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Tag: Office of Science

  • Machine Learning Techniques Enhance the Discovery of Excited Nuclear Levels in Sulfur-38

    Machine Learning Techniques Enhance the Discovery of Excited Nuclear Levels in Sulfur-38

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    The Science

    Newswise — Fixed numbers of protons and neutrons – the building blocks of nuclei – can rearrange themselves within a single nucleus. The products of this reshuffling include electromagnetic (gamma ray) transitions. These transitions connect excited energy levels called quantum levels, and the pattern in these connections provide a unique “fingerprint” for each isotope. Determining these fingerprints provides a sensitive test of scientists’ ability to describe one of the fundamental forces, the strong (nuclear) force that holds protons and neutrons together. In the laboratory, scientists can initiate the movement of protons and neutrons through an injection of excess energy using a nuclear reaction. In this study, researchers successfully used this approach to study the fingerprint of sulfur-38. They also used machine learning and other cutting-edge tools to analyze the data. 

    The Impact

    The results provide new empirical information on the “fingerprint” of quantum energy levels in the sulfur-38 nucleus. Comparisons with theoretical models may lead to important new insights. For example, one of the calculations highlighted the key role played by a particular nucleon orbital in the model’s ability to reproduce the fingerprints of sulfur-38  as well as neighboring nuclei. The study is also important for its first successful implementation of a specific machine learning-based approach to classifying data. Scientists are adopting this approach to other challenges in experimental design.

    Summary

    Researchers used a measurement that included a machine learning (ML) assisted analysis of the collected data to better determine the unique quantum energy levels – a “fingerprint” formed through the rearrangement of the protons and neutrons – in the neutron-rich nucleus sulfur-38. The results doubled the amount of empirical information on this particular fingerprint. They used a nuclear reaction involving the fusion of two nuclei, one from a heavy-ion beam and the second from a target, to produce the isotope and introduce the energy needed to excite it into higher quantum levels. The reaction and measurement leveraged a heavy-ion beam produced by the ATLAS Facility (a Department of Energy user facility), a target produced by the Center for Accelerator and Target Science (CATS), the detection of electromagnetic decays (gamma-rays) using the Gamma-Ray Energy Tracking Array (GRETINA), and the detection of the nuclei produced using the Fragment Mass Analyzer (FMA). 

    Due to complexities in the experimental parameters – which hinged between the production yields of the sulfur-38 nuclei in the reaction and the optimal settings for detection – the research adapted and implemented ML techniques throughout the data reduction. These techniques achieved significant improvements over other techniques. The ML-framework itself consisted of a fully connected neural network which was trained under supervision to classify sulfur-38 nuclei against all other isotopes produced by the nuclear reaction.

     

    Funding

    This work was supported by the Department of Energy Office of Science, Office of Nuclear Physics and by the National Research Council of Canada.



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    Department of Energy, Office of Science

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  • Scientists Probe the Emergent Structure of the Carbon Nucleus

    Scientists Probe the Emergent Structure of the Carbon Nucleus

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    The Science

    Newswise — The element carbon is critical to organic chemistry and life as we know it. The physics of its most common isotope, carbon-12, are extremely complex. Many experimental and theoretical investigations have been devoted to determining the energies and underlying structures of the nuclear states of carbon-12. In this work, researchers computed these states from first principles—the most basic components of physics theory. The approach used supercomputers and nuclear lattice simulations to calculate the three-dimensional shape formed by the protons and neutrons comprising the nucleus. The results show that all of the low-lying energy states of carbon-12 have a substructure where the six protons and six neutrons cluster together into alpha particles. Alpha particles are helium-4 nuclei, which contain two protons and two neutrons.

    The Impact

    One well-known nuclear state of carbon-12 is the Hoyle state. This state has an energy that sits near the energy threshold for three alpha particles or helium nuclei. This energy thereby greatly enhances the production of carbon in helium-burning stars. This helps to explain the presence of carbon in the Universe. The results obtained in this research show that the Hoyle state is composed of a “bent arm” or obtuse triangular arrangement of alpha particles. All the low-lying energy states of carbon-12 have an intrinsic shape composed of three alpha particles forming either an equilateral triangle or an obtuse triangle. The new results give information about the possible geometrical shapes of nuclear states.

    Summary

    The carbon atom provides the backbone for the complex organic chemistry composing the building blocks of life. The physics of the carbon nucleus in its predominant isotope, carbon-12, are also full of complexity. Researchers from the University of Bonn, Forschungszentrum Jülich in Germany, the Gaziantep Islamic Science and Technology University in Turkey, the Graduate School of China Academy of Engineering Physics, Tbilisi State University, and the Facility for Rare Isotope Beams at Michigan State University calculated the structure of the nuclear states of carbon-12 using the ab initio framework of nuclear lattice effective field theory.

    The research found that all the low-lying states of carbon-12 have an intrinsic shape composed of three alpha clusters forming either an equilateral triangle or an obtuse triangle. The states with the equilateral triangle shape also have a dual description in terms of particle-hole excitations in a mean-field picture. The results agree with experimental data and provide the first model-independent density map of the nuclear states of carbon-12. The results help to explain the origins of carbon from the helium and hydrogen that made up the Universe shortly after the Big Bang.

    Funding

    This research was funded by the Deutsche Forschungsgemeinschaft (the German Research Foundation), the National Natural Science Foundation of China , the Chinese Academy of Sciences President’s International Fellowship Initiative, the National Security Academic Fund of China, Volkswagen Stiftung, the European Research Council, the Department of Energy, and the Nuclear Computational Low-Energy Initiative SciDAC-4 project, as well as computational resources provided by the Gauss Centre for Supercomputing e.V. and the Oak Ridge Leadership Computing Facility.


    Journal Link: Nature Communications, May-2023

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    Department of Energy, Office of Science

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  • Nature Inspires a New Wave of Biotechnology

    Nature Inspires a New Wave of Biotechnology

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    The Science

    Newswise — Biological molecules called peptides play a key role in many biological activities, including the transport of oxygen and electrons. Peptides consist of short chains of amino acids, the building blocks of proteins. They are also the inspiration for new kinds of biotechnology. Researchers are developing a synthetic form of a peptide that self-assembles into nanoscale fibers that conduct electricity when combined with heme. Heme is a substance that helps proteins in nature move electrons from one place to another. The researchers determined how electrical conductivity of their peptide nanofibers was affected by the length of the sequence of amino acids in the peptide and their identity

    The Impact

    Structural parameters of  peptides in nature determine their function and their promise for biotechnology. These parameters include sequence length—the length of the peptide segments that make up complete peptide chains. They also include how some amino acids are arranged in a peptide. This study’s results help researchers design peptide assemblies that form nanoscale fibers and transport electrons over long distances, which could make these fibers useful in medical devices, biosensors for a wide range of applications, and robotics. They also have promise in the development of new enzymes, which companies use to make and improve things such as medical-grade and household cleaning products.

