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    The DOE Science News Source is a Newswise initiative to promote research news from the Office of Science of the DOE to the public and news media.
    • 2018-05-02 13:05:16
    • Article ID: 693882

    Tracking Down Helium-4's Quarks and Gluons

    Scientists obtain the first exclusive measurement of deeply virtual Compton scattering of electrons off helium-4, vital to obtaining an unambiguous 3-D view of quarks and gluons within nuclei.

    • Credit: Image courtesy of Mohammad Hattawy and John Arrington

      Scientists used a radial time projection chamber built at Argonne National Laboratory and used at Jefferson Lab to isolate the rare scattering events where the electron beam interacted with an entire helium-4 nucleus, rather than just a single proton or neutron.

    The Science

    We’ve long known that nuclei are made of protons and neutrons, which are in turn composed of quarks and gluons, the building blocks of matter. While we’ve mapped out the spatial and momentum distributions of the quarks, our understanding of the gluon distributions and the interaction of quarks and gluons in matter is still very limited. Recently, scientists demonstrated that certain reactions probe the correlations between the momentum and spatial distributions of quarks and gluons within an entire helium nucleus, rather than its component protons and neutrons, allowing new insight into their complex interactions. The team used the interactions to provide new insight into the structure of the helium nucleus, one of the most common elements in the universe.

    The Impact

    The probing reactions involve studying “generalized” parton distributions (GPDs). An important technique that is used is known as deeply virtual Compton scattering (DVCS). The DVCS reaction is the preferred probe of GPDs and yielded the first 3-D partonic images of the proton. New groundbreaking measurements of exclusive DVCS from the helium-4 nucleus are a critical step towards providing similar 3-D pictures of the quark structure of nuclei. Further, the measurements provide a new approach to understanding the modification of protons and neutrons within the dense environment of a nucleus.

    Summary

    The researchers’ new measurements provided the first beam-spin asymmetry data on exclusive DVCS from helium-4 using a highly polarized electron beam from the Continuous Electron Beam Facility (CEBAF) at Jefferson Lab. Scattering from a pressurized helium-4 target was measured in the CEBAF Large Acceptance Spectrometer (CLAS) in Hall B. Isolating exclusive scattering—where the nucleus is not broken up in the high-energy collision—requires detection of the recoil helium-4 nucleus. The recoil nucleus was detected using a new Radial Time Projection Chamber, built by Argonne National Laboratory, to ensure that this rare scattering process was cleanly identified. From the azimuthal dependence of the beam-spin asymmetry the real and imaginary parts of the helium-4 Compton form factor, which directly sample the nuclear GPD, were extracted in a model-independent way. This data, while limited in statistics, proved the experimental feasibility of measuring such nuclear exclusive reactions and led the way to the approval of the next generation of nuclear measurements. These future measurements will be carried out using the new CLAS12 spectrometer and the upgraded CEBAF 12-GeV electron beam. In addition to DVCS on helium-4, deeply virtual meson production of theta mesons will be measured, giving researchers the chance to compare directly the quark and the gluon 3-D tomography of the helium-4 nucleus. Another important aspect of this program is the study of the partonic structure of bound nucleons via the incoherent DVCS channels of the helium-4 nucleus, providing a new way to see if the dense nuclear environment and strong interactions between nucleons bound together change the internal structure of the protons and neutrons. Because helium-4 is a small but tightly bound nucleus, these measurements can be compared to the most sophisticated calculations available, making it the ideal nucleus for such studies.

    Funding

    This work was supported in part by the Chilean Comisión Nacional de Investigación Científica y Tecnológica (CONICYT), the Italian Instituto Nazionale di Fisica Nucleare, the French Centre National de la Recherche Scientifique, the French Commissariat à l’Energie Atomique, the Department of Energy Office of Science’s Office of Nuclear Physics, the UK Science and Technology Facilities Council, the Scottish Universities Physics Alliance, the National Research Foundation of Korea, and the Office of Research and Economic Development at Mississippi State University. M. Hattawy also acknowledges the support of the Consulat Général de France á Jérusalem. The Southeastern Universities Research Association operates the Thomas Jefferson National Accelerator Facility for the Department of Energy.

    Publication

    M. Hattawy, et al. (CLAS Collaboration), "First exclusive measurement of deeply virtual Compton scattering off 4He: Toward the 3D tomography of nuclei." Physical Review Letters 119, 202004 (2017). [DOI: 10.1103/PhysRevLett.119.202004]

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    Science Up-Close: Developing a Cookbook for Efficient Fusion Energy

    To develop a future fusion reactor, scientists need to understand how and why plasma in fusion experiments moves into a "high-confinement mode" where particles and heat can't escape. Scientists at the Department of Energy's Princeton Plasma Physics Laboratory simulated the transition into that mode starting from the most basic physics principles.

    Peering into the Mist: How Water Vapor Changes Metal at the Atomic Level

    New insights into molecular-level processes could help prevent corrosion and improve catalytic conversion.

    Neutron science publications reach new highs at ORNL's flagship facilities

    The High Flux Isotope Reactor and the Spallation Neutron Source at the Department of Energy's Oak Ridge National Laboratory have reached new levels of increased science productivity. In 2018, a record high of more than 500 scientific instrument publications were produced between HFIR and SNS--based on neutron beamline experiments conducted by more than 1,200 US and international researchers who used the world-leading facilities.

    Fiery sighting: A new physics of eruptions that damage fusion experiments

    Feature describes first direct sighting of a trigger for bursts of heat that can disrupt fusion reactions.

