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First five-quark particle turns up. (Wild Bunch).



Physicists on three international teams have recently spotted what's most likely a long-sought subatomic particle known as a pentaquark. It contains five components--four quarks and one antiquark--which are among the most fundamental bits of matter yet known. No subatomic particle detected previously contains more than three of those building blocks.

"After 30 years of failing to find any convincing evidence for something that ought to be there, this recent news is certainly met with excitement," says nuclear physicist Andrew M. Sandorfi of Brookhaven National Laboratory Brookhaven National Laboratory, scientific research center, at Upton (town of Brookhaven), Long Island, N.Y. It was founded in 1947 by Associated Universities, a management corporation sponsored by nine eastern U.S. universities.  in Upton, N.Y.

Although unusually complex, the newfound particle fits within the prevailing theoretical framework of particle physics, known as the standard model. The newly detected bit may be just the first member of a family of pentaquark particles. The find also underscores the possibility of discovering particles with four or six quarks.

To fathom how five quark components can coexist within one particle, theorists expect to reconsider their models of the interactions among quarks and 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
, the particles that bind quarks together. For instance, it's possible that the fivefold structure is not a spherical lump but rather a moleculelike arrangement in which a so-called kaon ka·on  
n. Abbr. K
Any of a subgroup of unstable mesons that consist of an electrically charged form with a mass 966 times that of an electron and a neutral form with a mass 974 times that of an electron, produced as a result of a
, which is made of a quark and an antiquark an·ti·quark  
n.
The antiparticle of a quark.



antiquark  

The antiparticle that corresponds to a quark.

Noun 1.
, orbits a neutron, which is made of three quarks.

"Exactly what form of the theory makes it work now becomes very interesting," says theorist Peter D. Barnes of Los Alamos (N.M.) National Laboratory.

If the pentaquark can exist in labs today, it probably also was present in the very first, fiery moments of the universe, says Takashi Nakano of Osaka University, leader of the team that found the pentaquark at Japan's SPring-8 synchrotron synchrotron: see particle accelerator.
synchrotron

Cyclic particle accelerator in which the particle is confined to its orbit by a magnetic field. The strength of the magnetic field increases as the particle's momentum increases.
 in Hyogo.

The experiments that appear to have bagged the elusive pentaquark weren't designed to look for it. "This is an example of serendipity serendipity

happy finding of an unexpected object or solution while searching for something else.
," says Kenneth H. Hicks of Ohio University in Athens. He's a member of both the SPring-8 team and a group at the Thomas Jefferson National Accelerator Facility Thomas Jefferson National Accelerator Facility (TJNAF), commonly called Jefferson Lab (JLAB), is a U.S. national laboratory operated as of 1 June 2006 by Jefferson Science Associates, LLC, a joint venture between Southeastern Universities Research Association, Inc.  in Newport News, Va., that has confirmed the SPring-8 finding.

[ILLUSTRATION OMITTED]

In 1997, Russian theorist Dmitri Diakonov and his colleagues predicted the existence of a pentaquark with a mass about 50 percent heavier than that of a hydrogen atom. The theorists then urged the SPring-8 team to reexamine re·ex·am·ine also re-ex·am·ine  
tr.v. re·ex·am·ined, re·ex·am·in·ing, re·ex·am·ines
1. To examine again or anew; review.

2. Law To question (a witness) again after cross-examination.
 data from an experiment in 2001 that might have inadvertently made the particle when it had gamma rays Gamma rays

Electromagnetic radiation emitted from excited atomic nuclei as an integral part of the process whereby the nucleus rearranges itself into a state of lower excitation (that is, energy content).
 striking a piece of plastic.

When Nakano, Hicks, and their coworkers combed that data, they in fact found signs for about 20 pentaquarks. The team is slated to present its evidence in an upcoming Physical Review Letters Physical Review Letters is one of the most prestigious journals in physics.[1] Since 1958, it has been published by the American Physical Society as an outgrowth of The Physical Review. .

Inspired by the SPring-8 findings, researchers at the Jefferson lab and the Institute of Theoretical and Experimental Physics in Moscow double-checked old data from different sorts of particle collisions and netted their own pentaquark candidates.

Besides its unprecedented quark count, a pentaquark is unusual in that it includes an exotic antiquark, the so-called strange antiquark. The composite particle also contains two up quarks and two down quarks--the same ones found in ordinary matter.

Nakano says the SPring-8 team is now analyzing data from new collisions that were generated explicitly to make pentaquarks. The aim is to nail down the identity and properties of this new entity. Meanwhile, the Jefferson lab has approved an experiment intended to boost its pentaquark production 20-fold, Hicks says.
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Author:Weiss, P.
Publication:Science News
Geographic Code:1USA
Date:Jul 5, 2003
Words:553
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