist T. Denny Sanford donated $70 million to the project. The South Dakota Legislature also created the South Dakota Science and Technology Authority to operate the lab. The state Legislature has committed more than $40 million in state funds to the project, and South Dakota also obtained a $10 million Community Development Block Grant to help rehabilitate the facility.

    In 2007, after the National Science Foundation named Homestake as the preferred site for a proposed national Deep Underground Science and Engineering Laboratory (DUSEL), the South Dakota Science and Technology Authority (SDSTA) began reopening the former gold mine.

    In December 2010, the National Science Board decided not to fund further design of DUSEL. However, in 2011 the Department of Energy, through the Lawrence Berkeley National Laboratory, agreed to support ongoing science operations at Sanford Lab, while investigating how to use the underground research facility for other longer-term experiments. The SDSTA, which owns Sanford Lab, continues to operate the facility under that agreement with Berkeley Lab.

    The first two major physics experiments at the Sanford Lab are 4,850 feet underground in an area called the Davis Campus, named for the late Ray Davis. The Large Underground Xenon (LUX) experiment is housed in the same cavern excavated for Ray Davis’s experiment in the 1960s.
    LUX/Dark matter experiment at SURFLUX/Dark matter experiment at SURF

    In October 2013, after an initial run of 80 days, LUX was determined to be the most sensitive detector yet to search for dark matter—a mysterious, yet-to-be-detected substance thought to be the most prevalent matter in the universe. The Majorana Demonstrator experiment, also on the 4850 Level, is searching for a rare phenomenon called “neutrinoless double-beta decay” that could reveal whether subatomic particles called neutrinos can be their own antiparticle. Detection of neutrinoless double-beta decay could help determine why matter prevailed over antimatter. The Majorana Demonstrator experiment is adjacent to the original Davis cavern.

    LUX’s mission was to scour the universe for WIMPs, vetoing all other signatures. It would continue to do just that for another three years before it was decommissioned in 2016.

    In the midst of the excitement over first results, the LUX collaboration was already casting its gaze forward. Planning for a next-generation dark matter experiment at Sanford Lab was already under way. Named LUX-ZEPLIN (LZ), the next-generation experiment would increase the sensitivity of LUX 100 times.

    SLAC physicist Tom Shutt, a previous co-spokesperson for LUX, said one goal of the experiment was to figure out how to build an even larger detector.
    “LZ will be a thousand times more sensitive than the LUX detector,” Shutt said. “It will just begin to see an irreducible background of neutrinos that may ultimately set the limit to our ability to measure dark matter.”
    We celebrate five years of LUX, and look into the steps being taken toward the much larger and far more sensitive experiment.

    Another major experiment, the Long Baseline Neutrino Experiment (LBNE)—a collaboration with Fermi National Accelerator Laboratory (Fermilab) and Sanford Lab, is in the preliminary design stages. The project got a major boost last year when Congress approved and the president signed an Omnibus Appropriations bill that will fund LBNE operations through FY 2014. Called the “next frontier of particle physics,” LBNE will follow neutrinos as they travel 800 miles through the earth, from FermiLab in Batavia, Ill., to Sanford Lab.

    Fermilab LBNE
    LBNE

    U Washington Majorana Demonstrator Experiment at SURF

    The MAJORANA DEMONSTRATOR will contain 40 kg of germanium; up to 30 kg will be enriched to 86% in 76Ge. The DEMONSTRATOR will be deployed deep underground in an ultra-low-background shielded environment in the Sanford Underground Research Facility (SURF) in Lead, SD. The goal of the DEMONSTRATOR is to determine whether a future 1-tonne experiment can achieve a background goal of one count per tonne-year in a 4-keV region of interest around the 76Ge 0νββ Q-value at 2039 keV. MAJORANA plans to collaborate with GERDA for a future tonne-scale 76Ge 0νββ search.

    LBNL LZ project at SURF, Lead, SD, USA

    CASPAR at SURF


    CASPAR is a low-energy particle accelerator that allows researchers to study processes that take place inside collapsing stars.

    The scientists are using space in the Sanford Underground Research Facility (SURF) in Lead, South Dakota, to work on a project called the Compact Accelerator System for Performing Astrophysical Research (CASPAR). CASPAR uses a low-energy particle accelerator that will allow researchers to mimic nuclear fusion reactions in stars. If successful, their findings could help complete our picture of how the elements in our universe are built. “Nuclear astrophysics is about what goes on inside the star, not outside of it,” said Dan Robertson, a Notre Dame assistant research professor of astrophysics working on CASPAR. “It is not observational, but experimental. The idea is to reproduce the stellar environment, to reproduce the reactions within a star.”

     
  • richardmitnick 10:43 am on November 14, 2018 Permalink | Reply
    Tags: , , LZ- LUX-ZEPLIN experiment, , , The search for Dark Matter, ,   

    From Sanford Underground Research Facility: “Success of experiment requires testing” 

    SURF logo
    Sanford Underground levels

    From Sanford Underground Research Facility

    November 13, 2018
    Erin Broberg

    1
    Tomasz Biesiadzinski, project scientist for SLAC National Accelerator Laboratory (SLAC), works on the mock PMT [photomultiplier tubes] array. Erin Broberg

    “The LZ detector is kind of like a spacecraft,” said Tomasz Biesiadzinski, project scientist for SLAC National Accelerator Laboratory (SLAC). “Repairing it after it’s installed would be very difficult, so we do everything we can to make sure it works correctly the first time.”

