Glimpsing glueballs in collider debris.
A calculation that took 2 years on a powerful special-purpose computer A computer designed from scratch to perform a specific function. Contrast with general-purpose computer. has provided evidence that a hypothesized subnuclear sub·nu·cle·ar
Of or located within the nucleus of an atom; smaller than the nucleus. particle called a glueball actually exists.
The result suggests that glueballs may be observed in particle accelerators when electrons or protons and their antimatter antimatter: see antiparticle.
Substance composed of elementary particles having the mass and electric charge of ordinary matter (such as electrons and protons) but for which the charge and related magnetic properties are opposite in sign. counterparts collide at high energies. Until now, glueballs had gone unrecognized because theorists had been unable to provide sufficient information on distinctive characteristics that would distinguish glueballs from other particles.
Physicists James Sexton, Alessandro Vaccarino, and Donald Weingarten of the IBM (International Business Machines Corporation, Armonk, NY, www.ibm.com) The world's largest computer company. IBM's product lines include the S/390 mainframes (zSeries), AS/400 midrange business systems (iSeries), RS/6000 workstations and servers (pSeries), Intel-based servers (xSeries) Thomas J. Watson Research Center The Thomas J. Watson Research Center is the headquarters for the IBM Research Division.
The center is on three sites, with the main laboratory in Yorktown Heights, New York, 45 miles north of New York City, a building in Hawthorne, New York, and offices in Cambridge, in Yorktown Heights, N. Y., describe their computation as "the largest single numerical calculation in the history of computing The history of computing is longer than the history of computing hardware and modern computing technology and includes the history of methods intended for pen and paper or for chalk and slate, with or without the aid of tables. ." They report their findings in the Dec. 18, 1995 Physical Review Letters Physical Review Letters is one of the most prestigious journals in physics. Since 1958, it has been published by the American Physical Society as an outgrowth of The Physical Review. .
The team based its calculation on a simplified version of the theory of quantum chromodynamics (QCD n. 1. (Physics) Quantum chromodynamics.
Noun 1. QCD - a theory of strong interactions between elementary particles (including the interaction that binds protons and neutrons in the nucleus); it assumes that strongly interacting particles ). This theory describes the force that binds different quarks and antiquarks together to create protons, neutrons, and other subatomic particles.
Just as an electrically charged particle generates an electric field, a quark gives rise to a so-called chromoelectric field. This force field can also be described in terms of the actions of particles called gluons Gluons
The hypothetical force particles believed to bind quarks into “elementary” particles. Although theoretical models in which the strong interactions of quarks are mediated by gluons have been successful in predicting, interpreting, and , which shuttle between quarks, seemingly gluing them together.
Quantum chromodynamics theory predicts that under certain circumstances, gluons themselves can stick together briefly to form composite particles called glueballs. However, the great difficulty of solving the relevant equations had prevented theorists from determining the masses and lifetimes of these hypothetical particles.
To help guide the search for glueballs, Weingarten and his coworkers turned to a simplification of quantum chromodynamics. In this formulation, quarks and antiquarks sit at points in a finite, four-dimensional lattice, and gluons correspond to the links between these points.
By solving the equations for a large number of quark and gluon gluon, an elementary particle that mediates, or carries, the strong, or nuclear, force. In quantum chromodynamics (QCD), the quantum field theory of strong interactions, the interaction of quarks (to form protons, neutrons, and other elementary particles) is arrangements, researchers can deduce characteristics of quark-containing particles. Increasing the number of points and expanding the region covered by the lattice, while decreasing the distance between the points, brings this approximation closer to the continuous space and time of the full theory. But this improvement occurs at the cost of greatly increased computation time.
To speed up the calculations, Weingarten and his coworkers used an experimental computer designed and built especially for this task. Called the GF11, it has 566 processors, each a powerful computer in its own right.
In 1993, the IBM team succeeded in computing from theory the masses of eight quark-containing subatomic particles (SN: 5/22/93, p. 325). Soon after, they calculated that the lightest glueball would have a mass (expressed in energy units) of about 1,707 megaelectronvolts (MeV).
To determine whether such a glueball would stick together long enough to be observed in a particle accelerator, the researchers calculated the glueball's rate of decay into different combinations of other particles.
The calculation demonstrated that a glueball has a sufficiently long lifetime for the particle to be detectable. Indeed, it's possible that physicists have already sighted a glueball in accelerator experiments. The best candidate is a particle labeled fJ (1710), which appears as the product of a quark-antiquark annihilation and has a mass of 1,710 MeV.