Researchers help world’s newest atom-smasher achieve ‘first turns’

Faculty and student researchers with Virginia Tech’s College of Science have helped Japan’s SuperKEKB particle accelerators achieve its “first turns” – circulating beams of particles – giving physicists access to a record rate of particle collisions and a unique chance to discover the mysteries of the universe’s origins.

Located on the campus of the High Energy Accelerator Research Organization (“KEK,” using its Japanese language acronym) in Tsukuba, the project comprises the SuperKEKB accelerator and the Belle II detector. The SuperKEKB colliding-beam accelerator and the Belle II detector are designed to create and observe more than 40 times the rate of particle collisions than their predecessors, KEKB and Belle, whose observation of the difference in behavior of matter and antimatter led to a 2008 Nobel Prize in Physics. Scientists on the new accelerator project say the particles produced during planned new collisions will give them a better understanding of the universe’s building blocks and provide opportunities to expand on known particle physics theories.

This is where Leo Piilonen, a professor with Virginia Tech’s Department of Physics, enters the picture. Since the late 1990s, Piilonen and teams of student and postdoctoral researchers have been heavily involved in the construction of the Belle and Belle II detectors, highly detailed “digital cameras” that observe the byproducts of the particle collisions. “We hope to discover new processes, new states of matter, and new evidence of the differing behavior of matter and antimatter in the Belle II experiment, similar to what my prior students and postdocs have done in the first-generation Belle experiment,” said Piilonen.

Belle II will run for the next decade and its scientific output will exceed that of Belle, which already has generated 460 peer-reviewed scientific papers with more to come, added Piilonen. With a $15 million infusion from the U.S. Department of Energy to more than a dozen U.S. partners, part of Belle II was built at Virginia Tech under Piilonen’s direction as an upgrade of the first-generation Belle’s muon-detection subsystem. The first Belle also was built in-part on campus at Robeson Hall.

During the breakthrough “first turns” of the upgraded accelerator in February, scientists in Japan circulated a beam positrons moving close to the speed of light through a narrow tube around the nearly 2-mile circumference of its main ring, 30 feet underground. The international team then succeeded in circulating a beam of electrons also at near the speed of light in the opposite direction. These two events mark the device’s “first turns” – a milestone when beams of particles are circulated through many revolutions of an accelerator for the first time, said project leaders.

SuperKEKB scientists will next accelerate the two beams simultaneously, compressing them into a smaller area than any other previous accelerator, then smash the beams together to produce heavy subatomic particles whose decays may reveal as yet undiscovered physics. To create such high intensity, scientists begin by creating beams of electrons and positrons and keeping them tightly corralled with more than 1,000 magnets as they zip around the accelerator 100,000 times per second. Once per revolution, the particles are focused into “nano-beams” that make the particles much more likely to collide. The copious collisions will allow scientists to study extremely rare subatomic processes with unprecedented precision.

Roughly the size of a house, the Belle II detector -- the result of work by 600 scientists spanning 99 institutions in 23 countries, including Virginia Tech – will take digital snapshots of the data from 30,000 collisions per second. Scientists who already have spent years designing SuperKEKB and Belle II will then carefully dig through the resulting data, likely to be the largest scientific sample of data ever, with hundreds of petabytes, equal to all of history’s written works.

Piilonen credits 12 undergraduates, two doctoral students -- Yao Li of Shiyan, China, and Kimberly Williams of Hattiesberg, Mississippi, who each graduated in December 2015 -- for working on the construction project for the upgraded muon-detection subsystem, beginning in 2013. 

More recently, physics doctoral students Zachary Stottler of Glenwood, Minnesota, and Taylor Kimmel of Greenville, South Carolina, have worked on the project with undergraduate physics majors junior W. Jesse Barber of Terrell, North Carolina, and senior James Butler of Herndon, Virginia, also assisting. Post-doctoral research associate XiaoLong Wang also has been working with Piilonen on Belle since 2013 and is scheduled to join Virginia Tech post-doctorate researcher Dmitri Liventsev at the KEK laboratory in Japan for an extended stay.

Virginia Tech is a founding member of the Belle II project; with U.S. partners Pacific Northwest National Laboratory, Carnegie Mellon University, Indiana University, Kennesaw State University, Luther College, University of Cincinnati, University of Florida, University of Hawaii, University of Mississippi, University of Pittsburgh, University of South Alabama, University of South Carolina, and Wayne State University.

Pacific Northwest National Laboratory contributed to this report.