The two antineutrino detectors in China before the pool was...

The two antineutrino detectors in China before the pool was filled with ultrapure water. The pool is lined with photomultiplier tubes to track any highly energetic cosmic rays that make it all the way through the overlying rock. Credit: Handout

The search to understand why matter dominates antimatter in the universe will be aided by a new experiment by Brookhaven National Laboratory and two partners in California and China.

After eight years of planning and construction, the Daya Bay Reactor Neutrino Experiment started this week in an underground facility in the mountains of southern China near the Daya Bay nuclear power plant.

The goal is to gather more information about neutrinos, the uncharged particles produced in nuclear reactions, such as those in the sun and power plants.

The experiment also involves scientists from the Institute of High Energy Physics of the Chinese Academy of Sciences, and the U.S. Department of Energy's Lawrence Berkeley National Laboratory in California.

The Brookhaven scientists "helped to design . . . the pool of water that the detectors sit in," said physicist David Jaffe of Brookhaven. "We helped design the software system."

Jaffe is working on the experiment along with the experiment's chief scientist, Steve Kettell, and chief engineer, Ralph Brown, both of Brookhaven.

After the Big Bang, matter and antimatter were created in equal quantities but antimatter has disappeared over time, in what Jaffe called "one of the great mysteries of physics."

Among the international scientific community, the Daya Bay experiment is considered the foremost effort in neutrino physics, Jaffe said.

"It's like there are six pieces in this puzzle for neutrino mixing. We know four of the pieces pretty well. One of the pieces we don't know anything about," Jaffe said. "The last one, we know a little bit about."

The Daya Bay experiment is built to gain more data about the little-known puzzle piece, including making very precise measurements of the neutrinos' oscillations.

"So we designed the detector to be much more sensitive than previous detectors," Jaffe said. "The reason for trying to measure this is to get a full picture of neutrino phenomena."

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