- 2019-11-04 10:45:32
- Article ID: 721893
New Measurement Yields Smaller Proton Radius
-
Credit: DOE's Jefferson Lab
Physicists get closer to solving the proton radius puzzle with unique new measurement of the charge radius of the proton.
The result, recently published in the journal Nature, is one of the most precise measured from electron-scattering experiments. The new value for the proton radius that was obtained is 0.831 fm, which is smaller than the previous electron-scattering value of 0.88 fm and is in agreement with recent muonic atomic spectroscopy results.
“We are happy that years of hard work of our collaboration is coming to an end with a good result that will help critically toward solution of the so-called proton radius puzzle,” says Ashot Gasparian, a professor at North Carolina A&T State University and the experiment’s spokesperson.
All visible matter in the universe is built on a cloud of three quarks bound together with strong force energy. The ubiquitous proton, which sits at the heart of every atom, has been the subject of numerous studies and experiments aimed at revealing its secrets. Yet, an unexpected result from an experiment to measure the size of this cloud, in terms of its root-mean-square charge radius, has united atomic and nuclear physicists in a flurry of activity to re-examine this basic quantity of the proton.
Prior to 2010, the most precise measurements of the proton’s radius came from two different experimental methods. In electron-scattering experiments, electrons are shot at the protons, and the proton’s charge radius is determined by the change in path of the electrons after they bounce off, or scatter from, the proton. In atomic spectroscopy measurements, the transitions between energy levels by electrons are observed (in the form of photons that are given off by the electrons) as they orbit a small nucleus. Nuclei that have typically been observed include hydrogen (with one proton) or deuterium (with a proton and a neutron). These two different methods yielded a radius of about 0.88 femtometers.
In 2010, atomic physicists announced results from a new method. They measured the transition between energy levels of electrons in orbit around lab-made hydrogen atoms that replaced an orbiting electron with a muon, which orbits much closer to the proton and is more sensitive to the proton’s charge radius. This result yielded a value that was 4% smaller than before, at about 0.84 femtometers.
In 2012, a collaboration of scientists led by Gasparian came together at Jefferson Lab to revamp electron-scattering methods in hopes of producing a novel and more precise measurement of the proton’s charge radius. The PRad experiment was given priority scheduling as one of the first experiments to take data and complete its run following an upgrade of the Continuous Electron Beam Accelerator Facility, a DOE User Facility for nuclear physics research. The experiment took electron-scattering data in Jefferson Lab’s Experimental Hall B in 2016.
“When we started this experiment, people were searching for answers. But to make another electron-proton scattering experiment, many skeptics didn't believe that we could do anything new,” says Gasparian. “If you want to come up with something new, you have to come up with some new tools, some new method. And we did that -- we did an experiment which is completely different from other electron-scattering experiments.”
The collaboration instituted three new techniques to improve the precision of the new measurement. The first was implementation of a new type of windowless target system, which was funded by a National Science Foundation Major Research Instrumentation grant and was largely developed, fabricated and operated by Jefferson Lab’s Target group.
The windowless target flowed refrigerated hydrogen gas directly into the stream of CEBAF’s 1.1 and 2.2 GeV accelerated electrons and allowed scattered electrons to move nearly unimpeded into the detectors.
“When we say windowless, we are saying that the tube is open to the vacuum of the accelerator. Which seems like a window - but in electron-scattering, a window is a metal cover on the end of the tube, and those have been removed,” says Dipangkar Dutta, an experiment co-spokesperson and a professor at Mississippi State University.
“So this is the first time that people actually put a gas-flow target onto the beamline at Jefferson Lab,” says Haiyan Gao, an experiment co-spokesperson and Henry Newson professor at Duke University. “The vacuum was good, so that we could have electron beam going through our target to do the experiment, and we actually have a hole in the entrance foil and another in the exit foil. Essentially, the beam just passed through directly to the hydrogen gas, not seeing any window.”
