Fwd: Largest Computer Calculation Ever Supports Theory of Elementary -- anyone for a Nobel

[Dave Farber <farber () central cis upenn edu>]

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Largest Computer Calculation Ever Supports Theory of Elementary
Particles

Wednesday, May 12, 1993    (US  NEWS)

A year-long calculation on the experimental IBM GF-11 massively
parallel computer has provided the strongest evidence yet that a
physics theory known as quantum chromodynamics, or QCD, is the
correct description of the properties and behavior of nature's
most fundamental subnuclear particles.

The calculation was so enormous -- more than a hundred million
billion arithmetic operations -- that it required a full year of
continuous operating time on as many as 480 of GF-11's 566
processors.

The calculation is the first to result in numerical values for
the masses predicted by QCD for eight fundamental particles.
Those calculated masses, say the IBM Researchers, are in
agreement with generally accepted values found by others in
actual laboratory measurements.

The work was performed by IBM Researcher Don Weingarten together
with Frank Butler, Hong Chen, Jim Sexton and Alessandro Vaccarino,
all of physical sciences and technology, Thomas J. Watson Research
Center.  A significant aspect of the work, is that it may add to
the legitimacy of computer experiments as the basis of a new branch
of physics -- "experimental theoretical physics" -- distinct from
both theory and laboratory experimentation.

Weingarten and his colleagues calculated the masses of the proton
and seven other members of a family of particles called hadrons.
The hadrons are particles that experience the "strong" nuclear
force that keeps nuclei intact.  QCD, proposed in the early 1970s,
describes how the hadrons are formed from combinations of either
two or three of the various kinds of particle building blocks
called quarks and antiquarks.  According to QCD, quarks and
antiquarks are permanently bound within hadrons and can never be
isolated.

QCD is somewhat analogous to a thoroughly verified theory called
quantum electrodynamics, or QED, in which electromagnetic fields
are created by electrons, and photons are the minimum bundles of
field energy, or quanta, that are emitted and absorbed during
interactions.  In QCD, there is a "color" field (hence the name
chromodynamics) created by quarks, and "gluons" are the quanta of
the color field that mediate interactions between quarks.

The work is a real milestone in the calculational technology of
elementary particle physics:  it's the first complete calculation
of hadron masses from QCD.  Previous calculations were incomplete
and more like tests of methods themselves.

At the very heart of the calculation is an algorithm called the
valence approximation.  It's a procedure that is required because
the vacuum causes the "color charge" of the quark to appear to be
reduced, as if it were screened.  In the valence approximation,
this screening is taken into account by simply replacing the
quark's true color charge with the reduced value.

Having shown with the mass calculations that QCD is correct and
that his calculational procedure is correct, Weingarten, with his
group, will now go on to look at other aspects of the theory.
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