    Summary

    Fields in materials and biochemistry research explore protein and peptide nanostructures found in nature. These nanostructures show great promise as bioelectronic materials. The development of a synthetic analog capable of forming one-dimensional (1D) nanostructures would greatly improve scientists’ understanding of the natural system and provide a platform for developing new materials. Researchers in the Center for Nanoscale Materials at Argonne National Laboratory investigated a series of peptides that self-assemble into 1D layered nanostructures. The peptides PA-(Kx)n are denoted simply as PA-Kxn, where PA is c16-AH with c16-A being modified alanine (A) and H is histidine, K is lysine, n is the sequence repeat length (1-4), and x is the amino acid leucine (L), isoleucine (I), or phenylalanine (F).

    The team determined how the length of the peptide sequence (n) and the identity of the hydrophobic amino acid affect key factors: the binding affinity of heme to pre-assembled peptides, the heme density, and the electronic properties. With a sequence length of 2, the peptide assembly yielded the greatest binding affinity. The resulting nanoscale assemblies produced ordered arrays of the electroactive molecule heme. All the peptides, with the exception of PA-KL1, had nanofibers with a long aspect ratio regardless of repeat unit length and sequence. Such structures have potential utility as supramolecular bioelectronic materials useful in biomedical sensing and the development of enzymatic materials.

    Funding

    Research at the Center for Nanoscale Materials, a Department of Energy (DOE) Office of Science user facility, was supported by DOE Office of Science, Office of Basic Energy Sciences.


    Journal Link: Nanoscale, Jun-2022

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    Department of Energy, Office of Science

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  • Probing the Intricate Structures of 2D Materials at the Nanoscale

    Probing the Intricate Structures of 2D Materials at the Nanoscale

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    The Science

    Two-dimensional (2D) materials are just a single or a few layers of atoms thick. These materials often have exotic properties that may be useful for next-generation technologies. When layers of these materials are stacked, the electronic properties that emerge can be manipulated by, for example, twisting the layers with respect to one another. To fully understand these properties and correlate them with the twist angle, scientists need advanced microscopy techniques. Researchers developed a novel operating mode for the interferometric four-dimensional scanning transmission electron microscopy (4D-STEM) technique. This special technique allows researchers to measure the atomic-scale structural distortions, twist angle, and interlayer spacings that influence the unique electronic properties of layered 2D materials.

    The Impact

    Layered 2D materials have special properties that can advance technology beyond existing capabilities. For example, they could lead to faster and more energy efficient computers or more reliable electricity storage. The individual layers that make up these materials may each be oriented differently. This creates challenges in fully understanding their 3D atomic structures with existing microscopy techniques. Interferometric 4D-STEM can reveal the relative positions of atoms within separate layers of stacked and twisted 2D materials. The technique opens avenues to the design and development of materials with useful properties.

    Summary

    Layered 2D materials have attracted considerable attention due to their interesting electronic properties, which can be modified by changing the twist angle of bilayer materials, the stacking sequence of trilayer materials, or other factors. To fully understand and control the properties of these materials, researchers need to study their atomic structures. However, visualizing the atomic structure of few-layered materials is often challenging using conventional microscopy techniques, such as when working with materials composed of light elements or when 3D information is needed. Researchers need new techniques to improve precision and locally measure distortions and interlayer spacings in twisted materials composed of two or three layers, especially when they contain light elements or high twist angles.

    Researchers developed a new interferometric 4D-STEM modality that can provide information about local structural deformations within layers, twist direction and magnitude between layers, and interlayer distances for few-layered 2D materials. This new operating mode of 4D-STEM is still based on Bragg interferometry but uses a defocused electron probe to directly provide information about the relative positions of atoms within separate layers, as demonstrated in this study in bilayer and trilayer graphene. The technique sheds new light on the interplay between electronic properties and the precise structural arrangements of few-layer 2D materials.

     

    Funding

    The research was supported by the Center for Nanophase Materials Sciences, a DOE Office of Science user facility, and by the DOE Office of Science Early Career Award Program. Additional support was provided by the European Research Council and resources at the Vienna Scientific Cluster.


    Journal Link: Small, Jun-2021

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    Department of Energy, Office of Science

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  • Scientists Amplify Superconducting Sensor Arrays Signals Near the Quantum Limit

    Scientists Amplify Superconducting Sensor Arrays Signals Near the Quantum Limit

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    The Science

    Newswise — Understanding how energy moves in materials is fundamental to the study of quantum phenomena, catalytic reactions, and complex proteins. Measuring how energy moves involves shining special X-ray light onto a sample to start a reaction. Detectors then collect the radiation the reaction emits. Conventional sensors usually lack the sensitivity needed for these studies. One solution is to use superconducting sensors. But amplifying the signals from these sensors is a major challenge. Building on advances from quantum computing, researchers added a special type of amplifiers, superconducting traveling-wave parametric amplifiers. While most amplifiers add noise to the measurement, these amplifiers are almost noiseless. In a major advance, researchers recently showed that the amplifiers can operate at 4 Kelvin, which is considered relatively high operating temperatures.

    The Impact

    Reducing the noise that is added during signal processing can improve a sensor’s performance. Amplification allows each sensor to operate faster and be more sensitive. Recent experiments have shown that parametric amplifiers can potentially analyze signals from many superconducting sensors at the same time. Superconducting sensors work at very low temperatures. At these temperatures, parametric amplifiers have very good noise performance, close to the limit of quantum mechanics. The advance paves the way to integrate such amplifiers with a variety of sensor technologies.

    Summary

    A superconducting sensor consists of a superconducting thermometer and an absorber. When X-rays are stopped in the absorber, they change the superconducting state of the sensor. This generates a small current in an electrical circuit. To make the detector more sensitive, many sensors are arranged into an array, like in a digital camera. Superconducting sensors operate at very cold temperatures (approximately 0.09 Kelvin), so they require specialized readout electronics and amplifiers. These amplifiers need to combine the signals from multiple sensors on a single readout line. Combining signals is known as multiplexing. One efficient way to do this is to couple each sensor in an array to a resonator. All of the resonators are coupled to a single output line. The current produced by an absorbed photon shifts the resonant frequency in a unique way for each sensor.

    Because these resonators work in microwave frequencies, the electronic chip that contains all the resonators as well as the output feedline is called the microwave multiplexer. Researchers are preparing to measure the signals from an array of sensors and a microwave multiplexer with a readout chain whose first amplifier is a kinetic-inductance traveling-wave parametric amplifier instead of a conventional semiconductor amplifier. Using the parametric amplifier will reduce readout noise and enable larger arrays of faster sensors.

     

    Funding

    This work was funded by the Department of Energy Office of Science, Basic Energy Sciences Accelerator and Detector Research Program, the National Institute of Standards and Technology’s Innovations in Measurement Science Program, and NASA.