    LZ Dark Matter Experiment at SURF lab

    LBNL LZ project at SURF, Lead, SD, USA

    Biesiadzinski himself is responsible for planning and carrying out tests during the assembly of time projection chamber (TPC), the main detector for LUX-ZEPLIN experiment (LZ). Currently being constructed on the 4850 Level at Sanford Underground Research Facility (Sanford Lab), this main detector consists of a large tank that will hold 7 tonnes of ultra-pure, cryogenic liquid xenon maintained at -100o C. All the pieces of this detector are designed to function with precision; it’s Biesiadzinski job to verify that each part continues to work correctly as they are integrated. That includes hundreds of photomultiplier tubes (PMT).

    Test run

    The most recent test was piecing together an intricate mock array for the PMTs, which will detect light signals created by the collision of a dark matter particle and a xenon atom, inside the main detector. In a soft-wall cleanroom in the Surface Laboratory at Sanford Lab, Biesiadzinski and his team carefully practiced placing instruments like thermometers, sensors and reflective covering. They practiced installing routing cabling, including PMT high voltage power cables, PMT signal cables and thermometer cables.

    “Essentially, we wanted to gain experience so we could be faster during the actual assembly. The faster we work, the more we limit dust exposure and therefore potential backgrounds,” said Biesiadzinski. “It was also an opportunity to test fit real components. We did find that there were some very tight places that motivated us to slightly redesign some small parts to make assembly easier.”

    These tests will make the installment of the actual LZ arrays much smoother.

    “LZ’s main detector will have two PMT arrays, one on the top of the tank and one on the bottom,” Biesiadzinski explained. “The bottom array will hold 241 PMTs pointing up into the liquid Xenon volume of the main detector. The top array will hold PMTs 253 pointing down on the liquid Xenon and the gas layer above it in the main detector.”

    In total, there will be 494 PMTs lining the main detector. If a WIMP streaks through the tank and strikes a xenon nucleus, two things will happen. First, the xenon will emit a flash of light. Then, it will release electrons, which drift in an electric field to the top of the tank, where they will produce a second flash of light. Hundreds of PMTs will be waiting to detect a characteristic combination of flashes from inside the tank—a WIMPs’ telltale signature.

    “Both arrays—top and bottom—record the light from particle interactions inside the detector, including, hopefully, dark matter,” said Biesiadzinski. “This data allows us to estimate both the energy created and 3D location of the interaction.”

    Catching light

    The PMTs used for LZ are extremely sensitive. Not only can they distinguish individual photons of light arriving just a few tens of nanoseconds apart, they can also see the UV light produced by xenon that is far outside the human vision range. The X-Y location of events in the detector can be measured using the top PMT array to within a few millimeters for sufficiently energetic events.

    To insure every bit of light makes its way to a PMT, the inside surfaces of the arrays are covered with Polytetrafluoroethylene (PTFE or teflon), a material highly reflective to xenon scintillation light, in between the PMT faces.

    “This way, photons that don’t enter the PMTs right away—and are therefore not recorded—are reflected and will get a second, third, and so on, chance of being detected as they bounce around the detector,” said Biesiadzinski.

    Researchers will also cover the outside of the bottom array, including all of the cables, with PTFE to maximize light collection there. Light recorded there by additional PMTs that are not part of the array, allow us to measure radioactive backgrounds that can contaminate the main detector.

    Keeping it “clean”

    In addition to being very specific, these PMTs are also ultra-clean.

    “By clean, we mean radio-pure,” said Briana Mount, director of the BHUC, where 338 of LZ’s PMTs have already been tested for radio-purity.

    The tiniest amounts of radioactive elements in the very materials used to construct LZ can also overwhelm the rare-event signal. Radioactive elements can be found in rocks, titanium—even human sweat. As these elements decay, they emit signals that quickly light up ultra-sensitive detectors. To lessen these misleading signatures, researchers assay, or test, their materials for radio-purity using low-background counters (LBCs).

    “Our PMTs are special made to have very low radioactivity so as to not overwhelm a very sensitive detector like LZ with background signal,” said Biesiadzinski.

    Testing the PMTs at the BHUC allows researchers to understand exactly how much of a remaining background they can expect to see from these materials during the experiment. Mount explained that most of the samples currently being assayed at the BHUC are LZ samples, including cable ties, wires, nuts and bolts.

    “We have assayed every component that will make up LZ,” said Kevin Lesko, senior physicist at Lawrence Berkeley National Lab (Berkeley Lab) and a spokesperson for LZ. “At this point we have performed over 1300 assays with another 800 assays planned. These have kept BHUC and the UK’s Boulby LBCs fully occupied for approximately 4 years. These assays permit us ensure no component contributes a major background to the detector and also allows us to assemble a model of the backgrounds for the entire detector before we turn on a single PMT.”

    For a visual description and breakdown of LZ’s design, watch this video created by SLAC.

    Fritz Zwicky discovered Dark Matter when observing the movement of the Coma Cluster.

