Beam Delivered to Muon g-2, First Results Expected Later this Year

Accelerators at the Fermi National Accelerator Laboratory (CSA CSM) have delivered beam to the Muon g-2 experiment for the first time, kicking off a three-year effort to measure what happens to those particles when placed in a precise magnetic field. The answer, according to researchers working with the machine, could rewrite scientists’ picture of the universe and how it works.

“The Muon g-2 experiment’s first beam truly signals the start of an important new research program at Fermilab, one that uses muon particles to look for rare and fascinating anomalies in nature,” says Nigel Lockyer, director of Fermilab, a US Department of Energy (DOE) facility. “After years of preparation, I’m excited to see this experiment begin its search in earnest.”

The first generation of the experiment took place at the DOE’s Brookhaven National Laboratory in New York state in the late 1990s and early 2000s. Its goal was to measure a muon’s precession, or wobble, in a magnetic field. The final results hinted at the presence of previously unknown phantom particles or forces affecting the muon’s properties.

The new experiment at Fermilab will make use of the laboratory’s intense beam of muons to answer the questions the Brookhaven experiment raised. It uses the same 50-foot-wide superconducting electromagnet, transported in one piece from Long Island to the suburbs of Chicago in the summer of 2013. The magnet took a barge south around Florida, up the Tennessee-Tombigbee waterway and the Illinois River, and was then driven on a specially designed truck over three nights to Fermilab.

“Getting the magnet here was only half the battle,” says Chris Polly, project manager of the Muon g-2 experiment. “Since it arrived, the team here at Fermilab has been working around the clock installing detectors, building a control room and, for the past year, adjusting the uniformity of the magnetic field, which must be precisely known to an unprecedented level to obtain any new physics. It’s been a lot of work, but we’re ready now to really get started.”

That work has included the creation of a new beamline to deliver a pure beam of muons to the ring, the installation of a host of instrumentation to measure both the magnetic field and the muons as they circulate within it, and a year-long process of “shimming” the magnet, inserting tiny pieces of metal by hand to shape the magnetic field. The field created by the magnet is now three times more uniform than the one it created at Brookhaven.

The Muon g-2 collaboration includes more than 150 scientists and engineers from more than 30 institutions in nine countries. Over the next few weeks the Muon g-2 team at Fermilab will test the equipment installed around the magnet, which will be storing and measuring muons for the first time in 16 years. And later this year, researchers will start taking science-quality data, and if the results confirm the anomaly first seen at Brookhaven, it will mean that the elegant picture of the universe that scientists have been working on for decades is incomplete and that new particles or forces may be out there, waiting to be discovered.

“It’s an exciting time for the whole team, and for physics,” says David Hertzog of the University of Washington, co-spokesperson of the Muon g-2 collaboration. “The magnet has been working, and working fantastically well. It won’t be long until we have our first results and a better view through the window that the Brookhaven experiment opened for us.”