    Journal Link: Physical Review Applied, Apr-2022

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    Department of Energy, Office of Science

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  • Scientists Discover a New Phase of High-Density, Ultra-Hot Ice

    Scientists Discover a New Phase of High-Density, Ultra-Hot Ice

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    The Science

    Newswise — The outer planets of our solar system, like Uranus and Neptune, are water-rich gas giants. These planets have extreme pressures of 2 million times the Earth’s atmosphere. They also have interiors as hot as the surface of the Sun. Under these conditions, water exhibits exotic, high-density ice phases. Researchers recently observed one of these phases, called Ice XIX, for the first time using high-power lasers to reproduce the necessary extreme conditions. They measured the Ice XIX structure using the Matter at Extreme Conditions instrument at the Linac Coherent Light Source, a pioneering X-ray laser facility, to show that oxygen atoms pack in a body-centered cubic structure, while the hydrogen atoms move freely like a fluid, dramatically increasing conductivity.

    The Impact

    Voyager II, a NASA solar system exploration spacecraft launched in 1977, measured highly unusual magnetic fields around Uranus and Neptune. Scientists considered exotic states of so-called superionic ice as a possible explanation due to these states’ increased electrical conductivity. This work demonstrates the existence of the previously undiscovered Ice XIX phase. It shows that this phase could form at the right depths and help explain the Voyager II magnetic data.

    Summary

    Water–a compound that is ubiquitous in our solar system and necessary for life–exhibits an exceptionally complex pressure-temperature phase diagram with 18 crystalline ice phases already identified. Nowhere are dense ice phases more important than in the interiors of gas giants like Uranus and Neptune. Scientists hypothesize that these planets’ complex magnetic fields are produced by exotic high-pressure states of water ice with superionic properties. However, the structure of ice at these extreme conditions is notoriously challenging to measure.

    Using the Matter at Extreme Conditions instrument at the Linac Coherent Light Source, an ultrafast X-ray Free Electron Laser and a Department of Energy (DOE) Office of Science user facility, to probe the ice structure during laser-driven dynamic compression, researchers found the first direct evidence of a new phase of high-density, ultra-hot water ice. At 200 GPa (2 million atmospheres) and 5,000 K (8,500 degrees Fahrenheit) this new high-pressure ice phase, deemed Ice XIX, has a body-centered cubic (BCC) lattice structure. Though other structures have been theorized to be stable at these conditions, Ice XIX’s BCC structure would enable an increase in the electrical conductivity much deeper into the interiors of ice giants than previously thought. The results provide an important and compelling origin of the multi-polar magnetic fields as measured by the Voyager II spacecraft for Uranus and Neptune.

     

    Funding

    Funding for this research included the DOE National Nuclear Security Administration; the DOE Office of Science, Fusion Energy Science; the Laboratory Directed Research & Development program of Los Alamos National Laboratory; and the National Science Foundation. The experimental measurements were conducted at the Matter at Extreme Conditions instrument (operated by the DOE Office of Science, Fusion Energy Science program) of the Linac Coherent Light Source, a DOE Office of Science, Basic Energy Sciences user facility operated by SLAC National Accelerator Laboratory.


    Journal Link: Scientific Reports, Jan-2022

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    Department of Energy, Office of Science

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  • New Material Enables an Ultrafast Electron Diffraction Probe for Quantum Materials

    New Material Enables an Ultrafast Electron Diffraction Probe for Quantum Materials

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    Newswise — The Science

    Quantum materials have a host of exotic electronic, magnetic, and optical properties that make them prime candidates for use in future computing and energy technologies. Their properties arise from a complex interaction of their electrons and atomic nuclei. Researchers can observe these interactions as they happen using short pulses of X-rays or electron beams. These pulses last less than a trillionth of a second. Using new materials that emits a narrow electron probe, researchers have developed an ultrafast electron beam technique to probe small, thin pieces of quantum materials with very high resolution.

    The Impact

    Scientists so far cannot create many newly emerging quantum materials as large crystals. Instead, these materials form crystals only one-tenth as wide as a human hair. This poses a challenge for researchers probing these materials using ultrafast electron beam accelerators, as electron beam quality often limits how small an area these beams can focus on. In this study, researchers used a specialized source of electrons to produce a substantial improvement in electron beam quality. This enables crisp images of samples only a few microns wide and of processes that take place in less than a trillionth of a second. This work could lead to a clearer image and understanding of how quantum materials function at atomic space and time scales.

    Summary

    These accelerators typically generate ultrafast electron pulses via a process called photoemission, wherein laser light knocks electrons out of a material, usually a simple metal like copper. If the laser pulse is short in duration, the emitted electron beam will also be short. One challenge with typical photoemission sources is that the electrons emitted do not all travel in the same direction. This spread in emission angle can ultimately limit researchers’ ability to focus the electron beam on a small spot.

    In this work, researchers developed a photoemission-based electron accelerator with an advanced, in-house grown photoemission material that produces many electrons with a much smaller spread in emission angle. Using this source in conjunction with precise electron focusing optics, the researchers performed proof-of-principle ultrafast electron diffraction experiments which showed the ability to resolve subtle atomic details in samples as small as just a few microns in size.

    Funding

    This research was supported by the Department of Energy Office of Science, Basic Energy Sciences and by the National Science Foundation.


    Journal Link: Structural Dynamics, Mar-2022

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    Department of Energy, Office of Science

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  • Scientists Make the First Observation of a Nucleus Decaying into Four Particles After Beta Decay

    Scientists Make the First Observation of a Nucleus Decaying into Four Particles After Beta Decay

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    The Science

    Not all of the material around us is stable. Some materials may undergo radioactive decay to form more stable isotopes. Scientists have now observed a new decay mode for the first time. In this decay, a lighter form of oxygen, oxygen-13 (with eight protons and five neutrons), decays by breaking into three helium nuclei (an atom without the surrounding electrons), a proton, and a positron (the antimatter version of an electron). Scientists observed this decay by watching a single nucleus break apart and measuring the breakup products.

    The Impact

    Scientists have previously observed interesting modes of radioactive decay following the process called beta-plus decay. This is where a proton turns into a neutron and emits some of the produced energy by emitting a positron and an antineutrino. After this initial beta-decay, the resulting nucleus can have enough energy to boil off extra particles and make itself more stable. This new decay mode is the first observation of three helium-nuclei (alpha particles) and a proton being emitted following beta-decay. The findings can inform scientists about decay processes and the properties of the nucleus before the decay.

    Summary

    In this experiment, researchers used a particle accelerator known as a cyclotron at the Cyclotron Institute at Texas A&M University to produce a beam of radioactive nuclei at high energies (approximately 10% the speed of light). They sent this beam of radioactive material, oxygen-13, into a piece of equipment known as the Texas Active Target Time Projection Chamber (TexAT TPC). The material stops inside this detector, which is filled with carbon dioxide gas, and decays after about ten milliseconds by emitting a positron and a neutrino (beta-plus decay). By implanting the oxygen-13 into the detector one nucleus at a time and waiting for it to decay, the researchers measured any particles that boil off following the beta-decay using the TexAT TPC. Next, they analyzed the data with a computer program to identify the tracks the particles leave in the gas. This allowed them to identify the rare events (occurring only once per 1,200 decays) as those where four of the particles are emitted following beta-decay.