    Fritz Zwicky from http:// palomarskies.blogspot.com

    Coma cluster via NASA/ESA Hubble

    But most of the real work was done by Vera Rubin a Woman in STEM

    Astronomer Vera Rubin at the Lowell Observatory in 1965, worked on Dark Matter (The Carnegie Institution for Science)


    Vera Rubin measuring spectra, worked on Dark Matter (Emilio Segre Visual Archives AIP SPL)


    Vera Rubin, with Department of Terrestrial Magnetism (DTM) image tube spectrograph attached to the Kitt Peak 84-inch telescope, 1970. https://home.dtm.ciw.edu

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings
    Please help promote STEM in your local schools.

    Stem Education Coalition

    About us.
    The Sanford Underground Research Facility in Lead, South Dakota, advances our understanding of the universe by providing laboratory space deep underground, where sensitive physics experiments can be shielded from cosmic radiation. Researchers at the Sanford Lab explore some of the most challenging questions facing 21st century physics, such as the origin of matter, the nature of dark matter and the properties of neutrinos. The facility also hosts experiments in other disciplines—including geology, biology and engineering.

    The Sanford Lab is located at the former Homestake gold mine, which was a physics landmark long before being converted into a dedicated science facility. Nuclear chemist Ray Davis earned a share of the Nobel Prize for Physics in 2002 for a solar neutrino experiment he installed 4,850 feet underground in the mine.

    Homestake closed in 2003, but the company donated the property to South Dakota in 2006 for use as an underground laboratory. That same year, philanthropist T. Denny Sanford donated $70 million to the project. The South Dakota Legislature also created the South Dakota Science and Technology Authority to operate the lab. The state Legislature has committed more than $40 million in state funds to the project, and South Dakota also obtained a $10 million Community Development Block Grant to help rehabilitate the facility.

    In 2007, after the National Science Foundation named Homestake as the preferred site for a proposed national Deep Underground Science and Engineering Laboratory (DUSEL), the South Dakota Science and Technology Authority (SDSTA) began reopening the former gold mine.

    In December 2010, the National Science Board decided not to fund further design of DUSEL. However, in 2011 the Department of Energy, through the Lawrence Berkeley National Laboratory, agreed to support ongoing science operations at Sanford Lab, while investigating how to use the underground research facility for other longer-term experiments. The SDSTA, which owns Sanford Lab, continues to operate the facility under that agreement with Berkeley Lab.

    The first two major physics experiments at the Sanford Lab are 4,850 feet underground in an area called the Davis Campus, named for the late Ray Davis. The Large Underground Xenon (LUX) experiment is housed in the same cavern excavated for Ray Davis’s experiment in the 1960s.
    LUX/Dark matter experiment at SURFLUX/Dark matter experiment at SURF

    In October 2013, after an initial run of 80 days, LUX was determined to be the most sensitive detector yet to search for dark matter—a mysterious, yet-to-be-detected substance thought to be the most prevalent matter in the universe. The Majorana Demonstrator experiment, also on the 4850 Level, is searching for a rare phenomenon called “neutrinoless double-beta decay” that could reveal whether subatomic particles called neutrinos can be their own antiparticle. Detection of neutrinoless double-beta decay could help determine why matter prevailed over antimatter. The Majorana Demonstrator experiment is adjacent to the original Davis cavern.

    LUX’s mission was to scour the universe for WIMPs, vetoing all other signatures. It would continue to do just that for another three years before it was decommissioned in 2016.

    In the midst of the excitement over first results, the LUX collaboration was already casting its gaze forward. Planning for a next-generation dark matter experiment at Sanford Lab was already under way. Named LUX-ZEPLIN (LZ), the next-generation experiment would increase the sensitivity of LUX 100 times.

    SLAC physicist Tom Shutt, a previous co-spokesperson for LUX, said one goal of the experiment was to figure out how to build an even larger detector.
    “LZ will be a thousand times more sensitive than the LUX detector,” Shutt said. “It will just begin to see an irreducible background of neutrinos that may ultimately set the limit to our ability to measure dark matter.”
    We celebrate five years of LUX, and look into the steps being taken toward the much larger and far more sensitive experiment.

    Another major experiment, the Long Baseline Neutrino Experiment (LBNE)—a collaboration with Fermi National Accelerator Laboratory (Fermilab) and Sanford Lab, is in the preliminary design stages. The project got a major boost last year when Congress approved and the president signed an Omnibus Appropriations bill that will fund LBNE operations through FY 2014. Called the “next frontier of particle physics,” LBNE will follow neutrinos as they travel 800 miles through the earth, from FermiLab in Batavia, Ill., to Sanford Lab.

    Fermilab LBNE
    LBNE

    U Washington Majorana Demonstrator Experiment at SURF

    The MAJORANA DEMONSTRATOR will contain 40 kg of germanium; up to 30 kg will be enriched to 86% in 76Ge. The DEMONSTRATOR will be deployed deep underground in an ultra-low-background shielded environment in the Sanford Underground Research Facility (SURF) in Lead, SD. The goal of the DEMONSTRATOR is to determine whether a future 1-tonne experiment can achieve a background goal of one count per tonne-year in a 4-keV region of interest around the 76Ge 0νββ Q-value at 2039 keV. MAJORANA plans to collaborate with GERDA for a future tonne-scale 76Ge 0νββ search.

