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    • 2018-07-06 10:05:02
    • Article ID: 697089

    Extracting Signals of Elusive Particles from Giant Chambers Filled with Liquefied Argon

    Scientists use software to "develop" images that trace neutrinos' interactions in a bath of -303 deg.F liquid argon

    • Credit: Colorado State University

      Brookhaven Lab's MicroBooNE research team. Front row, left to right: Veljko Radeka, Xin Qian, Hucheng Chen. Back row, left to right: Brian Kirby, Wenqiang Gu, Hanyu Wei, Chao Zhang, Mary Bishai, Yichen Li, Yale University graduate student Brooke Russell, Brett Viren, Xiangpan Ji. Missing from the photo: Bo Yu, Jyoti Joshi, and Michael Mooney

    • Two-dimensional images of a neutrino interaction in MicroBooNE shown at different stages of signal processing (left to right): the original data recorded by the detector with some excess noise (horizontal lines); the same data after removal of excess noise; the reconstructed distribution of ionization electrons after a signal processing technique called deconvolution was applied in one dimension; the reconstructed distribution of ionization electrons after the latest version of signal processing, which included 2D deconvolution, as described in the two just-published papers.

    • The latest improvements in MicroBooNE Time Projection Chamber (TPC) signal processing result in more completely reconstructed 3D particle tracks (bottom) than earlier techniques (top), which left gaps in the 3D images (see red circled areas for comparison). The improvement is crucial for distinguishing neutrino interaction signals (circled in green) from background signals generated by cosmic rays interacting with the fluid in the TPC. You can explore the controls that rotate and zoom in and out of these images at this link.

    • Credit: Fermilab

      The school-bus-size MicroBooNE Time-Projection Chamber

    Neutrinos are subtle subatomic particles that scientists believe play a key role in the evolution of our universe. They stream continuously from nuclear reactions in our Sun and other stars but pass through almost everything—even our bodies and Earth itself—without leaving a trace. Scientists who want to study these peculiar, lightweight particles must build extremely sensitive detectors.

    A revolutionary new kind of neutrino detector, designed in part by scientists from the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory, sits at the heart of the MicroBooNE experiment at DOE’s Fermi National Accelerator Laboratory (Fermilab). In two new papers, the MicroBooNE collaboration describes how they use this detector to pick up the telltale signs of neutrinos. The papers include details of the signal processing algorithms that are critical to accurately reconstruct neutrinos’ subtle interactions with atoms in the detector.

    According to physicist Xin Qian, leader of Brookhaven Lab’s MicroBooNE physics group, “The work summarized in these papers, which include comparisons of recently collected experimental data with simulations of detector signals and noise, demonstrates an excellent understanding of MicroBooNE’s millimeter-resolution detector performance. This understanding provides a solid foundation for using this detector technology for precision physics measurements not just in MicroBooNE but also in future experiments, such as the Deep Underground Neutrino Experiment.”

    Dynamic detector

    The central piece of the MicroBooNE detector is a liquid-argon time projection chamber (LArTPC)—a bus-sized tank filled with argon (kept liquid at a biting -303 degrees Fahrenheit) and lined with electronics designed to operate in that extremely cold environment. This assembly acts like a powerful tomographic 3D digital camera to capture the trajectories of particles generated when neutrinos interact with argon atoms in the tank.

    The neutrinos, which come in three “flavors” (electron, muon, and tau), originate from a proton accelerator at Fermilab. Mostly they sail on through the detector. But occasionally, a neutrino strikes an argon nucleus in the LArTPC. That interaction produces a number of other particles, some of which carry electric charge. As these charged particles zip through the tank, they ionize, or kick electrons off, other argon atoms in their path. The ousted electrons get caught in the powerful electric field surrounding the tank and drift toward an array of wires neatly arranged in three differently oriented planes at one end—the anode. Electronics inside the tank collect and amplify signals generated by electrons striking the wires and send those signals out to be recorded. By tracking the timing and locations of these signals, the detector can construct images of the electrons’ trajectories to reveal information about the energy and flavor of the neutrino that triggered each chain of events.