    Microbial Types May Prove Key to Gas Releases from Thawing Permafrost

    Scientists discover key types of microbes that degrade organic matter and release carbon dioxide and methane into the atmosphere.

    An effect that Einstein helped discover 100 years ago offers new insight into a puzzling magnetic phenomenon

    Experiments at the Department of Energy's SLAC National Accelerator Laboratory have seen for the first time what happens when magnetic materials are demagnetized at ultrafast speeds of millionths of a billionth of a second: The atoms on the surface of the material move, much like the iron bar did. The work, done at SLAC's Linac Coherent Light Source (LCLS) X-ray laser, was published in Nature earlier this month.

    Found: A precise method for determining how waves and particles affect fusion reactions

    Like surfers catching ocean waves, particles within plasma can ride waves oscillating through the plasma during fusion energy experiments. Now a team of physicists led by PPPL has devised a faster method to determine how much this interaction contributes to efficiency loss in tokamaks.

    Discovery adapts natural membrane to make hydrogen fuel from water

    In a recent study from the U.S. Department of Energy's (DOE) Argonne National Laboratory, scientists have combined two membrane-bound protein complexes to perform a complete conversion of water molecules to hydrogen and oxygen.

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    Scientists Identify Gene Cluster in Budding Yeasts with Major Implications for Renewable Energy

    How yeast partition carbon into a metabolite may offer insights into boosting production for biofuels.


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    Top 10 Discoveries of 2018

    Every year, the U.S. Department of Energy's (DOE) Brookhaven National Laboratory compiles a list of the biggest advances made by the Lab's staff scientists, engineers, and visiting researchers. From uncovering mysteries of the universe to building better batteries, here, in no particular order, are our picks for the top 10 discoveries of 2018.

    U.S. Department of Energy Announces $33 Million for Small Business Research and Development Grants

    The U.S. Department of Energy announced it will award 189 grants totaling $33 million to 149 small businesses in 32 states.

    DOE to Provide $16 Million for New Research into Atmospheric and Terrestrial Processes

    The U.S. Department of Energy (DOE) announced a plan to provide $16 million for new observational research aimed at improving the accuracy of today's climate and earth system models.

    Machine learning award powers Argonne leadership in engine design

    When attempting to design engines to be more fuel-efficient and emissions-free, automotive manufacturers have to take into account all the complexity inherent in the combustion process.

    ORNL partners with industry to address multiple nuclear technology challenges

    The Department of Energy's Oak Ridge National Laboratory is collaborating with industry on six new projects focused on advancing commercial nuclear energy technologies that offer potential improvements to current nuclear reactors and move new reactor designs closer to deployment.

    Lithium earns honors for three physicists working to bring the energy that powers the sun to Earth

    Feature describes research of three PPPL physicists who have won the laboratory's 2018 outstanding research awards

    DOE approves technical plan and cost estimate to upgrade Argonne facility; Project will create X-rays that illuminate the atomic scale, in 3D

    The U.S. Department of Energy has approved the technical scope, cost estimate and plan of work for an upgrade of the Advanced Photon Source, a major storage-ring X-ray source at Argonne.

    Costas Soukoulis elected to National Academy of Inventors

    Costas Soukoulis, Ames Laboratory senior scientist and Iowa State University Frances M. Craig Endowed Chair and Distinguished Professor, has been named as a 2018 National Academy of Inventors (NAI) Fellow.

    Biophysicist F. William Studier Elected Fellow of the National Academy of Inventors

    F. William Studier, a Senior Biophysicist Emeritus at the U.S. Department of Energy's Brookhaven National Laboratory and Adjunct Professor of Biochemistry at Stony Brook University, has been elected as a Fellow of the National Academy of Inventors (NAI). He is among 148 renowned academic inventors being recognized by NAI for 2018.

    Blast to the future

    A grant from DOE's Technology Commercialization Fund will help researchers at Argonne and industry partners seek improvements to U.S. manufacturing by making discovery and design of new materials more efficient.


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    Rapid Lake Draining on Ice Sheets Changes How Water Moves in Unexpected Ways

    Widespread fracturing during lake drainage triggers vertical shafts to form that affect the Greenland Ice Sheet.

    New Historical Emissions Trends Estimated with the Community Emissions Data System

    The data system will allow for more detailed, consistent, and up-to-date global emissions trends that will aid in understanding aerosol effects.

    Peering into the Mist: How Water Vapor Changes Metal at the Atomic Level

    New insights into molecular-level processes could help prevent corrosion and improve catalytic conversion.

    Microbial Types May Prove Key to Gas Releases from Thawing Permafrost

    Scientists discover key types of microbes that degrade organic matter and release carbon dioxide and methane into the atmosphere.

    New Method Knocks Out Yeast Genes with Single-Point Precision

    Researchers can precisely study how different genes affect key properties in a yeast used industrially to produce fuel and chemicals.

    How Plants Regulate Sugar Deposition in Cell Walls

    Identified genes involved in plant cell wall polysaccharide production and restructuring could aid in engineering bioenergy crops.

    Scientists Identify Gene Cluster in Budding Yeasts with Major Implications for Renewable Energy

    How yeast partition carbon into a metabolite may offer insights into boosting production for biofuels.

    More Designer Peptides, More Possibilities

    A combined experimental and modeling approach contributes to understanding small proteins with potential use in industrial, therapeutic applications.

    Deep Learning for Electron Microscopy

    Artificial intelligence on Summit to discover atomic-scale structures.

    Clarifying Rates of Methylmercury Production

    New model provides more accurate estimates of how fast microbes produce a mercury-based neurotoxin.


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