Science

Science in Mind

Electron’s spherical shape survives most intense scrutiny yet

Gerald Gabrielse, John Doyle, and David DeMille embarked on their quest last year to measure the electron’s “lumpiness.”

Matthew J. Lee/Globe Staff/File 2012

Gerald Gabrielse, John Doyle, and David DeMille embarked on their quest last year to measure the electron’s “lumpiness.”

Last year, I wrote about a small-scale Harvard and Yale University physics experiment with a lot riding on it: Scientists were trying to measure the electron’s “lumpiness.” That may sound like a pretty narrow pursuit, but if the electron’s negative charge was just a little egg-shaped and not distributed in a perfect sphere, it could point to the existence of never-detected heavy particles. It could provide evidence to support theories beyond the Standard Model of physics — the longstanding, but incomplete description of the universe’s fundamental building blocks.

The results are in, and the electron remains a sphere. In a study published online Thursday in the journal Science, the physicists report that they increased the sensitivity of their measurement of the electron’s charge by an order of magnitude. They still couldn’t find any hint that the shape was even a tad oblong.

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It doesn’t rule out other theories yet, but it means trouble for one popular theory called weak-scale Supersymmetry, which predicts new particles — and a tiny irregularity in the distribution of negative charge over the electron.

And it means scientists are still grappling with one of the biggest questions facing physics today: Something is wrong with the Standard Model — it can’t account for why the universe exists — but scientists haven’t been able to put their finger on the solution.

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“We know that it cannot be the final word because it cannot even describe why a universe of matter survived if the big bang produced essentially equal amounts of antimatter and matter that should then have annihilated as the universe cooled,” Harvard University physicist Gerald Gabrielse wrote in an e-mail.

Gabrielse, who leads the experiment with his colleague from Harvard, John Doyle, and physicist David DeMille of Yale University, said the new measurement can detect perturbations from a perfect sphere 10 times smaller than any previous measurements and found none. He admitted that was kind of disappointing.

“Even as we are proud to have confirmed the prediction of the Standard Model, we are frustrated that this much more sensitive measurement did not expose problems with the Standard Model which must be there at some level,” he wrote.

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The team isn’t finished: Members think they can make their technique 10 times more sensitive, continuing the hunt.

Perhaps the neatest thing about the experiment, which fits into a large basement room off Oxford Street in Cambridge, is that it probes much of the same territory as the Large Hadron Collider — at a fraction of the cost and the personnel.

The collider, which found evidence of a long-sought particle, the Higgs boson, last year, is an experiment that requires thousands of scientists, international cooperation, and billions of dollars. The Harvard-Yale experiment has a budget in the low millions and brings together fewer than two dozen people.

That’s not to suggest a tabletop physics experiment could replace the Large Hadron Collider. That accelerator experiment can probe other questions. But it’s an elegant example of how a well-designed experiment can be used to try to answer very large questions.

Carolyn Y. Johnson can be reached at cjohnson@globe.com. Follow her on Twitter @carolynyjohnson.
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