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In this issue:
An Elegant Approximation
Wanted: SLAC Mementos

SLAC Today

Thursday - March 5, 2009

An Elegant Approximation

(Photo)
SLAC theoretical physicist Stan Brodsky. (Photo by Lauren Schenkman.)

SLAC theoretical physicist Stan Brodsky and University of Costa Rica physicist Guy de Téramond have found a simple equation describing the behavior of the subatomic particles within the proton. Their paper, published in the February 27 issue of Physical Review Letters, is an important step in SLAC's long history of investigations into the quantum mechanical world of the proton.

"A better understanding of the structure of the proton has traditionally been one of the main goals of SLAC physics," Brodsky said. "How is it made up, at the fundamental level? That's one of our main driving points at SLAC, and, in fact, in the whole field of high energy physics and nuclear physics."

The SLAC tradition dates back to the 1960s, when Richard Taylor, Henry Kendall and Jerome Friedman used SLAC's linear accelerator to shoot high-energy electrons at the protons and neutrons in a liquid hydrogen target. The experiments confirmed a prediction of a young SLAC theorist named James Bjorken—the apparently fundamental protons and neutrons were made up of smaller particles called quarks. The discovery earned Taylor and his collaborators the 1990 Nobel Prize in physics.

Since that time, physicists have been wrestling with the mathematical description of the proton structure, a theory known as quantum chromodynamics, or QCD. The "chromo" refers to "color," a quality quarks have, similar to the way electrons have charge. Unfortunately, due to the complex nature of the fundamental force that binds quarks together, QCD so far has been extremely difficult to work with. In the language of QCD, asking the question, "Where are the quarks inside the proton, and how are they moving?" ties variables like color, spin, position and number of particles into a nightmarish Gordian knot.  Read more...

(Photo - Commemorative LCLS
The Linac Coherent Light Source commissioning team created these shot glasses to celebrate their successful steering adjustments December 13, 2008, requiring only two attempts to run the electron beam from injector to beam dump for the first time. (Photo by Shawne Workman.)

Wanted: SLAC Mementos

Ready to dust off your shelf full of project-milestone memorabilia? Symmetry magazine is looking for the best, quirkiest and most-fondly remembered among your physics mementos, to be commemorated with a photograph and a few words of description. Items ranging from new to not-so-new are of interest. Please e-mail suggestions to Symmetry editor Glennda Chui; we'll do the rest. 

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