     

    Funding

    This work was supported by the Department of Energy Office of Science, Office of Nuclear Science, and by the National Nuclear Security Administration through the Center for Excellence in Nuclear Training and University Based Research (CENTAUR). Several of the authors also acknowledge travel support from the IBS grant and the National Research Foundation of Korea grant, both funded by the government of the Republic of Korea.


    Journal Link: Physical Review Letters, Jun-2023

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    Department of Energy, Office of Science

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  • Researchers Test Quantum Theory with Precision-Engineered Thin Films

    Researchers Test Quantum Theory with Precision-Engineered Thin Films

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    The Science

    Comparing experimental results and theoretical calculations can be difficult for quantum materials. These are materials that have special properties, such as superconductivity, that can only be understood using the rules of quantum mechanics. One way that scientists compare experiments and computations is to use sample materials that isolate and emphasize an atomic line with one dimensional (1D) properties. In this study, scientists grew thin films of layered copper-oxygen (cuprate) materials to isolate 1D copper chains. This allowed them to test theories of how electrons interact in quantum materials. They grew the films under conditions that allowed them to carefully modify the films’ chemistry and electronic structure. They then measured the electronic structure. The research was possible in part because of a specialized synchrotron X-ray beam line designed and built for this purpose.

    The Impact

    Describing how the properties of quantum materials interact and testing related theories are mathematically very complex and time consuming. This work enabled a direct comparison of computational results against experimental measurements. The study indicates that standard theory is not sufficient and requires a new term to fit the experimental data. The work will help scientists refine theories that are essential to describing and engineering new quantum materials and effects. This could eventually lead to new quantum electronic devices.

    Summary

    It is currently impossible to computationally solve the electronic structure of multi-dimensional quantum materials. 1D theory is computationally possible but difficult to test because most materials have 3D structures. The structure of inherently layered 2D cuprate materials can be rearranged, when synthesized in the ultra-thin limit, resulting in 1D copper-oxygen chains that run parallel to the material surface. However, to fully test theories of electron interactions and transport, researchers also need well characterized “doping” defects in the cuprate oxygen stoichiometry.

    In this research, scientists figured out a synthesis method, using ozone during molecular beam epitaxial growth, to add extra oxygen atoms that grab electrons from the copper atoms and create holes in the electronic structure. This was done at a thin film deposition station connected to a synchrotron X-ray beamline that was designed with a sensitive X-ray photoemission spectroscopy capability that can map out the resulting electronic structure. By comparing experimental results with theory, the researchers showed that the standard theory of electron interactions and transport could not predict the 1D doping effects without a modification used to show an unusually strong attraction between certain electrons at longer separations. This attraction is mediated by atomic vibrations. Understanding the coupling between chemistry, defects, vibrations, and the spin direction of electrons are a necessary part of engineering quantum materials for future devices. This work provides a needed direct connection between theory and experiment at the level of correlated electron theory.

     

    Funding

    This work was supported by the Department of Energy (DOE) Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division. Film growth and X-ray ARPES experiments were performed at Beamline 5-2 of the Stanford Synchrotron Radiation Light Source, a DOE Office of Science user facility at SLAC National Accelerator Laboratory. Computational resources were provided by the National Energy Research Scientific Computing Center, a DOE Office of Science user facility.

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    Department of Energy, Office of Science

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  • Calculations Predict Surprising Quark Diffusion in Hot Nuclear Matter

    Calculations Predict Surprising Quark Diffusion in Hot Nuclear Matter

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    The Science

    Scientists can use powerful colliders to smash atomic nuclei together to create a quark-gluon plasma (QGP). This “soup” of quarks and gluons, some of the fundamental building blocks of matter, filled the early universe. Tracking how high energy jets of quarks travel through the QGP can reveal information about the QGP’s properties. Scientists’ simplest assumption is that local interactions with the quarks and gluons will deflect these energetic particles. But recent theoretical calculations that also include non-local quantum interactions—those interactions beyond a particle’s immediate surroundings—predict a super-diffusive process. This means that the complex  interactions in QGP deflect quarks faster and at wider angles than can be explained by local interactions alone.

    The Impact

    Testing these predictions at particle colliders will provide new insight into the interactions between quarks and gluons. These interactions are governed by the strong nuclear force, one of the four fundamental forces that govern the universe. The new theoretical explanation points to the importance of the non-local nature of these quantum interactions. The findings suggest that the description of the QGP as a collection of point-like particles may break down even at short distances. The discovery of the importance of longer-range quantum interactions might also offer a new perspective for understanding why the QGP flows like a nearly perfect fluid–a fluid with very low viscosity.

    Summary

    Scientists use particle colliders to recreate a form of early universe matter known as a QGP. Tracking how energetic jets of particles move through the QGP can reveal information about its properties. Early calculations based on the theory of strong interactions suggested that jets would undergo a diffusive process caused by random deflections as the energetic particles interacted with the quarks and gluons that make up the plasma—similar to the way pollen particles on the surface of a pond get “kicked” around by water molecules.

    Counter to these early calculations, nuclear theorists at Brookhaven National Laboratory recently discovered that including non-local quantum effects—which arise from long-lived gluon fluctuations—predicts significant deviations from the expected diffusion pattern in QGP. Including these non-local effects predicts that energetic jets will undergo a super-diffusive process, broadening the angle of the jet faster than local interactions alone can explain. The predictions can be tested by tracking energetic jets in the QGP created in high-energy heavy ion collisions at the Relativistic Heavy Ion Collider (a Department of Energy user facility at Brookhaven National Laboratory) and the Large Hadron Collider in Europe.

     

    Funding

    This research was funded by the Department of Energy Office of Science, Office of Nuclear Physics and by the National Science Foundation.


    Journal Link: Journal of High Energy Physics, Sep-2022
    Journal Link: Physical Review D, Sep-2022

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    Department of Energy, Office of Science

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  • In Preparation for DUNE, Scientists Examine Modern Nuclear Theory for Neutrino Oscillation Physics

    In Preparation for DUNE, Scientists Examine Modern Nuclear Theory for Neutrino Oscillation Physics

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    The Science

    Newswise — The U.S. particle physics community is preparing for a major research program with the Deep Underground Neutrino Experiment (DUNE). DUNE will study neutrino oscillations. These quantum mechanical oscillations are only possible because neutrinos have mass, albeit it very small masses. Research at DUNE will address key questions about neutrinos, such as whether they and their antineutrino counterparts behave differently. Answering these questions could help explain why the universe is composed of matter and not antimatter. These studies require a detailed understanding of how neutrinos interact with atomic nuclei and the nucleons (protons and neutrons) that make up nuclei. By providing new data, DUNE will help scientists advance beyond the current understanding of neutrino-nucleon interactions, which relies upon data from experiments in the 1970s and ‘80s.

    The Impact

    Scientists use the nuclear theory method called Lattice Quantum Chromodynamics (LQCD) to predict neutrino-nucleon interactions. The LQCD results predict a stronger neutrino-nucleon interaction than predictions determined from older, less precise, experimental data. This research demonstrated important implications of how scientists interpret neutrino oscillation signals from LQCD. It also identified the next results to tackle with LQCD. These findings, combined with modern many-body nuclear theory methods, will reduce the potential biases due to incorrect modeling. The findings will also improve scientists’ predictions of these interactions for DUNE and other neutrino experiments.

