To answer the questions of how the universe works, physicists must solve a series of problems, such as how to best collect the data allowing them to discover and learn about the building blocks of our world.

To help solve the problem of how to collect data to study matter and anti-matter, faculty and students at Virginia Tech built some novel equipment in the basement of Robeson Hall in the late 1990s that continues to have a definitive impact on how physicists understand the universe. This equipment forms a key component of the Belle detector, a subatomic physics experiment located at the High Energy Accelerator Research Organization (KEK) Laboratory in Tsukuba, Japan.

The Belle detector, built in segments and assembled in Japan, has more than 400 collaborators who have been making discoveries ever since, including the latest, a new state of matter consisting of a four-quark particle with an electrical charge.

There are six quarks – the elementary building blocks of matter – the Up, Down, Strange, Charm, Bottom, and Top quarks (and their anti-matter counterparts). Typically, researchers have found three-quark states like the proton or neutron but in June, the first four-quark state with a non-zero electrical charge was discovered.

“A team from China within the Belle collaboration found this new state of matter,” said Leo Piilonen, the William E. Hassinger Jr. Senior Faculty Fellow in Physics and chair of the department at Virginia Tech. “We weren’t looking for it, it just popped up in the data, and it’s one of the more intriguing results from the Belle experiment.” This new particle was discovered at the same time by an independent experiment named BESIII and the results from both experiments were published at the same time in Physical Review Letters.

Since it started taking data in 1999, the Belle experiment has led to the Nobel Prize in Physics in 2008 for Makoto Kobayashi and Toshihide Maskawa, and a host of other discoveries while studying the behavior of matter and anti-matter.

The newest four-quark particle consists of a quartet of Charm/anti-Charm quarks and Up/anti-Down quarks, which provide its electrical charge. Scientists don’t capture it and see it so much as measure it indirectly through the byproducts of its disintegration, as it exists for a fraction of a nano-second.

“A nano-second would be a long time for this particle,” Piilonen explained. “A nano-second is one billionth or 10^-9 of a second whereas this quark state exists for only 10^-23 second.”

Still, that’s enough time for physicists to get excited about what the discovery could mean.

“There’s a theory that explains how quarks interact with each other called Quantum Chromodynamics,” Piilonen said. “The QCD theory is very difficult to work with mathematically, so this discovery will help people tune their ideas of how to work with QCD.  The new four-quark particle points the way toward more complicated combinations of quarks that have not yet been found.”

This summer, work was again underway in the basement of Robeson Hall to upgrade the Belle accelerator for the start of the next-generation Belle II project. A team from Virginia Tech went to Japan in August to help install their portion of the system upgrade that will allow the Belle II detector to give researchers 50 times more data.

“We had 160 events worth of data that we used for our last paper with the four-quark particle,” Piilonen said. “The improvements we’re making for Belle II will help us collect vastly more data from the increase in particle collision frequency.”

Virginia Tech’s elementary particle physics research in Japan has been continuously funded through the Department of Energy since 1986 and Piilonen’s research group’s latest grant started in May for $810,000 over three years. Other groups at Virginia Tech also have grants as part of the project umbrella. A number of nations as well as Pacific Northwest National Laboratory and the Universities of Hawaii, Cincinnati, Pittsburgh, Indiana, Wayne State, Carnegie Mellon, and several others are also involved with the project.



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