Physicists Make Surprising Observation

N E W   Y O R K, Feb. 8, 2001 -- Physicists may have poked a hole in theircurrent theory of how the universe operates.

Researchers at the Brookhaven National Laboratory on Long Islandreported experiments today that showed a subatomic particledeviating slightly from its expected behavior. That tinydiscrepancy could provide support for exotic theories such assupersymmetry, which hypothesizes that every particle has a muchheavier, yet-to-be-observed counterpart.

'Beautiful Work'

"I would say it's a glimpse or a suggestion that there'ssupersymmetry out there," said James Miller, a physicist at BostonUniversity and member of the team that conducted the Brookhavenresearch.

But team members and physicists uninvolved with the experimentcautioned that the case is not yet proven.

"These people are doing beautiful work," said Charles Prescottof the Stanford Linear Accelerator Center. "But it is too early tosay they're seeing supersymmetry."

Much of physics today is based on the Standard Model, a complexset of equations that describes how all the fundamental forcesexcept gravity interact with known particles. For decades,physicists have designed experiments to challenge the model.

First Contradiction in Decades

The Brookhaven experiment may be the first time physicists havecontradicted the Standard Model in more than three decades oftrying.

"If you find an experiment that disagrees with it then that'sfairly significant," Miller said.

The experiment examined the behavior of muons, heavier relativesof electrons, as they floated in a powerful magnetic field. In amagnetic field, a muon modifies its spin, a subatomic propertysimilar to the rotation of a toy top.

Earlier experiments had found a spin modification fairly closeto that predicted by the Standard Model. But the Brookhavenexperiment, called g — 2 (gee minus two), was several times moreprecise than previous measurements. It concluded that the actualchange in the muons' spin differed from predictions by just a fewparts in a million.

That small discrepancy suggests there is something lacking inthe Standard Model, though there is still a chance that furtherresults could bring theory and experiment back into line.

The most likely explanation for the anomalous result issupersymmetry, a theory that goes beyond the Standard Model. Insupersymmetry, every known particle has a much heavier counterpartpaired with it. Unlike the Standard Model, the theory has a placefor gravity, and explains why the various particles have the massesthey do.

Today's results were presented by Brookhaven physicistWilliam Morse in a colloquium at the laboratory, and have beensubmitted to the journal Physics Review Letters for publication.The results are based on measurements made in 1999, but do notinclude another set made last year.

If the result stays the same once those data are analyzed,Miller said, it will be much more certain.