    Summary

    A recent project by researchers at the University of California, Berkeley and Lawrence Berkeley National Laboratory demonstrated the importance of incorporating state-of-the-art theoretical predictions of the “nucleon axial form factor” into simulations of neutrino-nucleus reactions (a form factor is a measure of the “squishiness” of a particle — the smaller the value, the squishier). Scientists need these form factors to determine oscillation properties of the elusive neutrinos that will be explored by DUNE and other leading neutrino oscillation experiments. The most advanced LQCD predictions conflict with the older phenomenological models of the axial form-factor, leading to a 30% larger neutrino-nucleon cross-section. This has important implications for the interpretation of the oscillation experiments. These LQCD calculations are made possible by the Department of Energy’s Leadership Class Computing Facilities, which house the fastest supercomputers in the world.

    In the exascale computing era, scientists will further refine the LQCD results and tackle additional, more complicated processes. The results will be combined with modern many-body nuclear theory methods to provide more robust predictions of the neutrino-nucleus reactions. These predictions are essential ingredients for interpreting the next-generation neutrino oscillation experiments, such as DUNE, and inferring properties of neutrinos.

     

    Funding

    This work is supported in part by the Department of Energy Office of Science, High Energy Physics and Nuclear Physics programs.


    Journal Link: Annual Reviews in Nuclear and Particle Science, Sep-2022

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    Department of Energy, Office of Science

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  • Novel Metric Examines the Role of Organic Matter and Microbes in Ecological Communities

    Novel Metric Examines the Role of Organic Matter and Microbes in Ecological Communities

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    The Science

    Ecological researchers study the relationships among different organisms and between organisms and their surroundings. This makes it critical to understand how individual features in a community, like microbes or types of chemicals, affect the overall community’s development. By examining individual features, researchers can begin to identify those community or assemblage members that drive similarities across communities. To assist in this goal, scientists developed a novel ecological metric, called βNTIfeat. Many microbes do not grow in laboratory conditions. The new metric found that these “unculturable” microbes shape the microbial communities in river corridors. The metric also revealed that organic matter is influenced by a variety of compounds that contain nitrogen and phosphorus.

    The Impact

    βNTIfeat will help researchers answer longstanding questions about ecosystems. For example, βNTIfeat can help uncover a common group of microbes that significantly affect various river corridors at different local or global scales. This will allow researchers to incorporate the dynamics of these microbes into models. In turn, these models will help scientists to generate predictions about how ecosystems may change due to climate change, wildfires, and other future disturbances.

    Summary

    Evaluating how ecological communities develop and change is one of the primary goals of ecology. By examining processes that give rise to specific community configurations across varied conditions, researchers will have a better understanding of the fundamental principles that govern community structure and will be able to improve predictions. Unfortunately, comparatively few studies examine the effects that individual features within a community or assemblage play on its overall structure. As part of this study, researchers from Pacific Northwest National Laboratory and California Lutheran University developed a new metric, called βNTIfeat, that investigates the contributions that these features make within a community.

    Researchers used βNTIfeat to evaluate feature-level ecological processes in a riverine ecosystem to reveal some key dynamics. First, the team observed that unclassified and unculturable microbial lineages often contribute to differences across the microbial communities; this observation suggests that these unclassified/uncultured lineages play an outsized role relative to their abundance. Secondly, the organic matter assemblages were often driven by nitrogen- and phosphorus-containing molecular formulas, indicating a potential connection to nitrogen/phosphorus-biogeochemical cycles. Finally, by relating the βNTIfeat values for microbes and molecular formulas using a network analysis, researchers determined that members of the microbial family Geobacteraceae often had coordinated contributions to ecological structure with both nitrogen- and phosphorous-containing molecular formulas. This observation suggests there is a complex network of ecological interactions across community types.

     

    Funding

    The initial experimental stages of this work were supported by the PREMIS Initiative at the Pacific Northwest National Laboratory (PNNL) with funding from the Laboratory Directed Research and Development Program at PNNL. The later stages of this work (e.g., data analysis, conceptual interpretation manuscript development) were supported by the Department of Energy (DOE) Office of Science, Biological and Environmental Research program, as part of an Early Career Award to James C. Stegen at PNNL. A portion of the research was performed at the Environmental Molecular Sciences Laboratory, a DOE Office of Science user facility at PNNL.


    Journal Link: Frontiers in Microbiology, Feb-2022

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  • Thanks to Trapped Electrons, a Material Expected to be a Conducting Metal Remains an Insulator

    Thanks to Trapped Electrons, a Material Expected to be a Conducting Metal Remains an Insulator

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    The Science

    New research sheds light on the mechanism behind how a special material changes from an electrically conducting metal to an electric insulator. The researchers studied lanthanum strontium nickel oxide (La1.67Sr0.33NiO4) derived from a quantum material La2NiO4. Quantum materials have unusual properties that result from how their electrons interact. Below a critical temperature, the strontium doped material is an insulator. This is due to the separation of introduced holes from the magnetic regions, forming “stripes.” As the temperature increases, these stripes fluctuate and melt at 240K. At this temperature, researchers expected the material to become a conducting metal. Instead, it remains an insulating material. Neutron scattering sheds light on this intriguing phenomenon. The results indicate that the material stays an insulator because of certain atomic vibrations that trap electrons and thus impede electrical conduction.

    The Impact

    Quantum materials have properties that aren’t predicted by the parts that make up those materials. For example, they can transition from metals to insulators or act as superconductors. They hold tremendous promise for applications in science and technology. This research describes the tunability of electron-phonon interaction on the metal-insulator transition in one quantum material. The results will help validate theoretical models of materials that have strongly interacting electrons. These theories will help scientists design new quantum materials for future technologies.

    Summary

    In metals, electrons can be considered as free particles flying along trajectories enforced by the crystal structure. In recent decades, scientists discovered new materials where electrons strongly repel each other and bounce off atomic vibrations in the host crystal. These materials exhibit unusual and technologically useful properties. These properties can include dramatic electrical resistance drop in magnetic fields, electron conduction only on the surface, and high temperature superconductivity. Understanding these properties in different materials remains a grand challenge for the scientific community.

    This work used high intensity neutron beams at the Spallation Neutron Source, a Department of Energy user facility at Oak Ridge National Laboratory (ORNL), to look deep inside an archetype quantum material La2NiO4 in which one sixth of the lanthanum (La) atoms are replaced with strontium (Sr) atoms (La1.67Sr0.33NiO4). The team included researchers from the University of Colorado Boulder, ORNL, Brookhaven National Laboratory, and the RIKEN Center for Emergent Matter Science in Japan. These materials are insulating at low temperatures due to the so-called “stripe” order that results from the complex interplay between electronic spins and the holes introduced due to strontium doping. The doped material is expected to become metallic above 240K when the stripes melt. However, the material remains insulating. The collaboration uncovered strong friction between the holes and certain vibrations of oxygen ions and found evidence for this interaction in other materials of similar structure. The microscopic mechanism could pave way for the design of new materials with unusual properties useful for various quantum technologies.

