Muon g-2 Collaboration to Solve Mystery

Muon g-2 collaboration
The Muon g-2 collaboration

Scientists from three Department of Energy national laboratories, Fermilab, Brookhaven and Argonne, along with scientists from seven foreign countries and more than a dozen U.S. universities are collaborating on a new physics experiment that will probe fundamental properties of matter and space. Muon g-2 (pronounced gee minus two) is an Intensity Frontier experiment that will allow researchers to peer into the subatomic world to search for undiscovered particles that may be hiding in the vacuum.

Soon to be built at Fermilab's new Muon Campus, the experiment will use the Fermilab accelerator complex to produce an intense beam of muons traveling at nearly the speed of light. Scientists will use the beam to precisely determine the value of a property known as the g-2 of the muon.

The muon, like its lighter sibling the electron, acts like a spinning magnet. The parameter known as "g" indicates how strong the magnet is and the rate of its gyration. The value of g is slightly larger than 2, hence the name of the experiment. This difference from 2 is caused by the presence of virtual particles that appear from the vacuum and then quickly disappear into it again.

In measuring g-2 with high precision and comparing its value to the theoretical prediction, physicists will discover whether the experiment agrees with theory. Any deviation would point to as yet undiscovered subatomic particles that exist in nature.

An experiment that concluded in 2001 at Brookhaven National Laboratory found a tantalizing greater-than-3-sigma (standard deviation) discrepancy between the theoretical calculation and the measurement of the muon g-2. The level necessary for claiming a discovery is 5 sigma. Fermilab will pick up where Brookhaven left off, making an even more precise measurement.

With a four-fold increase in the measurement's precision, Muon g-2 will be more sensitive to virtual or hidden particles and forces than any previous experiment of its kind. About 100 scientists from China, England, Germany, Italy, Japan, the Netherlands, Russia and more than 15 institutions in the United States are collaborating with Fermilab on this experiment.

The centerpiece of the Muon g-2 experiment at Fermilab is a large, 50-foot-diameter superconducting muon storage ring. This one-of-a-kind ring, made of steel, aluminum and superconducting wire, was built for the previous g-2 experiment at Brookhaven. The ring will be moved from Brookhaven to Fermilab during the second half of 2013. Making use of Fermilab's intense particle beams, scientists will be able to significantly increase the science output of this unique instrument. The experiment will start taking data in 2016.