Unusual Subatomic Particle Discovered

Sookyung Choi of Gyeongsang University, Korea, and Stephen Olsen, professor of physics at the University of Hawaii, members of an international team of researchers at the High Energy Accelerator Organization (KEK) in Tsukuba, Japan, have announced the discovery of a new and unusual sub-atomic particle. One member of that team is Leo Piilonen of Blacksburg, professor of physics in the College of Science at Virginia Tech.

The discovery is described in a report ("Observation of a new narrow charmonium state in exclusive B -K pi pi J/psi decays") published in the Nov. 21, 2003, edition of Physical Review Letters, the world's most prestigious journal for physics research. Piilonen reported on the discovery of the X(3872) meson at the 19th International Workshop on Weak Interactions and Neutrinos on Oct. 8 in Lake Geneva, Wisconsin.

The new particle, which the researchers are calling the X(3872), weighs about the same as a single atom of helium and exists for only about one billionth of a trillionth of a second before it disintegrates to other longer-lived, more familiar particles. Although extremely short-lived by any human standard, this is nearly an eternity for a particle that is this heavy.

The new particle was found among the decay products of so-called beauty mesons that are produced in large numbers at the KEKB "B-factory," an electron-positron collider at the KEK laboratory that is specialized for producing large numbers of particles that contain a b ("beauty") quark. There, the Belle collaboration, an international team of faculty and student researchers from universities and laboratories from 11 different countries, operate the Belle detector, which is tailored to study the particles produced by KEKB. Belle is a complex assortment of highly sensitive radiation detectors mounted inside of a large superconducting electromagnet. The device took nearly 10 years to design and build. (Faculty and staff in the physics department at Virginia Tech built components of the Belle detector. Learn more at www.research.vt.edu/resmag/1998mag/articles/antimattter.html)

There are hundreds of sub-atomic particles, and the discovery of a new one is usually not an extraordinary event. However, the X(3872) particle is peculiar in that it does not easily fit into any known particle scheme and, as a result, has attracted a considerable amount of attention from the world's physics community. The Belle discovery was recently confirmed by researchers with the CDF experiment at the Fermi National Accelerator Laboratory in Illinois, home of the Tevatron, the world's largest atom smasher. There, the X(3872) is referred to as the "mystery meson."

A "normal" meson particle is comprised of a quark and an antiquark that are held together by the "color" force, the most powerful force in nature. The large variety of meson particles that have been found to date reflect the many different ways that these combinations can be accomplished. However, the mass and the decay properties of the X(3872) do not match theoretical expectations for any conceivable quark-antiquark arrangement.

Theoretical physicists around the world are considering a number of potential explanations. These include modifications to the theory of the color force, or the possibility that the X(3872) is the first example to be seen of a new type of meson, one that is made from two quarks and two antiquarks.

Participating universities:

Budker Institute of Nuclear Physics, Novosibirsk

Chiba University, Chiba

University of Cincinnati, Cincinnati, Ohio 45221

University of Frankfurt, Frankfurt

Gyeongsang National University, Chinju

University of Hawaii, Honolulu, Hawaii 96822

High Energy Accelerator Research Organization (KEK), Tsukuba

Hiroshima Institute of Technology, Hiroshima

Institute of High Energy Physics, Chinese Academy of Sciences, Beijing

Institute of High Energy Physics, Vienna

Institute for Theoretical and Experimental Physics, Moscow

J. Stefan Institute, Ljubljana

Kanagawa University, Yokohama

Korea University, Seoul

Kyungpook National University, Taegu

Institut de Physique des Hautes Energies, Universite de Lausanne, Lausanne

University of Ljubljana, Ljubljana

University of Maribor, Maribor

University of Melbourne, Victoria

Nagoya University, Nagoya

Nara Women's University, Nara

National Kaohsiung Normal University, Kaohsiung

National Lien-Ho Institute of Technology, Miao Li

Department of Physics, National Taiwan University, Taipei

H. Niewodniczanski Institute of Nuclear Physics, Krakow

Nihon Dental College, Niigata

Niigata University, Niigata

Osaka City University, Osaka

Osaka University, Osaka

Panjab University, Chandigarh

Peking University, Beijing

Princeton University, Princeton, New Jersey 08545

RIKEN BNL Research Center, Upton, New York 11973

Saga University, Saga

University of Science and Technology of China, Hefei

Seoul National University, Seoul

Sungkyunkwan University, Suwon

University of Sydney, Sydney NSW

Tata Institute of Fundamental Research, Bombay

Toho University, Funabashi

Tohoku Gakuin University, Tagajo

Tohoku University, Sendai

Department of Physics, University of Tokyo, Tokyo

Tokyo Institute of Technology, Tokyo

Tokyo Metropolitan University, Tokyo

Tokyo University of Agriculture and Technology, Tokyo

Toyama National College of Maritime Technology, Toyama

University of Tsukuba, Tsukuba

Utkal University, Bhubaneswer

Virginia Polytechnic Institute and State University (Virginia Tech), Blacksburg, Virginia 24061

Yokkaichi University, Yokkaichi

Yonsei University, Seoul