    LBNL LZ project at SURF, Lead, SD, USA

     
  • richardmitnick 10:23 pm on October 30, 2018 Permalink | Reply
    Tags: Fritz Zwiky and Vera Rubin, , LZ- LUX-ZEPLIN experiment, ,   

    From Sanford Underground Research Facility: “Five years later, the hunt continues” 

    SURF logo
    Sanford Underground levels

    From Sanford Underground Research Facility

    October 29, 2018
    Erin Broberg

    Second-generation dark matter detector prepares to continue the search for WIMPs.

    1
    The LZ cryostat undergoes leak tests in the Surface Lab cleanroom. Matthew Kapust

    Five years ago, lead scientists for the Large Underground Xenon (LUX) experiment presented the first scientific results to come from the 4850 Level of Sanford Lab since Ray Davis’ Nobel-winning research in the 1960s. And the results were big.

    After a run of just over three months operating a mile underground, LUX had proven itself the most sensitive dark matter detector in the world.

    “LUX is blazing the path to illuminate the nature of dark matter,” said Brown University physicist Rick Gaitskell, co-spokesperson for LUX with physicist Dan McKinsey of Yale University, at the time.

    Dark matter, so far observed only by its gravitational effects on galaxies and clusters of galaxies, is the predominant form of matter in the universe—making up more than 80 percent of all matter.

    Women in STEM – Vera Rubin
    Fritz Zwicky discovered Dark Matter when observing the movement of the Coma Cluster

    Coma cluster via NASA/ESA Hubble

    But most of the real work was done by Vera Rubin

    Fritz Zwicky from http:// palomarskies.blogspot.com


    Astronomer Vera Rubin at the Lowell Observatory in 1965, worked on Dark Matter (The Carnegie Institution for Science)


    Vera Rubin measuring spectra, worked on Dark Matter (Emilio Segre Visual Archives AIP SPL)


    Vera Rubin, with Department of Terrestrial Magnetism (DTM) image tube spectrograph attached to the Kitt Peak 84-inch telescope, 1970. https://home.dtm.ciw.edu

    Weakly interacting massive particles, or WIMPs—so-called because they rarely interact with ordinary matter except through gravity—are the leading theoretical candidates for dark matter. The mass of WIMPs is unknown, but theories and results from other experiments suggest a number of possibilities.

    LUX’s mission was to scour the universe for WIMPs, vetoing all other signatures. It would continue to do just that for another three years before it was decommissioned in 2016.

    U Washington Large Underground Xenon at SURF, Lead, SD, USA


    U Washington Lux Dark Matter 2 at SURF, Lead, SD, USA

    In the midst of the excitement over first results, the LUX collaboration was already casting its gaze forward. Planning for a next-generation dark matter experiment at Sanford Lab was already under way. Named LUX-ZEPLIN (LZ), the next-generation experiment would increase the sensitivity of LUX 100 times.

    LBNL LZ project at SURF, Lead, SD, USA


    LZ Dark Matter Experiment at SURF lab

    SLAC physicist Tom Shutt, a previous co-spokesperson for LUX, said one goal of the experiment was to figure out how to build an even larger detector.

    “LZ will be a thousand times more sensitive than the LUX detector,” Shutt said. “It will just begin to see an irreducible background of neutrinos that may ultimately set the limit to our ability to measure dark matter.”

    This month, we celebrate five years of LUX, and look into the steps being taken toward the much larger and far more sensitive experiment. The following are just a few of the steps being taken by the LZ collaboration to make an experiment 30 times bigger and 100 times more sensitive—all in the pursuit of WIMPs.

    Renovating the Davis Cavern

    To make room for this scaled-up experiment, renovations had to occur inside the Davis Cavern.

    “Planning for this renovation started several years ago—even before LUX was built,” said John Keefner, underground operations engineer. “We had to refit the cavern and existing infrastructure to allow for the installation of LZ.”

    The Davis Cavern renovation project included removing an existing cleanroom, tearing down a wall between two former low-background counting rooms, installing a new hoist system, building a work deck and preparing the water tank itself to accommodate the larger cryostat.

    Reducing radon

    In addition to hosting the experiment nearly a mile underground to escape cosmic radiation, additional protections had to be put in place, including a radon-reduction system that was installed to further ensure the experiment remains free of backgrounds that could interfere with the results.

    Radon, a naturally occurring radioactive gas, significantly increases background noise in sensitive physics projects. The radon reduction system pressurizes, dehumidifies and cools air to minus 60 degrees Celsius before sending it through two columns, each filled with 1600 kg of activated charcoal, which remove the radon. The pressure is released, warmed and humidified before flowing into the cleanroom.

    “Our detectors need very low levels of radon,” said Dr. Richard Schnee, who is head of the physics department at SD Mines and a collaborator with LZ. Schnee heads up the SD Mines team that designed a radon reduction system that will be used underground. While the radon levels at the 4850 Level are safe for humans, they are too high for sensitive experiments like LZ, which go deep underground to escape cosmic radiation, Schnee explained. “We will take regular air from the facility and the systems will reduce the levels by 1,000 times or more.”

    Cryostat

    The arrival of the LZ cryostats at Sanford Lab in May 2018 marked a significant milestone in the LZ project, as the cryostat was several years in the making and is a key component in the experiment.