     

    Funding

    Work at the University of Colorado Boulder was supported by the Department of Energy Office of Science, Basic Energy Sciences program. One of the researchers was supported by a Japan Science and Technology Agency CREST Grant. Work at Brookhaven National Laboratory was supported by the Department of Energy Office of Science, Basic Energy Sciences program.


    Journal Link: Scientific Reports, Jul-2020

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  • Nuclear Charge Distribution Measurements May Solve Outstanding Puzzle In Particle Physics

    Nuclear Charge Distribution Measurements May Solve Outstanding Puzzle In Particle Physics

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    The Science

    What scientists call the “nuclear weak distribution” describes the distribution of “active” protons in a nucleus. These are protons that are eligible to transition into neutrons through what scientists call the “weak interaction.” Researchers recently reviewed the existing standard procedure to determine this distribution. In the study, they abandoned previous treatments using nuclear shell models. Instead, they related the weak distribution to the distribution of electric charges in a nucleus. Scientists can measure this distribution by scattering electrons off nuclear targets or by studying energy levels through atomic spectroscopy.

    The Impact

    The new data-driven analysis found significant differences with the results of previous model-based determinations of the nuclear weak distribution. This result advances the search for new physics based on nuclear beta decay experiments. It does so by providing a partial explanation for a discrepancy between predictions from particle physics theory and experimental measurement of a fundamental quantity called “Vud.” This term describes how quarks transition from one type to another inside a proton or neutron, thus changing the particles.

    Summary

    The extracted value of “Vud” from nuclear beta decays seems to be substantially smaller than what is required by the Standard Model of Particle Physics, the commonly-acknowledged best theory for elementary particle physics. This observed anomaly stimulates vibrant discussions of possibilities of new physics discoveries. To study its origin, researchers at the Facility for Rare Isotope Beams (FRIB) at Michigan State University investigated the so-called “nuclear weak distribution.” They found that the current understanding of this distribution is based on rather simple models that assume non-interacting nucleons inside a nucleus. Furthermore, they showed that this distribution may be determined independently of models using measurements of nuclear charge distributions, which can be done either through electron-nucleus scattering experiments or through atomic spectroscopy.

    Upon analyzing existing data, the researchers found that the value of Vud moved closer to the Standard Model prediction. Future measurements of nuclear charge distributions, for example at FRIB, may provide further insights towards the resolution of the Vud anomaly.

     

    Funding

    This work is supported in part by the Department of Energy Office of Science, Office of Nuclear Physics.


    Journal Link: Physical Review Letters, Apr-2023

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  • U.S. Department of Energy Releases Plan to Ensure Free, Immediate, and Equitable Access to Federally Funded Research

    U.S. Department of Energy Releases Plan to Ensure Free, Immediate, and Equitable Access to Federally Funded Research

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    Newswise — WASHINGTON, D.C. — The U.S. Department of Energy (DOE) today released a plan to ensure the Department’s Federally funded research is more open and accessible to the public, researchers, and journalists as part of a broader effort by the Biden-Harris Administration to make government data more transparent. With 17 National Laboratories and scores of programs that fund university and private research, DOE directly supports thousands of research papers per year, and, when this plan goes into effect, those findings will be available immediately and at no cost.

    “Science and innovation cannot flourish in the dark—they require openness, scrutiny, and reexamination so that we can build on them to create the knowledge and technologies that will change the world,” said U.S. Secretary of Energy Jennifer M. Granholm. “As one of the Federal Government’s leading sponsors of research, DOE is proud and excited to get our data and research out into the public’s hands faster and more efficiently, and we look forward to expanding and accelerating that access by engaging the American public in DOE’s mission.”

    DOE’s public access plan supports the August 2022 White House Office of Science and Technology Policy (OSTP) memo that called for Federal agencies to “make publications and their supporting data resulting from federally funded research publicly accessible without an embargo on their free and public release.” The new plan describes the steps DOE will take to enable equitable access to the unclassified and unrestricted results of its multi-billion dollar annual investments in climate, energy, environment, and basic and applied research and development.

    Since 2014, when DOE released its first plan to grant the public more access to research, the Department has provided free public access to nearly 200,000 articles and accepted manuscripts and has enabled broader access to scientific data through rigorous data management planning requirements.

    Key elements of the new DOE public access plan, as laid out by OSTP, will include elimination of any “embargo” period before the public gains free access to journal articles or final accepted manuscripts resulting from federal funding; immediate access to scientific data displayed in or underlying publications and expanded access to scientific data not displayed in publications; and broad adoption of persistent identifiers (PIDs) for research outputs, organizations, awards and contracts, and people.

    Most requirements and guidance will be in place by the end of 2024 with implementation by the end of 2025. DOE’s model for implementing access to publications and scientific data will be similar to existing practices—for publications, through submissions of accepted manuscripts or open access articles which will be made available through DOE’s public access repository, and for data, through submission of data management and sharing plans to DOE.

    Key changes include the requirement to submit accepted manuscripts or open access journal articles immediately upon publication and an increased focus on immediate and broader sharing of scientific data.

    DOE has played a leading role in the assignment and use of PIDs among Federal research agencies, and the new plan builds on this record and expands DOE’s support of PIDs for research outputs, such as data and software, research and sponsoring organizations, and for researchers themselves. DOE will work internally, and with other agencies, to develop options for PIDs for research and development awards and contracts and will update its public access plan when those details are finalized. 

    The Department engaged with numerous communities in developing its plan and will continue to encourage participation and input from researcher communities, libraries, professional societies, publishers, Federal agency partners, and the public.

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  • New Insights on the Prevalence of Drizzle in Marine Stratocumulus Clouds

    New Insights on the Prevalence of Drizzle in Marine Stratocumulus Clouds

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    The Science

    Drizzle is light precipitation in droplets smaller than rain drops. Detecting drizzle in its early stages in marine stratocumulus clouds is important for studying how water in these clouds becomes rainfall. These clouds form off the west coasts of large land areas and are important to the Earth’s energy balance.  Drizzle and rain formation can alter their lifetime, structure, and how much sunlight they reflect to space. However, detecting the initial stages of drizzle is challenging for ground-based remote-sensing observations. Researchers developed a machine learning-based approach using unique radar Doppler spectra observations to identify the early stage of drizzle drops.

    The Impact

    The results demonstrate that drizzle is far more frequent than previously recognized by traditional methods. The method also provides essential information on light precipitation. This information challenges the detection limits of satellite-borne observations used in precipitation climate analyses for global climate model (GCM) evaluation.