The next major difference was the use of a calorimeter rather than the traditionally used magnetic spectrometer to detect scattered electrons resulting from the incoming electrons striking the hydrogen’s protons or electrons. The repurposed hybrid calorimeter HyCal measured the energies and positions of the scattered electrons, while a newly built gas electron multiplier, the GEM detector, also detected the electrons’ positions with even higher accuracy.
The data from both detectors was then compared in real time, which allowed the nuclear physicists to classify each event as an electron-electron scattering or an electron-proton scattering. This new method of classifying the events allowed the nuclear physicists to normalize their electron-proton scattering data to electron-electron scattering data, greatly reducing experimental uncertainties and increasing precision.
The last major improvement was placement of these detectors extremely close in angular distance from where the electron beam struck the hydrogen target. The collaboration was able to get that distance down to less than one degree.
“In electron scattering, in order to extract the radius, we have to go to as small a scattering angle as possible,” says Dutta. “To get the proton radius, you need to extrapolate to zero angle, which you cannot access in an experiment. So, the closer to zero you can get, the better.”
“The region that we explored is at such a forward angle and at such small four-momentum transfer squared that it has never been reached before in electron-proton scattering,” adds Mahbub Khandaker, an experiment co-spokesperson and a professor at Idaho State University.
The collaborators say the result is unique, because it used a new technique via electron-scattering to determine the proton charge radius. Now, they are looking forward to comparing the result to new spectroscopic determinations of the proton radius and upcoming electron- and muon-scattering measurements that are being conducted worldwide.
Further, this result also sheds new light on conjecture of a new force of nature that was proposed when the proton radius puzzle first surfaced.
“When the initial proton radius puzzle came out in 2010, there was hope in the community that maybe we have found a fifth force of nature, that this force acts differently between electrons and muons,” says Dutta. “But the PRad experiment seems to shut the door on that possibility.”
They say the next step is to consider conducting further investigations using this new experimental method to achieve even higher precision measurements on this and related topics, such as the radius of the deuteron, the nucleus of deuterium.
“There is a very good chance we can improve our measurements by a factor of two or maybe even more,” Gao says.
Further Reading
Physicists Team Up to Tackle Proton Radius Problem
-end-
Jefferson Science Associates, LLC, a joint venture of the Southeastern Universities Research Association, Inc. and PAE, manages and operates the Thomas Jefferson National Accelerator Facility, or Jefferson Lab, for the U.S. Department of Energy's Office of Science.
DOE’s 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, visit https://energy.gov/science.
MORE NEWS FROM
Thomas Jefferson National Accelerator Facility
comments 
commenting policy
Participating Labs
- DOE Office of Science
- Argonne National Laboratory
- Oak Ridge National Laboratory
- Pacific Northwest National Laboratory
- Iowa State University, Ames Laboratory
- Brookhaven National Laboratory
- Princeton Plasma Physics Laboratory
- Lawrence Berkeley National Laboratory
- Thomas Jefferson National Accelerator Facility
- Fermi National Accelerator Laboratory (Fermilab)
- SLAC National Accelerator Laboratory
Freeze Frame: Scientists Capture Atomic-Scale Snapshots of Artificial Proteins
Scientists at Berkeley Lab are the first to use cryo-EM (cryogenic electron microscopy), a Nobel Prize-winning technique originally designed to image proteins in solution, to image atomic changes in a synthetic soft material.
Argonne Collaboration Shows Benefits of Better Corn Residue Management Strategies
Sustainable corn stover removal can maintain soil carbon stock, according a new Argonne-led study.
Study Sheds Light on the Really Peculiar 'Normal' Phase of High-Temperature Superconductors
Experiments at SLAC and Stanford probe the normal state more accurately than ever before and discover an abrupt shift in the behavior of electrons in which they suddenly give up their individuality and behave like an electron soup.
