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In this issue:
A Tale of Two Light Sources
Profile: Eric Lee: Searching for Fractional Electric Charge and Studying Dark Matter
New Editor Joins symmetry
SPring-8 Seminar to Review XFEL Status

SLAC Today

Wednesday - March 14, 2007

(From left) Vlad Vinetskiy, Renato Avilar, and Graeme Card working on SSRL's new protein crystallography station at Beamline 12. Protein crystallography is an important area of user research for which SPEAR3 is uniquely suited.

A Tale of Two Light Sources

With the construction of the Linac Coherent Light Source (LCLS) moving ahead, SLAC is well on its way to having two x-ray light sources. SPEAR3, the synchrotron accelerator storage ring at SSRL, produces x-rays used by more than 2000 users and scientists a year. The LCLS will likewise produce powerful x-rays for a variety of research applications, but these two light sources will operate in fundamentally different yet complementary ways.

Several key distinctions will make the LCLS a very different machine from SPEAR3. Unlike SPEAR3, the LCLS will produce a coherent beam of x-ray laser light. Coherent x-rays are easier to focus to an extremely tiny spot size, making the LCLS a much more powerful microscope, and giving it the ability to make three-dimensional holographic images of sample molecules. The LCLS will also have the advantage of producing extraordinarily short pulses of x-rays—on the order of 100 femtoseconds, equivalent to the time light takes to travel the width of a human hair. Ultra-fast pulses will enable the LCLS to make stroboscopic images of ultra-fast phenomena, such as molecular vibration and chemical reactions as they happen. Each pulse will be billions of times brighter than those produced by SPEAR3—more x-rays per pulse mean more information can be obtained from a sample in a much shorter time.  Read more...

(Weekly Column - Profile)

Eric Lee: Searching for Fractional Electric Charge and Studying Dark Matter

(Image - Eric Lee)
Eric Lee in front of his fractional charge search apparatus.
(Click on image for larger version.)

Eric Lee—inventor, electronic engineer, expert computer user, machinist, amateur astronomer, graduate student mentor—joined SLAC's Group E in 1994 after a dozen years working on novel cancer therapies in the Stanford Medical School. Since then, he has worked on a variety of projects including the search for particles with fractional electric charge and the development of the very large CCD camera for the Large Synoptic Survey Telescope (LSST).

All known free elementary particles such as neutrinos, photons, muons and taus have an electric charge of either zero or ± q. The one exception to this is the quark, which has a charge of ± 2/3q or ± 1/3q. Yet because quarks are always bound in nucleons or mesons, the observed charge is either zero or ± q. For the past 100 years, physicists have been looking without success for free particles with fractional electric charge using accelerators, colliders, searches in cosmic rays and searches in ordinary matter. Several modern particle physics theories predict the existence of just such particles, and we do not know of any fundamental reason why particles with fractional electric charge do not exist. Yet they have never been observed.

In science, the final test of theories and ideas is observation and experiment. With this in mind, Lee joined with Martin Perl to search for fractional charge using a modern version of the Millikan Oil Drop method. Lee’s experiments use liquid drops about 20 microns in diameter—about one fifth the diameter of a human hair. These drops are allowed to fall vertically through the air while an oscillating electric field moves the drops back and forth horizontally. The drop trajectory is recorded in real time by a CCD camera and analyzed by a computer system, to measure the drop's charge with a precision of about one twentieth of an electron charge.

Over the past 12 years, the sensitivity and range of the searches has steadily improved through the work of Lee and three Stanford graduate students who received their PhDs working with Lee. The earlier phase of the experiment published results on the largest amount of terrestrial material ever studied. The present search—which has been going on for almost three years—involves exotic asteroidal material obtained from the Allende meteorite that fell in Mexico in 1969. Lee has almost fully automated the experiment so that it requires his intervention only a day or so every two weeks, which he does between checking and analyzing the data as it comes in. While no fractional charge particles have yet been found, Lee and Perl would like the current search to continue until the apparatus can no longer be repaired or maintained.

South Gallery Closed From 8-10 a.m. Today

The South Gallery will be closed from Sector 1.4 through Sector 27 on Wednesday morning from about 8:00 until 10:00 a.m. to allow heavy equipment to be removed from Sector 20. Thank you for your understanding.

New Editor Joins symmetry

(Photo - Glennda Chui)The joint Fermilab/SLAC particle physics magazine, symmetry, has recently added a new editor to its staff: Glennda Chui became the publication's deputy editor last Monday. Chui has worked as a science writer at the San Jose Mercury News for 21 years and shared a Pulitzer Prize for her coverage of the 1989 Loma Prieta earthquake in the San Francisco Bay area.

A native of California, Chui received a bachelor's degree in biology from California State University at Hayward and a master's in journalism at the University of California at Berkeley. In 1984, she began working as a staff reporter covering education for the Mercury News, but within two years she became the newspaper's full-time science writer. "I kind of weaseled my way into science writing," she said.

In addition to researching, writing and editing articles, Chui is also excited about working with the graphics team that designs symmetry's signature style. Although she has covered particle physics news stories in the past, she is eager to delve deeper into the particle world. "I'm really looking forward to getting out and meeting people in the physics community and learning what they're doing," she said.

Currently Chui serves on the board of directors of the National Association of Science Writers, teaches at the University of California at Santa Cruz's science writing program, and spends her free time with her son and daughter. She will work closely with symmetry editor-in-chief David Harris. "We're very excited to have a journalist of Glennda's skill and experience joining the symmetry team," Harris said.

Shintake to Discuss
X-ray Laser at Spring-8

(Photo - Undulators)
Two in-vacuum undulators will enable Spring-8's free electron laser to produce hard x-rays.

Much like the Linac Coherent Light Source (LCLS) currently under construction at SLAC, researchers at SPring-8 in Japan are busily building a hard x-ray free electron laser of their own. Tsumoru Shintake, R&D leader of Japan's XFEL project, will give a talk on the status of the new laser today at 4:00 p.m. in the Kavli Auditorium.

Last June, a prototype accelerator successfully lased at soft x-ray wavelengths, demonstrating the principle of the new machine. Crews are now installing a brand new 400-m-long, 8 GeV electron accelerator at the SPring-8 site. The completed laser is scheduled to deliver first beam by the end of FY 2010.

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