symmetry · than it did in the first half of 2008. 3 Commentary: Seth Zenz “As a physics graduate student and W ikipedia editor and ... planets, and people exist. 22 A Bumper Crop

A joint Fermilab/SLAC publication

symmetry

august 08

issue 03

volume 05dimensionsofparticlephysics

On the coverBattered or shiny, personalized license plates are a whimsical part of physics culture. On one level they’re inside jokes, told with a wink to those in the know; on another, an invitation to approach and learn more. In response to a call from symmetry, readers sent dozens of their favorites. “It’s a memento from one of the most intense times I’ve been through,” one wrote. “It’s a treasure from that great time.”

Inside front coverAccording to Greek mythology, the Argonauts sailed across the Mediterranean Sea to retrieve the Golden Fleece. Scientists of the ArgoNeuT project use an argon-filled particle detector to explore the interactions of the neutrino, one of the most abundant particles in the universe [see story, p. 16].

symmetryA joint Fermilab/SLAC publication

volume 05 | issue 03 | august 08

2 Editorial: Positive News for Particle PhysicsWith a new plan and the backing of the Department of Energy and Congress, the future of high-energy physics in the United States is now looking much more positive than it did in the first half of 2008.

3 Commentary: Seth Zenz “As a physics graduate student and Wikipedia editor and administrator, I argue that Wikipedia’s rules for reliable sourcing of articles are stronger than is often believed, and that academics can play a very positive role in improving and expanding Wikipedia.”

4 Signal to BackgroundPhysicist turns bicycle pro; the fastest way to stuff an airplane; trashy hot rod steals the show; making dark matter sing; Faraday Cup cartoons; trumpets blast for GLAST; letters; where your symmetry magazines have been.

10 New Tools Forge New FrontiersUS particle physics is pushing forward on three frontiers. Each has a unique approach to making discoveries, and only by pursuing all three can scientists address key questions about the laws of nature and the cosmos.

16 Bonnie and the ArgoNeuTsInspired by heroes of Greek mythology, physicists are on a quest to find a cheaper, more efficient way to capture neutrinos—one of the strangest and most fascinating par-ticles in the universe. Liquid-argon detectors may hold the key to discovering whether neutrinos are the reason that stars, planets, and people exist.

22 A Bumper Crop of Physics PlatesIn our October/November issue, we asked readers to share stories and photographs of physics-related license plates. Here are the responses.

Office of ScienceU.S. Department of Energy

Illustration: Sandbox Studio

In March 2008 we launched our blog, symmetrybreaking. Here are some highlights of the stories we have posted to date. You can read more at www.symmetrymagazine.org/breaking/.

Physicists discover the bottom-most “bottomonium”July 9, 2008, 4:30 pm: Bottomoniums are particles that contain both a bottom quark and an anti-bottom quark but are bound together with different energies. Now researchers have detected and measured the lowest-energy particle of the family.

Code crackers wanted!May 15, 2008, 5:12 pm: A little over a year ago, the Fermilab Office of Public Affairs received a curious letter in code. You can read partial solutions of the top and bottom sections in the comments. However, the middle section remains unsolved.

Are the laws of physics the same throughout the universe?June 19, 2008, 6:32 pm: Observations of a quasar about 6 billion light years away have shown that one of the funda-mental properties of physics is the same there as here: protons there are 1836.15 more massive than electrons.

Mariah Carey vs. Albert EinsteinApril 1, 2008, 12:01 am: On April 15, pop star Mariah Carey will release her new album, E=MC2. Here is a quick look at how Carey compares to the master of E=MC2, Albert Einstein.

ANTARES neutrino telescope completeJuly 14, 2008, 5:59 pm: The latest generation of neutrino telescopes uses vast bodies of water or ice as the medium for detecting neutrinos. The ANTARES experiment, at the bottom of the Mediterranean Sea, is a real engineering accomplishment.

The cosmic quantum bounce (APS April 2008)April 12, 2008, 2:57 pm: Plenty of theories suggest there was something before the big bang. This morning I heard more about an interesting addition that involves a “quantum bounce.”

28 Day in the Life: Mr. FreezeHis mind drifts to freezing fog, explosions shooting a ball 16 stories high, and children gasping in awe. A mischie-vous twinkle enters his eye. The studious physicist and computer expert has morphed into a charismatic showman.

32 Deconstruction: COUPP Bubble ChamberScientists retool a classic technology for a modern quest: the search for dark matter.

34 Essay: Elizabeth Wade “The cyclotron was an artifact of an age before the atomic bomb when excitement, wonder, and hope outweighed the fear that is so familiar today. It was an artifact of decades of tunnel spelunking, Columbia’s most public secret. It was an artifact of my college experience, bringing me closer to the people who shared my first Columbia adventure and setting the tone for all the rest that followed.”

C3 Logbook: Z BosonIn May 1983, physicists working on the UA1 detector for the Super Proton Synchrotron accelerator at CERN made the first definitive observations of the Z boson.

C4 Explain it in 60 Seconds: Z BosonThe Z boson is a heavy particle that is one of the carriers of the weak force. Its discovery completed the Standard Model of particle physics and allowed physicists to probe the characters and interactions of many of the other fundamental particles.

The high-energy physics community suffered a battering in 2008. The omnibus bill passed by Congress in late 2007 sharply reduced funding, causing layoffs at Stanford Linear Accelerator Center and furloughs at Fermi National Accelerator Laboratory. Various projects were put on ice for the year, or closed prematurely. Those cuts hit hard and left physi-cists reeling.

