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The DOE Science News Source is a Newswise initiative to promote research news from the Office of Science of the DOE to the public and news media.
  • 2017-10-10 09:05:35
  • Article ID: 682498

OLYMPUS Experiment Sheds Light on Inner Workings of Protons

Seven-year study explains how packets of light are exchanged when protons meet electrons.

  • Credit: Image courtesy of the OLYMPUS collaboration

    The OLYMPUS detector, shown from the downstream end, during installation at the DORIS storage ring in the German Electron Synchrotron, let scientists precisely measure the results of electron beams colliding with protons.

The Science

To understand the structure of matter in the visible universe, scientists need to determine the structure and behavior of protons. In studying the electric charge and magnetic moments inside the proton, the results varied. Scientists disagreed as to why two different types of beams yielded two different results. The OLYMPUS team carried out a precise experiment that showed why. They proved that a proton and electron exchange two packets of light, one intense and one not. That is, they validated the theoretical description of the basic scattering process, known as the elastic lepton-proton scattering process, that occurs during the collision.

The Impact

Scientists thought that interpreting the collision data required either a small or a significant correction factor. If a significant correction was needed, it called into question the scientific description of the proton. The OLYMPUS data showed that the small corrections are accurate. Further, the OLYMPUS data validated that the description used for over half a century to determine proton structure was correct.  


The OLYMPUS experiment was conceived at the Massachusetts Institute of Technology (MIT) in 2007 and carried out by an international collaboration from 2010 to 2013 at the DORIS particle storage ring at DESY, Hamburg, Germany. It was motivated by the claim that significant new two-photon contributions were essential to describe elastic lepton-proton scattering at multi-GeV beam energies. Positron and electron beams of 2-GeV energy were sequentially scattered from an internal hydrogen gas target. The elastically scattered leptons and protons were detected in coincidence in a large acceptance toroidal spectrometer that was designed and constructed at MIT. The analysis involved a careful evaluation of systematic uncertainties arising from experimental effects as well as from radiative corrections. They used a measured ratio of positron-proton elastic scattering to electron proton elastic scattering as a function of scattering angle to determine the high-energy two-photon contribution, up to momentum transfers of 2.5 (GeV/c)2. The OLYMPUS data validate that the single photon approximation is a good description of elastic lepton-proton scattering to +/- 1 percent up to these momentum transfers. The OLYMPUS data are not well described by the theoretical prediction based on two-photon exchange. Confirmation of the explanation of the discrepancy will require further precision measurements at higher energies beyond those studied with OLYMPUS. The accurate and precise theoretical description of elastic lepton-nucleon scattering is a cornerstone of the scientific program at a possible future electron-ion collider.


U.S. Department of Energy, Office of Science, Office of Nuclear Physics; National Science Foundation; Ministry of Education and Science of Armenia; the Deutsche Forschungsgemeinschaft; the European Community-Research Infrastructure Activity; the United Kingdom Science and Technology Facilities Council and the Scottish Universities Physics Alliance; the Ministry of Education and Science of the Russian Federation; and the Alexander von Humboldt Foundation, Germany.


B.S. Henderson, et al. (The OLYMPUS Collaboration), “Hard two-photon contribution to elastic lepton-proton scattering determined by the OLYMPUS experiment” Physical Review Letters 118, 092501 (2017). [DOI: 10.1103/PhysRevLett.118.092501]

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Ames Laboratory, UConn Discover Superconductor with Bounce

The U.S. Department of Energy's Ames Laboratory has discovered extreme "bounce," or super-elastic shape-memory properties in a material that could be applied for use as an actuator in the harshest of conditions, such as outer space, and might be the first in a whole new class of shape memory materials.

Experiment Provides Deeper Look into the Nature of Neutrinos

The first glimpse of data from the full array of a deeply chilled particle detector operating beneath a mountain in Italy sets the most precise limits yet on where scientists might find a theorized process to help explain why there is more matter than antimatter in the universe.

Transparent Solar Technology Represents 'Wave of the Future'

See-through solar materials that can be applied to windows represent a massive source of untapped energy and could harvest as much power as bigger, bulkier rooftop solar units, scientists report today in Nature Energy.

Electricity From Shale Gas vs. Coal: Lifetime Toxic Releases From Coal Much Higher

Despite widespread concern about potential human health impacts from hydraulic fracturing, the lifetime toxic chemical releases associated with coal-generated electricity are 10 to 100 times greater than those from electricity generated with natural gas obtained via fracking, according to a new University of Michigan study.

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Taming 'Wild' Electrons in Graphene

Graphene - a one-atom-thick layer of the stuff in pencils - is a better conductor than copper and is very promising for electronic devices, but with one catch: Electrons that move through it can't be stopped. Until now, that is. Scientists at Rutgers University-New Brunswick have learned how to tame the unruly electrons in graphene, paving the way for the ultra-fast transport of electrons with low loss of energy in novel systems. Their study was published online in Nature Nanotechnology.

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New studies of behaviors of particles containing heavy quarks shed light into what the early universe looked like in its first microseconds.

Cool Roofs Have Water Saving Benefits Too

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The Blob That Ate the Tokamak: Physicists Gain Understanding of How Bubbles at the Edge of Plasmas Can Drain Heat and Reduce Fusion Reaction Efficiency

Scientists at PPPL have completed new simulations that could provide insight into how blobs at the plasma edge behave. The simulations, produced by a code called XGC1 developed by a national team based at PPPL, performed kinetic simulations of two different regions of the plasma edge simultaneously.

