symmetryA joint Fermilab/SLAC publication

dimensionsof particle physics

volume 03

issue 07

september 06

symmetryA joint Fermilab/SLAC publication

P-377, 2002 acrylic on canvas 27 x 24 1 ⁄4 inches

Painting byRobert Straight

On the coverPainting by number represents a sophisticated mathematical approach by artist Robert Straight, a professor of painting at the University of Delaware, who uses prime numbers to construct forms and establish color placement on the canvas. The image on the cover is a segment of a painting in Straight's exhibition, “Toroids and Plaids,” which has been on display at the National Academy of Sciences in Washington, DC.

Contents symmetry | volume 03 | issue 07 | september 06

3 Commentary: Lee Sawyer “ In the wake of Katrina and Rita, at least 17 college and uni-versity campuses were closed, displacing around 80,000 students in Louisiana. At the K-12 level, nearly a quarter of a million students were without schools.”

4 Signal to Background Secret of the hidden ledger; zoo events; Brookhaven celebrates diversity; making science K’nex-tions; vacuum cleaners rescue neutrino horn; Einstein still a big earner; poker-playing physicist; Antarctica in California; cartoons by design; pentaquark references; particle ‘Jeopardy.’

10 New Life for a Linac How the Stanford Linear Accelerator Center is transforming the world’s longest linear accelerator into a novel X-ray laser.

16 The Rise and Fall of the Pentaquark The pentaquark search serves as a model for the ways in which particle physics explores the nature of matter—even when the search is unsuccessful.

20 Packing It In Globe-traveling physicists put some of their best thinking into strategies for their bags—all carry-ons, of course.

24 Gallery: Robert Straight In his exhibit, “Toroids and Plaids,” painter Robert Straight uses prime numbers to construct forms and establish color placement on the canvas.

26 Deconstruction: Particle Pocket Card In the early 1950s, Nobel-Laureates-to-be Norman Ramsey and Ed Purcell created cards of physical constants they found themselves using most frequently.

28 Essay: Mikhail Shifman “The young people who will build our future appear to be largely unaware of how attractive and rewarding careers in science can be. We should not be surprised.”

ibc Logbook: Particle Data Book This year, the Particle Data Group celebrates its 50th anniversary with a release of a 1230-page edition of the Review of Particle Physics.

bc 60 Seconds: X-ray Lasers X-ray lasers will deliver extraordinarily intense beams of X-rays in very short bursts ten billion times brighter than those in other light sources.

Office of ScienceU.S. Department of Energy

from the editor

SymmetryPO Box 500MS 206Batavia Illinois 60510USA

630 840 3351 telephone630 840 8780 faxwww.symmetrymagazine.orgmail@symmetrymagazine.org

(c) 2006 symmetry All rights reserved

symmetry (ISSN 1931-8367) is published 10 times per year by Fermi National Accelerator Laboratory and Stanford Linear Accelerator Center, funded by the US Department of Energy Office of Science.

Editor-in-ChiefDavid Harris650 926 8580

Executive EditorMike Perricone

Managing EditorKurt Riesselmann

Staff WritersElizabeth ClementsBrad Plummer Heather Rock Woods Siri Steiner Kelen Tuttle

InternsBen Berger Jennifer Lauren Lee Dave Mosher Krista Zala

PublishersNeil Calder, SLACJudy Jackson, FNAL

Contributing EditorsRoberta Antolini, LNGSDominique Armand, IN2P3Peter Barratt, PPARCStefano Bianco, LNFReid Edwards, LBNLCatherine Foster, ANLBarbara Gallavotti, INFNJames Gillies, CERNSilvia Giromini, LNFJacky Hutchinson, RALYouhei Morita, KEKMarcello Pavan, TRIUMFMona Rowe, BNLYuri Ryabov, IHEP ProtvinoYves Sacquin, CEA-SaclayBoris Starchenko, JINRMaury Tigner, LEPPJacques Visser, NIKHEFLinda Ware, JLabUte Wilhelmsen, DESYTongzhou Xu, IHEP Beijing

Print Design and ProductionSandbox Studio Chicago, Illinois

Art DirectorMichael Branigan

DesignersAaron Grant Tara Kennedy Sharon Oiga

Web Design and ProductionXeno MediaHinsdale, Illinois

Web ArchitectKevin Munday

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Web ProgrammerMike Acklin

Photographic Services Fermilab Visual Media Services

symmetry

Physicists are people tooPhysicists are dedicated to their work, but it often bleeds into their home and personal lives. Reading this issue of symmetry gives me a converse impression—just how human physicists are as they work.

In his commentary, Lee Sawyer talks about physicists in the aftermath of last year’s hurricanes. He witnessed the scientific community help displaced physicists and students both to continue their work and to just get by.

I’ve heard physicists described as “quirky” many times, and the story about what and how physicists pack when they travel highlights what some see as those quirks. Of course, the physicists see themselves as extremely logical, and yet every person interviewed has a distinct approach to their frequent travel. One person’s quirk is another’s survival technique!

This issue also contains many stories about the human sides of members of our community: Brookhaven’s Unity Day emphasizes the diversity of peo-ple who work in science; a SLAC engineer created chalk drawings that have survived on a communal blackboard for over a decade, a remarkable feat considering how physicists love to scribble ideas on any available surface; and a theorist who just graduated from Stanford plays and wins professional poker—a new model for funding your way through graduate school.

Sometimes human nature seems to get the better of physicists. As the pentaquark story describes, the desire for discovery might have pushed some scientists to be too optimistic about the significance of their findings. It was a case of intense enthusiasm, but nobody crossed any lines of acceptable scientific behavior. Even though the pentaquark hunt didn’t turn up the big prize, it still stimulated a lot of new ideas. And the enthusiasm reflects the excitement among physicists as they pursue new science.

In the day-to-day of pushing the boundaries of science, it is possible to lose sight of the human face of physics. Fortunately, that never lasts long. There is always a fresh story about how a member of our community is so much more than the job they do. Together with the great discoveries ahead of us, the people around us make our scientific adventure fun.David Harris, Editor-in-chief

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commentary: lee sawyer

Katrina aftermath challenges research institutionsThe history of Louisiana is closely intertwined with tragedies. My father, who turns 90 this fall, vividly remembers the Great Flood of 1927. “You could take a boat from Monroe, Louisiana, to Jackson, Mississippi,” he says, a trip of over 120 miles.

Less than eighty years later, in fall 2005, the combined fury of hurricanes Katrina and Rita produced the worst natural disaster ever to strike the United States. New Orleans, one of our most unique and most beautiful cities, was emp-tied. Many other towns along the coast, where the Cajun and Creole cultures have endured for centuries, were wiped off the map.

In the wake of Katrina and Rita, at least 17 college and university campuses were closed, displacing around 80,000 students in Louisiana. At the K-12 level, nearly a quarter of a million students were without schools, a result of dam-aged school buildings. Among the universities affected was Xavier University in New Orleans, which graduates the largest number of African-American physics baccalaureates in the nation. Two research universities in New Orleans, Tulane University and the University of New Orleans (UNO), were hit hard as well.

Louisiana Tech University, where I teach and do research in particle physics, is located in Ruston, 300 miles northwest of New Orleans, far enough inland to spare it from the worst. Even here, the hurricanes disrupted life and delayed the start of classes until September 12.

One of my physics major students, who had gone home to New Orleans for the summer, called me from an evacuee center in Houston. When he called, he just wanted to talk about carbon nanotubes, not the two days he and his mother had spent on an on-ramp of Interstate I-10, waiting to be evacuated. He was able to get a flight from Houston, and he stayed with me until he could move into a dormitory.

