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IU physicists awarded $2 million to investigate neutrons

A grant from the National Science Foundation will support an experiment that could shed light on the existence of matter in the universe

Sep 12, 2018

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.

Description of the following video:

[Words appear: Indiana University presents]

[Words appear: The National Science Foundation has awarded researchers at Indiana University $2 million to lead an experiment on neutrons.]

[Video: Large machinery in a lab used for studying neutrons. The machinery is long and has hundreds of wires connecting it.]

Joshua Long speaks: Neutrons are subatomic particles; they are constituent particles of atomic nuclei, like the proton.

[Video: Long, an Indiana University associate professor, appears on camera.]

Long speaks: They are electrically neutral. They are charge-less, but nothing in principle prevents them from having a division of charge, a positive and negative electric pole, and that’s what we are looking for.

Long speaks: If there was a positive signal … well, that’s, in some sense, is a Holy Grail.

[Video: Large machinery in a lab used for studying neutrons.]

[Words appear: IU scientists and engineers will build key parts of the experiment at the IU Multidisciplinary Engineering and Sciences Hall at IU Bloomington.]

[Video: Equipment in a lab used to measure pressure.]

Long speaks: According to the Big Bang models of the creation and evolution of the universe, matter and antimatter are created in equal amounts.

[Video: Long appears on camera.]

Long speaks: When matter and antimatter mix, they annihilate completely to pure energy or light. So, it’s a mystery as to why didn’t that annihilation proceed entirely, and why is there any matter in the universe at all.

[Video: A chalkboard in a lab with equations written on it in chalk. Large machinery in a lab used for studying neutrons. A large tank in a lab.]

[Video: Long appears on camera.]

[Video: Large machinery in a lab used for studying neutrons. A close-up of a sign on a piece of equipment that notes it is a Drift Tube Linac, along with more equipment in a lab.]

Long speaks: There must be processes to explain this imbalance. It turns out that the same mechanisms which have been proposed to explain this imbalance also predict a small but measurable nonzero electric dipole moment or electric polarization of individual neutrons.

[Video: Long appears on camera.]

[Text appears: To conduct their research, IU scientists will ‘tilt’ neutrons in a specially shielded room filled with advanced measuring equipment.]

[Video: Long appears on camera.]

Long speaks: We’re doing this experiment under a very controlled applied magnetic field.

[Video: A close-up of a countdown clock. A close-up of a ‘danger’ sign in a laboratory.]

Long speaks: We’re looking for something like a tilt of maybe like a 10 millionth of a degree, a part per billion measurement. So that gives you some idea of how sensitive these experiments have to be.

[Video: Long appears on camera.]

[Words appear: The work will take place in collaboration with the Department of Energy’s Los Alamos National Laboratory in New Mexico.]

[Video: Long appears on camera.]

Long speaks: Essentially all of the equipment that we’re building here, and all of our collaborating institutions are going to build, will eventually have to be shipped out to Los Alamos because that’s where the neutron source is.

[Video: Tools in a lab used to build and design equipment. A close-up of a ‘caution’ sign in a laboratory.]

Long speaks: The measurement cells will likely be fabricated here. Then there’s the electric field system, high-voltage electrodes.

[Video: Long appears on camera.]

Long speaks: And then the vacuum system. All of that’s going to be assembled here. There’s lots of experience just in the machine shop here, building experimental equipment of that type and of that scale.

[Video: Tools in a lab used to build and design equipment. A close-up of a ‘caution’ sign in a laboratory. A large tank in a laboratory.]

Long speaks: It’s the principal investigators – myself, Chen-Yu Liu, Mike Snow – one or two post-doctoral assistants, and several graduate students, and a few engineers and technicians – all of us will be spending our time both here and at Los Alamos.

[Video: Long appears on camera.]

[Words appear: Indiana University]

[Words appear: Fulfilling the promise]

[Words appear:]


IU associate professor Joshua Long talks about research on neutrons

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.

Chen-Yu Liu
An arial view of the Los Alamos Neutron Science Center at Los Alamos National Laboratory

Photos courtesy of Indiana University and Los Alamos National Laboratory

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.

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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