From RIKEN[理研(JP): “Exotic six-quark particle predicted by supercomputers”

RIKEN bloc

From RIKEN[理研(JP)

Dec. 10, 2021

A new particle predicted by supercomputers could shed light on how matter is formed.

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Figure 1: An artist’s impression of a newly predicted six-quark state (dibaryon) consisting of two baryons. © 2021 Keiko Murano.

The predicted existence of an exotic particle made up of six elementary particles known as quarks by RIKEN researchers could deepen our understanding of how quarks combine to form the nuclei of atoms.

Quarks are the fundamental building blocks of matter. The nuclei of atoms consist of protons and neutrons, which are in turn made up of three quarks each. Particles consisting of three quarks are collectively known as baryons.

Scientists have long pondered the existence of systems containing two baryons, which are known as dibaryons. Only one dibaryon exists in nature—deuteron, a hydrogen nucleus made up of a proton and a neutron that are very lightly bound to each other. Glimpses of other dibaryons have been caught in nuclear-physics experiments, but they had very fleeting existences.

“Although the deuteron is the only known stable dibaryon, many more dibaryons may exist,” says Takuya Sugiura of the RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program. “It’s important to study which pairs of baryons form dibaryons and which do not because this provides valuable insights into how quarks form matter.”

Quantum chromodynamics is a highly successful theory that describes how quarks interact with each other. But the strong coupling that occurs between quarks in baryons complicates quantum chromodynamics calculations. The computations become even more complex when considering bound states of baryons such as dibaryons.

Now, by calculating the force acting between two baryons each containing three charm quarks (one of the six types of quarks), Sugiura and his co-workers have predicted the existence of a dibaryon they called the charm di-Omega.

For this calculation, the team solved quantum chromodynamics with large-scale numerical calculations. Since the calculations involved a vast number of variables, they used two powerful supercomputers: the K computer and the HOKUSAI supercomputer.

Riken Fujitsu K supercomputer manufactured by Fujitsu, installed at the Riken Advanced Institute for Computational Science campus in Kobe, Hyōgo Prefecture, Japan.

Riken HOKUSAI Big-Waterfall supercomputer built on the Fujitsu PRIMEHPC FX100 platform based on the SPARC64 processor.

“We were extremely fortunate to have had access to the supercomputers, which dramatically reduced the cost and time to perform the calculations,” says Sugiura. “But it still took us several years to predict the existence of the charm di-Omega.”

Despite the complexity of the calculations, the charm di-Omega is the simplest system for studying interactions between baryons. Sugiura and his team are now studying other charmed hadrons using the supercomputer Fugaku, which is the K computer’s more powerful successor. “We’re especially interested in interactions between other particles containing charmed quarks,” says Sugiura. “We hope to shed light on the mystery of how quarks combine to form particles and what kind of particles can exist.

Science paper:
Physical Review Letters

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RIKEN campus

RIKEN [理研](JP) is Japan’s largest comprehensive research institution renowned for high-quality research in a diverse range of scientific disciplines. Founded in 1917 as a private research foundation in Tokyo, RIKEN has grown rapidly in size and scope, today encompassing a network of world-class research centers and institutes across Japan. Founded in 1917, it now has about 3,000 scientists on seven campuses across Japan, including the main site at Wakō, Saitama Prefecture, just outside Tokyo. Riken is a Designated National Research and Development Institute, and was formerly an Independent Administrative Institution.
Riken conducts research in many areas of science including physics; chemistry; biology; genomics; medical science; engineering; high-performance computing and computational science and ranging from basic research to practical applications with 485 partners worldwide. It is almost entirely funded by the Japanese government, and its annual budget is about ¥88 billion (US$790 million).

Organizational structure:

The main divisions of Riken are listed here. Purely administrative divisions are omitted.

Headquarters (mostly in Wako)
Wako Branch
Center for Emergent Matter Science (research on new materials for reduced power consumption)
Center for Sustainable Resource Science (research toward a sustainable society)
Nishina Center for Accelerator-Based Science (site of the Radioactive Isotope Beam Factory, a heavy-ion accelerator complex)
Center for Brain Science
Center for Advanced Photonics (research on photonics including terahertz radiation)
Research Cluster for Innovation
Cluster for Pioneering Research (chief scientists)
Interdisciplinary Theoretical and Mathematical Sciences Program
Tokyo Branch
Center for Advanced Intelligence Project (research on artificial intelligence)
Tsukuba Branch
BioResource Research Center
Harima Institute
Riken SPring-8 Center (site of the SPring-8 synchrotron and the SACLA x-ray free electron laser)

Riken SPring-8 synchrotron, located in Hyōgo Prefecture, Japan.

RIKEN/HARIMA (JP) X-ray Free Electron Laser
Yokohama Branch (site of the Yokohama Nuclear magnetic resonance facility)
Center for Sustainable Resource Science
Center for Integrative Medical Sciences (research toward personalized medicine)
Center for Biosystems Dynamics Research (also based in Kobe and Osaka) [6]
Program for Drug Discovery and Medical Technology Platform
Structural Biology Laboratory
Sugiyama Laboratory
Kobe Branch
Center for Biosystems Dynamics Research (developmental biology and nuclear medicine medical imaging techniques)
Center for Computational Science (R-CCS, home of the K computer and The post-K (Fugaku) computer development plan)

Riken Fujitsu K supercomputer manufactured by Fujitsu, installed at the Riken Advanced Institute for Computational Science campus in Kobe, Hyōgo Prefecture, Japan.

Fugaku is a claimed exascale supercomputer (while only at petascale for mainstream benchmark), at the RIKEN Center for Computational Science in Kobe, Japan. It started development in 2014 as the successor to the K computer, and is officially scheduled to start operating in 2021. Fugaku made its debut in 2020, and became the fastest supercomputer in the world in the June 2020 TOP500 list, the first ever supercomputer that achieved 1 exaFLOPS. As of April 2021, Fugaku is currently the fastest supercomputer in the world.