'Pentaquark' theory on more solid ground

Experiment delves deeper into atoms' exotic inner workings

An experiment expressly designed to detect "pentaquarks" confirms the existence of these exotic physics particles, researchers reported Sunday.

The discovery involves tiny particles called quarks, the bricks and mortar of particles inside atoms. Previously, physicists had seen only quarks packed into two- or three-quark combinations inside subatomic particles. But last year, several international research labs discovered signs of five-quark combinations. This intrigues scientists who are trying to unravel the mystery of how the innards of atoms hang together.

Until now, 10 experiments supporting the pentaquark's existence and three that cast doubt upon it relied on data from experiments designed to look for other phenomena. But the new results from Japan's Laser-Electron Photon Facility represent a first direct attempt to spot the pentaquark experimentally, and they provide strong evidence of pentaquarks' existence. "Now we have a new testing ground," says physicist Ken Hicks of Ohio University in Athens, who presented the pentaquark data at the American Physical Society meeting here. "Everything is consistent with our first results."

Physicists are cautious about leaping onto the pentaquark bandwagon because of past bad experiences, says physicist Ted Barnes of the Energy Department's Oak Ridge (Tenn.) National Laboratory. In the 1970s, theories predicting all sorts of multiple quark particles bloomed. Better experiments knocked these theories down, he says.

Such experiments are underway, Hicks says, at Thomas Jefferson National Accelerator Facility in Newport News, Va. They are expected to conclude this month.