One of the fundamental building blocks of matter, a particle known as the muon, could help unlock basic questions about the nature of the universe. Scientists from around the world are collaborating on an experiment, Mu2e, that aims for an unprecedented milestone in understanding this subatomic particle.
Argonne physicist Karen Byrum has been named a deputy project manager for this multimillion-dollar international effort, an expansion of her current and continuing role as electronics integration team leader.
The Mu2e project involves three U.S. Department of Energy (DOE) Office of Science laboratories: Fermi National Accelerator Laboratory, which hosts the project, Argonne National Laboratory and Lawrence Berkeley National Laboratory. DOE’s High Energy Physics program funds Mu2e, which is also funded by Italy’s National Institute of Nuclear Physics and the National Laboratory of Frascati.
The goal of the Mu2e experiment is to observe a muon’s conversion into a related but lighter particle, the electron. This event is incredibly rare: It is equivalent to finding a marked penny hidden in one of 234 piles of pristine pennies, with each pile amounting to $831 trillion in pennies.
Being able to see a muon’s decay into an electron could reveal new forces or particles beyond the Standard Model of Particle Physics, our current explanation of the universe’s building blocks.
“The probability of this event occurring within the Standard Model prediction is very, very, tiny — essentially, it’s not supposed to happen,” Byrum said. “If we can detect this signal with Mu2e, that just tells you immediately that there’s something else going on that we don’t understand.”
Mu2e involves building a complex apparatus designed to make a staggering number of muons annually: 200 million billion or so. The muons will be generated and moved through a system of three superconducting solenoids, which are coiled, cylinder-shaped magnets. A particle detector embedded within the magnets will look for the muon-to-electron conversion as traveling muons are halted within an aluminum target that fosters their decay.
The vast majority of muons will spin off an electron and two fundamental particles with almost no mass called neutrinos. What the researchers will look for is a muon that converts fully to an electron with no neutrinos.
To detect this seemingly undetectable rarity, scientists from around the world are constructing an experimental setup at Fermilab that aims to be 10,000 times more sensitive than previous experiments seeking out this muon conversion. Byrum and colleagues are working on building the various subcomponents — a new beamline (a stream of particles that produces the muons), solenoids, detectors, electronics, hardware and software. All of them must be assembled and then integrated together with the goal of launching the experiment in 2025.
As one of two deputy project managers, Byrum is making sure each of the subsystems undergoes the proper reviews and meets requirements moving toward the 2025 launch. The project is already more than 85% complete with the remaining pieces in the final phases of design. This spring and summer, the remaining pieces will undergo construction readiness reviews, Byrum said — a critical step before fabrication begins. Some of the electronics Byrum is working on are being tested at Argonne’s 4 Tesla Magnet Facility. The facility provides a strong and uniform magnetic field that can help ensure equipment will function among the solenoids at Mu2e.
Byrum has been working on the Mu2e experiment, which launched in the late 2000s, since spring of 2015. She has known many of her colleagues on the project since her graduate school days, she said.
“What we are doing at Mu2e is a huge scientific challenge,” Byrum said. “I like the fact that I am working on that challenge within a really good team that I’m confident in. It’s a lot of fun.”
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