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University
of Illinois scientists, along with collaborators around
the world, draw a bead on the subatomic muon, hoping
to better understand the Standard Model of physics.
Nature has a way of making a mess
of subatomic particles' balance sheets. "Particles
chuck out other particles--sometimes even particles
more massive than themselves," says David Hertzog,
a physics professor at the University of Illinois. "Then
they grab them back [in an instant], before anyone notices.
These particles would be good working at Enron."
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Hertzog is part of a large,
international team known as the g-2 (gee minus two) collaboration.
Made up of some 70 researchers at 11 institutions, the
team is in the business of checking these particles' books.
The behavior of a subatomic particle known as the muon
allows the g-2 collaboration to peer into the Standard
Model of physics. With the Standard Model and a predilection
for number crunching, researchers can predict the workings
of three of nature's fundamental forces--electromagnetism,
the strong nuclear interaction that binds atomic nuclei,
and the weak nuclear interaction that governs processes
like nuclear decay--and the type and behavior of subatomic
particles. |
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Despite an impressive,
decades-long track record, the Standard Model is not
perfect. Many researchers suspect that there's more
out there, that the physical universe is more complex
than even the knotty Standard Model can explain. If
researchers can show that the muon acts in a certain
way, they can prove that it is being influenced by subatomic
particles that the Standard Model does not account for.
"The process [of muons flinging off other particles
and then snatching them back] alters properties of the
muon that we can measure," says Hertzog. "And
if those properties don't match the Standard Model,
that implies something. We just don't know what that
is yet."
After releasing a set of results in 1999,
the g-2 collaboration caused a stir. Their experimental
results were well outside what the Standard Model predicted
should have been the case. Motivating theoreticians
to go back and re-examine the Standard Model's every
tittle and jot, the results provoked about 230 citations
in journal articles. Within a few months, scientists
discovered a math error (a single negative sign was
off) that made the theoretical numbers hew much more
closely to the measured numbers.
Nonetheless, "it's a very exciting
time" in the field, according to Hertzog. The team
published new data in August 2002. Relying in part on
NCSA's newest Linux clusters, these results confirm
the quality of the team's earlier experimental data.
They differ from theoretical numbers, however, by between
3 and 1.5 standard deviations, depending upon which
of the several, well-founded theoretical approaches
is used. Needless to say, this data, and the mismatch,
give theoreticians and experimentalists more to pore
over in their probing of the Standard Model. The team
intends to release further data in mid-2003.
Access Online | Posted 4-8-2003
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