Scientists devise catalyst that uses light to turn carbon dioxide to fuel
In a recent study from Argonne, scientists have used sunlight and a catalyst largely made of copper to transform carbon dioxide to methanol.
Science Snapshots - microbiome matchmakers, solid-liquid interfaces, undersea earthquakes
Science Snapshots from Berkeley Lab
SLAC scientists invent a way to see attosecond electron motions with an X-ray laser
Researchers at the Department of Energy's SLAC National Accelerator Laboratory have invented a way to observe the movements of electrons with powerful X-ray laser bursts just 280 attoseconds, or billionths of a billionth of a second, long.
Bank on it: Gains in one type of force produced by fusion disruptions are offset by losses in another
Simulations show that halo currents can serve as a proxy for the total force produced by vertical disruptions.
Story Tips from the Department of Energy's Oak Ridge National Laboratory, December 2019
An additively manufactured polymer layer applied to specialized plastic proved effective to protect aircraft from lightning strikes in lab test; injecting shattered argon pellets into a super-hot plasma, when needed, could protect a fusion reactor's interior wall from runaway electrons; ORNL will celebrate the life and legacy of Dr. Liane Russell on December 20.
Scientists find new way to identify, manipulate topological metals for spintronics
A recent study gives researchers an easier way of finding Weyl semimetals and manipulating them for potential spintronic devices.
Big trucks, little emissions
Researchers reveal a new integrated, cost-efficient way of converting ethanol for fuel blends that can reduce greenhouse gas emissions.
University of Kentucky Grant Seeks to Turn Coal Into Carbon Fiber
UK's Center for Applied Energy Research (CAER) has received a $1.8 million U.S. Department of Energy (DOE) grant to transform coal tar pitch into high-value carbon fiber for use in aircraft, automobiles, sporting goods and other high-performance materials.
Six Berkeley Lab Scientists Named AAAS Fellows
Six scientists from the Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) have been named Fellows of the American Association for the Advancement of Science (AAAS).
PPPL is recognized for being green
The U.S. Department of Energy's Princeton Plasma Physics Laboratory was recognized by the U.S. Environmental Protection Agency for its green practices in reducing waste, energy, and water, and transportation, and for green purchasing and electronics recycling.
Dmitri Zakharov Recognized with the 2019 Chuck Fiori Award
The award honors Dmitri Zakharov's contributions to environmental transmission electron microscopy at Brookhaven Lab's Center for Functional Nanomaterials.
Two Argonne projects earn Secretary of Energy Honor Awards
With this year's Nobel Prize in Chemistry awarded for the development of lithium-ion batteries, directors of the Joint Center for Energy Storage Research share perspectives on the future of energy storage.
Argonne teams up with Altair to manage use of upcoming Aurora supercomputer
Argonne National Laboratory and Altair, a global technology company, have created a new scheduling system that will be employed on the Aurora supercomputer.
University of Maryland, Baltimore County wins DOE's 2019 CyberForce Competition(tm)
After a long suspenseful day, University of Maryland, Baltimore County earned the top spot as national winner of the U.S. Department of Energy's CyberForce Competition.
In its 15th year, INCITE advances open science with supercomputer grants to 47 projects
The U.S. Department of Energy's Office of Science announced allocations of supercomputer access to 47 science projects for 2020--awarding 60 percent of the available time on some of the nation's most powerful supercomputers, with the ultimate goal of accelerating discovery and innovation. In 2020, 14 projects will run on Theta and 39 projects on Summit, where six of these projects will receive an allocation on both systems.
ASU solar awards eclipse other universities in latest round of DOE funding
ASU receives $9.8 million in Solar Energy Technologies Office Awards.
DOE to Provide $10 Million for New Research into Ecosystem Processes
The U.S. Department of Energy (DOE) announced a plan to provide $10 million for new observational and experimental studies aimed at improving the accuracy of today's Earth system models. Research will focus on three separate types of environments--terrestrial, watershed, and subsurface--where current models fall short of providing fully accurate representation.
