The standard model of particle physics passed one of its strictest tests yet

Nobody has ever probed a particle extra stringently than this.

In a brand new experiment, scientists measured a magnetic property of the electron extra fastidiously than ever earlier than, making essentially the most exact measurement of any property of an elementary particle, ever. Often known as the electron magnetic second, it’s a measure of the energy of the magnetic discipline carried by the particle.

That property is predicted by the usual mannequin of particle physics, the speculation that describes particles and forces on a subatomic degree. In truth, it’s essentially the most exact prediction made by that concept.

By evaluating the brand new ultraprecise measurement and the prediction, scientists gave the speculation one in all its strictest exams but. The brand new measurement agrees with the standard model’s prediction to about 1 half in a trillion, or 0.1 billionths of a %, physicists report within the February 17 Bodily Evaluation Letters.

When a concept makes a prediction at excessive precision, it’s like a physicist’s Bat Sign, calling out for researchers to check it. “It’s irresistible to a few of us,” says physicist Gerald Gabrielse of Northwestern College in Evanston, In poor health.

To measure the magnetic second, Gabrielse and colleagues studied a single electron for months on finish, trapping it in a magnetic discipline and observing the way it responded when tweaked with microwaves. The group decided the electron magnetic second to 0.13 components per trillion, or 0.000000000013 %.

A measurement that exacting is a sophisticated activity. “It’s so difficult that no person besides the Gabrielse group dares to do it,” says physicist Holger Müller of the College of California, Berkeley.

A team of physicists stand behind their experimental apparatus which captured a single electron in a trap.
A group of physicists (pictured) captured a single electron in a lure (experimental equipment proven) and studied it for months to measure a property known as the electron magnetic second.Laura Nevins

The brand new result’s greater than twice as exact because the earlier measurement, which stood for over 14 years, and which was additionally made by Gabrielse’s group. Now the researchers have lastly outdone themselves. “Once I noticed the [paper] I stated, ‘Wow, they did it,’” says Stefano Laporta, a theoretical physicist affiliated with College of Padua in Italy, who works on calculating the electron magnetic second based on the usual mannequin.

The brand new check of the usual mannequin could be much more spectacular if it weren’t for a conundrum in one other painstaking measurement. Two latest experiments, one led by physicist Saïda Guellati-Khélifa of Kastler Brossel Laboratory in Paris and the opposite by Müller, disagree on the worth of a quantity known as the fine-structure constant, which characterizes the energy of electromagnetic interactions (SN: 4/12/18). That quantity is an enter to the usual mannequin’s prediction of the electron magnetic second. So the disagreement limits the brand new check’s precision. If that discrepancy have been sorted out, the check would grow to be 10 occasions as exact as it’s now.

The stalwart normal mannequin has stood as much as a barrage of experimental exams for many years. However scientists don’t suppose it’s the be-all and end-all. That’s partly as a result of it doesn’t clarify observations such because the existence of darkish matter, an invisible substance that exerts gravitational affect on the cosmos. And it doesn’t say why the universe contains more matter than antimatter (SN: 9/22/22). So physicists maintain searching for instances the place the usual mannequin breaks down.

One of the vital tantalizing hints of a failure of the usual mannequin is the magnetic second not of the electron, however of the muon, a heavy relative of the electron. In 2021, a measurement of this property hinted at a possible mismatch with standard model predictions (SN: 4/7/21).

“Some individuals imagine that this discrepancy may very well be the signature of latest physics past the usual mannequin,” says Guellati-Khélifa, who wrote a commentary on the brand new electron magnetic second paper in Physics journal. If that’s the case, any new physics affecting the muon might additionally have an effect on the electron. So future measurements of the electron magnetic second may also deviate from the prediction, lastly revealing the usual mannequin’s flaws.


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