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UH Manoa physicists discover a new sub-atomic particle

The hybrid meson may be the first found by scientists after a search of 25 years

University of Hawaiʻi at Mānoa
Posted: May 17, 2005

HONOLULU — A team of physicists from the University of Hawaiʻi at Mānoa, along with scientists from universities and laboratories in America, Asia, Australia and Europe, recently reported the discovery of an enigmatic and unexpected new sub-atomic particle called Y(3940). The scientists are part of the "Belle experiment" and their findings will be published in this month‘s issue of Physical Review Letters, the world‘s premier physics journal.

The Belle experiment involves the study of charge conjugation parity (CP) violation — the differences between matter and antimatter. The experiment operates at the KEK High Energy Physics Laboratory in Tsukuba, Japan, home to the world‘s highest intensity particle accelerator. The Hawaiʻi group has been part of the project since 1994 when preparations for the experiment started.

The newly observed Y(3940) is very short-lived and quickly decays into two well-known particles, omega and J/psi. All that is known about the sub-atomic particle to date hints at the possibility that it may be an example of a so-called "hybrid meson," a particle that is assumed to be comprised of a quark, an antiquark and a gluon. A gluon is a particle that mediates the very strong forces that bind quarks together to form particles.

"The existence of hybrid quark-antiquark-gluon particles was first predicted theoretically in 1978," said UH physicist Stephen Olsen. "However, in spite of 25 years of searching for one, none have been seen, until, maybe now."

Although many of the properties of the Y(3940) match expectations for a hybrid meson, its mass, which is about the same as a single atom of helium, is somewhat below theoretical estimates. As a result, the interpretation of this new particle remains an enigma. Further investigations of its properties, currently in progress, should help clarify the situation.

The observation of the Y(3940) is the result of analysis of Belle data by professors Stephen Olsen of the University of Hawaiʻi at Mānoa and Sookyung Choi of Gyeongsang University in Korea.

Other UH Mānoa participants in the Belle experiment include faculty members Tom Browder, Mike Jones, Mike Peters and Gary Varner; postdoctoral researchers Marlon Barbero and Karim Trabelsi; and graduate students Eric Dodson, Hulya Guler, Himansu Sahoo and Kirika Uchida. The work by Hawaiʻi physicists in the Belle experiment is supported in part by the U.S. Department of Energy.For more information, visit the KEK Laboratory Web site at or the Belle experiment Web site at