Demolition Derby of Physics Jars Loose Clues on Subatomic Glue
By JAMES GLANZ
 article
physicists are known as the demolition crews of the very small,
smashing tiny bits of matter together to find the even tinier bits that
they are made of. So it may come as a surprise that the field has
recently found a powerful new engine of discovery: gluing it all back
together again, sometimes in weird ways that seldom occur in nature, if
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The glue linking these discoveries is the "strong force," which is
normally relegated to holding together quarks, the building blocks of
humdrum particles like protons and neutrons. But theorists have long
suspected that the strong force has a wild side and that it should be
able to take the subatomic equivalent of a Tudor chimney here, an Art
Deco facade there, and stick them together into entirely new particle
types.
Hints of those strange creations began turning up this year. Although
quarks normally congregate in twos and threes, several laboratories
said this summer that they were seeing what appeared to be ungainly
clumps of five quarks.
In a paper to be published tomorrow, the High Energy Accelerator
Research Organization in Tsukuba, Japan (called KEK for its Japanese
acronym) describes what the researchers believe were two pairs of
quarks dancing close enough to form a single new particle.
The finding at KEK, which followed a related discovery at the Stanford
Linear Accelerator Center this year, could also turn out to be a rare
combination of just two quarks called charmonium, some theorists
believe. Either way, the rush of results is expected to lend fresh
insights on the strong force, widely considered among the most opaque
and intractable parts of the Standard Model, the theory physicists use
to explain matter's basic structure.
"We don't understand how this force really works when it gets very
strong - when it makes atomic nuclei, for example, or makes these
particles," said Dr. Frank Close, a professor of theoretical physics at
Oxford University in England.
Dr. Close likened scattered clues on the way the strong force works to
undeciphered hieroglyphs. "We need more hieroglyphs to decode them," he
said. "These three discoveries are very important hieroglyphs."
The discoveries are especially welcome in a field that is in some ways
adrift, lacking any big new machine to smash matter into ever-finer
pieces. In 1993, Congress killed the Superconducting Super Collider, a
vast particle accelerator that was to have begun collecting data by
this year. A multibillion-dollar, multinational collaboration in Geneva
called the Large Hadron Collider is not expected to be ready before
2007.
Dr. Robert Cahn, a particle physicist at Lawrence Berkeley National
Laboratory who works on what is called the BaBar experiment at
Stanford, gave the particle interregnum a name: the non-S.S.C. era.
But then, he said, "Here this thing comes in from left field."
It is not hard to see why a full understanding of the strong force has
eluded theorists for decades. Although physicists know that protons and
neutrons are made of groups of three quarks, not even these great
demolition experts of science have been able to knock a quark free.
That is because the strong force does not become weaker - in contrast
to gravity or electrical forces - the farther the particles are apart.
They can never escape the sticky embrace of another quark.
The swarming particles that transmit the strong force from quark to
quark, called gluons, are shape-shifters. They spend part of the time
in the guise of other quarks. That habit means that heavy particles
like protons and neutrons are also filled with these more evanescent
quarks winking in and out of existence.
Just to make things as complicated as possible, there are eight
different kinds of gluons, each with a different type of "charge." And
there are six varieties of quarks, each with its own cute name: up,
down, top, bottom, charm and strange.
With a good-natured dig at ambitious theoretical efforts to unify the
forces in the Standard Model (strong, weak and electromagnetic) with
gravitation, Dr. Chris Quigg, a particle theorist at the Fermi National
Accelerator Laboratory in Illinois, said: "It's only a theory of
everything if you can explain all the things. The experiments are
forcing us to try to understand the theory in places where the
calculations are difficult."
He added, "If you call yourself a theorist and have any self-respect, you have to take the challenge."
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