UPTON, NY—Tammy Walton, a Research Associate at the U.S. Department of Energy’s (DOE) Fermi National Accelerator Laboratory (Fermilab), has been named the second recipient of the Leona Woods Distinguished Postdoctoral Lectureship Award, given by the physics department at DOE’s Brookhaven National Laboratory. Walton is working on the “Muon g-2” experiment now underway at Fermilab following a cross-country journey of the experiment’s giant electromagnet from Brookhaven in 2013. The new experiment is conducting precision measurements to follow up on results reported in the early 2000s by Brookhaven’s version of the experiment. Those measurements suggested that muons, heavy cousins of electrons, were interacting with a powerful magnetic field in a subtly different way than expected, potentially pointing to “new physics” inexplicable by today’s reigning theory of particle physics.
“Physicists are always intrigued by experimental measurements that cannot be explained by ‘the Standard Model’ of particle physics,” Walton said. “Discovering a large deviation between the g-2 experiment’s measurement and the theoretical prediction of the muon’s ‘anomalous magnetic moment’—the property we measure—would be proof of physics beyond the Standard Model.” Such a discovery could point the way to the discovery of a new particle or interaction.
As recipient of the Leona Woods Lectureship Award, Walton will receive a prize of $1,000 and the opportunity to give a general-interest colloquium and a technical talk about her work during a weeklong stay at Brookhaven. She will also participate in informal discussions with Brookhaven physicists, including some who worked on the earlier version of the Muon g-2 experiment and theorists who are continually improving the precision of their predictions for g-2.
“I am honored to receive an award that is named after someone leading the development of nuclear physics, and unknowingly was a pioneer for women in physics. I have never visited Brookhaven, so I’m excited about seeing the lab,” Walton said.
“I also think this award shows that the community is excited about the Muon g-2 experiment at Fermilab,” she added. While at Brookhaven, Walton may get a chance to soak up some of the experiment’s history. “I’d like to see the hall where the Muon g-2 storage ring lived, before it was transported to Fermilab,” she said.
Muons produced by the AGS were essential to Brookhaven’s g-2 experiment. In the late 1990s and early 2000s, these muons, whose spins were lined up with the direction of their motion, were fed into a powerful circular electromagnet storage ring. As the muons went round and round, their own internal spins and magnetism interacted with the storage ring’s magnetic field, as well as other virtual particles known to pop in and out of existence according to the rules of the Standard Model. If the Standard Model is right, these interactions should cause the spinning muons to precess, or “wobble” away from its spin-aligned path. Sensors surrounding the magnet can measure the muons’ precession with extreme precision.
These Brookhaven measurements indicated that the muons wobbled a tiny bit more than the prediction calculated from what physicists know about the Standard Model. This difference between the experiment’s measurement and the theory’s prediction—which was confirmed with repeated experimental runs and improvements in the precision of the calculations—suggested there was something else going on that the Standard Model could not explain. It was a hint that some yet-to-be discovered particle might be interacting with the muons—“new physics”—but the result was not quite strong enough to declare a discovery. There might be other explanations for the anomalous result, including that there was possibly something wrong with the experiment.
That’s why Fermilab wants to repeat the experiment at even higher precision. Fermilab’s muon beam is much more intense and stable than the one used at Brookhaven, so it should reduce the uncertainties in the measurement. After transporting the storage ring across the country in 2013, physicists at Fermilab tuned up its properties, and are now collecting data with an experiment that’s more sensitive to virtual or hidden particles and forces than any previous experiment of its kind.
Tammy Walton, who witnessed the assembly of the magnetic storage ring at Fermilab, is eager to see the results.
“I write computing software programs used to analyze the data recorded from the Muon g-2 experiment. My primary goal is to produce a measurement and evaluate the uncertainties associated with it,” she said. Ideally, those uncertainties will be low enough to reveal whether the anomalous wobble still stands, and potentially point the way to new discoveries.
Tammy Walton majored in physics at the University of Tennessee, earning her B.S. in 2006. Beginning in 2008, as a graduate student at Hampton University, she conducted research on the MINERvA Experiment at Fermilab, and joined the staff as a Research Associate on the Muon g-2 experiment after earning her Ph.D. in 2014.