On Saturday, July 26, Fermilab moved a 50-foot-wide superconducting electromagnet across its campus to a newly constructed experimental building. Made of steel, aluminum and superconducting wire, the magnet is easily the largest component of a machine that will be used in the Muon g-2 experiment, involving scientists and engineers from 26 institutions around the world.
The scientists aim to study the properties of the mysterious muon. A better understanding of the subatomic particle could lead to discovery of new physics and unknown particles that form the most basic building blocks of nature.
“Working on the Muon g-2 project from the ground up is valuable because it has broadened and strengthened my research skills,” says Mary Shenk of Rockford, who will earn her master’s degree in physics this fall at NIU and plans to go on for a Ph.D. “I now understand how much planning and preparation goes into a project of this size.”
While most of the Muon g-2 machine was disassembled and brought to Fermilab in trucks, the 700-ton circular electromagnet had to be transported in one piece from its original home at Brookhaven National Laboratory in New York. It arrived last year with much fanfare, rolling down a closed-off Reagan Memorial Tollway (I-88), and has been in storage while its new home was constructed.
With the building now complete, scientists and engineers will reassemble and fine tune the muon machine, also known as the g-2 particle storage ring. NIU research professors and nearly 20 physics and engineering students played a significant role in preparations, and students also will be helping with the reassembly.
Michael McEvoy of St. Charles, a second-year graduate student, hopes to be part of the experiment “for a long time” as he works toward a master’s degree and Ph.D. in physics.
“I find the initial process of the rebuild very interesting,” says McEvoy, who is helping develop particle tracking and monitoring systems.
“Not only did they have to build a new temperature-controlled building with a removable wall so they can bring in the storage ring, but the sheer number of pieces the storage ring came in is incredible—and putting it back together is an enormous feat.”
Once the experiment is up and running in 2016, student researchers will help with quality control, equipment monitoring and data analyses. Some will base their master’s theses and dissertations on Muon g-2 discoveries.
While Shenk, McEvoy and several other NIU students have been stationed at Fermilab this summer, NIU senior Octavio Escalante-Aguirre of Aurora traveled to Naples, Italy. There he is working with scientists on calibration of the experiment’s calorimeters, which measure the energy of particles.
“Studying the building blocks of the universe is pretty cool, if you ask me,” says the 20-year-old Escalante-Aguirre, who has been involved in the experiment for more than a year.
“Not only have I been able to conduct invaluable research that will prepare me for graduate studies, but I have been able to step beyond my textbooks and use the physics knowledge that I’ve learned from my peers and professors,” he says.
So what are muons, anyway? And why are scientists and students so excited about the particles?
Outside of physicists, most people are unfamiliar with muons. But these particles are plentiful in the universe, says NIU Physics Professor Michael Eads, who leads NIU’s contingent on Muon g-2.
“For example, muons are created when cosmic rays strike our upper atmosphere,” Eads says. “As a result, we are hit by muons all the time—several every second.”
Like its lighter sibling the electron, the muon acts like a spinning magnet, and scientists are interested in its wobble. 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.
A Brookhaven experiment that concluded in 2001 produced a surprise. Its measurement of the muon’s wobble didn’t match what is predicted by the Standard Model of particle physics. That could be big news in the physics world, where mathematical precision reigns. But the margin of error for that experiment couldn’t provide definitive proof of a deviation.
“The Standard Model correctly predicts lots of things—for instance, it famously predicted the existence of the Higgs boson—but it doesn’t seem to properly predict this muon g-2 value,” Eads says. “If the theorized prediction doesn’t match the value, it’s telling us the Standard Model is somehow incomplete or incorrect.”
The Standard Model’s muon g-2 value is one of the most well defined measurements in physics — a single number that nearly every physics theory has required as a baseline. The new Muon g-2 experiment will have four times more precision than its Brookhaven counterpart. If Fermilab discovers a value different from the Standard Model prediction, it could usher in a new era of particle physics.
Eads notes that Einstein’s theory of special relativity plays a role in scientists’ ability to study the short-lived muon, which has a life span of just two microseconds, or two millionths of a second.
As Einstein’s theory predicts, when particles are traveling at nearly light speed, time dilates. So, when circulating in the superconducting storage ring at close to the speed of light, the muon appears to the observer to live much longer — about 64 microseconds. That’s enough time to allow scientists to make precise measurements of its properties.
“The anomalous magnetic moment of the muon is one of the currently unexplained phenomena in physics,” says Aaron Epps of Dixon, a first-year NIU graduate student who plans to earn his Ph.D. in physics. “If this anomaly is confirmed, it points to physics that we do not presently understand and will lead to new theories to explain the phenomena.”
One of NIU’s main roles in g-2 is quality-control testing for a complex straw tube tracker—a type of particle detector being built in Liverpool, England. The device detects particles known as positrons, which result from the decay of muons.
Beginning as an NIU undergraduate two years ago, Epps has worked with Professor Eads on projects related to the tracking system. He designed, coded and tested a method to determine wire tensions to be used in quality control tests and is learning the simulation software used in the experiment.
“It seems as if I will be able to see it through to the end and do my doctoral thesis on the subject,” Epps says. “The experiment will be a large part of my life for the coming years.”
Over the past two years, Pohlman has brought in 11 undergraduates and two graduate students to work on engineering aspects of the experiment. And he and Eads recently received a $325,000 Department of Energy grant that will provide funds for more student workers on g-2.
“Essentially, we act as the engineering team helping balance the idealized physics requirements with the feasibility of manufacturing and implementation,” Pohlman says. “We get a lot of support from our collaboration colleagues at Fermilab, Boston University, the University of Liverpool and others.”
Pohlman’s students have performed a wide range of engineering tasks. For instance, they conducted three-dimensional modeling of electronics, designed aspects of the tracker modules and determined how many modules could be placed in the beam line to maximize data resolution. A new team of senior design students likely will be involved in the project next fall as well.
“Our students learn by doing, and they also benefit by speaking to and learning from practicing engineers who are managing multiple projects simultaneously,” Pohlman says. “They find out just how much they have to balance in the real world.”