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Four Argonne Researchers Appointed Fellows of Scientific Societies

A select group of scientists at the U.S. Department of Energy's (DOE) Argonne National Laboratory has been honored as fellows of the American Physical Society and the Electrochemical Society. Physicists Kawtar Hafidi and Michael Carpenter have been appointed as American Physical Society fellows and Materials Scientist Khalil Amine and Chemist Chris Johnson have been elected as Electrochemical Society fellows.

Berkeley Lab and Hydro-Quebec Announce Partnership for Transportation Electrification and Energy Storage

Hydro-Quebec and the U.S. Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) have agreed to explore collaborations toward the research and development of manufacturing and scale-up technology to advance transportation electrification and energy storage.

Two ORNL-Led Research Teams Receive $10.5 Million to Advance Quantum Computing for Scientific Applications

DOE's Office of Science has awarded two research teams, each headed by a member of ORNL's Quantum Information Science Group, more than $10 million over 5 years to both assess the feasibility of quantum architectures in addressing big science problems and to develop algorithms capable of harnessing the massive power predicted of quantum computing systems. The two projects are intended to work in concert to ensure synergy across DOE's quantum computing research spectrum and maximize mutual benefits.

Department of Energy Awards Flow Into Argonne

DOE Secretary Rick Perry awarded Argonne with nearly $4.7 million in projects as part of the DOE's Office of Technology Transition's Technology Commercialization Fund (TCF) in September.

NIH Awards $6.5 Million to Berkeley Lab for Augmenting Structural Biology Research Experience

The NIH has awarded $6.5 million to Berkeley Lab to integrate existing synchrotron structural biology resources to better serve researchers. The grant will establish a center based at the Lab's Advanced Light Source (ALS) called ALS-ENABLE that will guide users through the most appropriate routes for answering their specific biological questions.

LIGO Announces Detection of Gravitational Waves From Colliding Neutron Stars

The U.S.-based Laser Interferometer Gravitational-Wave Observatory and the Virgo detector in Italy announced on Oct. 16 that all three of their detectors had picked up the ripples, or gravitational waves, from two neutron stars that collided 130 million years ago. Among other discoveries, the detection allowed scientists to use gravitational waves to directly calculate the rate at which the universe is expanding.

WVU Energy Conference to Address State's Economic Opportunities

West Virginia University will look at the state's emerging energy economy through industry experts, public policy organizations, environmental groups and academic institutions at the sixth annual National Energy Conference Oct. 20.

Exploring the Exotic World of Quarks and Gluons at the Dawn of the Exascale

As nuclear physicists delve ever deeper into the heart of matter, they require the tools to reveal the next layer of nature's secrets. Nowhere is that more true than in computational nuclear physics. A new research effort led by theorists at DOE's Thomas Jefferson National Accelerator Facility (Jefferson Lab) is now preparing for the next big leap forward in their studies thanks to funding under the 2017 SciDAC Awards for Computational Nuclear Physics.

Matthew Latimer Receives 2017 Lytle Award

A staff member at the Department of Energy's SLAC National Acceleratory Laboratory, Matthew Latimer is in charge of seven spectroscopy beamlines at SSRL. He was recently selected for the 2017 Farrel W. Lytle Award, established by the SSRL Users' Organization Executive Committee. The award promotes accomplishments in synchrotron science and supports collaboration among visiting scientists and staff who conduct research at SSRL.

Jefferson Lab Completes 12 GeV Upgrade

Nuclear physicists are now poised to embark on a new journey of discovery into the fundamental building blocks of the nucleus of the atom. The completion of the 12 GeV Upgrade Project of the Continuous Electron Beam Accelerator Facility (CEBAF) at the Department of Energy's Thomas Jefferson National Accelerator Facility (Jefferson Lab) heralds this new era to image nuclei at their deepest level.

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Hybrid Material Glows Like Jellyfish

Scientists combine biology, nanotechnology into composites that light up upon chemical stimulation.

Tiny Tornados at the Dawn of the Universe

Swirling soup of matter's fundamental building blocks spins ten billion trillion times faster than the most powerful tornado, setting new record for "vorticity."

On-Demand 3-D Printing of Tiny Magic Wands

Direct writing of pure-metal structures may advance novel light sources, sensors and information storage technologies.

Heavy Quarks Probe the Early Universe

New studies of behaviors of particles containing heavy quarks shed light into what the early universe looked like in its first microseconds.

Discovering the Genetic Timekeepers in Bioenergy Crops

A new class of plant-specific genes required for flowering control in temperate grasses is found.

New Technology Illuminates Microbial Dark Matter

Demonstrating the microfluidic-based, mini-metagenomics approach on samples from hot springs shows how scientists can delve into microbes that can't be cultivated in a laboratory.

Tiny Green Algae Reveal Large Genomic Variation

First complete picture of genetic variations in a natural algal population could help explain how environmental changes affect global carbon cycles.

A Complex Little Alga that Lives by the Sea

The genetic material of Porphyra umbilicalis reveals the mechanisms by which it thrives in the stressful intertidal zone at the edge of the ocean.

Precise Radioactivity Measurements: A Controversy Settled

Simultaneous measurements of x-rays and gamma rays emitted in radioactive nuclear decays show that the vacancy left by an electron's departure, not the atomic structure, influences whether gamma rays are released.

OLYMPUS Experiment Sheds Light on Inner Workings of Protons

Seven-year study explains how packets of light are exchanged when protons meet electrons.


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