Physicists Make Surprising Observation

Physicists may have poked a hole in their current theory of how the universe operates.

Researchers at the Brookhaven National Laboratory on Long Island reported experiments today that showed a subatomic particle deviating slightly from its expected behavior. That tiny discrepancy could provide support for exotic theories such as supersymmetry, which hypothesizes that every particle has a much heavier, yet-to-be-observed counterpart.

'Beautiful Work'

"I would say it's a glimpse or a suggestion that there's supersymmetry out there," said James Miller, a physicist at Boston University and member of the team that conducted the Brookhaven research.

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

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

Much of physics today is based on the Standard Model, a complex set of equations that describes how all the fundamental forces except 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 have contradicted the Standard Model in more than three decades of trying.

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

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

Earlier experiments had found a spin modification fairly close to that predicted by the Standard Model. But the Brookhaven experiment, called g — 2 (gee minus two), was several times more precise than previous measurements. It concluded that the actual change in the muons' spin differed from predictions by just a few parts in a million.

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

The most likely explanation for the anomalous result is supersymmetry, a theory that goes beyond the Standard Model. In supersymmetry, every known particle has a much heavier counterpart paired with it. Unlike the Standard Model, the theory has a place for gravity, and explains why the various particles have the masses they do.

Today's results were presented by Brookhaven physicist William Morse in a colloquium at the laboratory, and have been submitted to the journal Physics Review Letters for publication. The results are based on measurements made in 1999, but do not include another set made last year.

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