During those most difficult times, however, the community continued to make the case for particle physics research. Through the P5 process (see page 10), it worked with the Department of Energy and the National Science Foundation to develop a strategic plan for the future, designed to provide options for funding agencies under four potential funding scenarios.

Panel members needed to make some tough decisions but ultimately developed a compelling road map for US particle physics to make significant scientific advances with a balanced and sustainable program of research.

Then, just as Fermilab was preparing to lay off workers, Congress stepped in. Lawmakers appropriated an additional $32 million for high-energy physics, directed to prevent the imminent layoffs at Fermilab, allow the NOvA neutrino experiment to proceed, and preserve critical accelerator R&D and computing at SLAC.

Notably, the House Appropriation Committee’s language in its draft budget documents for FY09 reads: “The Committee commends the Department [of Energy] for its efforts to engage the high energy physics scientific community to provide a bold vision for the future of the Nation’s efforts in this area that is both realistic and scientifically compelling, particularly given the difficult budget constraints faced by the field in fiscal year 2008.

“...the Committee believes that a balanced effort that addresses oppor-tunities at the energy, luminosity, and cosmic frontiers by leveraging existing physical capital and facilities to the maximum extent possible and by engag-ing in international scientific cooperation is critical for the future of this field.”

In early July, Fermilab celebrated the news at an event with Congressional, DOE, and laboratory representatives and a newly uplifted Fermilab staff.

Budget challenges remain, but with a new plan and the backing of the Department of Energy and Congress, the future of high-energy physics in the United States is now looking much more positive than it did in the first half of 2008.David Harris, Editor-in-chief

Positive news for particle physics

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from the editor

SymmetryPO Box 500MS 206Batavia Illinois 60510USA

630 840 3351 telephone630 840 8780 [email protected]

(c) 2008 symmetry All rights reserved

symmetry (ISSN 1931-8367) is published 6 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

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Contributing EditorsRoberta Antolini, LNGSPeter Barratt, STFC Romeo Bassoli, INFNStefano Bianco, LNFKandice Carter, JLabLynn Yarris, LBNLJames Gillies, CERNSilvia Giromini, LNFYouhei Morita, KEKTim Meyer, TRIUMFPerrine Royole-Degieux, IN2P3 Yuri Ryabov, IHEP ProtvinoYves Sacquin, CEA-SaclayKendra Snyder, BNLBoris Starchenko, JINRMaury Tigner, LEPP Ute Wilhelmsen, DESYTongzhou Xu, IHEP BeijingGabby Zegers, NIKHEF

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commentary: seth zenz

Wikipedia needs more physicistsWikipedia, the popular online encyclopedia, has often been criti-cized as having misin-

formation and inadequate references. By allowing any user to edit, it runs the risk of having “truth” defined by majority vote or a persistent vocal minority; it has the potential to deliver the public’s perception of science into the hands of fringe groups with an ax to grind.

However, as a physics graduate student and Wikipedia editor and administrator, I argue that Wikipedia’s rules for reliable sourcing of articles are stronger than is often believed, and that aca-demics can play a very positive role in improving and expanding Wikipedia.

Using Google is enough to see why we are stuck with Wikipedia as a major source of popu-lar knowledge and we ought to make the best of it: Wikipedia articles turn up among the first hits for most physics topics. For most people of my generation, a Google search is now the first stop in almost any search for information. This means that if an undergraduate is trying to get a quick refresher on a topic for her physics exam, or a worried member of the public is trying to get an independent assessment of whether the Large Hadron Collider will really make black holes that eat the Earth, they will end up reading Wikipedia. The quality of those articles will ultimately determine whether thousands of searchers come away informed, confused, or misled.

One of the main sources of the misinformation is the author who has no formal training in physics but an enthusiasm for the subject, and who promulgates their own theories with no credibility in the scientific community. On Wikipedia, such people have the same ability to contribute as anyone else, and they do. They try to reinterpret the Wikipedia policies to have their edits accepted, but those policies are actually quite strict about using verifiable and reliable sources. These individ-uals are persistent and editors spend a significant fraction of their time holding the line against them, often simply by watching articles and reverting unsupported edits. This makes article improvement on Wikipedia more like a random walk than a steady progression, but at least Wikipedia policy makes sure that the random walk goes in the right direction.

These individuals can also fight dirty. I once blocked from editing someone who was

persistently adding unsourced nonsense to Wikipedia and harassing other users; he responded by sending a letter to one of the high-level admin-istrators on my real-life experiment to complain that I was suppressing The Truth about how Relativity is false. I ultimately had to explain the situation to my PhD advisor, and of course the decision was made to ignore the letter, but it was certainly jarring to have personal volunteer work interfere with my real job in that manner.

One frustration for many academics is that no Wikipedia user has special authority because of personal experience and knowledge. Editors have to back up what we know—even some-times the most seemingly obvious facts—by includ-ing citations for our statements. Although this may seem irritating and time-consuming, these policies ultimately help experts because our knowledge can be supported by reliable sources. There are examples of scientists having tre-mendous influence over Wikipedia articles in their areas of expertise and creating excellent, well-sourced articles.

One can ask if it is possible to create a better version of Wikipedia by giving experts special authority, as does Wikipedia co-founder Larry Sanger’s new project, Citizendium. But ultimately the question is moot, because replacing Wikipedia simply isn’t practical. Wikipedia’s willingness to accept any warm body gives it vast armies of contributors, while Citizendium’s requirement that the most trusted editors be faculty members or equivalent means that that project has very few. Wikipedia’s strategy of appealing to non-experts’ desires to make a difference, chaotic though it is, has so far proven far more empirically successful; it has about a thousand times as many articles as Citizendium, and Citizendium’s sixty-eight officially approved articles so far do not appear to me to be much better sourced or better written than the equivalent topics on Wikipedia.