Harvesting Energy from Light using Bio-inspired Artificial Cells
Scientists designed and connected two different artificial cells to each other to produce molecules called ATP (adenosine triphosphate).
Engineering Living Scaffolds for Building Materials
Bone and mollusk shells are composite systems that combine living cells and inorganic components. This allows them to regenerate and change structure while also being very strong and durable. Borrowing from this amazing complexity, researchers have been exploring a new class of materials called engineered living materials (ELMs).
Excavating Quantum Information Buried in Noise
Researchers developed two new methods to assess and remove error in how scientists measure quantum systems. By reducing quantum "noise" - uncertainty inherent to quantum processes - these new methods improve accuracy and precision.
How Electrons Move in a Catastrophe
Lanthanum strontium manganite (LSMO) is a widely applicable material, from magnetic tunnel junctions to solid oxide fuel cells. However, when it gets thin, its behavior changes for the worse. The reason why was not known. Now, using two theoretical methods, a team determined what happens.
When Ions and Molecules Cluster
How an ion behaves when isolated within an analytical instrument can differ from how it behaves in the environment. Now, Xue-Bin Wang at Pacific Northwest National Laboratory devised a way to bring ions and molecules together in clusters to better discover their properties and predict their behavior.
Tune in to Tetrahedral Superstructures
Shape affects how the particles fit together and, in turn, the resulting material. For the first time, a team observed the self-assembly of nanoparticles with tetrahedral shapes.
Tracing Interstellar Dust Back to the Solar System's Formation
This study is the first to confirm dust particles pre-dating the formation of our solar system. Further study of these materials will enable a deeper understanding of the processes that formed and have since altered them.
Investigating Materials that Can Go the Distance in Fusion Reactors
Future fusion reactors will require materials that can withstand extreme operating conditions, including being bombarded by high-energy neutrons at high temperatures. Scientists recently irradiated titanium diboride (TiB2) in the High Flux Isotope Reactor (HFIR) to better understand the effects of fusion neutrons on performance.
Better 3-D Imaging of Tumors in the Breast with Less Radiation
In breast cancer screening, an imaging technique based on nuclear medicine is currently being used as a successful secondary screening tool alongside mammography to improve the accuracy of the diagnosis. Now, a team is hoping to improve this imaging technique.
Microbes are Metabolic Specialists
Scientists can use genetic information to measure if microbes in the environment can perform specific ecological roles. Researchers recently analyzed the genomes of over 6,000 microbial species.
Spotlight
Barbara Garcia: A first-generation college student spends summer doing research at PPPL
Princeton Plasma Physics Laboratory
Argonne organization's scholarship fund blazes STEM pathway
Argonne National Laboratory
Brookhaven Lab, Suffolk Girl Scouts Launch Patch Program
Brookhaven National Laboratory
From an acoustic levitator to a "Neutron Bloodhound" robot, hands-on research inspires PPPL's summer interns
Princeton Plasma Physics Laboratory
Brookhaven Lab Celebrates the Bright Future of its 2019 Interns
Brookhaven National Laboratory
PPPL apprenticeship program offers young people chance to earn while they learn high-tech careers
Princeton Plasma Physics Laboratory
JSA Awards Graduate Fellowships for Research at Jefferson Lab
Thomas Jefferson National Accelerator Facility
ILSAMP Symposium showcases benefits for diverse students, STEM pipeline
Argonne National Laboratory
Integrating Scientific Computing into Science Curricula
Brookhaven National Laboratory
Students from Minnesota and Massachusetts Win DOE's 29th National Science Bowl(r)