    The cryostat works in a similar way to a big thermos flask and keeps the detector at freezing temperatures. This is crucial because the detector uses xenon, which at room temperature is a gas. For the experiment to work, the xenon must be kept in a liquid state, which is only achievable at about minus 148 degrees Fahrenheit.

    After being delivered to the surface facility at Sanford Lab, the outer cryostat vessel of the cryostat chamber spent five weeks being fully assembled and leak-checked in the Assembly Lab clean room. It has now been disassembled and packaged for transportation from the surface to the underground location on the 4850 Level. The inner cryostat vessel also passed its leak test.

    Water tank passivation

    To ensure unwanted particles are not misread as dark matter signals, LZ’s liquid xenon chamber will be surrounded by another liquid-filled tank and a separate array of photomultiplier tubes that can measure other particles and largely veto false signals.

    “The LUX water tank needed a number of ports added or modified to support the LZ infrastructure. We also added the capability to install small hoisting equipment on the ceiling of the tank,” said Simon Fiorucci, a physicist with Lawrence Berkeley National Laboratory, who oversaw LUX operations at Sanford Lab and will serve in a similar role for LZ.

    Once these steps were completed, the entire inside of the tank had to be re-passivated to prevent rusting during its many years of service ahead. Finally, the tank was filled to the brim and monitored for a week to ensure there were no leaks.

    Acrylic tanks

    Additionally, LZ will include a component not present in LUX—nine acrylic tanks, filled with a liquid scintillator, will form a veto system around the experiment, allowing researchers to better recognize a WIMP if they see one.

    The acrylic tanks, or more precisely the liquid scintillator inside the tanks, are crucial in bringing the experiment to a new level of sensitivity—100 times greater than LUX—by identifying neutrons, which can mimic dark matter signals.

    “Recent dark matter searches have found that neutrons can be a pernicious background,” said Carter Hall, former LZ spokesperson and professor of physics at the University of Maryland. “The acrylic tanks and their liquid scintillator payload will provide a powerful neutron rejection signal so LZ is not fooled.”

    These are just a few of the many steps being taken to ensure that LZ once again scours the universe with pristine accuracy.

    “We want to do again what we did five years ago—create the most sensitive dark matter detector in the world,” said Dr. Markus Horn, research scientist at Sanford Lab and a member of the LZ collaboration.

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings
    Please help promote STEM in your local schools.

    Stem Education Coalition

    About us.
    The Sanford Underground Research Facility in Lead, South Dakota, advances our understanding of the universe by providing laboratory space deep underground, where sensitive physics experiments can be shielded from cosmic radiation. Researchers at the Sanford Lab explore some of the most challenging questions facing 21st century physics, such as the origin of matter, the nature of dark matter and the properties of neutrinos. The facility also hosts experiments in other disciplines—including geology, biology and engineering.

    The Sanford Lab is located at the former Homestake gold mine, which was a physics landmark long before being converted into a dedicated science facility. Nuclear chemist Ray Davis earned a share of the Nobel Prize for Physics in 2002 for a solar neutrino experiment he installed 4,850 feet underground in the mine.

    Homestake closed in 2003, but the company donated the property to South Dakota in 2006 for use as an underground laboratory. That same year, philanthropist T. Denny Sanford donated $70 million to the project. The South Dakota Legislature also created the South Dakota Science and Technology Authority to operate the lab. The state Legislature has committed more than $40 million in state funds to the project, and South Dakota also obtained a $10 million Community Development Block Grant to help rehabilitate the facility.

    In 2007, after the National Science Foundation named Homestake as the preferred site for a proposed national Deep Underground Science and Engineering Laboratory (DUSEL), the South Dakota Science and Technology Authority (SDSTA) began reopening the former gold mine.

    In December 2010, the National Science Board decided not to fund further design of DUSEL. However, in 2011 the Department of Energy, through the Lawrence Berkeley National Laboratory, agreed to support ongoing science operations at Sanford Lab, while investigating how to use the underground research facility for other longer-term experiments. The SDSTA, which owns Sanford Lab, continues to operate the facility under that agreement with Berkeley Lab.

    The first two major physics experiments at the Sanford Lab are 4,850 feet underground in an area called the Davis Campus, named for the late Ray Davis. The Large Underground Xenon (LUX) experiment is housed in the same cavern excavated for Ray Davis’s experiment in the 1960s.
    LUX/Dark matter experiment at SURFLUX/Dark matter experiment at SURF

    In October 2013, after an initial run of 80 days, LUX was determined to be the most sensitive detector yet to search for dark matter—a mysterious, yet-to-be-detected substance thought to be the most prevalent matter in the universe. The Majorana Demonstrator experiment, also on the 4850 Level, is searching for a rare phenomenon called “neutrinoless double-beta decay” that could reveal whether subatomic particles called neutrinos can be their own antiparticle. Detection of neutrinoless double-beta decay could help determine why matter prevailed over antimatter. The Majorana Demonstrator experiment is adjacent to the original Davis cavern.

