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IU physicists receive $5.4 million for subatomic particle research

August 26, 2013

A team of Indiana University Bloomington physicists will receive more than $5.4 million over the next three years from the National Science Foundation to study the subtle properties of subatomic particles.

The team consists of Will Jacobs, Lisa Kaufman, Chen-Yu Liu, Josh Long, Hans-Otto Meyer, Hermann Nann, William Snow, Ed Stephenson, Rex Tayloe, Anselm Vossen, and Scott Wissink, all members of IU Bloomington’s College of Arts and Sciences Department of Physics, along with several postdocs, graduate students, and undergraduate students. All are also affiliated with the Center for Exploration of Energy and Matter, a research center supported by the Office of the Vice Provost for Research on the Bloomington campus.

No one knows how the angular momentum of protons — the subatomic particles present in the nucleus of every atom — is distributed among a proton’s internal quarks and gluons, but IU physicists are leading a major effort to address this question.

They have already contributed to STAR Detector — the Solenoidal Tracker at Relativistic Heavy Ion Collider — at Brookhaven National Laboratory by designing and constructing its Endcap Electromagnetic Calorimeter. This device is designed to see how gluons, the particles that bind quarks within protons, contribute toward angular momentum. The IU team will follow up on recent hints of evidence for spinning gluons.

The research also addresses important scientific questions in astrophysics and cosmology, with some experiments measuring the properties and interactions of neutrinos — electrically neutral (unlike electrically charged electrons and protons) and weakly interacting subatomic particles created by nuclear reactions in the sun, in nuclear reactors, when cosmic rays hit atoms, and from certain types of radioactive decay.

Neutrino experiments at Fermilab are searching for possible new types of neutrinos which, if present, could greatly change the expansion rate of the universe at early times, and the IU team continues to improve the sensitivity of this search.

Another neutrino experiment in an underground laboratory with very low background radioactivity, the Enriched Xenon Observatory, searches for evidence that neutrinos are their own antiparticles and constrains the masses of neutrinos. The IU team has played a major role in the installation and operation of this underground experiment, which has already measured the slowest radioactive decay process ever seen.

IU physicists will also employ precision measurements of slow neutrons and are already working on two different experiments to measure the decay rate of the free neutron, which sets the relative proportions of hydrogen and helium in the universe.

They are also performing important research and development to search for an electric “dipole moment” of the neutron, which would come from a slight separation of positive and negative electric charge inside the neutron. If present, this electric dipole moment might well influence the theory for why the universe seems to have so little antimatter.

Other neutron experiments will test the theory behind radioactive decay and search for very subtle interactions involving neutrons that violate mirror symmetry. Initial versions of these experiments have set the best limits on possible exotic long-range, mirror-asymmetric neutron interactions.

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