The Muon Guys: On The Hunt for New Physics

muon guys

Symmetry Magazine, June 2010

Amid the sprawl of mysterious equipment in a workroom at Fermi National Accelerator Laboratory, Gueorgui Velev and Alexander Makarov leaned over an elegant metal box the size of a single file cabinet. Suffused by a warm halo of late-afternoon sunlight, the two men, a physicist and an engineer, had the look of modern-day priests of industry gently handling a beloved reliquary.

Velev lifted the box top, revealing a thin slice of dark-gray ferrite—a ceramic compound used in powerful magnets. Although the ferrite was wired up like an intensive-care patient, for the moment it felt cool and deliciously smooth to the touch.

Velev and Makarov have been testing ferrites like this one for almost a year now, sending powerful currents through the compound, pushing the material to its limits. Far from being a relic of something dead, the ferrite is a symbol of resurrection for an experiment that could star in its own soap opera. Attempts to carry out this experiment have died two deaths on two continents over the course of two decades.

Velev and Makarov, along with a host of collaborators, are once again bringing it to life.

The experiment’s newest name, in its incarnation at Fermilab, is Mu2e (pronounced Mew to E), which stands for muon-to-electron conversion; and it is a testament to the strength of the science behind this experiment that physicists are still fighting to do it. Scientists plan to break ground at Fermilab in Batavia, Illinois, in 2013 and begin taking data four years later.

The experiment will search for a phenomenon so incredibly rare that, according to the Standard Model of physics, humans could never build a machine sensitive enough to actually see it. Which is exactly why scientists want to build this experiment. Mu2e is on the hunt for new physics.

Specifically, Mu2e is trying to catch a glimpse of one kind of particle turning into another. The experiment will look for signs of a muon—which is basically an electron’s fatter cousin—converting, in a Cinderella-like transformation, into its more slender and well-known relative.

If a muon does undergo this transformation, the signs will be unmistakable. This fact alone sets Mu2e apart from many other particle physics experiments, where scientists must sort through a huge amount of “background” data that bury the sought-after results in a torrent of distractions. Finding the result you’re looking for can be like picking out a whisper amidst the cacophony of Times Square. In Mu2e, the signal will blare out from the background like a siren.

The Mu2e experiment will use aluminum atoms to capture muons— heavy, electron-like particles. The muon begins to orbit the nucleus of the atom, just as ordinary electrons do. Scientists predict that a tiny fraction of the time a bound muon will change directly into an electron, with no other particles emerging from the decay, and fly off into the detector. The signal from this single, energetic electron will blare like a siren against a background of other events.

Choreographing an invisible dance

To pick up this signal, physicists must build a system of jaw-dropping precision and complexity that is capable of producing 500 million billion muons per year. In a slow-motion, subatomic ballet, it must gently capture these muons within the orbits of aluminum atoms, which will provide the staging ground for the predicted transfiguration. If the Large Hadron Collider is a high-energy particle mosh pit, Mu2e is a delicate and sophisticated pas de deux. Orchestrating such minute choreography requires the combined efforts of more than 100 scientists at universities and laboratories around the globe.

Even humanity’s boldest endeavors must endure one painful fact of life: meetings. Surely the Romans held meetings before they built their aqueducts, and Ernest Shackleton must have met with his crews before setting out on his famed expeditions to Antarctica.

To plan their own undertaking, Mu2e collaborators gather every Thursday in a conference room on the 12th floor of Fermilab’s Wilson Hall.

On a bright morning last February, physicists clad in what seems to be the experiment’s unofficial uniform (subdued sweaters over neat button-downs, jeans, a preponderance of suspenders) drifted in, carrying laptops and clutching coffee cups. Mu2e co-spokesperson Robert Bernstein was already set up at the conference table, laptop open, hurling curses at the LCD projector.

“I am pushing the right button, right? Why isn’t this working?!” he said, waving a remote control toward the ceiling. “I am pushing the right button, right?”

Somebody crawled under the conference table to fiddle with cables, and was soon joined by two more physicists.

“Wait, it just reacted!” said another physicist, peering at the uncooperative machine.

“This is how all meetings begin,” said Ron Ray, the Mu2e project manager, from his post near the front of the room.

“We always think we’re going to start on time, and then we have these technical difficulties,” said Jim Miller, a professor at Boston University and Mu2e’s other co-spokesperson. “And we think we’re going to mount this complicated experiment.”

He was kidding. Mostly.

Read the rest of the story here.

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