Physicists awarded $2 million to investigate neutrons

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Indiana University has been awarded $2 million from the National Science Foundation to lead an experiment that could resolve a fundamental mystery about the universe.

The experiment, led by physicists at the IU Center for the Exploration of Energy and Matter, will seek to detect a small separation of electrical charges in neutrons, one of three subatomic particles that comprise all atoms.

Although neutrons are electrically neutral, nothing prevents them from possessing an electric charge split across a positive and negative electrical "pole." The existence of this division -- also known as an "electric dipole moment," or neutron EDM -- would validate theories about the imbalance between matter and antimatter in the universe.

That imbalance accounts for the existence of the universe since a perfect balance between these materials would have caused all matter to annihilate as light energy shortly after the Big Bang.

"The simplest theories of the origin of the universe predict that matter and antimatter exist in equal parts, but we know there is an imbalance because the universe exists," said Chen-Yu Liu, a professor in the IU Bloomington College of Arts and Sciences' Department of Physics, who serves as lead scientist on the grant. "What we don't fully understand is the underlying physics. The theories that explain the existence of a matter-antimatter imbalance also predict there should be an observable neutron EDM.

"Measurement of the electric dipole moment of the neutron, it's the holy grail in our field," she added.

The detection of the neutron EDM has been a goal in physics for over 50 years. It's remained elusive since it's predicted to be almost infinitesimally small.

To provide a sense of scale, a neutron is about 10 millionth the size of an atom -- and the effect of the neutron EDM is 1 trillionth the size of a neutron. This means the detection of the neutron EDM is akin to the search for a single human hair on an object the size of the Earth, said Joshua Long, an associate professor of physics at IU and a co-leader on the grant.

An important difference between IU's experiment and past attempts to detect the neutron EDM is access to one of the most abundant sources of low-energy neutrons on Earth: the Ultracold Neutron source at Los Alamos National Laboratory in New Mexico. Under the grant, IU scientists and researchers at the University of Michigan, the University of Kentucky and Yale University will collaborate with the national lab to conduct the experiment.

Specifically, the team will place neutrons from the proton accelerator in Los Alamos in a specially shielded room and apply a magnetic field. Because neutrons are known to possess magnetic poles, this will cause the neutrons to spin like gyros. The researchers will then introduce an electrical field. If the neutrons spin faster compared to the first experiment, this would suggest they also possess electrical poles -- that is, the existence of a neutron EDM.

The anticipated change of the neutrons' spinning speed is a "parts per billion" measurement. The challenge is creating the conditions and technologies sensitive enough to detect such a remarkably small change.

Key parts of the experiment are slated for construction in the machine shop in the Multidisciplinary Engineering and Science Hall at IU Bloomington, a mile north of Memorial Stadium. Those parts include an electrical field system, high-voltage electrodes and a vacuum system to remove contaminants from the experiment site. The magnetically shielded chamber used in the experiment will also be outfitted with highly advanced magnetometers, including several types built by IU and the other university partners. All equipment will then be transported to Los Alamos for installation.

The timeline for the project is estimated at three years to construct, install and test the equipment. Data collection and analysis will take another three years.

IU's history as the site of a national research center, the IU Cyclotron Facility, played a key role in the researchers' success landing the federal grant, Liu said. The National Science Foundation has previously awarded IU large equipment awards to construct a device for measuring the behavior of gluons for the Brookhaven National Laboratory's STAR Experiment as well as magnetic field components for a device measuring neutron decay for the National Institute of Standards and Technology's aCORN experiment.

"We've still got all the capabilities and expertise from the cyclotron for building major instrumentation for large experiments," Liu said. The center also boasts a top-of-its-class machine shop; an underground workspace the size of small airplane hangar, including moveable concrete ceiling blocks; and a "sky crane," all of which allow for the construction of very large and highly specialized pieces of equipment.

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Another collaborator on the project is Mike Snow, a professor in the IU Bloomington Department of Physics. The grant will also support one to three postdoctoral researchers and multiple undergraduate research assistants at IU. All members of the experiment will spend time in Los Alamos over the course of the grant.

The project will also receive laboratory support and other contributions valued at $4.5 million from Department of Energy's Los Alamos National Laboratory and more than $860,000 from IU, including the IU Bloomington College of Arts and Sciences and the Office of the Vice Provost for Research.

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