    “Unfurling the ionization signal at the anode plane is analogous to processing photographic film in a dark room, except instead of chemical agents and solutions physicists apply signal-processing algorithms to reconstruct the picture of the neutrino interaction,” said Brooke Russell, a Yale University graduate student currently stationed at Brookhaven Lab.

    Signal processing

    But just as it’s important to get the chemistry right when processing film, neutrino-tracking scientists face challenges in developing their algorithms.

    For one thing, the currents induced by drifting ionization electrons are generally small in magnitude and can be reduced further if the electrons arrive at the wires over a prolonged period of time. In addition, the “waveform” of current produced by one set of drifting electrons might be canceled out by that of another set of electrons arriving later—like ocean waves that get flattened out when the high crests of one wave line up with the low points of another. This makes it particularly difficult to discriminate the tiny signals from background “noise”—electronic distortions generated by excess charge stored on the wires used to carry the signals, the external power supplies that generate the detector’s electric field, or other sources.


    Keeping some of the electronics inside the liquid argon chamber helps to minimize noise by reducing the distance signals have to travel before being read out. As Brookhaven Lab postdoctoral research associate Brian Kirby noted, these low-noise “cold electronics,” designed by Brookhaven’s Instrumentation Division, are a crucial technology for large LArTPCs. “They simplify detector design and provide the electronic noise performance required to make a full use of induction wire plane signals,” he said.

    A second challenge is that drifting electrons can induce current over an expanse of several nearby wires, introducing the possibility that the waveform produced by electrons passing by a particular wire can cancel one produced by electrons passing a nearby wire. These cancellations depend on the distribution of ionization electrons, leading to highly complex signals. 

    To address this challenge, the MicroBooNE collaboration developed a novel algorithm to extract the distribution of electrons from the measured induced current on the wires. The foundation of the algorithm is a mathematical technique called deconvolution, which greatly simplified the “signal” by removing the very complex induction response of the liquid argon chamber, so scientists can extract the location and distribution of electrons arriving at the wire planes.

    This deconvolution is performed in two dimensions (2D). According to Brookhaven postdoctoral research associate Hanyu Wei, the first ‘D’ is a common mathematical analysis of the waveform over time, and the second ‘D’ takes into account the long-range effect of the induction signals across multiple wires. By identifying specific “regions of interest” in the signal, the scientists can also mitigate the magnification of low-frequency noise from the deconvolution technique.

    MicroBooNE is the first detector able to match the number of detected electrons across the three wire planes of a LArTPC.

    “Since the same clusters of drifting electrons are detected by each of the wire planes, you’d expect to measure the same amount of charge from each plane,” said Michael Mooney, a former Brookhaven Lab postdoctoral research associate who is now a new faculty member at Colorado State University. But because of the complexity of the signals in the induction wire planes, no previous LArTPC detector has been able to do this.

    “Our data-driven demonstration that local cross-plane matching of charge is feasible in a LArTPC opens doors to new types of reconstruction techniques that aim first to create a 3D image of the neutrino-argon interaction—and could greatly improve our ability to precisely determine the properties of the neutrino,” Mooney said.

    Simulations vs. data

    The MicroBooNE team also developed significantly improved simulations of expected TPC signals and noise—taking into account the aforementioned long-range induction effect and the exact drifting electron’s position within a wire region—and used these new simulations to quantitatively evaluate their signal-processing algorithm. Comparing the simulations with results extracted from real data produced consistent results, which is a crucial step toward using the detector for physics studies.

    “The consistency between the new simulation and the data gives us confidence that we understand our detector at the fundamental level, which is critical for upcoming physics analyses in MicroBooNE,” said Brookhaven Lab physicist Chao Zhang.


