Experiment challenges long-standing physics model

From Alex Walker
CNN Science Producer

UPTON, New York (CNN) -- The so-called Standard Model of particle physics, which has withstood experimental challenge for 30 years, may finally be showing some cracks.

Scientists at Brookhaven National Laboratory announced Thursday that an experiment under way since 1997 has come up with results at odds with the model.

"We are now 99 percent sure that the present Standard Model calculations cannot describe our data," said Brookhaven physicist Gerry Bunce, project manager for the experiment.

Scientists involved in the experiment say more study is needed to determine the full impact of the results.

The Standard Model, in development since the 1960s, is a theoretical explanation that ties together three of the four forces known to exist in the universe -- the strong force, the electromagnetic force, and the weak force -- but not the fourth force, gravity.

Other theories have been put forward to go beyond the Standard Model, but no experimental measurement that deviates so significantly from the model has previously been reported

In the Brookhaven experiment, scientists used the world's largest superconducting magnet to create a very intense source of muons, a type of subatomic particle. They then attempted to precisely measure something called the anomalous magnetic moment of the muons. Their findings show the measurement deviates from the value predicted by the Standard Model.

"There are three possibilities for the interpretation of this result," said Yale physicist Vernon Hughes, co-researcher in the experiment.

"Firstly, new physics beyond the Standard Model, such as supersymmetry, is being seen. Secondly, there is a small statistical probability that the experimental and theoretical values are consistent. Thirdly, although unlikely, the history of science in general has taught us that there is always the possibility of mistakes in experiments and theories."

Supersymmetry is a theory that predicts the existence of so-far undiscovered companion particles for all known particles.

"This work could open up a whole new world of exploration for physicists interested in new theories," said Boston University physicist Lee Roberts, co-spokesperson for the experiment.

Scientists at Brookhaven collaborated with researchers from 11 institutions in the U.S., Russia, Japan, and Germany to conduct the tests, known as the muon g-2 (G minus two) experiment. The scientists say there is still a year's worth of data from the experiment to analyze.

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Brookhaven National Laboratory

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