While Louisiana Tech students had a university they could return to, students at universities in New Orleans were less fortunate. They were desperate to find a new academic institution as quickly as possible, despite having no transcripts or other records. Helping as much as possible, campuses throughout the state, and beyond, allowed these students to register, basically accepting a student’s word about which classes were needed and whether prerequisites were fulfilled.

Louisiana State University in Baton Rouge, about 90 miles from New Orleans, accepted nearly 3500 displaced students; Louisiana Tech

University welcomed several hundred students. A physics major from UNO stayed with me throughout the fall quarter; he had arrived with only the clothes on his back.

Louisiana Tech also helped displaced families. The university reopened a dormitory that had been scheduled for demolition and made it available to both displaced students and their families. Three hot meals a day were provided at no cost to the occupants, as well as clothes, linens, and other necessities. Some displaced families stayed until January 2006. Land belonging to the university was made available for a “FEMA Village” of trail-ers. We hosted the Tulane football team and coaching staff.

The hurricanes seriously damaged the region’s research infrastructure: labs and equipment were damaged; biological and chemical samples were destroyed; MRI magnets quenched; computers were flooded; papers were lost. The list goes on and on. Facing this desperate situation, graduate students and postdocs permanently abandoned their projects. The life’s work of many researchers was lost; some faculty members who had evacu-ated simply did not return to their universities.

While funding agencies have been extremely helpful to researchers, the lost infrastructure will take years to rebuild. According to one estimate, the storms affected 54 percent of Louisiana researchers who are eligible for National Science Foundation funding.

Louisiana is making progress, however, with its research infrastructure. The LIGO observatory in Livingston and the NASA-Michoud assembly plant in New Orleans quickly resumed operations. Louisiana Tech took deliver of its new super-computer last fall. Within a year, the Louisiana Optical Network Initiative grid will become the nation's largest university computing facility: computing power of 100 teraflops, connected by 40-gigabits-per-second optical fiber bundles.

Natural disasters have tested the resilience of Louisianans repeatedly. This is, after all, the home of a drink called a Hurricane (known for knocking over the uninitiated). Now the resil-ience of Louisiana’s research infrastructure is being tested as well.

Lee Sawyer is associate professor of physics and physics pro-gram chair at Louisiana Tech University. He works on the DZero experiment at Fermilab and on R&D for the proposed International Linear Collider.

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Secret of the hidden ledger; zoo events; Brookhaven celebrates diversity; making

science K’nex-tions; vacuum cleaners rescue neutrino horn; Einstein still a

big earner; poker-playing physicist; Antarctica in California; cartoons by design;

pentaquark references; particle ‘Jeopardy.’

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Secret of the hidden ledgerWhen exploring the mysteries of the universe, don’t neglect the floorboards. Last December at Fermilab, repairs to the ceiling over the kitchen in the Aspen East users’ center, tar-geting a joist that had distorted the floor of the dorm room above, produced some startling debris. A small black book lay among the rubble, with the words “Aurora National Bank— ‘The Bank under the Chime Clock’” engraved in faded gold letters on the cover, and the name “A.C. Logan” peeking through a clear plastic window. Inside, brittle and mildewed pages showed handwritten deposit and credit statements spanning from January 8, 1927, to December 3, 1927. Many of the entries were for hundreds

of dollars—the equivalent of thousands of dollars today, according to the Bureau of Labor Statistics.

A story in Fermilab Today prompted quick and thorough detective work. Bill Griffing, head of the lab’s Environment, Health, and Safety office, came up with a match in US census records. Arthur Chester Logan was born in Illinois on January 12, 1885. Logan worked in Aurora, Illinois, as an electri-cal contractor, living with his wife Stella at 312 Bangs Street. The Aspen East building was originally located on Bangs Street before being moved to the Fermilab site. Logan died in 1938 at 53. Sue Populorum, of the lab’s Facilities Engineering Services, found his gravestone information in a registry for Spring Lake Cemetery in Aurora.

There has been no answer to Logan’s ledger entries. “I think more than anything it’s kind of fun and exciting to try to figure out a little bit of a mystery—a Fermi mystery,” says Linda Olson-Roach of the lab’s Accommodations Office, housed in Aspen East. “We wish the person was alive to talk to so we could fill in the blanks.”Jennifer Lauren Lee

Zoo eventsWhen physicists at Fermilab smash particles together, most of what comes out of the colli-sions is well understood. But every once in awhile strange things appear in the data— incidents popularly known as zoo events.

Dave Toback, a Texas A&M University professor who works on the CDF experiment, says

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zoo events are rare by defini-tion, but occur frequently enough to catalogue—like ani-mals in a zoo. “The idea is that you try and collect these animals so you can study them,” he says. Toback uses a program called “ZooFinder” that monitors collision data and sends emails to him and other physicists when zoo events occur. “Every so often,” he says, “we’ll get other physi-cists together to try and look at the zoo.”

Although the exact origin of the “zoo event” term is cloudy, Henry Frisch of the University of Chicago says the concept has evolved into a systematic strategy for finding new phys-ics. “Keeping a sharp eye out for anomalies is a big part of trying to bust the Standard Model of physics,” Frisch says, “because we really don’t know what we’re looking for.”

Because anomalies like cosmic rays and improper detector readouts can cause

zoo events, some physicists are cautious about using them as a basis for discovery. But Frisch says using the correct approach can be fruitful.

“One has to be very careful not to attribute new physics in cases where it’s not, and not to ignore new physics when it is,” Frisch says. Toback argues that unexplainable events are especially hard to ignore. “Many great discoveries weren’t made with a ‘eureka,’” Toback says. “They were made with a ‘hmmm, that’s funny.’” Dave Mosher

Brookhaven high-lights unityFlags, arts and crafts from dif-ferent nations, and a warm welcome transformed the DOE Brookhaven Site Office’s Second Annual Unity Day into a celebration of people and cultures working together. Says Site Office manager Michael Holland: “We’re fortunate here at BNL. We are a little slice

of the world community, all dif-ferent, yet we work toward a common goal: to perform world class scientific research.”

Diversity Office manager Shirley Kendall was accompa-nied by representatives of several Brookhaven Employee Recreation Association cultural clubs: the African American Club; the Asian Pacific American Association; the Gay, Lesbian, or Bisexual Employee Club (GLOBE); and the Hispanic Heritage Club. Deborah Bauer of GLOBE emphasized the need to treat each other with respect. “If the target of a joke or remark is offended, that’s harassment,” she explains. “It’s how the target feels that is the deciding factor.”

An international buffet and quiz games based on interna-tional cultures completed the day. Kendall concluded: “Unity Day is one tradition I hope has a long life at BNL.”Liz Seubert, Brookhaven National Laboratory

DOE Brookhaven Site Office personnel who helped provide or organize the international exhibits for the Second Annual Unity Day were: (from left) Patricia Quit, Emily Lalima, Mohammad Ali, Nand Narain, Judy Badal, Lou Sadler, and Jerald Bond.

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Making science “K’nex”tionsStanford Linear Accelerator Center librarian Lesley Wolf needed a creative idea for the next library display. Ten-year-old Connor Reed had lots of free time this summer and an extensive set of K’nex, the flexible equivalent of Lego.

The results of their collabo-ration are now on display in the library: a lime-green, blue, and orange model of the Linac Coherent Light Source (LCLS), complete with a rubber-band-powered injector that acceler-ates a smiley-faced ball dubbed “the happy electron.”

A flag reading “Pief’s portion” flies above the linear accelera-tor part of the model, “because he knows Pief built the linac,” says Connor’s mom, Ellie Lwin. She works for lab founder Wolfgang K. H. “Pief” Panofsky.