For a scientist, then, editing Wikipedia may prove to be a difficult experience, but ultimately a successful one. As things stand now, though, the physics articles are rather understaffed, resulting in longer delays in removing rubbish and very little time to improve content. A relatively modest number of expert contributors could make a big difference in the quality and scope of Wikipedia’s physics articles. As measured in the number of people reached, such an effort may be a more important form of outreach and edu-cation than almost any other.

Seth Zenz is a University of California, Berkeley, graduate stu-dent, working with the Lawrence Berkeley National Laboratory group on the ATLAS experiment at CERN and living in Geneva, Switzerland. He is a contributor to the US/LHC Blogs.

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Call of the bikeAs Reid Mumford pedals, some-times he thinks about how to break away from the pack. Other times he thinks about how the smallest bits of the universe break apart in high-energy collisions.

Mumford, who studies rare subatomic particles at Fermilab, is a rarity himself: a particle physicist who is also a profes-sional bicycle racer. Riding gives him a physical workout; analyzing data from the world’s highest-energy particle accel-erator, the Tevatron, exercises his mind.

“Cycling is a tough sport. You don’t win much, but the one day that everything works is a beautiful thing,” he says. “Just like high-energy physics research.”

The 32-year-old finds a grueling physical trainer in the

prairie-powered winds that sometimes threaten to topple strollers at the laboratory. On the most blustery days, wind speeds average 26 mph and gusts blow nearly 80 mph.

“The wind makes training here hard, which is a good thing,” Mumford says. “Most of the people I race against live in high altitudes. If I didn’t have the wind, it would be hard to get faster.”

He practices 17 hours a week, even in the snow, using the time to recharge and work out complex theories in his head.

Mumford started racing as a graduate student at Johns Hopkins University. In 2007 he joined Kelly Benefit Stategies/Medifast, a Minneapolis-based professional team. In a sport that requires half the team fall under age 27, Mumford had to work extra hard to secure a spot.

After breaking his leg in a colli-sion with a van during practice, he had to work even harder to recover and reclaim his position.

His Johns Hopkins profes-sors and co-workers from the lab’s CDF experiment support his bid for bicycling fame, helping him fit training—and weekend races all over the country—into grueling grad- student hours of data analysis.

Mumford is wrapping up his PhD thesis and plans to take a break from physics in the fall to focus full-time on racing. But once that challenge runs its course, he hopes to return and tackle the new energy fron-tier at CERN’s Large Hadron Collider.

You can find Mumford’s team bio at www.symmetrymag.org/bikeracer/.Tona Kunz

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signal to background

Physicist turns bicycle pro; the fastest way to stuff an airplane; trashy hot rod

steals the show; making dark matter sing; Faraday Cup cartoons; trumpets blast

for GLAST; letters; where your symmetry magazines have been

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All aboardJason Steffen waited to board a plane in the Seattle airport. He waited to get his boarding pass scanned. Then he walked a few steps down the jet way, and waited some more. His frustration grew.

“I thought, I’ve got to be able to do something about this,” Steffen says.

After brooding for 18 months, Steffen, a physicist in the Particle Astrophysics Center at Fermilab, came up with a mathematical solution. It would allow passen-gers to board four to 10 times faster, depending on the size of the airplane.

The secret: load passengers in groups, spaced two to three rows apart, so they can simul-taneously stow their luggage.

Steffen posted his method in the Physics and Society section of arXiv.org, a Web site where physicists share results.

In the 3 1/2 months since, he’s been contacted by dozens of media outlets all over the globe. But guess who hasn’t called? The airlines. Steffen says he heard from a friend of a friend of a friend who works at Boeing that the airline manu-facturer has taken note of the study, but his phone has yet to ring.

Since posting his results, Steffen has learned that four or five other groups, including one in Arizona and one in Belgium, had also done airplane boarding studies. Only one was contacted by an airline, and the interest died when the air-line was bought out shortly after the initial contact, he says.

Steffen says he never really expected airline interest, and did the study just for his own satisfaction.

“I knew that there had to be a reason for this, and it is nice to know there is a better way to board,” he says. “But that hasn’t make the time waiting in airport lines go any faster.”

What’s next? Steffen says he is thinking of examining how the layouts of construction

barriers affect the flow of cars per second—a topic of special interest in Illinois, a land of nearly perpetual road construction.

“I would look at how they minimize the number of cars through per second,” he says. “That seems to be the goal—not to maximize the flow.”

To read Steffen’s paper, visit www.symmetrymag.org/boardingstudy/.Rhianna Wisniewski and Tona Kunz

Rat rodParked between a shiny green Camaro and a remodeled ’63 Mustang, a 1929 Ford Model A pickup-turned-hot rod is a mosaic of rust and rot. A rag plugs the radiator, and ancient wooden slats border the truck bed. The car looks fresh from the junkyard, and hardly at home with such classy competitors at the Stanford Linear Accelerator Center’s Hot Rides Car Show.

But the car’s owner, Jeff Jones, stands self-assured next to what is known around SLAC as the Rat Rod. To him, the car is exactly what he wants it to be. He proudly declares, “It’s a work of art.”

Jones is the precision sheet metal engineer at SLAC. Two years ago he pulled the truck body out of a friend’s yard, planning to turn it into a hot rod. The Rat Rod has certainly met that expectation: It can go 120

mph before the front wheel starts to wobble, and it’s been known to out-race a Harley Davidson. But along the way the car became more than a test of engineering—it turned into Jones’ personal canvas “That car is me,” he says. “It’s a little different; I’ve always been a little different. I made myself my car.”