    Summary

    Researchers commonly use radar reflectivity from millimeter-wavelength radar for drizzle detection, but it is unable to identify weak drizzle signals. Doppler skewness—a measure of Doppler spectral symmetry—has proven to be a more sensitive quantity for the detection of drizzle embryos. In this study, researchers from Brookhaven National Laboratory and Stony Brook University detected small drizzle droplets using a newly developed machine-learning technique from unique drizzle retrievals based on radar reflectivity and skewness from millimeter-wavelength radars operated by the Department of Energy’s Atmospheric Radiation Measurement (ARM) user facility. The researchers evaluated the drizzle detection algorithm on aircraft in situ measurements and then applied them to ARM observational campaigns at three different sites (Eastern North Atlantic [ENA], Measurements of Aerosols, Radiation, and Clouds over the Southern Ocean [MARCUS], and Marine ARM GPCI Investigation of Clouds [MAGIC]) to investigate drizzle occurrence in marine stratocumulus clouds.

    The results show that drizzle is far more ubiquitous than previously recognized, and that the traditional approach significantly underestimates the drizzle occurrence, especially in thin clouds with low liquid water paths. Drizzle occurrence in marine boundary-layer clouds differs among the three ARM campaigns, indicating that drizzle formation and distribution is regime dependent, controlled by microphysical and dynamical processes in the local region. Further, spaceborne radar (i.e., CloudSat) observations used to generate precipitation climatologies have low sensitivity in the light precipitation region. The new method provides essential information in this region to challenge the conventional light precipitation climatology and can be used to improve the warm rain parameterization in GCMs.

     

    Funding

    Zeen Zhu’s contributions have been supported by the Department of Energy (DOE) Office of Science, Atmospheric System Research (ASR) program’s Eastern North Atlantic Site Science award. Pavlos Kollias, Edward Luke, and Fan Yang have been supported by the DOE Office of Science ASR Program (contract no. DE-SC0012704).


    Journal Link: Atmospheric Chemistry and Physics, Jun-2022

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  • Resolving a Mathematical Puzzle in Quarks and Gluons in Nuclear Matter

    Resolving a Mathematical Puzzle in Quarks and Gluons in Nuclear Matter

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    The Science

    The building blocks of atomic nuclei are protons and neutrons, which are themselves made of even more fundamental particles: quarks and gluons. These particles interact via the “strong” force, one of the four fundamental forces of nature. They make up the nuclei at the heart of every atom. They also make up forms of hot or dense nuclear matter that exhibit exotic properties. Scientists study the properties of hot and cold nuclear matter in relativistic heavy ion collision experiments and will continue to do so using the future Electron-Ion Collider. The ultimate goal is to understand how complex forms of matter emerge from elementary particles affected by strong forces.

    The Impact

    Theoretical calculations involving the strong force are complex. One aspect of this complexity arises because there are many ways to perform these calculations. Scientists refer to some of these as “gauge choices.” All gauge choices should produce the same result for the calculation of any quantity that can be measured in an experiment. However, one particular choice, called “axial gauge,” has puzzled scientists for years because of difficulties in obtaining consistent results upon making this choice. This recent study resolves this puzzle and paves the way for reliable calculations of hot and cold nuclear matter properties that can be tested in current and future experiments.

    Summary

    The exotic form of nuclear matter that physicists study in relativistic heavy ion collisions is called the quark-gluon plasma (QGP). This form of matter existed in the early universe. Physicists explore its properties in heavy ion collision experiments by recreating the extremely high temperatures last seen microseconds after the Big Bang. By analyzing experimental data from the collisions and comparing them with theoretical calculations, physicists can ascertain various properties of the QGP. Using a calculation method called “axial gauge” had previously seemed to imply that two QGP properties that describe how heavy quarks move through the QGP were the same. 

    Researchers at the Massachusetts Institute of Technology and the University of Washington have now found this implication to be incorrect. The study also carefully analyzed the subtle conditions for when axial gauge can be employed and explained why the two properties are different. Finally, it showed that two distinct methods for measuring how gluons are distributed inside nuclei must yield different results. Gluons are the particles that carry the strong force, This prediction will be tested at the future Electron-Ion Collider.

     

    Funding

    This work is supported by the Department of Energy Office of Science, Office of Nuclear Physics and by the Office of Science, Office of Nuclear Physics, InQubator for Quantum Simulation (IQuS).


    Journal Link: Physical Review Letters, Feb-2023

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  • New Insights on the Interplay of Electromagnetism and the Weak Nuclear Force

    New Insights on the Interplay of Electromagnetism and the Weak Nuclear Force

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    The Science

    Outside atomic nuclei, neutrons are unstable particles, with a lifetime of about fifteen minutes. The neutron disintegrates due to the weak nuclear force, leaving behind a proton, an electron, and an antineutrino. The weak nuclear force is one of the four fundamental forces in the universe, along with the strong force, the electromagnetic force, and the gravitational force. Comparing experimental measurements of neutron decay with theoretical predictions based on the weak nuclear force can reveal so-far undiscovered interactions. To do so, researchers must achieve extremely high levels of precision. A team of nuclear theorists has uncovered a new, relatively large effect in neutron decay that arises from the interplay of the weak and electromagnetic forces. 

    The Impact

    This research identified a shift in the strength with which a spinning neutron experiences the weak nuclear force. This has two major implications. First, scientists have known since 1956 that due to the weak force, a system and one built like its mirror image do not behave in the same way. In other words, mirror reflection symmetry is broken. This research affects the search for new interactions, technically known as “right-handed currents,” that, at very short distances of less than one hundred quadrillionths of a centimeter, restore the universe’s mirror-reflection symmetry. Second, this research points to the need to compute electromagnetic effects with higher precision. Doing so will require the use of future high-performance computers.

    Summary

    A team of researchers computed the impact of electromagnetic interactions on neutron decay due to the emission and absorption of photons, the quanta of light. The team included nuclear theorists from the Institute for Nuclear Theory at the University of Washington, North Carolina State University, the University of Amsterdam, Los Alamos National Laboratory, and Lawrence Berkeley National Laboratory. 

    The calculation was performed with a modern method, known as “effective field theory,” that efficiently organizes the importance of fundamental interactions in phenomena involving strongly interacting particles. The team identified a new percent-level shift to the nucleon axial coupling, gA, which governs the strength of decay of a spinning neutron. The new correction originates from the emission and absorption of electrically charged pions, which are mediators of the strong nuclear force. While effective field theory provides an estimate of the uncertainties, improving on the current precision will require advanced calculations on Department of Energy supercomputers. The researchers also assessed the impact on searches of right-handed current. They found that after including the new correction, experimental data and theory are in good agreement and current uncertainties still allow for new physics at a relatively low mass scale.

     

    Funding

    This research was supported by the Department of Energy Office of Science, Office of Nuclear Physics; the Laboratory Directed Research and Development program at Los Alamos National Laboratory; the National Science Foundation; and the Dutch Research Council.

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  • Rouven Essig: Then and Now / 2012 Early Career Award Winner

    Rouven Essig: Then and Now / 2012 Early Career Award Winner

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    WHAT DID THE 2012 EARLY CAREER AWARD ALLOW YOU TO DO?

    Extensive evidence suggests that a staggering 85% of the matter in our universe is dark matter. However, its identity remains unknown. Even its most basic properties – such as how much it weighs and how it interacts with known matter – remain unknown.