    Another major experiment, the Long Baseline Neutrino Experiment (LBNE)—a collaboration with Fermi National Accelerator Laboratory (Fermilab) and Sanford Lab, is in the preliminary design stages. The project got a major boost last year when Congress approved and the president signed an Omnibus Appropriations bill that will fund LBNE operations through FY 2014. Called the “next frontier of particle physics,” LBNE will follow neutrinos as they travel 800 miles through the earth, from FermiLab in Batavia, Ill., to Sanford Lab.

    Fermilab LBNE
    LBNE

    U Washington Majorana Demonstrator Experiment at SURF

    The MAJORANA DEMONSTRATOR will contain 40 kg of germanium; up to 30 kg will be enriched to 86% in 76Ge. The DEMONSTRATOR will be deployed deep underground in an ultra-low-background shielded environment in the Sanford Underground Research Facility (SURF) in Lead, SD. The goal of the DEMONSTRATOR is to determine whether a future 1-tonne experiment can achieve a background goal of one count per tonne-year in a 4-keV region of interest around the 76Ge 0νββ Q-value at 2039 keV. MAJORANA plans to collaborate with GERDA for a future tonne-scale 76Ge 0νββ search.

     
  • richardmitnick 12:50 pm on March 20, 2018 Permalink | Reply
    Tags: , Beyond the WIMP: Unique Crystals Could Expand the Search for Dark Matter, , LZ- LUX-ZEPLIN experiment, , ,   

    From LBNL: “Beyond the WIMP: Unique Crystals Could Expand the Search for Dark Matter” 

    Berkeley Logo

    Berkeley Lab

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

    1
    A computerized simulation of the large-scale distribution of dark matter in the universe. An overlay graph (in white) shows how a crystal sample intensely scintillates, or glows, when exposed to X-rays during a lab test. This and other properties could make it a good material for a dark matter detector. (Credit: Millennium Simulation, Berkeley Lab)

    A new particle detector design proposed at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) could greatly broaden the search for dark matter – which makes up 85 percent of the total mass of the universe yet we don’t know what it’s made of – into an unexplored realm.

    While several large physics experiments have been targeting theorized dark matter particles called WIMPs, or weakly interacting massive particles, the new detector design could scan for dark matter signals at energies thousands of times lower than those measurable by more conventional WIMP detectors.

    The ultrasensitive detector technology incorporates crystals of gallium arsenide that also include the elements silicon and boron. This combination of elements causes the crystals to scintillate, or light up, in particle interactions that knock away electrons.

    This scintillation property of gallium arsenide has been largely unexplored, said Stephen Derenzo, a senior physicist in the Molecular Biophysics and Integrated Bioimaging Division at Berkeley Lab and lead author of a study published March 20 in the Journal of Applied Physics that details the material’s properties.

    “It’s hard to imagine a better material for searching in this particular mass range,” Derenzo said, which is measured in MeV, or millions of electron volts. “It ticks all of the boxes. We are always worried about a ‘Gotcha!’ or showstopper. But I have tried to think of some way this detector material can fail and I can’t.”

    The breakthrough came from Edith Bourret, a senior staff scientist in Berkeley Lab’s Materials Sciences Division who decades earlier had researched gallium arsenide’s potential use in circuitry. She gave him a sample of gallium arsenide from this previous work that featured added concentrations, or “dopants,” of silicon and boron.

    Derenzo had previously measured some lackluster performance in a sample of commercial-grade gallium arsenide. But the sample that Bourret handed him exhibited a scintillation luminosity that was five times brighter than in the commercial material, owing to the silicon and boron that imbued the material with new and enhanced properties. This enhanced scintillation meant it was far more sensitive to electronic excitations.

    “If she hadn’t handed me this sample from more than 20 years ago, I don’t think I would have pursued it,” Derenzo said. “When this material is doped with silicon and boron, this turns out to be very important and, accidentally, a very good choice of dopants.”

    Derenzo noted that he has had a longstanding interest in scintillators that are also semiconductors, as this class of materials can produce ultrafast scintillation useful for medical imaging applications such as PET (positron emission tomography) and CT (computed tomography) scans, for example, as well as for high-energy physics experiments and radiation detection.

    The doped gallium arsenide crystals he studied appear well-suited for high-sensitivity particle detectors because extremely pure crystals can be grown commercially in large sizes, the crystals exhibit a high luminosity in response to electrons booted away from atoms in the crystals’ atomic structure, and they don’t appear to be hindered by typical unwanted effects such as signal afterglow and dark current signals.

    Some of the larger WIMP-hunting detectors – such as that of the Berkeley Lab-led LUX-ZEPLIN project now under construction in South Dakota, and its predecessor, the LUX experiment – incorporate a liquid scintillation detector. A large tank of liquid xenon is surrounded by sensors to measure any light and electrical signals expected from a dark matter particle’s interaction with the nucleus of a xenon atom. That type of interaction is known as a nuclear recoil.

    2
    A crystal of gallium arsenide. (Credit: Wikimedia Commons)

    In contrast, the crystal-based gallium arsenide detector is designed to be sensitive to the slighter energies associated with electron recoils – electrons ejected from atoms by their interaction with dark matter particles. As with LUX and LUX-ZEPLIN, the gallium arsenide detector would need to be placed deep underground to shield it from the typical bath of particles raining down on Earth.