Looking closely, one can see symmetric designs drilled into the rusting doors and hood—Jones’ own handiwork. Antique Coca Cola serving trays function as floor boards, an oversized bullet plugs the overflow tank, and safety pins keep the spark-plug wires together. The cable bracket is a silver spoon. “I had the stock bracket,” he says with a shrug. “It was just too normal.” The words “Straight 2 Hell,” bor-rowed from the title of a Hank Williams III album, are fading from the doors, but are still bold enough to proclaim the car’s attitude.

The Rat Rod has won three car-show awards, most notably the Chrome and Suede Award at a Good Guys show, where it was the only car in the winners’ circle without a paint job.

To Jones, the car is complete. “People still ask me what color I’m going to paint it,” he laughs, “but it’s done.” Then he pauses and adds, “Except for front brakes. And seat belts. It should have seat belts.”Calla Cofield

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Dark matter musicThe search for dark matter strikes a new note with a multi-media art work that turns data from an underground experi-ment into colored light and musical tones.

Karl Ramberg’s creations often blend sound and visuals; one of his most recent works, for example, combined art made from musical scores with the music they contained. But a trip with his brother, Fermilab physi-cist Erik Ramberg, took his work in a more scientific direction.

Their destination was a mine in Soudan, Minnesota, where Erik was scheduled to work in the control room of the Cryogenic Dark Matter Search experiment.

“The whole notion of being at the bottom of an abandoned iron mine—there is something kind of romantic or mysterious about it,” Karl says.

The Cryogenic Dark Matter Search detects particles such as neutrons, electrons, and cosmic rays that rain in from space. It hasn’t recorded any dark matter particles yet, but scientists are hopeful.

After spending the better part of a week in the mine, Karl built a full-scale plastic model of the detector with the help of his brother and CDMS collabo-rator Prisca Cushman, a physics professor at the University of Minnesota, who translated the

data into light and sound. “I spent a lot of time program-

ming it,” Cushman says. “I had to get CDMS files in the proper format and figure out what sounds good.” Her neighbor’s 10-year-old nephew helped film the musical model and post it on YouTube.

Cushman translated the energy of each incoming particle into a musical note, and the point where it struck the detector into color. In addition, each type of particle got a unique instrumental voice. Midway through the perfor-mance, Cushman had the model play the familiar six-note melody from Close Encounters of the Third Kind and a snippet of “When You Wish Upon a Star.” (“That is a little joke,” she confesses in the comments fol-lowing the video clip. “I couldn’t help myself.”)

The end result, Karl says, is that “you get an experience, aurally and visually, of sub-atomic effects. You get a better understanding of what the data is saying.”

Cushman says she and the Rambergs would eventually like to display the model, or one just like it, at a science or uni-versity museum.

“This could be a great out-reach tool,” Cushman says. “It has a lot of potential to spark people’s interest.”Rhianna Wisniewski

Pécub’s CupA Faraday Cup is (pick one) 1) a gadget named after the great experimentalist Michael Faraday, used to measure the current of a charged-particle beam, or 2) an award that rec-ognizes the inventors of inno-vative instruments for particle accelerators.

Trick question. It’s both. This year the Faraday Cup, awarded biannually since 1992, was pre-sented on the opening day of the 2008 Beam Instrumentation Workshop, sponsored by Lawrence Berkeley National Laboratory and held at Lake Tahoe in early May. In keeping with the workshop’s theme—the challenges of beam diag-nostics—Suren Arutunian, head of the Low Temperature Physics Laboratory at Armenia’s Yerevan Physics Institute, won the award for inventing a beam-diagnostic “vibrating wire scanner” for the Yerevan Synchrotron.

Second trick: the Faraday Cup Award isn’t a cup at all. It’s a work of art. In 1981 the Italian Swiss artist Pierpaolo Pugnali, better known as Pécub (“P cubed”), illustrated some ads in the CERN Courier for a new company, Bergoz Instrumentation. Pécub and the company’s founder, Julien Bergoz, became friends, and in 1992 Bergoz asked him to design the certificate for a new

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award his company was spon-soring. Voilá.

“You can’t tell Pécub what he should draw,” says Bergoz. “You tell him what you want to communicate; he listens intently, then draws four or five sketches on a large sheet of paper —less than two minutes per sketch.” Once a sketch is chosen, “he gets his set of seven or eight small pots of colored ink, dips his fingers in a few... Another four minutes and it’s done.”

Bergoz thinks of Pécub as both an artist and a philoso-pher of science: “I am always amazed how he can imagine things I have not told him.” It was Bergoz who introduced Pécub, who has a scientific background in pharmaceutical research, to high-energy physics.

Says Pécub, “The invisible in biology and the invisible of basic matter are closely con-nected. Bridges to put imagi-nation into the big bang... Your atomic world is so infinite in questions.”

Although there’s no poster this year, Pécub has drawn a handsome certificate for the winner.Paul Preuss, Berkeley Lab

Gamma-rays inspire brass quintetWhen you hear the descending flurry of 16th notes in the trum-pets, you know the gamma rays are coming. They speed toward the detector in the Gamma-ray Large Area Space Telescope in chromatically har-monized notes. The rays split with a sharp accent, and an electron and positron speed away from each other in the GLAST detector, their move-ment conveyed by short bursts of notes sliding in opposite directions along the scale.

That’s how Nolan Gasser interprets the science of GLAST in his original composition GLAST Prelude for Brass Quintet, op. 12, which made its

debut at the June 9 pre-launch party in Cocoa Beach, Florida. The piece can be rhythmically complex when evoking the wavelengths of the electro-magnetic spectrum, or simple and beautiful when depicting GLAST’s elegant orbit. A video created by the NASA Goddard Television and Multimedia Group accompanies the music. “The visuals,” Gasser explains, “allow for that rare mix of an aesthetic experience with scientific appreciation and education.”

