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PNNL collaborating on world’s newest atom smasher

Annette Cary Tri-City Herald

A new atom smasher with the potential to help physicists explain some of the mysteries of the universe has circulated beams for the first time.

The SuperKEKB particle accelerator is in Japan, but Pacific Northwest National Laboratory in Richland is playing a key role in the scientific discoveries that it could make possible.

Scientists expect it to do a better job than similar accelerators at creating rare particles, perhaps even dark matter, that could provide information about why there seem to be exceptions to the standard model of particle physics. They are looking for the “new physics,” beyond the standard model, that ruled the early universe.

Last week, the accelerator circulated a beam of electrons moving near the speed of light through a narrow tube around the nearly 2-mile circumference of its main ring 32 feet underground. On Feb. 10, it sent a beam of positrons – the antimatter equivalent to an electron – the other direction around the tube.

Those “first turns,” as circulating particles through many revolutions of an accelerator are called, are a key step in commissioning the accelerator.

When the accelerator begins operating next year, the beams of electrons and positrons will be compressed and crash together head-on in a smaller area than any other accelerator of the type has yet done. The collisions will occur in a region just 100 nanometers high, which is smaller than a barely visible dot of text.

Previous unexplained measurements have indicated there are some holes in the standard model (of particle physics).

The result should be 40 to 50 times the number of collisions produced by similar accelerators, including the Japan accelerator before it was upgraded.

More collisions increase the odds of important observations.

The new particles created in the collisions should include some particles that have not been seen naturally in the universe since the first moments of the Big Bang. They could help answer questions such as why, if matter and antimatter were created in equal amounts at the start of the universe, they did not annihilate each other but left stars and planets.

“We are looking for very, very rare events,” said James Fast of PNNL.

The accelerator will operate for a decade to catch events that might happen one in a billion times or one in 10 billion times.

The upgraded collider in Tsukuba, Japan, was designed and created by a team in Japan. But the project also includes the three-story-tall Belle II detector, which will detect and record data from 30,000 collisions per second.

“It is equivalent to a very, very complicated digital camera,” Fast said. “We are measuring where particles are going at the level of a human hair.”

The detector was designed by a team of more than 600 scientists in 23 countries, including 75 scientists in the United States led by Fast as project manager for the U.S. work, along with the chief scientist, David Asner of PNNL. The Department of Energy’s Office of Science is paying for the U.S. work.

“Global cooperation is necessary to address the most compelling questions in particle physics,” said James Siegrist, associate director of science for high energy physics in the Office of Science, in a statement.

The centerpiece of the U.S. contribution to Belle II is the “Imaging Time of Propagation,” or iTOP detector.

The accelerator keeps beams of electrons and positrons tightly corralled with more than 1,000 magnets as they zip around the accelerator 100,000 times per second.

As the collisions occur, they throw off 10 to 20 particles. The iTOP measures the velocity of the particles, which can be moving at about the speed of light, and another detector in Belle II measures their momentum to together come up with the mass.

The information can be used to determine what the particles were, including heavy particles that decay quickly before they can be detected. They could include types of elementary matter such as “tau leptons,” which were not observed until the ‘90s, or particular types of quarks discovered just decades ago.

“We need to observe more of them,” Fast said.

Scientists are trying to understand how all particles are held together at the subatomic level.

It also is possible that dark matter – the label for matter of unknown type that makes up 30 percent of the universe – may be produced and observed.

After the Fukushima nuclear disaster caused power rationing in Japan, accelerator data was transferred to PNNL for use by scientists around the world. All data from the improved accelerator until at least 2019 also will be stored on PNNL computers dedicated to the project, drawing on PNNL expertise in high-performance computing and data management.

Of the two dozen scientists working on Belle II at PNNL, about half have contributed to designing and building the detector and the other half are assigned to helping manage the data.

Massive amounts of data are expected to be generated during a decade of accelerator operation. The amount of data also will scale up by a factor of 50, Fast said.

It will be one of the largest scientific samples of data ever, exceeding all the written works in the history of the world several times over, according to PNNL.

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