    It would also need to be coupled to light sensors that could detect the very few infrared photons (particles of light) expected from a low-mass dark matter particle interaction, and the detector would need to be chilled to cryogenic temperatures. The silicon and boron dopants could also possibly be optimized to improve the overall sensitivity and performance of the detectors.

    Because dark matter’s makeup is still a mystery – it could be composed of one or many particles of different masses, for example, or may not be composed of particles at all – Derenzo noted that gallium arsenide detectors provide just one window into dark matter particles’ possible hiding places.

    While WIMPs were originally thought to inhabit a mass range measured in billions of electron volts, or GeV, the gallium arsenide detector technology is well-suited to detecting particles in the mass range measured in millions of electron volts, or MeV.

    Berkeley Lab physicists are also proposing other types of detectors to expand the dark matter search, including a setup that uses an exotic state of chilled helium known as superfluid helium to directly detect low-mass dark matter particles.

    “Superfluid helium is scientifically complementary to gallium arsenide since helium is more sensitive to dark matter interactions with atomic nuclei, while gallium arsenide is sensitive to dark matter interacting with electrons,” said Dan McKinsey, a faculty senior scientist at Berkeley Lab and physics professor at UC Berkeley who is a part of the LZ Collaboration and is conducting R&D on dark matter detection using superfluid helium.

    LBNL LZ project at SURF, Lead, SD, USA

    SURF-Sanford Underground Research Facility


    SURF Above Ground

    SURF Out with the Old


    SURF An Empty Slate


    SURF Carving New Space


    SURF Shotcreting


    SURF Bolting and Wire Mesh


    SURF Outfitting Begins


    SURF circular wooden frame was built to form a concrete ring to hold the 72,000-gallon (272,549 liters) water tank that would house the LUX dark matter detector


    SURF LUX water tank was transported in pieces and welded together in the Davis Cavern


    SURF Ground Support


    SURF Dedicated to Science


    SURF Building a Ship in a Bottle


    SURF Tight Spaces


    SURF Ready for Science


    SURF Entrance Before Outfitting


    SURF Entrance After Outfitting


    SURF Common Corridior


    SURF Davis


    SURF Davis A World Class Site


    SURF Davis a Lab Site


    SURF DUNE LBNF Caverns at Sanford Lab

    FNAL DUNE Argon tank at SURF

    U Washington LUX Xenon experiment at SURF


    SURF Before Majorana


    U Washington Majorana Demonstrator Experiment at SURF

    “We don’t know whether dark matter interacts more strongly with nuclei or electrons – this depends on the specific nature of the dark matter, which is so far unknown,” he said.

    Another effort would employ gallium arsenide crystals in a different approach to the light dark matter search based on vibrations in the atomic structure of the crystals, known as optical phonons. This setup could target “light dark photons,” which are theorized low-mass particles that would serve as the carrier of a force between dark matter particles – analogous to the conventional photon that carries the electromagnetic force.

    Still another next-gen experiment, known as the Super Cryogenic Dark Matter Search experiment, or SuperCDMS SNOLAB, will use silicon and germanium crystals to hunt for low-mass WIMPs.

    LBNL SuperCDMS, at SNOLAB (Vale Inco Mine, Sudbury, Canada)

    LBNL SuperCDMS, at SNOLAB (Vale Inco Mine, Sudbury, Canada)


    LBNL Super CDMS, at SNOLAB (Vale Inco Mine, Sudbury, Canada)

    SNOLAB, a Canadian underground physics laboratory at a depth of 2 km in Vale’s Creighton nickel mine in Sudbury, Ontario

    SNOLAB, a Canadian underground physics laboratory at a depth of 2 km in Vale’s Creighton nickel mine in Sudbury, Ontario

    “These would be complementary experiments,” Derenzo said of the many approaches. “We need to look at all of the possible mass ranges. You don’t want to be fooled. You can’t exclude a mass range if you don’t look there.”

    Stephen Hanrahan, a staff scientist in Berkeley Lab’s Molecular Biophysics and Integrated Bioimaging Division; and Gregory Bizarri, a senior lecturer in manufacturing at Cranfield University in the U.K., also participated in this study. The work was supported by Advanced Crystal Technologies Inc.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    A U.S. Department of Energy National Laboratory Operated by the University of California

    University of California Seal

    DOE Seal

     
  • richardmitnick 11:45 am on October 17, 2017 Permalink | Reply
    Tags: , , LZ- LUX-ZEPLIN experiment, , ,   

    From SURF: “LZ team installs detector in water tank” 

    SURF logo
    Sanford Underground levels

    Sanford Underground Research facility

    October 16, 2017
    Constance Walter

    1
    Sally Shaw, a post-doc with the University of California Santa Barbara, poses next to the sodium iodide detector recently installed inside the water tank. Courtesy photo.

    The huge water tank that for four years housed the Large Underground Xenon (LUX) dark matter detector now stands empty. A small sign over the opening that reads, “Danger! Confined space,” bars physical entry, but a solitary note sung by Michael Gaylor, a science professor from Dakota State University, once jumped that barrier and reverberated for 35.4 seconds.

    Starting this week, the tank will be filled with the sounds of collaboration members installing a small detector that will be used to measure radioactivity in the cavern. It’s all part of the plan to build and install the much larger, second-generation dark matter detector, LUX-ZEPLIN (LZ).