The gamma-ray telescope, designed and constructed in part at Stanford Linear Accelerator Center, will be the first to survey the entire sky every day searching for the most energetic form of radia-tion in the universe. Until about a year ago, Gasser knew almost nothing about the sci-ence related to GLAST. He is a classically trained composer and artistic director of the Classical Archives, an online classical music site. Then his friend and Classical Archives CEO Pierre Schwob, a science enthusiast who is one of the major donors to the Kavli Institute for Particle Astro- physics and Cosmology, com-missioned him to compose a piece for the GLAST launch and mission.

Gasser spent months immersing himself in scientific literature. He traveled to the NASA Goddard Flight Center to meet with the mission’s project scientist, Steve Ritz, and deputy scientist, Neil Gehrels, and learn about the history, mission, and expecta-tions of GLAST.

The art, Gasser says, is an invitation to the science, a doorway through which the public, and hopefully the press and the government, will enter the world he has become so passionate about.Calla Cofield

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Photo courtesy of NASA

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Letters

The Big Bang TheoryJennifer Ouellette missed one major unfortunate connection to reality provided by the TV show The Big Bang Theory: the main female character Penny not only is treated primarily as an object of sexual fantasy by the physicists, but is also the main representation of all womankind in the show. When Penny’s intelligence is questioned, so is that of all women. When Penny, the non-physicist, is excluded from the conversation, so are all women. The identification is nearly set in concrete (modulo a few glimpses of Leslie): woman equals non-physicist equals dumb sex object. The physics community (maybe especially high-energy theory) has plenty of clones of Leonard, Sheldon, Howard, and Rajesh.

Having struggled for acceptance in this community all my career life, I must admit this represents the reality I experienced. Yeah, I get the physics humor, but—as so often happens in real life—as a woman, I’m also the butt of the rest of the jokes.Name withheld on request

CBS projects a second season for The Big Bang Theory—a “very smart, savvy series” with evolving characters and humor, says essayist Jennifer Ouellette (January/February 08). Could a sitcom that began by shallowly caricaturing physicists end up branding physics? Given that comedy at its best instructs as well as delights, could physicists somehow suggest story ideas leading not only to laughing but to learning?

What about Sheldon in conflict with a global-warming denier? Sheldon would condescend sarcastically, lecturing accurately but highly technically. Sensible non-scientist Penny might turn his jargon into plain English—making fools of Sheldon for snide pomposity and of the denier for denial.

Or what if Leonard, seeking to continue dating a young woman, had to calibrate how much scientific truth to tell her dad—a bit of a nut who loves to talk science, especially concerning his lawsuit alleging that a new collider’s startup could destroy the planet?

Last fall this sitcom seemed a science-outreach disaster, with only slapstick resemblances to the physics world that it might nevertheless have begun branding. But Ouellette is right: it’s evolving now. Maybe physicists should speak up.Steven T. Corneliussen, Jefferson Lab, Newport News, Virginia

The Iron Lady and the bosonI enjoyed seeing the confidential letter from CERN Director General Herwig Schopper to UK Prime Minister Margaret Thatcher in the Jan/Feb 08 issue of symmetry. It reminded me of a related letter.

I was one of the people who showed Mrs. Thatcher round the UA1 experiment when she visited CERN in August 1982. It was a private visit, and we were not told who was coming, merely that it was a senior UK person and “she was very important,” so we should take the visit seriously. Indeed we did, and before the visit I spent some time crawling through the apparatus checking that no bomb had been hidden there.

Alan Astbury, the leader of the Rutherford Lab group and co-spokesperson of UA1, gave a short presentation of our experiment. He ended on a cautiously optimistic note: “If we are lucky, and there is a Father Christmas, we will see the W by the end of this year.” “Right,” said the Iron Lady, point-ing her finger at Alan. “I will phone you in January to see whether you have found it.” She did not say what would happen to our funding if we did not discover the W.

The discovery of the W was announced at a CERN press conference on 25 January 1983. I remember the date well: It was my 50th birthday, and I gave a talk about the discovery to a packed audience in London. After publication of the results, I received a letter of congratulation from Mrs. Thatcher. Coming from our Prime Minister it was perhaps understandable that it was a bit nationalistic in its tone, emphasizing the British participation. The UA1 and UA2 experiments were of course international, and I did not have the heart to tell Mrs. Thatcher that even in the Queen Mary College group from London, the eight participants included two American physicists, one Canadian physicist, one Italian graduate student and another with a Greek mother, and that I was born in Czechoslovakia.Peter Kalmus was the leader of the Queen Mary College group in UA1

Letters can be submitted via [email protected]

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I am so fascinated by the lat-est particle physics news (and quips and quotes from the crews), symmetry keeps me stimulated even on other-wise restful vacation days! The Abacos archipelago in north-eastern Bahamas is a destina-tion of turquoise water, devel-oped and deserted cays, pastel houses, bougainvillea, sandy beaches, snorkeling reefs, and starfish the size of a human torso. What better means to explore nature and exercise the mind (thereby avoiding the hazard of falling into lethargy from the intense sun and steamy climate) than a boat, a mask and fins, a cool one, and thou? Two friends joined me in January for an excellent excur-sion on a chartered 31-foot sailboat based in Hope Town, Elbow Cay. Even running aground on sandbars didn’t faze us—raid the cooler, put Jimmy Buffett on the stereo, and wait for the tide to rise. Between black holes, sea tur-tles, and rum punches, our Abacos vacation “sailed” by!Amber Jones

A beautiful day at McMurdo Station, Antarctica, found me reading my symmetry magazine while taking a break from pack-ing up the CREAM instrument after its recovery from the Ross Ice Shelf, where it came down after a 28-day flight circling

high above the Antarctic conti-nent in its quest for answers to questions about the supernova acceleration mechanism of cos-mic rays (see http://cosmicray.umd.edu/cream). CREAM was launched on December 19th from the ice shelf near McMurdo Station, and my job since early January was to wait for it to come back down to earth and then go out to pick up the pieces, so to speak. Balloon cosmic-ray experiments are really high-energy experiments, but done in a smaller space and on a smaller budget.

