Physicists Predict Existence of ‘Most Strange’ Dibaryon Particle


Physicists from the HAL QCD Collaboration predict the existence of a new type of dibaryon, a particle that contains six quarks instead of the usual three. Their work appears in the journal Physical Review Letters.

di-Omega dibaryon. Image credit: Keiko Murano.

di-Omega dibaryon. Image credit: Keiko Murano.

Particles known as baryons (protons and neutrons) are composed of three quarks bound tightly together, with their charge depending on the ‘color’ of the quarks that make them up.

A dibaryon is essentially a system with two baryons. There is one known dibaryon in nature — deuteron, a deuterium nucleus that contains a proton and a neutron that are very lightly bound.

Physicists have long wondered whether there could be other types of dibaryons. Despite searches, no other dibaryon has been found.

The HAL QCD Collaboration has now used powerful theoretical and computational tools to predict the existence of a ‘most strange’ dibaryon, made up of two ‘Omega baryons’ that contain three strange quarks each.

The researchers named the new particle ‘di-Omega.’ They also suggested a way to look for these strange particles through experiments with heavy ion collisions.

The finding was made possible by a fortuitous combination of three elements: better methods for making QCD calculations, better simulation algorithms, and a powerful supercomputer.

“The first essential element was a new theoretical framework called the ‘time-dependent HAL QCD method.’ It allows us to extract the force acting between baryons from the large volume of numerical data obtained using a supercomputer,” the scientists said.

“The second element was a new computational method, the unified contraction algorithm, which allows much more efficient calculation of a system with a large number of quarks.”

“The third element was one of the most powerful computers in the world — the K computer at RIKEN, Japan.”

“We were very lucky to have been able to use the K computer to perform the calculations. It allowed fast calculations with a huge number of variables,” said Dr. Shinya Gongyo, of the RIKEN Nishina Center.

“Still, it took almost three years for us to reach our conclusion on the di-Omega particle.”

“We believe that these special particles could be generated by the experiments using heavy ion collisions that are planned in Europe and in Japan, and we look forward to working with colleagues there to experimentally discover the first dibaryon system outside of deuteron,” added Dr. Tetsuo Hatsuda, of the RIKEN Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS) program.

“This work could give us hints for understanding the interaction among strange baryons (called hyperons) and to understand how, under extreme conditions like those found in neutron stars, normal matter can transition to what is called hyperonic matter (made up of protons, neutrons and hyperons), and eventually to quark matter (composed of up, down and strange quarks).”


Shinya Gongyo et al (HAL QCD Collaboration). 2018. Most Strange Dibaryon from Lattice QCD. Phys. Rev. Lett 120 (21); doi: 10.1103/PhysRevLett.120.212001