    LBNL Lux Zeplin project at SURF

    “We need to pin down the background event rate to better shield our experiment,” said Sally Shaw, a post doc form from the University of California, Santa Barbara (UCSB).

    The detector, a 5-inch by 5-inch cylinder of sodium iodide, will be placed inside the water tank and surrounded by 8 inches of lead bricks. The crystal will be covered on all sides except one, which will be left bare to measure the gamma rays that are produced when things like thorium, uranium and potassium decay. Over the next two weeks, the team will change the position of the detector five times to determine the directionality of the gamma rays.

    Scott Haselschwardt, a graduate student at UCSB, said this is especially important because there is a rhyolite intrusion that runs below the tank and up the west wall of the cavern.

    “This rock is more radioactive than other types of rock, so it can create more backgrounds,” he said. This wasn’t a problem for LUX, Haselschwardt said, but it was smaller than LZ and, therefore, surrounded by more ultra-pure water.

    But LZ is 10 times larger and still must fit inside the same tank, potentially exposing it to more of the radiation that naturally occurs within the rock cavern. And while this radiation is harmless to humans, it can wreak havoc on highly sensitive experiments like LZ.

    “Because it is so much closer to the edges of the water tank, there was a proposal to put in extra shielding—perhaps a lead ring at the bottom of the tank to shield the experiment,” Shaw said.

    Like its much smaller cousin, LZ hopes to find WIMPs, weakly interacting massive particles. Every component must be tested to ensure it is free of any backgrounds, including more than 500 photomultiplier tubes, the titanium for the cryostat and the liquid scintillator that will surround the xenon container. But if the backgrounds emanating from the walls of the cavern are too high, it won’t matter.

    “The whole point is to see whether the lead needs to be used in the design of the shield,” said Umit Utku, a graduate student at University College in London. “Maybe we will realize we don’t need it.”

    Shaw, who created a design for lead shielding within the tank, said it’s critical to fully understand the backgrounds now.

    “If we do need extra shielding, we must adjust the plans before installation of the experiment begins,” she said.

    See the full article here .

    Please help promote STEM in your local schools.
    STEM Icon

    Stem Education Coalition

    About us.
    The Sanford Underground Research Facility in Lead, South Dakota, advances our understanding of the universe by providing laboratory space deep underground, where sensitive physics experiments can be shielded from cosmic radiation. Researchers at the Sanford Lab explore some of the most challenging questions facing 21st century physics, such as the origin of matter, the nature of dark matter and the properties of neutrinos. The facility also hosts experiments in other disciplines—including geology, biology and engineering.

    The Sanford Lab is located at the former Homestake gold mine, which was a physics landmark long before being converted into a dedicated science facility. Nuclear chemist Ray Davis earned a share of the Nobel Prize for Physics in 2002 for a solar neutrino experiment he installed 4,850 feet underground in the mine.

    Homestake closed in 2003, but the company donated the property to South Dakota in 2006 for use as an underground laboratory. That same year, philanthropist T. Denny Sanford donated $70 million to the project. The South Dakota Legislature also created the South Dakota Science and Technology Authority to operate the lab. The state Legislature has committed more than $40 million in state funds to the project, and South Dakota also obtained a $10 million Community Development Block Grant to help rehabilitate the facility.

    In 2007, after the National Science Foundation named Homestake as the preferred site for a proposed national Deep Underground Science and Engineering Laboratory (DUSEL), the South Dakota Science and Technology Authority (SDSTA) began reopening the former gold mine.

    In December 2010, the National Science Board decided not to fund further design of DUSEL. However, in 2011 the Department of Energy, through the Lawrence Berkeley National Laboratory, agreed to support ongoing science operations at Sanford Lab, while investigating how to use the underground research facility for other longer-term experiments. The SDSTA, which owns Sanford Lab, continues to operate the facility under that agreement with Berkeley Lab.

    The first two major physics experiments at the Sanford Lab are 4,850 feet underground in an area called the Davis Campus, named for the late Ray Davis. The Large Underground Xenon (LUX) experiment is housed in the same cavern excavated for Ray Davis’s experiment in the 1960s.
    LUX/Dark matter experiment at SURFLUX/Dark matter experiment at SURF

    In October 2013, after an initial run of 80 days, LUX was determined to be the most sensitive detector yet to search for dark matter—a mysterious, yet-to-be-detected substance thought to be the most prevalent matter in the universe. The Majorana Demonstrator experiment, also on the 4850 Level, is searching for a rare phenomenon called “neutrinoless double-beta decay” that could reveal whether subatomic particles called neutrinos can be their own antiparticle. Detection of neutrinoless double-beta decay could help determine why matter prevailed over antimatter. The Majorana Demonstrator experiment is adjacent to the original Davis cavern.

    Another major experiment, the Long Baseline Neutrino Experiment (LBNE)—a collaboration with Fermi National Accelerator Laboratory (Fermilab) and Sanford Lab, is in the preliminary design stages. The project got a major boost last year when Congress approved and the president signed an Omnibus Appropriations bill that will fund LBNE operations through FY 2014. Called the “next frontier of particle physics,” LBNE will follow neutrinos as they travel 800 miles through the earth, from FermiLab in Batavia, Ill., to Sanford Lab.

    Fermilab LBNE
    LBNE

     
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