“This is how it shoots parti-cles,” Connor says, pulling back on the pinball-like handle and releasing it. He’s used this

rubber band technology before to make a pinball machine out of K’nex. The lime-green waves are the undulators, the magnets that force the electrons to make X-rays.

“I built it. I got a little help from my mom and Leslie,” he says.

Lwin says her son was happy to delegate construction of the more monotonous parts while he napped.

After spending months in the hospital last school year, Connor liked learning that LCLS will look at the proteins in cell membranes to find ways to keep viruses out of our cells and let medicines in. His version has a virus getting through the cell membrane and bright green medicine perched on top, ready “to take away the virus.”

Lwin said it took six or seven hours of trial and error to build the entire model and get the injector to roll the happy electron to the end of the machine. But Connor didn’t get frustrated; he delved into

solving the challenges, just like his mentor, Pief Panofsky. Heather Rock Woods

Shop-vacs to the rescueIn creating neutrinos for the MINOS experiment at Fermilab, the NuMI focusing horn deliv-ers batches of protons using intense magnetic fields gener-ated by 200,000-ampere pulses of electric current. The pulses deliver enormous amounts of heat. Without 36 gallons per minute of low-conductivity (or de-ionized) water for cooling, the horn would burn itself up. At 4:40 p.m. on Friday, June 30, the worst happened: there was no water flowing to the horn’s cooling nozzles.

About a gallon of tiny, leak-clogging resin beads, each each one fiftieth of an inch (half a millimeter) thick, had moved the wrong way through the de-ionized water system loop due to a failed check valve. They clogged the nozzles completely. Unclogging took more than three weeks of 20-hour days for the repair crews.

Sticky when wet, the beads blow away like grains of sand when completely dry. Using two vacuum cleaners on prototype components in another loca-tion, crews were able to suction out the beads. Kris Anderson, the engineer directing the cleanup, told some crew mem-bers go out and buy industrial-size vacuum cleaners. With 50 nozzles cooling the horn’s inner conductor, and 19 in the outer conductor, 69 nozzles had to be cleared. The horn was finally “buttoned up” on July 26, some 27 straight days of work later including the July 4 holiday and weekends.

Anderson can’t say enough about the dedication of the crews, some of whom worked near-80-hour weeks. Even the vacuum cleaners rated special mention. “They came right off the shelf, and they weren’t

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expensive,” Anderson says. “We ran those things 20 hours a day for three weeks, and none of them burned out. Whoever makes those things has a pretty good product.”Mike Perricone

E=mc($$$)With his genius and his unmis-takable appearance, Albert Einstein is an icon of both sci-ence and culture. Since his passing Einstein has inspired films, books, and even an opera, Einstein on the Beach. Not surprisingly, his popularity pays off handsomely.

In its July 3 issue, Forbes magazine ranked deceased celebrities according to their annual revenues. Einstein came in third, earning $20 mil-lion in 2005 for the Hebrew University of Jerusalem, which inherited his estate.

Approximately $5 million came from the use of his image, and more royalties came from Disney’s line of educational vid-eos and toys, “Baby Einstein,” which generated $400 million in sales last year.

Einstein’s earnings followed those of Elvis Presley ($53 million) and Kurt Cobain ($50 million) on the list. Rounding out the top five were Andy Warhol ($16 million) and Marilyn Monroe ($8 million). Benjamin Berger

Theorist dreams big and wins $4 million “Since middle school, I’ve always had plans to get rich,” says Michael Binger, a theoretical particle physicist at Stanford Linear Accelerator Center. On August 11, 2006 his dream came true: Binger placed third at the World Series of Poker Championships in Las Vegas and walked away with $4,123,310. The no-limit Texas Hold’em tournament drew nearly 9000 entrants, with each paying a $10,000 “buy-in” to supply the $87 million later apportioned among the top 10 percent of players.

“The championship included all the best players on earth, and a lot of the worst players,” Binger says. “It’s about knowing how to weave your way through

people and survive.” Stakes were raised every two hours. At the 36th level, the minimum bet was $400,000. After another player folded, leading chip holder Jamie Gold drew a straight to beat Binger’s pair of tens, landing the SLAC physicist in third place.

Binger recalls a year-long surreptitious game of seven-card stud in his high school sophomore chemistry class. He moved from blackjack to poker in 2001. After winning a thou-sand dollars on a good day at Lucky Chances south of San Francisco, he tried a table with higher stakes. “I stepped into that and got killed,” he says. “I realized there was more to the game than I’d known.” Binger studied books on poker with the goal of winning back the $10,000 he had lost, and did so within months. “Blackjack is entirely solvable,” he says, “but poker always involves adjust-ing to the precise environment. That environment includes the vagaries of opponents’ psy-chology—as well as luck.”

Over the last five years, Binger has spliced forays into poker with earning a doctorate in theoretical particle physics from Stanford. Beyond skills in probability and statistics, Binger says “there’s very little direct overlap” between physics and poker. While doing research at SLAC, Binger plans to com-pete on the poker tournament circuit about once a month. He says he will keep financial plans modest—unless he’s bluffing.Krista Zala

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signal to background

Antarctica, CaliforniaWhen researchers at Stanford Linear Accelerator Center realized their distance from Antarctica was a scientific inconvenience, they set about crafting an icy world of their own in Menlo Park, California.

For two months beginning December 2006, the Antarctic Impulsive Transient Antenna (ANITA) array, a new NASA probe, will circle the South Pole aboard a high-altitude balloon, seeking signs of neutrinos hitting the ice below. But for researchers to make sense of ANITA’s measurements, they needed to first calibrate the 20-foot-tall detector. They brought the detector to SLAC in June where the high-energy electron beam was ready to use. All they needed was ice.

A truck rolled in through SLAC’s gates, loaded with more than 10 tons of ice for a crew of workers to build a mini-Antarctica within a hangar-sized experimental hall. Overhead, the antenna array dangled from a gantry crane, ready to observe.

Collaborators then blasted the ice with a beam of electrons to create radio waves, perfectly tuned for calibrating the detec-

tor. When ultra-high-energy cosmic neutrinos strike the Antarctic ice sheet, they can also generate radio waves for ANITA to detect.

In addition to radio waves, the electron beam causes bright blue flashes of Čerenkov radiation, created whenever a charged particle moves faster than light through a dense medium, such as ice.

Just as those present saw the flashing blue light in a Californian ice sheet, a lucky observer on the Antarctic ice might occasionally see a similar Čerenkov flash, the sign of passing cosmic neutrinos.Brad Plummer

See a video clip of the ice glowing with Čerenkov light in the online edition of symmetry

Cartoons by designAs a mechanical designer, Catherine Carr’s first big under-taking at SLAC was a vacuum transporter system that let oper-ators install electron cathodes, under vacuum, into the injector gun of the Stanford Linear Collider. The previous system of exposing the gun to air in order to replace the cathode required shutting down the collider for

long periods. By eliminating the need to expose the cathode gun to air, the new equipment increased the uptime of the accelerator and improved its most important characteristic, high electron polarization.

Over the course of the proj-ect, Carr would frequently leave her office to visit her team members in Building 40. Each time, she spent a few minutes adding to a cartoon drawing on a chalkboard located outside Room G137.

“It was a way to channel lots of nervous energy,” she says.

The chalk-and-pastel work remains today. Pictured are project supervisor Bob Kirby and machining supervisor Jerry Collet driving a caravan to the edge of contemporary knowl-edge, with the magician’s rabbit —and SLC Injector project man-ager—Lowell Klaisner along for the ride. A young woman peeks out of a window below. “I’m running away with the circus, and I’m pretty happy,” says Carr.Krista Zala

Carr created several other cartoons over the course of the project, one of which is featured in the online version of this story at www.symmetrymag.org.