I get symmetry to stay in touch with my earth-bound brethren, and have caught up on several back issues during my wait. The view here is unbeatable. In the photos, you can see the sea crates I have been putting the support equipment and recovered instruments into, and in the background the glacier-covered Ross Island, upon which McMurdo Station is built. I am out on the permanent ice of the shelf itself, in the area where the balloon instruments are prepared and launched. You can see Mount Erebus, the southernmost active volcano in the world, in the background of the more distant photo, although it was a bit cloud-covered that day. The weather has been pretty poor this year, and I had to wait for two

weeks after the instrument came down before a plane was available to go get it.

You can see more of what I have been doing here and going through via my blog at http://antarctic-scott.blogspot.com.Scott Nutter

I have been doing science on the Late Show with David Letterman for 18-plus years. The first eight were me alone, but for the last 10 I had kids from the Naperville, Illinois, area doing the science. The Kid Scientists appeared on February 27. I had a picture taken with symmetry and the kids at Dave’s desk. I get sym-metry magazine because I “worked” with Fermilab edu-cation programs for 20 years with Friends of Fermilab and Marge Bardeen.Lee Marek

Editor’s note: A video clip of part of the February 27 Kid Scientist segment, titled “Magic Carpet Ride,” is at www.sym-metrymag.org/lateshowclip/.

Contest results…Oh, the places your symmetry went! In August 2007, we asked readers to send photos of places their copies of symmetry have been. Here are three letters with photographic evidence of the magazine’s travels.

The Energy Frontier

The Cosmic Fr

ontie

rThe Intensity Frontier

10Photo-Illustration: Sandbox Studio

The Energy Frontier

The Cosmic Fr

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rThe Intensity Frontier

US particle physics is pushing forward on three frontiers. Each has a unique approach to making discoveries, and all three are essential to answering key questions about the laws of nature and the cosmos. By Elizabeth Clements

New tools forge new frontiers

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In 1665, when natural philosopher Robert Hooke first looked through a microscope at a slice of cork, his view of the world around him changed forever.

Using a microscope he had made himself, Hooke looked at the apparently solid cork and saw a honeycomb of tiny individual structures. He called them cells for their resemblance to monks’ cells in a monastery. Astonished, he quickly focused his microscope on other natural mater-ials and saw that they too had a cellular structure. Hooke’s microscope had opened up an unseen world for observation and pointed the way to the cell theory of living organisms.

Hooke’s fascination with lenses led him to build some of the earliest telescopes. Training them on the heavens, he encountered still more wondrous phenomena.

In Micrographia, his famous account of his research, Hooke wrote:

Every age confronts its own scientific questions and develops its own tools and techniques to address them. In the 17th century, microscopes and telescopes revealed for the first time aspects of the universe invisible to the naked eye. Nearly four centuries later, the tools for observation have changed, but the human imperative to use advances in technology to reveal the nature of the world around us remains.

A new report published by the Particle Physics Project Prioritization Panel (P5), “US Particle Physics: Scientific Opportunities,” presents 21st century scientific questions about the physics of the universe and describes a set of tools to address them. It defines three frontiers of discovery—the Energy Frontier, the Intensity Frontier, and the Cosmic Frontier—with distinct approaches to particular scientific questions.Scientific questions

Fundamental questions about the universe and forces of nature define the path ahead for particle physicists:

1. Are there undiscovered principles of nature?2. How can we solve the mystery of dark energy?3. Are there extra dimensions of space?4. Do all the forces become one?5. Why are there so many kinds of particles?6. What is dark matter? How can we make it in the lab?7. What are neutrinos telling us?8. How did the universe come to be?9. What happened to the antimatter?

“By the means of Telescopes, there is nothing so far distant but may be represented to our view; and by the help of Microscopes, there is nothing so small as to escape our inquiry; hence there is a new visible World discovered to the understanding. By this means the Heavens are open’d, and a vast number of new Stars, and new Motions, and new Productions appear in them, to which all the ancient Astronomers were utterly Strangers. By this the Earth itself, which lyes so near us, under our feet, shews quite a new thing to us, and in every little particle of its matter, we now behold almost as great a variety of Creatures, as we were able before to reckon up in the whole Universe it self.”

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Energy, intensity and cosmicAt the energy frontier, scientists build advanced particle accelerators to explore the Terascale. There, in this new scientific territory named for the Teravolts of energy that will open it up for discovery, they expect to encounter new phe-nomena not seen since the immediate aftermath of the big bang. Subatomic collisions at the energy frontier will produce particles that signal these new phenomena, from the origin of mass to the existence of extra dimensions.

At the intensity frontier, scientists use accel-erators to create intense beams of trillions of particles for neutrino experiments and measure-ments of ultra-rare processes in nature. Measure-ments of the mass and other properties of the neutrinos are key to the understanding of new physics beyond today’s models and have critical implications for the evolution of the universe. Precise observations of rare processes provide a way to investigate energy scales at the Terascale and beyond.