    Brookhaven Lab physicist Brett Viren noted, “The ability to provide more accurate simulation of both noise and signals from LArTPC wires enables us to validate reconstruction techniques and quantitatively evaluate their efficiencies. These improvements will also facilitate the use of these simulations and modern machine learning techniques—which must have training sets that closely mimic the real thing—to improve LArTPC detector accuracy.”

    The team has developed software for both the signal-processing algorithm and the improved signal and noise simulations in a “Wire-Cell Toolkit.” This software package can run on conventional central-processing-unit (CPU) computing architectures and could also be configured for the highly parallel architectures of high-performance computing (HPC) systems as well.

    “All of these achievements in signal processing, simulation, and data-simulation comparison bring us closer to realizing the full potential of LArTPC detector technology,” said Brookhaven’s Qian. “We now look forward to the exciting results that will come from MicroBooNE.

    “In addition, the advances at MicroBooNE build the foundation for detection and signal-processing techniques that will be used with larger LArTPC detectors—including those being developed for DUNE, which is scheduled to come online in the mid-2020s.”


    For DUNE, Fermilab’s Long-Baseline Neutrino Facility will shoot a beam of neutrinos through Earth from Illinois to an old gold mine deep underground in South Dakota. Up to four detectors in the cavern will build on bus-size MicroBoone’s ability to track particles with high precision by having colossal tanks each with 100 times the volume able to pin down particles’ positions to within a couple of millimeters. 

    “LArTPC detectors are the only technology that can achieve this precision at this large scale. That’s what makes them truly revolutionary,” Qian said.

    Brookhaven’s role in MicroBooNE is funded by the DOE Office of Science.

    Brookhaven National Laboratory is supported by the Office of Science of the U.S. Department of Energy. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit

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    Researchers switch material from one state to another with a single flash of light

    Scientists from the Department of Energy's SLAC National Accelerator Laboratory and the Massachusetts Institute of Technology have demonstrated a surprisingly simple way of flipping a material from one state into another, and then back again, with single flashes of laser light.

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    Surprise finding: Discovering a previously unknown role for a source of magnetic fields

    Feature describes unexpected discovery of a role the process that seeds magnetic fields plays in mediating a phenomenon that occurs throughout the universe and can disrupt cell phone service and knock out power grids on Earth.

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    Scientists studying a valuable, but vulnerable, species of poplar have identified the genetic mechanism responsible for the species' inability to resist a pervasive and deadly disease. Their finding could lead to more successful hybrid poplar varieties for increased biofuels and forestry production and protect native trees against infection.

    Pushing the (Extra Cold) Frontiers of Superconducting Science

    Ames Laboratory has developed a method to measure magnetic properties of superconducting and magnetic materials that exhibit unusual quantum behavior at very low temperatures in high magnetic fields.

    Scientists Find Unusual Behavior in Topological Material

    Argonne scientists have identified a new class of topological materials made by inserting transition metal atoms into the atomic lattice of a well-known two-dimensional material.

    Wind Farms and Reducing Hurricane Precipitation

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    New simulations confirm efficiency of waste-removal process in plasma device

    PPPL scientists have found evidence suggesting that a process could remove the unwanted ash produced during fusion reactions and make the fusion processes more efficient within a type of fusion facility known as a field-reversed configuration device.

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    Missing gamma-ray blobs shed new light on dark matter, cosmic magnetism

    Scientists, including researchers from the Department of Energy's SLAC National Accelerator Laboratory, have compiled the most detailed catalog of such blobs using eight years of data collected with the Large Area Telescope (LAT) on NASA's Fermi Gamma-Ray Space Telescope. The blobs, including 19 gamma-ray sources that weren't known to be extended before, provide crucial information on how stars are born, how they die, and how galaxies spew out matter trillions of miles into space.