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The pentaquark rushIn 2003, results published by three experimental collabora-tions initiated a flood of papers about a class of particles known as pentaquarks. Physicists working on the LEPS, DIANA, and CLAS experiments had observed subatomic processes that seemed to indicate the existence of composite particles consisting of five quarks. Ordinary matter particles, such as protons and neutrons, only contain three quarks. The exis-tence of pentaquarks would provide an important test for the theory of the strong nuclear force.

Since then more than 445 papers with the word “pen-taquark” in the title have been recorded in the spires data-base (see graphic), including over 50 papers with experi-mental results. The majority of the papers has come from theorists performing analyses and computations to provide further insight into the obser-vations and to make predic-tions for additional five-quark signals.

Standard particle theory allows for many types of quark-composite particles, a fact that theorists have known for more than 30 years. While some quark combinations are forbidden, the quark model permits the existence of pentaquarks. Yet physicists

published few papers dedicated to pentaquarks before the 2003 announcements. For the period from 1974 to 2002, the spires database contains only 32 papers that refer to “pen-taquark” in their titles. The first of these papers was published in 1989, twenty years after Murray Gell-Mann received the Nobel prize for developing the quark model.

The pentaquark, however, might return to oblivion. Experimental results of the last three years have raised doubts whether the signals published in 2003 represent pentaquarks (see story on page 16). The CLAS experiment at Jefferson Laboratory as well as other experiments with large data samples that should have con-firmed the initial results have found no significant signals.Heath O’Connell

Particle JeopardyNext time you watch the Jeopardy quiz show on TV, don’t be surprised if you learn about a particle physics experi-ment at Fermilab. Earlier this year, candidates were asked to give the question whose answer is: “This 8-letter particle, named for its lack of charge, is being studied by beaming it 450 miles in .0025 seconds.” For physicist Jeff Nelson, assistant professor at the College of William & Mary, the answer was

easy; unfortunately, he was watching at home, not partici-pating on the show.

Together with about 200 col-leagues, Nelson works on the MINOS experiment. The scien-tists examine the properties of this sought-after particle as it travels close to the speed of light from Fermilab to a particle detector located in an old iron mine in Soudan, Minnesota. “You know you’ve made it when you’ve inspired Jeopardy,” Nelson says with a smile.

So how did he manage to get a photo of the Jeopardy question on TV when a rerun of “Episode 172-Tournament of Champions” aired in August? “I do tape Jeopardy every day on my digital video recorder,” he says. “My wife and I have a nightly grudge match. One point for the first correct answer to each question.”

On this particular night, Nelson took advantage of his MINOS research, being the first to shout the correct answer: “What is a neutrino?”Kurt Riesselmann

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New life for a linac

by Heather Rock Woods

How the Stanford Linear Accelerator Center is transforming the world’s longest linear accelerator into a novel X-ray laser.

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The Linac Coherent Light Source, currently under con-struction at Stanford Linear Accelerator Center, starts with the existing linear acccelera-tor and adds new sections to complete an X-ray laser.

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Forty-year-old scientific equipment tends to live in storage closets, recycling yards, or the occasional museum. However, the 3-kilometer-long Stanford Linear Accelerator, built in 1966, is merely reaching middle age.

Still doing what it knows best—boosting bunches of electrons to near the speed of light—the linear accelerator, or “linac” to its friends, will soon start a new stage of life. As the source of electrons for a new type of laser, it will be able to see materials, atoms, and molecules, in a completely new way, illuminating new vistas on clean energy, medicine, nanotechnology, and planetary science.

The linac already has an impressive résumé. At the top of the list, no doubt, are the three Nobel prizes it helped to win. It has contributed to a surprisingly wide range of experiments in particle physics, astrophysics, photon science, high-energy nuclear physics, and accelerator science. It also holds a number of titles, such as longest linac and first linear collider.

A cadre of engineers, construction crews, physicists, and designers is preparing the linac for its completely new job—electron production for a powerful, innovative X-ray laser, the Linac Coherent Light Source (LCLS). In seizing this exciting opportunity, the linac repositions itself as a major player in the future of light source science and the future of Stanford Linear Accelerator Center (SLAC). Tunnel digging and other major civil construction will begin in the coming fiscal year, but signs of LCLS construction are already evident at SLAC.

“SLAC’s got a huge advantage. We’ve got the linac. We’re saving hundreds of millions of dollars and we have the infrastructure and expertise of the lab itself.”

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Free electronsLCLS will operate as a light source with a two-stage process. First, it will create extremely short, tightly-focused electron bunches, the kind only linear accelerators can make. Then, those bunches of electrons will be used to create X-rays of the intensity, duration, and coherence needed for experiments.

When the LCLS commences operations, it will join a new breed of light source called the free electron laser (FEL). Existing FELs operate in wavelengths from the low-energy infrared through to the higher-energy X-ray region. However, LCLS will be the first to operate at the highest-energy hard X-ray wavelengths, ideal for probing the fleeting motions of atoms and molecules. Using the linac’s well-shaped bunches of electrons, “free” from being bound to atoms, LCLS will turn out pulses of light that are mere millionths of billionths of a second in duration, blindingly brilliant, and coherent like a laser, with all the light waves lining up in step.

Thanks to the linac, these amazingly useful pulses will start flashing soon, in 2009. “SLAC’s got a huge advantage. We’ve got the linac. We’re saving hundreds of millions of dollars and we have the infrastructure and expertise of the lab itself,” says John Arthur, LCLS systems manager for photons. Even with those savings, the LCLS is still an enormous project, with the US Department of Energy’s Office of Science contributing about $400 million.

Instead of having to build from scratch, the lab saves years of construc-tion time as well. LCLS partners, including the Advanced Photon Source at Argonne National Laboratory, Lawrence Livermore National Laboratory, and the University of California, Los Angeles, are designing and building some of the essential parts, such as the undulator magnets and X-ray optics.

Several other FEL projects are being planned or constructed around the world. The German laboratory DESY opened a far-ultraviolet/soft X-ray FEL in 2005 and is planning a hard X-ray FEL to start operation in 2012. SPring-8 in Japan begins construction this year on an X-ray FEL to be completed in 2010 after a prototype operated successfully in July.

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A sketch of the new under-ground facility that will extend the linac to create the LCLS.

Source: Image courtesy of the LCLS project, SLAC

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Outfitting the linacX-rays only appear after electrons flow from an initial electron injector, through the linac, and finally into the undulator hall. Although the front and back ends will be entirely new, the linac requires surprisingly few changes.

The process starts one kilometer before the end of the existing three-kilometer linac. There, a new injector is being installed to make electrons. From the very beginning, the electron bunches are shorter and more tightly focused (called low-emittance) than those currently made by the linac’s main injector.

In the new injector, a laser strikes a copper plate, called a cathode, forcing it to emit electrons. With each pulse of the laser, the cathode lets loose about six billion electrons. Right away, the newly-freed electrons are accelerated to near the speed of light, the only way they can tolerate being closely packed. New accelerating structures boost the electrons’ energy symmetrically from two sides. Like controlling a soccer ball with two feet instead of one, this dual boost keeps the electron bunches better contained and prepared for acceleration in the linac.

“You need a very high-quality electron beam. It’s all designed to put elec-trons into a very small volume and keep them there,” says Arthur; it takes a very dense clump of electrons moving in the same direction to make them act as a laser.

Crews finished construction on the building that houses the new injec-tor in May. The drive laser arrived from France in July.

Views of a 3-D model of the linac and LCLS from an animation available online at www.symme-trymagazine.org

Animation: Greg Stewart, SLAC

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SqueezedFollowing the electrons downstream, the biggest change to the linac takes place almost immediately, where bunch compressors will cram the electrons into even tighter packages.