At the cosmic frontier, astrophysicists use the cosmos as a laboratory to investigate the funda-mental laws of physics from a perspective that complements experiments at particle accelerators. Thus far, astrophysical observations, including the bending of light known as gravitational lens-ing and the properties of supernovae, reveal a universe consisting mostly of dark matter and

dark energy. A combination of underground exper-iments and telescopes, both ground- and space-based, will explore these mysterious dark phenom-ena that constitute 95 percent of the universe.

All of these approaches “ultimately aim at the same transformational science,” the report says.

“We need a diversity of approaches to these questions—a mix of projects both on different tim-escales and with different scientific reach,” says P5 Subpanel member Josh Frieman, a theoretical astrophysicist at Fermilab and the University of Chicago.

Some questions are unique to a single frontier: Only at the cosmic frontier, using highly advanced instruments to observe the evolving universe, can scientists directly explore the mystery of dark energy. In contrast, shedding light on dark mat-ter requires a combination of astrophysical observations and experiments at high-energy particle accelerators. For example, physicists anticipate that experiments at the Large Hadron Collider, soon to begin operating near Geneva, Switzerland, may identify dark matter particles in high-energy collisions. The Cryogenic Dark Matter Search, an experiment half a mile under-ground in Minnesota, uses a sensitive detector to search for naturally occurring dark matter particles. Gamma-ray detectors in space, such as the recently launched GLAST satellite, may see the glow created when dark matter particles

Origin of Mass

Dark Matter

Neutrino Physics

Proton Decay Cosmic Particles

Dark Energy

Unification of Forces

Matter/Antimatter Asymmetry

New PhysicsBeyond the Standard Model

Origin of Universe

The Energy Frontier

The Cosmic Fr

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rThe Intensity Frontier

Diagram courtesy of P5

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and their opposites collide. Thus a clue from one frontier sheds light on another.

“You need to pursue all three frontiers to make progress in particle physics,” P5 Subpanel Chair Charlie Baltay, a physicist at Yale University, says.

Facing new realitiesIn the United States, the field of particle physics is in a time of transition. In a year or two, Fermilab’s Tevatron, the world’s highest-energy particle accelerator, will turn off. The energy frontier will move to Switzerland, where the Large Hadron Collider is about to turn on at the European par-ticle physics lab, CERN. More than 1200 US scientists, the largest contingent of CERN experimenters from a single nation, will collaborate in experiments at the LHC.

New budget realities, however, cloud the future of particle physics in the United States.

The proposed International Linear Collider figured as the centerpiece in previous plans for the future of US particle physics. A large cost estimate for the ILC made it likely that a delay in the proposed schedule would occur and led the US particle physics community to re-examine the scientific opportunities ahead.

In December 2007, the Omnibus Funding Bill delivered an unexpected blow, eliminating $90 million in funding for particle physics from the expected budget level for FY08. The diminished funding had a powerful impact on US particle physics, stopping work on several projects, including Fermilab’s NOvA neutrino experiment, SLAC’s B-factory, and all ILC R&D, and leading to layoffs and furloughs.

“This is a pivotal point in the US program,” says Dennis Kovar, acting associate director of the US Department of Energy’s Office of High Energy Physics. “We need to think harder about how to get at the key science questions with the resources that we have.”

The DOE and the National Science Foundation asked P5 to recommend priorities for the future of US particle physics under four budget scenarios:

• ConstantlevelofeffortattheFY08funding level of $688 million

• ConstantlevelofeffortattheFY07fundinglevelof$752million

• DoublingofbudgetovertenyearsstartinginFY07

• Additionalfundingabovethepreviouslevel, associated with specific activities needed to mount a world-leading program.

By defining scientific opportunities for the field’s existing experiments and future proposals, the report attempts to make a balanced plan that maintains the nation’s leadership role in world-wide particle physics regardless of funding levels.

“The scientific priorities have not changed in the last few years, but the context has,” Baltay says. “The present P5 Subpanel has developed a strategic plan that takes these new realities into account.”

The lure of cutting-edge scienceBecause the United States will soon shut off the Tevatron and doesn’t have plans to build another massive accelerator any time soon, the energy frontier is likely to remain in Europe for 20 years or more. However, significant discoveries are within reach at the intensity and cosmic frontiers, leading to proposals for new projects that fit within the new budget realities.

In the immediate future, the physics of neu-trinos and the study of rare processes offer unique opportunities to address basic questions of particle physics.

At the time of the big bang, nearly equal amounts of matter and antimatter existed. Since then, however, the antimatter has vanished. Stars, people and everything else that exists consists of matter. What happened to the antimatter?

Physicists believe that neutrinos may be the only particles with mass that are their own anti-particles. If so, they follow a different set of rules from other particles regarding the symmetry between matter and antimatter. Hence, neutri-nos have profound implications for the evolution of a universe made of matter. Physicists are eager to build intense proton sources to make unprecedented numbers of neutrinos for experi-ments that will illuminate their unique properties.

Physicists can also use intense proton sources to observe rare processes in nature. Rare particle decays can peek into a higher-energy regime—far in excess of the energies the LHC can directly reach. By observing the decay pat-terns of particles with long lifetimes, such as muons and kaons, scientists may catch glimpses of heavy new particles whose brief cameo appearances can alter normal decay processes.

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Physicists must sift through billions of particle decays to find these rare events that could answer questions about the nature of matter and energy, the evolution of the universe and the subtle differences between matter and antimat-ter. High-intensity accelerators can create the immense numbers of particles they need.

“The more, the better,” says P5 subpanel mem-ber Robert Tschirhart, a physicist at Fermilab. “The currency here isn’t energy. It’s intensity.”

