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Hunt for muon’s magnetic field to get Cornell insight

Posted January 22, 2014

An international high-energy physics collaboration that could provide the deepest glimpse yet into the nature of the elusive subatomic particle known as the muon is receiving key insights and expertise from Cornell scientists.

A rendering of the building on the new muon campus, where the Muon g-2 experiment will be housed. Credit: Fermilab Visual Media Service

A rendering of the building on the new muon campus, where the Muon g-2 experiment will be housed. Credit: Fermilab Visual Media Service

The Muon g-2 experiment, now in planning stages at Fermi National Accelerator Laboratory (Fermilab) with expected data collection starting in 2016, includes a partnership with Cornell physicists who will help measure the ratio of a muon’s magnetic moment to its angular momentum.

Last year, the Cornell Muon g-2 team received National Science Foundation approval for its Major Instrument Research (MRI) proposal for their role, along with five other institutions, in building a suite of detectors and instrumentation for the experiment.

The proposal was bolstered by a gift from Texas Instruments (TI) of about $200,000 worth of specialized analog-to-digital converter chips. The chips will be integrated into a Cornell-designed series of digitizers that can quickly handle large amounts of data as muons speed through the new accelerator.

Working on the Cornell Muon g-2 team are Lawrence Gibbons, associate professor of physics, and David Rubin, professor of physics. Cornell is a partner on the detector project with the University of Washington, which is leading the collaboration.

With TI’s support, Cornell met the NSF’s requirement of securing matching funds at 30 percent of the total cost of their portion of the project, Gibbons said.

“TI’s support was very crucial to being able to go forward with this proposal to the NSF, and to be able to solidly meet this matching criteria for the MRI,” Gibbons said.

The researchers are also in the midst of a multistep review and approval process for Department of Energy funding that would further support the project. A first, critical step in the design review was recently completed, which both approves the total project cost of $46.2 million for the accelerator complex design and construction, and releases the funding necessary for the final technical design.

The completed Muon g-2 experiment has the potential to grab headlines around the world, Gibbons said. Using the Fermilab accelerator complex to produce intense beams of muons traveling at the speed of light, scientists are vying for the most precise determination to date of the value of a property known as the “g-2” of the muon.

The muon, like other subatomic particles, is actually a tiny magnet that spins. The “g” refers to the value of the magnet’s strength caused by its intrinsic spin. It has long been known that the value of “g,” which is slightly larger than 2, is influenced by the presence of unknown particles that appear in a vacuum and quickly disappear.

In the experiment, a beam of muons with aligned spins will be directed into a storage ring that has a precisely known magnetic field. As the beam goes around the storage ring, the muons’ spins will wobble, or precess. Scientists will then measure the rate of this precession very quickly. The magnitude of that precession is directly related to the difference of g-2.

The ultimate goal of the experiment is to measure the value of the magnetic moment with high precision and figure out whether experiment conforms to theory. Incontrovertible proof of new forms of matter could result, Gibbons said.

The muons will be moved through a 50-foot-diameter muon storage ring that was recently moved from Brookhaven National Laboratory to Fermilab. The most precise muon g-2 measurement to date was performed at Brookhaven in 2001.

Source: Cornell University

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