This fall and next, during the linac’s scheduled maintenance shutdowns, workers will remove 39 meters of existing accelerator structures to make room for the two bunch compressors. The first bunch compressor bends the beam through a series of magnets to squeeze each electron bunch from one-millimeter length down to 200 micrometers (one fifth of a millimeter).

Trouble starts in the second bunch compressor, where the bunch is squeezed down by a factor of ten, to 20 micrometers. Here is where the scourge of particle-physics experiments rears its ugly head.

When an electron bunch changes direction, as when it is bent by a magnet, it emits light—synchrotron radiation. If that light is emitted in step rather than randomly, it is called coherent.

“Coherent radiation is what you want in the undulator [laser cavity]. It’s why we’re making short pulses and low-emittance beam in the linac,” says David Schultz, LCLS systems manager for electrons.

While coherent light is what makes lasers so useful and powerful, it disrupts the electron bunches as they travel through the linac. To restrain in the linac the exact thing that they count on later to make the X-ray beam, physicists are making the second bunch compressor much longer than the first, which allows the electrons to take a gentler path and emit less radiation.

“Coherent synchrotron radiation is a problem all FELs face. We control it in one stage, and use it to our advantage in another stage,” says Paul Emma, head of the LCLS accelerator physics group.

After the bunch compressors, the electrons will see few changes. The linac will accelerate the beam from 4.5 GeV (billions of electronvolts energy) to 14 GeV, and keep it focused with new magnets. These magnets can be turned off when the linac runs at higher energy for particle-physics experiments.

“We have to be able to switch between the old and the new ways of operating. We don’t want to destroy old functionality,” says Emma.

SLAC’s main high-energy physics experiment, BaBar, can continue running unhindered because it uses only the first two-thirds of the linac.

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Just add lightThe end of the linac is not the end of the line for the electrons. The bunches, now 20 micrometers long and 50 micrometers in diameter, will coast 500 meters through new beam pipe to the undulator hall.

The electrons enter 130 meters of undulator magnets, containing 6000 north and south magnetic poles. As the poles flip signs, the electrons take a slalom course, emitting photons as they go. The emitted photons interfere with the electrons in each bunch, forcing electrons to clump together in “micro-bunches.” Each micro-bunch then radiates the desired coherent X-ray light with a wavelength of 1.5 Ångstroms (0.15 billionths of a meter).

In a self-amplifying loop characteristic of a laser, the emitted X-rays stimulate the micro-bunches to release even more photons, flooding the beam pipe with a brilliant beam of coherent X-ray light.

At the end of the undulator hall, the X-ray beam heads off to the exper-imental hutches where it is used for experiments, while the electrons are sent to a “beam dump,” a chunk of copper that soaks up the once-free electrons.

Construction zoneMuch construction work will take place in the next two years before the electrons can venture beyond the linac.

David Saenz, systems manager for conventional facilities, presides over the additions: half a mile of new beam enclosures, above and below ground. A research and office building will also be erected above the near experimental hall.

Last spring, crews removed a relatively small but extremely successful research facility, the Final Focus Test Beam, to make room for the beam pipe that will carry electrons from the linac to the undulator. They are also clearing smaller buildings in the Research Yard at SLAC to make way.

In the Magnetic Measurement Facility, completed in April, physicists and technicians have begun testing and tuning the first of 33 individual undulator magnets to arrive from Argonne National Lab. The LCLS will begin operating with one linac, one undulator hall, and six experimental stations. In the future, the one-and-only linac might call upon two-thirds or even all of its length to supply up to six undulator halls, and many more experimental stations.

As major construction readies, Saenz says, “It’s going to be so much fun, I just can’t wait.” Indeed the laboratory eagerly anticipates the next stage of life for the linac. Conversion to an X-ray lightsource makes the 40-year-old linac young again, with as much accomplishment ahead of it as has gone before.

Although initial results were encouraging, physicists searching for an exotic five-quark particle now think it probably doesn’t exist. The debate over the pentaquark search shows how science moves forward.

The rise and fall of the PE NTAQUAR K

by Kandice Carter, Jefferson Lab

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Three years ago, research teams around the world announced they had found data hinting at the existence of an exotic particle containing five quarks, more than ever observed in any other quark-composite particle. More than two dozen experiments have since taken aim at the particle, dubbed the pentaquark, and its possible partners, in the quest to turn a hint into a discovery. It’s a scenario that often plays out in science: an early theory or observation points to a potentially important discovery, and experimenters race to corroborate or to refute the idea.

“Research is the process of going up alleys to see if they are blind,” said Marston Bates, a zool-ogist whose research on mosquitoes led to an understanding of how yellow fever is spread. Throughout history, taking different pathways has often led to new research tools, far-reaching insights and even great scientific discoveries.

But whether any particular alley leads to a discovery or a dead end can only be determined by experiment.

A historical debateThe æther is a classic example of an alley that led to nowhere. Greek philosophers introduced the idea of the æther thousands of years ago, arguing about the nature of the universe. Ancient Sanksrit tablets refer to the æther as the fifth element (after earth, air, fire, and water), and Aristotle proposed it as the substance of which

stars are made. Yet he and his peers had no means to verify its existence.

Luminaries of 16th-19th century physics, including Newton, Fresnel, Stokes, and Maxwell, debated at length the properties of their physi-cal version of the philosophical concept, which they called ether.

The ether was a way to explain how light could travel through empty space. In 1881, Albert A. Michelson began to explore the ether concept with experimental tools. But his first experiments, which seemed to rule out the existence of the ether, were later realized to be inconclusive.

Six years later, Michelson paired up with Edward W. Morley to devise the now-famous experiment that ruled out the ether by examining the speed of light in two different directions. Known as the Michelson-Morley experiment, it produced the most famous null result in history, signaling the scientific end of an idea that pre-dates science itself. Like many scientific debates today, getting to the conclusion about the ether was a back and forth process between theory and experiment, with no lightning-flash answer deliv-ered from a single experiment.

Experiments that first hinted at signs of a pentaquark produced graphs like the one shown. The peak seemed like it might be the signal for a pentaquark but determining whether it was a random fluctuation or a real signal required more data collection.

2003 2004 2005

Key existence no evidence

Experiments searching for the pentaquarks either showed evidence for their existence (yellow dots) or found no evidence of pentaquarks (blue dots). After a series of early suggestive results, an increasing number of experiments seemed to rule out the pentaquarks.

Source: Chart created by Sandbox Studio from data in R.A. Schumacher, Particles and Nuclei International Conference (PANIC'05), 2005, nucl-ex/0512042

Predicting a five-quark particleExperiments in the 1950s and 1960s were crucial to establish quarks as the fundamental building blocks of matter. Clumping in pairs and triplets, quarks and antiquarks make up particles such as pions and protons.

In 1997, theorists from the Petersburg Nuclear Physics Institute in Russia were investigating the implications of quantum chromodynamics, the theory that describes the behavior of quarks. QCD, formulated in the 1970s, is a complicated theory; performing calculations with it often involves approximate models and techniques. Maxim Polyakov, Dmitri Diakonov, and Victor Petrov were using a specific model that had pre-viously had some impressive predictive suc-cesses to better understand some features of quark behavior.

As they studied the model, they discovered that it predicted the existence of a new family of particles, the pentaquarks. Unlike protons, which consist of three quarks, or pions, which contain a quark and an antiquark, each pentaquark has four quarks and one antiquark. Although pen-taquarks had never been observed, the general rules of quark theory allow this combination of quarks and antiquarks to exist.