Department of Energy, Office of Science
DOE's Science Graduate Student Research Program Selects 70 Students to Pursue Research at DOE Laboratories
Department of Energy, Office of Science
Young Women's Conference in STEM seeks to change the statistics one girl at a time
Princeton Plasma Physics Laboratory
Students team with Argonne scientists and engineers to learn about STEM careers
Argonne National Laboratory
Lynbrook High wins 2019 SLAC Regional Science Bowl competition
SLAC National Accelerator Laboratory
Equipping the next generation for a technological revolution
Argonne National Laboratory
Chemistry intern inspired by Argonne's real-world science
Argonne National Laboratory
Argonne intern streamlines the beamline
Argonne National Laboratory
Research on Light-Matter Interaction Could Lead to Improved Electronic and Optoelectronic Devices
Rensselaer Polytechnic Institute (RPI)
Innovating Our Energy Future
Oregon State University, College of Engineering
Physics graduate student takes her thesis research to a Department of Energy national lab
University of Alabama at Birmingham
"Model" students enjoy Argonne campus life
Argonne National Laboratory
Writing Code for a More Skilled and Diverse STEM Workforce
Brookhaven National Laboratory
New graduate student summer school launches at Princeton Plasma Physics Laboratory
Princeton Plasma Physics Laboratory
The Gridlock State
California State University (CSU) Chancellor's Office
Meet Jasmine Hatcher and Trishelle Copeland-Johnson
Brookhaven National Laboratory
Argonne hosts Modeling, Experimentation and Validation Summer School
Argonne National Laboratory
Undergraduate Students Extoll Benefits of National Laboratory Research Internships in Fusion and Plasma Science
Princeton Plasma Physics Laboratory
Students affected by Hurricane Maria bring their research to SLAC
SLAC National Accelerator Laboratory
Brookhaven Lab Pays Tribute to 2018 Summer Interns
Brookhaven National Laboratory
CSUMB Selected to Host Architecture at Zero Competition in 2019
California State University, Monterey Bay
From Hurricane Katrina Victim to Presidential Awardee: A SUNO Professor's Award-Winning Mentoring Efforts
Brookhaven National Laboratory
Department of Energy Invests $64 Million in Advanced Nuclear Technology
Rensselaer Polytechnic Institute (RPI)
Professor Miao Yu Named the Priti and Mukesh Chatter '82 Career Development Professor
Rensselaer Polytechnic Institute (RPI)
2018 RHIC & AGS Annual Users' Meeting: 'Illuminating the QCD Landscape'
Brookhaven National Laboratory
High-School Students Studying Carbon-Based Nanomaterials for Cancer Drug Delivery Visit Brookhaven Lab's Nanocenter
Brookhaven National Laboratory
Argonne welcomes The Martian author Andy Weir
Argonne National Laboratory
UW Professor and Clean Energy Institute Director Daniel Schwartz Wins Highest U.S. Award for STEM Mentors
University of Washington
Creating STEM Knowledge and Innovations to Solve Global Issues Like Water, Food, and Energy
Illinois Mathematics and Science Academy (IMSA)
Professor Emily Liu Receives $1.8 Million DoE Award for Solar Power Systems Research
Rensselaer Polytechnic Institute (RPI)
Celebrating 40 years of empowerment in science
Argonne National Laboratory
Introducing Graduate Students Across the Globe to Photon Science
Brookhaven National Laboratory
Students from Massachusetts and Washington Win DOE's 28th National Science Bowl(r)
Department of Energy, Office of Science
Q&A: Al Ashley Reflects on His Efforts to Diversify SLAC and Beyond
SLAC National Accelerator Laboratory
Insights on Innovation in Energy, Humanitarian Aid Highlight UVA Darden's Net Impact Week
University of Virginia Darden School of Business
Ivy League Graduate, Writer and Activist with Dyslexia Visits CSUCI to Reframe the Concept of Learning Disabilities
California State University, Channel Islands
Photographer Adam Nadel Selected as Fermilab's New Artist-in-Residence for 2018
Fermi National Accelerator Laboratory (Fermilab)
Showing results
0-4 Of 2215