    As a theoretical particle physicist, I conceive of new ideas for what constitutes dark matter. I also develop new experimental concepts for how to detect dark matter particles and any unknown forces that allow dark matter to interact with ordinary matter. My theoretical research impacts how other scientists do research at the cosmic, intensity, and energy frontiers.

    For the cosmic frontier, I have helped pioneer novel detection concepts to search for dark matter below the mass of protons. This has led to new exciting experiments, such as SENSEI, as well as new DOE research and development efforts, such as OSCURA. These projects have unprecedented sensitivity to a multitude of dark matter candidates that were previously unexplored.

    For the intensity frontier, I have conceived of new experiments. In these experiments, intense beams of electrons hit a target and potentially create particles that mediate new forces beyond the known electromagnetic, strong, and weak forces. This has led to new fixed-target experiments at DOE’s Jefferson Lab, including APEX and HPS.  

    For the energy frontier, I have shown how the Higgs bosons produced in high-energy proton-proton collisions at the Large Hadron Collider can shed light on dark matter and new forces. This has led to new searches for non-standard decays of the Higgs boson, in which it disintegrates in ways not expected by our standard theory.

    Most importantly, the DOE Early Career Award allowed me to train several graduate students and a postdoctoral researcher in particle physics. It enabled me to establish a strong research program and research group early on in my career, providing a strong foundation from which I continue to benefit.

    ABOUT:

    Rouven Essig is a professor in the C.N. Yang Institute for Theoretical Physics at Stony Brook University.

    SUPPORTING THE DOE SC MISSION:

    The Early Career Research Program provides financial support that is foundational to early career investigators, enabling them to define and direct independent research in areas important to DOE missions. The development of outstanding scientists and research leaders is of paramount importance to the Department of Energy Office of Science. By investing in the next generation of researchers, the Office of Science champions lifelong careers in discovery science.

    For more information, please go to the Early Career Research Program.

    THE 2012 PROJECT ABSTRACT:

    Title: Particle Physics at the Cosmic, Intensity, and Energy Frontiers

    Abstract

    Major efforts at the intensity, cosmic, and energy frontiers of particle physics are rapidly furthering our understanding of the fundamental constituents of Nature and their interactions. The overall objectives of this research project are (1) to interpret and develop the theoretical implications of the data collected at these frontiers and (2) to provide the theoretical motivation, basis, and ideas for new experiments and for new analyses of experimental data.

    Within the Intensity Frontier, an experimental search for a new force mediated by a GeV‐scale gauge boson will be carried out with the A’ Experiment (APEX) and the Heavy Photon Search (HPS), both at Jefferson Laboratory. Within the Cosmic Frontier, contributions are planned to the search for dark matter particles with the Fermi Gamma‐ray Space Telescope and other instruments. A detailed exploration will also be performed of new direct detection strategies for dark matter particles with sub‐GeV masses to facilitate the development of new experiments. In addition, the theoretical implications of existing and future dark‐ matter‐related anomalies will be examined. Within the Energy Frontier, the implications of the data from the Large Hadron Collider will be investigated. Novel search strategies will be developed to aid the search for new phenomena not described by the Standard Model of particle physics. By combining insights from all three particle physics frontiers, this research aims to increase our understanding of fundamental particle physics.

    RESOURCES:

    D Curtin, R Essig, S Gori, P Jaiswal, A Katz, T Liu, Z Liu, D McKeen, J Shelton, M Strassler, Z Surujon, B Tweedie, and YM Zhong, “Exotic decays of the 125 GeV Higgs boson.” Phys Rev D 90, 75004 (2014). [DOI: /10.1103/PhysRevD.90.075004]

    R Essig, M Fernández-Serra, J Mardon, A Soto, T Volansky & TT Yu, “Direct detection of sub-GeV dark matter with semiconductor targets.” Journal of High Energy Physics 2016, 46 (2016). [DOI: /10.1007/JHEP05(2016)046]

    R Essig, T Volansky, and TT Yu, “New constraints and prospects for sub-GeV dark matter scattering off electrons in xenon.” Phys Rev D 96, 043017 (2017). [DOI: 10.1103/PhysRevD.96.043017] 

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  • Zeroing in on a Fundamental Property of the Proton’s Internal Dynamics

    Zeroing in on a Fundamental Property of the Proton’s Internal Dynamics

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    The Science

    Inside the proton are elementary particles called quarks. Quarks and protons have an intrinsic angular momentum called spin. Spin can point in different directions. When it is perpendicular to the proton’s momentum, it is called a transverse spin. Just like the proton carries an electric charge, it also has another fundamental charge called the tensor charge. The tensor charge is the net transverse spin of quarks in a proton with transverse spin. The only way to obtain the tensor charge from experimental data is using the theory of quantum chromodynamics (QCD) to extract the “transversity” function. This universal function encodes the difference between the number of quarks with their spin aligned and anti-aligned to the proton’s spin when it is in a transverse direction. Using state-of-the-art data science techniques, researchers recently made the most precise empirical determination of the tensor charge.

    The Impact

    Due to the phenomenon known as “confinement,” quarks are always bound in the proton or other hadrons (particles with multiple quarks). The challenge is to connect the theory of quark interactions (QCD) to experimental measurements of high-energy collisions involving hadrons. In this study, researchers used a complete collection of transverse-spin data from electron-positron, electron-proton, and proton-proton scattering in the first global analysis of its kind. They employed this data to make the most precise known empirical calculation of the tensor charge. Scientists need a precise and accurate determination of the proton’s tensor charge to understand the proton’s internal structure and the dynamics of QCD strong interactions. This information is also very important in searches for new physics.

    Summary

    Researchers from the Coordinated Theoretical Approach to Transverse Momentum Dependent Hadron Structure in QCD Topical Collaboration (TMD Collaboration) , working in conjunction with the Thomas Jefferson National Accelerator Facility (Jefferson Lab) Angular Momentum Collaboration (JAM Collaboration), analyzed data from a wide range of experiments where protons and/or quarks were transversely polarized. This allowed for the most precise empirical determination of the proton’s tensor charge. The tensor charge is not only a fundamental property of the proton but also needed in searches for new physics. The results were then compared to computations of the proton’s tensor charge by lattice QCD, which simulates the proton’s structure on a supercomputer. After about a decade of results showing disagreement between empirical methods and lattice QCD for the proton’s tensor charge, researchers for the first time found agreement between the two.

    The empirical study was performed using QCD theory and state-of-the-art numerical methods. A crucial part of the analysis was the utilization of data from electron-positron, electron-proton, and proton-proton scattering. This opens a new frontier in QCD global analyses to simultaneously include all possible measurements, like those from the future Electron-Ion Collider and Jefferson Lab 12 GeV, to continue to increase the precision and accuracy of extracting the proton’s tensor charge.

     

    Funding

    This work was supported by the Department of Energy Office of Science, Nuclear Physics program under the Coordinated Theoretical Approach to Transverse Momentum Dependent Hadron Structure in QCD (TMD Topical Collaboration). This work was also supported in part by the Department of Energy and the National Science Foundation and the agencies’ Early Career Programs.


    Journal Link: Physical Review D, Aug-2022

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