The calculations performed by the Petersburg trio predicted a pentaquark, named “Theta-plus,” that contains three different flavors of quarks: two up quarks, two down quarks, and a strange anti-quark. The presence of the strange antiquark should make the particle uniquely identifiable in experimental searches, giving it a property called strangeness. Armed with this specific informa-tion, several experimenters turned their attention to the finding the Theta-plus and its partners.

Hint at a discoveryIn the spring of 2003, experimenters from the SPring-8 laboratory in Japan announced the first potential pentaquark sighting, finding hints of the particle in experiments in which energetic gamma rays hit carbon-12 atoms, creating quark clusters. That same year, researchers from Jefferson Lab, the Alikhanov Institute for Theoretical and Experimental Physics (ITEP) in the Russian Federation, and the Electron Stretcher and Accelerator (ELSA) in Germany, announced that they, too, might have spotted tantalizing hints of the Theta-plus in data previ-ously taken in other experiments.

It is in a hint of a new particle that the chal-lenges of particle physics become very obvious. The data recorded in a particle physics experi-ment are rather messy as lots of particles emerge from a single high-energy particle colli-sion. Because of their short-lived nature, most particles leave no obvious signature in the parti-cle detectors, and experimenters need to rely on sophisticated particle reconstruction software and detailed statistical analyses to determine the properties, or even the existence of a particle.

Raising doubtsIn the case of the pentaquark, physicists not involved in the initial experiments soon ques-tioned the observations. Simultaneously, authors of some of the original papers began refining the statistical analyses of their results; careful re-evaluations of the data and more sophisti-cated statistical methods led to less confidence in the existence of the pentaquark.

Pentaquark enthusiasm, however, had taken hold, and many more experimental groups were

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conducting their own searches for the exotic parti-cle. While some higher-statistics searches for the pentaquark began reporting null results, others seemed to find signs that pentaquarks existed.

Meanwhile, theorists were busy trying to understand the potential particle, performing cal-culations for production mechanisms and proba-bilities. Some of those calculations confirmed the possible existence of pentaquarks, but not always at the same energies where experiments were seeing hints.

To resolve the issue, physicists began to set up dedicated experiments that would either make precise measurements of the pentaquark or rule out certain production mechanisms. In April 2005, a group from Italy’s Istituto Nazionale di Fisica Nucleare in Genova announced results from a high-precision measurement at Jefferson Lab. Examining the same reaction that pro-duced the positive result at ELSA in 2003, the new experiment, which collected one hundred times more data and hence produced much bet-ter statistics, found no evidence of the pen-taquark. Other higher-statistics results have done likewise. “If it’s there, I don’t see how it could have escaped the higher statistics in this experiment,” says Ken Hicks, an Ohio University researcher in the field.

What is the final answer? As it turns out, the tales of both the ether and the pentaquark are still incomplete; hidden doors may lurk at the end of what appeared to be blind alleys. Although the ether as defined by Newton—as a medium needed for the propagation of

light—does not exist, space is not empty either. Quantum theory describes the vacuum less like an expanse of emptiness between subatomic particles and more like a field transmitting force and energy, a seething breeding ground of sub-atomic particles. Although this description of the vacuum doesn’t fit with Newton’s narrower defi-nition, it does mesh eerily well with the ancient concept of the æther as an unseen, all-pervasive medium filling space.

And the pentaquark is not dead either. Some production channels remain open. “The evidence is not conclusive. Is there something that is irrefut-able? No, not yet,” says Andrew Sandorfi, a scien-tist at Brookhaven National Lab who’s reviewed the literature.

The pentaquark’s legacy is still unknown. “It certainly stimulated a lot of thinking in the area of quantum chromodynamics,” says pentaquark expert George Trilling, a Lawrence Berkeley National Laboratory researcher who provided the pentaquark summary in the Particle Data Group’s Review of Particle Physics.

Whether positive or null, each experimental result brings physicists closer to an understand-ing of the universe. Ruling out the presence of possible subatomic particles is just as important as finding new ones. Without the searches, sci-entists would never know if these particles were out there, waiting to be discovered.

Even though the pentaquark seems to be illusory, at least in the form physicists have pursued so far, the alley leading toward it has been full of interesting revelations.

Pentaquark

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In one type of experiment, gamma rays hit carbon-12 nuclei, which leads to the creation of various other particles. Theoretically, these could include a pentaquark, which would quickly decay into other particles. Physicists try to reconstruct this process from the final particles seen in the experiment to determine whether the pentaquark was actually created.

Illustration: Sandbox Studio

2020

Globe-traveling physicists put some of their best thinking into strategies for their bags—all carry-ons, of course.

by Ben Berger

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Physicists are regularly dashing all over the world for collaboration meetings, conferences, lectures, and summer schools. Trying to contact them to ask about their travels invariably yields the same response: “I can’t talk right now. I’m traveling.” Once they’re finally pinned down, their travel tales extend to the most exotic realms.

“When I was younger, like nine or 10, I used to read National Geographic a lot,” says Barry Barish, now the Director of the Global Design Effort for the International Linear Collider. “I remember reading about Antarctica and Lake Baikal in Russia. Then, as a physicist, I got a chance to visit those places. I went to Antarctica because I am on the board of the National Science Foundation, which supports several Antarctic research projects, including the neutrino experiments, amanda and Ice Cube. The scenery was amazing—makes the Grand Canyon look like, well, I don’t know, but not as special as we think of it. Lake Baikal was amazing, too. The Lake Baikal Neutrino Telescope experiment places detectors at the bottom of the lake. In winter, they cut holes in the ice in order to lower the detectors.”

Albrecht Karle of the University of Wisconsin-Madison says, “Whenever I go to Antarctica for Ice Cube, I always pack my own coffee, coffee maker, and some chocolates. They don’t have chocolate down there, and they make awful coffee.”

Three principles seem true for all peripatetic physicists. One: Avoid checking a bag if humanly possible; if you must check a bag, it should never contain work-related items. Two: The most important item you have with you is your laptop; it should never leave your side. Three: Try to appreciate the uniqueness of every destination, but in the end, the best airport to reach is the one at home.

Photos: Sandbox Studio

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Bag it “On my first trip to Japan I was to attend a conference at KEK. I landed in Tokyo and knew I had to take a bus to Tsukuba. Unfortunately, no one spoke English and I don’t speak any Japanese. I tried to find the bus, but couldn’t figure out what bus I needed and no one could help me. I was com-pletely lost and felt very pan-icked. It was only by chance that I happened to see a physi-cist in the airport who could help me. I could tell because he had a bag from a physics conference.” —Olga Mena, Fermilab

Gender specific “I don’t think I pack too lightly, but my wife does hate me. Wife: ‘Four days and just a shoulder bag?!’ Ted: ‘Why do I need more shoes then the ones I’m wear-ing? And if I don’t spill anything on these pants then I’m fine.’” — Ted Baltz, Stanford Linear

Accelerator Center

Keeping orderly “Computer. Charger. Cell phone. Cell phone charger. I can buy anything else I need. Being able to charge through USB was brilliant. Whoever figured that out deserves a medal. It’s a religion thing—never check a bag. When you go through security, you learn to put the things through in the order that enables you to most efficiently put them on again on the other side, so your shoes go on first and so on.” — Gordon Watts, University

of Washington

1-2-3 by Kaiser1. Ritualize your traveling as much as you can. Buy the same bottled water (San Pellegrino), the same choco-late (Rolo, perhaps Toblerone), the same magazine (Wired, or perhaps a film magazine, otherwise Vanity Fair. Avoid The Economist.)

2. If you are traveling with a colleague, you should still take an aisle seat, not a middle seat. Convince your colleague to take the seat across the aisle. Taking the middle seat because you are traveling with a colleague (or your group leader, or your student) leads only to resentment.