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    Engineering professor receives Department of Energy grant

    New Mexico State University Department of Civil Engineering Assistant Professor Ehsan Dehghan Niri has received a United States Department of Energy grant. This is a three-year award for $400,000 and is a collaboration with Arizona State University.

    AVS and AIP Publishing Expand Partnership to Launch AVS Quantum Science

    AIP Publishing and AVS: Science and Technology of Materials, Interfaces, and Processing (AVS) today announced an agreement to publish AVS Quantum Science, a new online interdisciplinary journal. The announcement coincides with the AVS 65th International Symposium & Exhibition in Long Beach, California, from October 21-26, 2018.

    Prototype Solar Energy, Battery Systems to Fuel Commercialization

    Designing, building and testing prototype systems that show how renewable energy can power devices, such as a weather and soil sensor station, can help bridge the gap between basic science research and commercialization.

    Argonne to Advance High Performance Computing in Manufacturing

    Argonne awarded funding to partner with Industry to advance the use of high performance computing in manufacturing.

    "Invisible Glass" Wins 2018 Create the Future Design Contest Grand Prize

    Scientists from the Center for Functional Nanomaterials developed a technique for making nonreflecting glass, silicon, and plastic surfaces.

    Missouri S&T researchers win multimillion dollar grant to build fast-charging stations for electric cars

    Researchers from Missouri S&T and three private companies will combine their expertise to create charging stations for electric vehicles that could charge a car in less than 10 minutes - matching the time it takes to fill up a conventional vehicle with gasoline."The big problem with electric vehicles is range, and it's not so much range as range anxiety.

    Making batteries store more energy, last longer

    A new solid polymer electrolyte may help make cell phone batteries store more energy and last longer.

    Three Brookhaven Lab Scientists Named Fellows of American Physical Society

    The American Physical Society (APS), the world's largest physics organization, has elected three scientists from the U.S. Department of Energy's (DOE) Brookhaven National Laboratory as 2018 APS fellows.

    Southern Research first to win accreditation under ISO 14034

    Southern Research has become the first organization in the United States to earn accreditation under ISO 14034, a new international standard for evaluating and verifying environmental technologies that was recently adopted by the American National Standards Institute.

    Kawtar Hafidi to head Physical Sciences and Engineering directorate at Argonne

    Physicist Kawtar Hafidi has been appointed Associate Laboratory Director, Physical Sciences and Engineering at the U.S. Department of Energy's (DOE) Argonne National Laboratory.

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    Cryocooler Cools an Accelerator Cavity

    Researchers demonstrated cryogen-free operation of a superconducting radio-frequency cavity that might ease barriers to its use in societal applications.

    Shining Light on the Separation of Rare Earth Metals

    New studies identify key molecular characteristics to potentially separate rare earth metals cleanly and efficiently with light.

    Placing Atoms for Optimum Catalysts

    Precise positioning of oxygens could help engineer faster, more efficient energy-relevant chemical transformations.

    How to Make Soot and Stardust

    Scientists unlock mystery that could help reduce emissions of fine particles from combustion engines and other sources.

    Breaking the Symmetry Between Fundamental Forces

    Scientists improve our understanding of the relationship between fundamental forces by re-creating the earliest moments of the universe.

    Water Plays Unexpected Role in Forming Minerals

    Water molecules line up tiny particles to attach and form minerals; understanding how this happens impacts energy extraction and storage along with waste disposal.

    Heavy Particles Get Caught Up in the Flow

    First direct measurement show how heavy particles containing a charm quark get caught up in the flow of early universe particle soup.

    Seeing Between the Atoms

    New detector enables electron microscope imaging at record-breaking resolution.

    Scaling Up Single-Crystal Graphene

    New method can make films of atomically thin carbon that are over a foot long.

    Discovered: Optimal Magnetic Fields Suppress Instabilities in Tokamak Plasmas

    U.S. and Korean scientists show how to find and use beneficial 3-D field perturbations to stabilize dangerous edge-localized modes in plasma.


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