Nature: There’s a cheaper way to break open physics

How tabletop experiments could find evidence of new particles, offering a glimpse beyond the standard model.

It’s possible that no one knows the electron as well as physicist Gerald Gabrielse. He once held one in a trap for ten months to measure the size of its internal magnet. When it disappeared, he searched for two days before accepting that it was gone. “You get kind of fond of your particles after a while,” he says.

And Gabrielse has had ample time to become fond of the electron. For more than 30 years, he has been putting sophisticated electromagnetic traps and lasers to work to reveal the particle’s secrets, hoping to find the first hints of what’s beyond the standard model of particle physics — the field’s long-standing, but incomplete, foundational theory. Yet for many of those years, it seemed as if he was working in the shadow of high-energy facilities such as the Large Hadron Collider (LHC), the 27-kilometre-circumference, US$5-billion particle accelerator near Geneva, Switzerland. “There was a time in my career when there weren’t very many people doing this kind of thing, and I wondered if it was the right choice,” he says.

Now, he’s suddenly moving from the fringes of physics to the limelight. Northwestern University in Evanston, Illinois, is about to open a first-of-its-kind research institute dedicated to just his sort of small-scale particle physics, and Gabrielse will be its founding director.

The move signals a shift in the search for new physics. Researchers have dreamed of finding subatomic particles that could help them to solve some of the thorniest remaining problems in physics. But six years’ worth of LHC data have failed to produce a definitive detection of anything unexpected.

More physicists are moving in Gabrielse’s direction, with modest set-ups that can fit in standard university laboratories. Instead of brute-force methods such as smashing particles, these low-energy experimentalists use precision techniques to look for extraordinarily subtle deviations in some of nature’s most fundamental parameters. The slightest discrepancy could point the way to the field’s future.

Even researchers long associated with high-energy physics are starting to look to low-energy experiments for glimpses beyond the standard model. If such hints emerge, they could point the way to explaining the mysteries of dark matter and dark energy, which collectively constitute some 95% of the Universe. “This is sort of a tectonic shift in the way we think of doing physics,” says Savas Dimopoulos, a theorist at Stanford University in California.

Squashed sphere

In some ways, these small-scale experiments are a return to how particle physics was once done. Gabrielse drew particular inspiration from a 1956 experiment by physicist Chien-Shiung Wu. In a laboratory at what is now the US National Institute of Standards and Technology in Gaithersburg, Maryland, Wu found an asymmetrical spatial pattern in how radioactive cobalt-60 atoms emit electrons. The finding, along with theoretical work, confirmed that two particles discovered almost a decade before were actually one and the same. It also helped to solidify faith in the burgeoning theoretical framework for the Universe’s fundamental particles and most of its fundamental forces, which would soon evolve into the standard model.

But physics was already moving towards bigger and more-expensive experimental machinery. Buoyed by a flush of post-Second World War cash and prestige, and by predictions that new particles would emerge in high-energy collisions, physicists proposed increasingly powerful and expensive particle accelerators. And they got them: facilities sprung up at Stanford; at Fermilab near Batavia, Illinois; at CERN near Geneva; and elsewhere. Quarks, muons, neutrinos and, finally, the Higgs boson were discovered. The standard model was complete.

And yet, as a description of the Universe, it is incomplete. The standard model doesn’t explain, for example, why antimatter and matter were not created in equal parts at the start of the Universe. If they had been, they would have annihilated each other, leaving behind a featureless void. The standard model also says nothing about dark matter, which seems to bind galaxies together, or about the dark energy that is pushing the Universe apart at an accelerating rate. “I like to call the standard model the great triumph and the great frustration of modern physics,” says Gabrielse. On the one hand, he says, it lets physicists predict some quantities “to ridiculous accuracy. On the other hand, we have a hole we can drive the Universe through.”

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