3. You also need the gold or platinum frequent flyer card to pre-board together with the business passengers, so that you can get all of your carry-on luggage stored in the overhead bin right at your seat.— Ralf Kaiser, University of

Glasgow, United Kingdom

Battery life “I avoid airplane chargers, extra laptop batteries and all that stuff. It’s just gotten to be ridic-ulous. I used to try and bring everything, but it’s become too much. I can’t take it anymore. I’ll do my 3 hours of work, or however long the battery lasts and that’s it.” — Albrecht Karle, University

of Wisconsin

The ‘Cosmo’ Physicist “I have to work on flights. During the school year, I’m con-stantly traveling between New York and Chicago, and I need my flights to prepare my class lectures. I have a really good trick for getting rid of really chatty guys, but it only works for women. I always carry a Cosmopolitan magazine with me. I just pull it out and they leave me alone. It really works. I just carry one with me for that purpose; there’s nothing in there really worth reading.” — Janet Conrad, Columbia

University

Read other physicists’ tales of packing and travel online at www.symmetrymagazine.org

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No surplus socks… “I pack the absolute minimum possible. I avoid checking anything into the hold if at all possible. Every sock is counted. By the end of a trip there is no surplus item. I can live out of two carry-on bags—a roll-on suitcase and a small backpack—for two weeks. But I’m stuffed now. With the new regulations I will have to check a bag, but I will maintain how I pack.” — Phil Burrows, John Adams

Institute at Oxford University, United Kingdom

…and no skyscrapers “Recently I was leaving SLAC, and a friend had given me, as a joke, a small metal model of the Hancock Building in Chicago. I was going through security and my bag got intense interest. They put it through the X-ray machine three times. They came over to me and asked what item in my bag had aroused suspi-cion. I responded, honestly, that I didn’t know. They asked me to open my bag, and they took out the model. It was run through the X-ray machine by itself and they were satisfied. I guess the Hancock building looks like an offensive weapon if it’s small enough.”—Phil Burrows

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gallery: robert straight

Pick a number: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97, 101, 103, 107, 109, 113…and so on…and on…and on…and on…

Get the picture? They did, in one way or another: Pythagoras, Eratosthenes, and Euclid, among the classical Greeks; Regius in the 16th century; Cataldi, Marsenne, and Fermat in the 17th cen-tury; Goldbach in the 18th century; Riemann, Landry, and Lucas in the 19th century; then computer after computer in the 20th and 21st centuries.

But Robert Straight gets the picture on prime numbers in a unique manner. A professor of painting at the University of Delaware, Straight had his work on display at the National Academy of Sciences in Washington, DC, through the end of September. In the exhibit, “Toroids and Plaids,” Straight uses prime numbers to construct forms and establish color placement on the canvas. He superimposes grids onto toroids, or curved lines that never meet. The grids are stable; the toroids create a sense of movement; it’s up to the observer to resolve the tension between stability and movement, and create an individual experience.

“Foremost, I hope that the paintings are visually compelling,” Straight says. “I hope that my audience will also see that the paintings are not arbitrary abstractions, but that they are related to the universe and our world. These paintings have many con-cepts and visual layers. They are influenced by artists such as Mondrian and Karl Blossfeldt, as well as by constellations. For instance, the grids are also a screen that can be seen as a mea-suring device, as well as a decorative plaid. Each of the visual elements is related to several ideas and meanings, which include science, art, and our society.”

With little formal exposure to mathematics or science, Straight has nonetheless adapted geometry as a basic element of his work. He has also integrated his growing interest in number sequences, along with what he describes as “the way computer technology has changed our world.”

“I have made paintings in the past, which are not in this exhibit, which were polygonal canvases with equal sides of 5, 7, or 11,” he continues. “The circle has been a major element in my work. I am drawn to absolutes in forms as well as sequences and for this reason I have used forms or sequences that are prime numbers. Almost all of the forms and shapes that I use in my work are constructed through simple geometry.”

While describing the forms as “simple geometry,” Straight acknowledges that the paintings in “Toroids and Plaids” repre-sent specific challenges to his skill and craft—as well as expanding both.

“There are certain painting techniques that were a result of these paintings,” he says. “The construction of the toroids required me to figure out ways of painting them without simply filling in

P-378, 2002acrylic on canvas60 1/4 x 48 1/8 inches

P-367, 2001–2003acrylic on canvas27 x 24 1/4 inches

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“Toroids and Plaids” Numbers are the prime elementBy Mike Perricone

the color. The grids are made by covering the paintings with color and then removing all but the lines with a squeegee. The way the paintings are executed, and the construction of the images, is all tied together in a fairly logical way which hopefully is not too easily detected.”

Throughout the spectrum of their individual visions and tech-niques, all artists share one particular interest in numbers—the numbers of people viewing their work. Straight welcomes the chance to reach new eyes and minds.

“I’m really excited about this exhibit,” he says, “because it’s at an institution that not only attracts art enthusiasts, but also those interested in the sciences. It’s wonderful that my work will be seen by a larger audience.”

P-366, 2001acrylic on canvas62 1/4 x 50 inches

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In the early 1950s, Nobel-Laureates- to-be Norman Ramsey and Ed Purcell created cards of physical constants they found themselves using most frequently. A few months later, an Addison-Wesley publisher’s representa-tive handed Ramsey a card filled with trivia. Ramsey responded, “Why don’t you give out something people really want?” The pocket table was born.

Harvey Lynch paid about fifty cents for his table when he was an undergraduate at MIT. Forty years later, now at Stanford Linear Accelerator Center, he still carries it. “I was always using it to find some constant,” Lynch says. “Of course, it would come up in the wrong unit and I would have to convert it.”

The switch to the SI system has obviated the mixed units. But the bigger change is with the numbers them-selves. “These numbers aren’t accurate anymore,” says Lynch. “I keep the card for purely sentimental value—though π is still good.”

Physicists’ obsession over what F. K. Richtmyer called in 1932 “the romance of the next decimal place” drives

innovations in technology, theoretical calculation, and exper-imental design. It also uncovers other information along the way: detecting the Lamb shift of energy levels in a hydrogen atom’s electron led to the whole foundation of quantum electrodynamics. Our capacity to sense mil-lionths-of-a-degree differences in cosmic microwave radi-ation lets astrophysicists compose a picture of the early universe.

Some research suggests that α, the fine structure constant, which determines the strength of the elec-tromagnetic force, may have decreased by a few parts in a hundred million since the dawn of time. Its relation to the speed of light would mean c has correspond-ingly increased. Any such change in nature’s “constants,” even at such a tiny level, throws physics into a scramble for new theories.

While some may see the pocket table as Ramsey saw the earlier trivia card, this quest for precision, ever fur-thered by comparing experimental values of constants calculated by different approaches, tests the overall coherence of physics.

Constant changes

deconstruction: particle pocket card

Front

Back

Actual size

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Text: Krista ZalaPocket card courtesy of Harvey Lynch

c What was then a measured value has shifted to a defined quantity. For decades c was measured to a precision of some few parts per billion using wavelengths from krypton-86, but the advent of lasers made the old approach obsolete. Rather than continually choosing more stable transitions, the Bureau International des Poids et Mesures decided to fix c, thereby shifting any uncertainty in its value to the definition of a meter. In 1983, del- egates for the international body governing such measures made the decision official. At the Conference Generale des Poids et Mesures, the speed of light was defined as exactly 299,792,498 meters per second. No experimental results will alter that value. Conference delegates also redefined the SI unit of the meter, without changing its value, based on this set quantity.

hRecent findings have landed Planck’s constant in the hot seat: values for h, derived from four electri-cal experiments and one X-ray crystal density experiment with silicon, differ significantly. Such uncertainty calls into question the related physical values. Current work is investigating this discrep-ancy by measuring anew the volume of highly enriched silicon. The BIPM is looking to fix Planck’s constant as a defined quantity by 2011.

G G, the Newtonian constant of gravitation, was first calculated using results from Henry Cavendish’s 1798 experiment to determine Earth’s density. Since then, it has seen little refining. G is perhaps the most difficult constant to measure. Strong though it may seem, at the subatomic level gravity’s tug barely compares to that of the other funda-mental forces. No shield exists to isolate experi-mental effects from the influence of other bodies’ gravity, so G’s precision is limited by experimenters knowing exactly what mass surrounds an experi-ment. Although an unusual result some years ago spurred a host of new experiments, “doing any better than 10 parts per million in precision is tough,” says National Institute of Standards and Technology scientist emeritus Barry Taylor.

R∞Rydberg’s constant, R∞, related to the wavelengths of an element’s spectral lines, ranks both among the most precise and most improved. Its precision, with an uncertainty of 6.6 parts per trillion, has increased by four and a half orders of magnitude since the pocket table was first published. It owes such gains to advances in theoretical work—particularly predic-tions of energy levels of the hydrogen atom—that broke new ground for experimental work.

αThe fine structure constant, α, has recently seen a great leap forward in precision to 0.7 parts per billion. The improvement came from a combination of a much better measurement of the electron’s magnetic moment µe, with an uncertainty of 0.76 parts per trillion, and a new set of theoretical cal-culations that relate α to µe. Any more refining by this approach will take a serious commitment: supercomputer calculations conducted over more than 10 years evaluated the 891 Feynman diagrams needed for the theoretical calculation. The next level of precision requires 12,672 diagrams.

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Visualizing physicsThe young people who will build our future appear to be largely unaware of how attractive and rewarding careers in science can be. We should not be surprised. In many high schools, physics is an elective subject lasting just a year, not nearly enough time to ignite curiosity in hungry minds.

For comparison, the Russian school curriculum makes physics mandatory from the fifth grade to the tenth. Thus, we should also not be surprised that the majority of graduate physics students in US universities are foreigners.

In this environment, popular books, magazines, and TV shows about physics must play a special role: elements of entertainment and education should go hand in hand. Science writers carry a mission of transmitting the appeal of physics to the general public, especially young people. The ability to envision physical concepts is critical to effective communication.

On April 5, 2005, I received a message from Leigh Simmons, a student at Minneapolis College of Art and Design. She wrote that she was part of a team in a Visualizing Physics class, developing a magazine on modern high-energy physics tar-geting the general public and high-school stu-dents in Minnesota. She asked whether I would agree to discuss the scientific aspect of their project with her team.

She wrote: “At the very least, we want to encourage students to be open-minded about modern theory, such as supersymmetry and strings, and future developments in physics.”

This message resonated with my persistent thoughts and concerns. My first encounter with Courtney Davis, Jesse Gadola, Leigh Simmons, and Katy Smith, which took place a few days later, showed that these charming students with vivid imaginations did their homework more thoroughly than I had expected. They went through Brian Greene’s The Elegant Universe with pencil in hand; carefully read Patricia Schwarz’s “Official string theory web site;” and compiled a large list of relevant questions that I was supposed to answer. Immediately, I under-stood that working with them would be fun.

During the next year, we had regular sessions, about once a month. My task was telling them about the finest aspects of modern high-energy physics in the way I thought they could under-stand. I recommended some additional literature. Their task was bringing me successive versions of stories and essays they produced, so I could look through them and tell them what needs to be done next. En route they did lots of graphic work creating illustrations based on ideas dis-cussed during the sessions.

What was the result? (m)agazine: (Genius I.Q. Not Required), a publication about modern physics for the general public, is available at http://stu-dents.mcad.edu/~lsimmons/m/magazine3.pdf.

Courtney, Jesse, Leigh, and Katy invested their hearts and minds in every word and every illustration. (m)agazine contains a wealth of funny articles, such as “Dealing with Dimensions:” “Supersymmetry,” and “String Landscape;” humor-ous fiction about Lenny Susskind, string theory’s advocate; a gallery, “Faces of the String Theory,” with imaginative comments; two incredible quizzes and lots of captivating pictures. It is hard to be impartial, for someone as deeply involved as I. Therefore, in search of an unbiased judgment, I gave it to a young string theorist, a graduate student couple, and a 15-year-old neighbor of mine, and asked for their reactions.

They all were fascinated. An example of their comments: “The girls did a great job, at a solid pro-fessional level.” My neighbor, a curious boy, said: “I knew nothing about physics and thought it was boring. After (m)agazine I changed my mind and will probably take physics in high school.” His inter-est was the best reward I could have expected.

(m)agazine is the culmination of one inspiring story, and the beginning of another. More such innovative publications could have a chance to produce a cumulative impact on the general public, and on the imaginations of young people.

Mikhail A. Shifman is the Ida Cohen Fine professor of physics at the William I. Fine Theoretical Physics Institute of the University of Minnesota.

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essay: mikhail shifman

In 1957 Murray Gell-Mann and Art Rosenfeld published the Particle Properties Tables in the 1957 Annual Review of Nuclear Science. Their intent was to amass experimental and theoretical information on decays of particles called hyperons and heavy mesons.

Rosenfeld and Walter Barkas decided to update that paper’s “table of masses and mean lives” even before the 1957 Review was in print. The update appeared as an unpublished Lawrence Radiation Laboratory Report, UCRL-8030. They revised the report in 1958 and, with it, issued a wallet card (above) summarizing the information.

“This was the Particle Data Book,” says Michael Barnett, who now heads the Particle Data Group. Each summary sheet had twin copies of the card, with perforated holes to tear them apart. A publishing oversight reversed the image of the imperial ruler.

“The damn thing just grew,” says Rosenfeld. “Pretty soon they became wallet sheets. The Russian word for bedsheet is different from a regular paper sheet, but they called it the Rosenfeld Bedsheet.”

This year, the Particle Data Group celebrates its 50th anniversary with a release of a 1230-page edition of the Review of Particle Physics. With the wallet card long gone, the current abridged version, the Particle Physics Booklet, now fills 320 pages. “And we struggled to keep it short,” says Barnett. Krista Zala

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logbook: particle data book

X-ray lasers will be the next generation of light source. They will deliver extraordinarily intense beams of X-rays in very short bursts that are ten billion times brighter than those in any other light source. They will find applications in sciences ranging from new material design to astrophysics research to drug development as scientists use the lasers to reveal molecular structures never seen before.

X-rays lasers are driven by high-current, high-energy electron beams such as those produced in linear accelerators. Wiggling back and forth between rows of magnets called undulators, the electron beams emit coherent bursts of X-rays. The first generation of X-ray lasers is currently under construction in Germany (at the DESY laboratory), Japan (at the SPring-8 laboratory), and the United States (at Stanford Linear Accelerator Center).

Applications for X-ray lasers include: making movies of chemical reactions that proceed faster than can be observed in any other way; determining the structure of single molecules or small clusters of mol-ecules that cannot be examined with less intense sources; and pro-ducing and studying new states of matter called warm dense plasmas, similar to what might exist in the interior of stars and other astronomical objects. Herman Winick, Stanford Linear Accelerator Center/Stanford Synchrotron Radiation Laboratory

symmetry

explain it in 60 seconds

SymmetryA joint Fermilab/SLAC publicationPO Box 500MS 206Batavia Illinois 60510USA

Office of ScienceU.S. Department of Energy