At the cosmic frontier, physicists observe naturally occurring particles such as gamma rays to investigate the nature of the universe. High-energy gamma rays are photons, or particles of light, that are millions to hundreds of billions more energetic than the light people see. They are typically emitted from powerful astrophysical phenomena such as supermassive black hole sys-tems and rapidly spinning neutron stars, revealing fundamental physical processes that are impossi-ble to investigate in terrestrial laboratories.

Gamma rays may also be emitted when mas-sive particles interact weakly with their surround-ings—the same weak interactions that are a hypothesized property of dark matter particles. The recently launched Gamma-ray Large Area Space Telescope, or GLAST, a NASA/DOE collaboration with international partners, hopes to find these dark matter signatures, among other intriguing phenomena. Stanford Linear Accelerator Center managed the construction project for the pri-mary instrument, the Large Area Telescope, or LAT, and played a key role in the instrument assembly. Scientists based the LAT on accelerator-based particle detector technology adapted for use in space.

Where frontiers convergeThe intensity and cosmic frontiers could meet in the Homestake Mine in South Dakota. There the proposed Deep Underground Science and Engineering Laboratory, or DUSEL, presents an opportunity for scientists from multiple fields to conduct experiments.

In this dedicated underground laboratory, geol-ogists would study the Earth’s subsurface; micro-biologists would have access to organisms living in the Earth’s depths; experts in rock mechanics would analyze how rock reacts to pressure over time; and particle physicists would move closer to solving the mysteries of the universe.

Making such a large, diverse undertaking a reality requires a high degree of cooperation and collaboration from multiple funding agencies. The agencies already have begun collaborating on big projects. The DOE and NSF, for example, jointly funded the US contributions to the Large Hadron Collider at CERN. The DOE and NASA jointly fund GLAST.

DUSEL is also a collaboration, in this case between DOE and the NSF. At 2400 meters below ground, DUSEL would provide more shielding from cosmic rays and other surface “noise” than any previous underground particle physics envi-ronment. At the cosmic frontier, DUSEL would make an ideal spot for directly detecting dark matter particles. At the intensity frontier, it could host neutrino experiments. The P5 report calls for sending a high-intensity neutrino beam from Fermilab to Homestake Mine, where a large detector would record any changes that occurred during the particles’ 1300-kilometer journey.

“Experiments at DUSEL would address many issues, including neutrino physics, proton decay, dark matter, and neutrinoless double beta decay,” Baltay says. “DOE and NSF should define clearly the stewardship responsibilities for such an exper-imental program.”

“Helps for the eye”At the dawn of the era of modern science, the extraordinary power of early microscopes and telescopes to reveal the nature of the world around them gave 17th–century scientists a sense of nearly limitless scientific opportunity, and they foresaw future generations of increasingly pow-erful tools for discovery.

“Tis not unlikely,” Hooke wrote in Micrographia, “but that there may be yet invented several other helps for the eye, as much exceeding those already found, as those do the bare eye, such as by which we may perhaps be able to discover living Creatures in the Moon, or other Planets, the figures of the compounding Particles of matter, and the particular Schematisms and Textures of Bodies.”

As 21st-century physicists contemplate the power of such “helps for the eye” as next-generation accelerators, detectors, telescopes, and cameras, they have a similar sense that these tools at the frontiers of particle physics are about to change their view of the universe forever.

Photos courtesy of CERN and NASA

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Bonnie and the ArgoNeuTs

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by Kurt Riesselmann

Inspired by heroes of Greek mythology, physicists are on a quest to find a cheaper, more efficient way to capture neutrinos—one of the strangest and most fascinating particles in the universe. Liquid-argon detectors may hold the key to discovering whether neutrinos are the reason that stars, planets, and people exist.

W hen Bonnie Fleming graduated with a bachelor’s degree in physics from Barnard College, a small all-women’s

college in Manhattan, she wasn’t sure she wanted a career in research. She worked as a particle beam operator at a Department of Energy labo-ratory for three years before deciding to go to graduate school.

“All my bosses were accelerator physicists,” she says of her time at Brookhaven National Laboratory. “I decided I wanted to get a PhD and do research, too.”

Today, Fleming is a junior faculty member at Yale University and principal investigator of the Argon Neutrino Test project, or ArgoNeuT. With physicists from six institutions, she works on a technology that could be the key to unveiling the role neutrinos played in the early universe.

Neutrinos are one of the most abundant particles in space, and one of the most peculiar. They emerge from nuclear reactions inside stars and from other nuclear processes, such as radioactive decays. Although the Standard Model of particles and their interactions predicts

that neutrinos have no mass, experiments have shown, to the surprise of many scientists, that they do have a tiny mass.

Neutrinos come in three types that transform into each other as they travel. Physicists think even more types of neutrinos may exist. Short-lived, ultra-heavy neutrinos may have been pres-ent in the early universe, and might have played a crucial role in determining that everything we know today would be made of matter rather than antimatter.

So, are neutrinos the reason we exist? “It’s such a compelling question,” Fleming says.

“People are made of matter; they can relate to that.”

Catching neutrinosDespite their abundance, neutrinos are hard to detect. They can easily travel all the way through the Earth without interacting with the atoms that make up matter.

“Hold out your hand and count to three,” Fleming says with a smile. “A trillion neutrinos just went through your hand.”

To increase the likelihood of observing the

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Bonnie Fleming leads the Argon Neutrino Test project at Fermilab. To catch neutrinos, scientists place the ArgoNeuT time projection chamber (right) into a vessel (in the back) and fill it with liquid argon. ArgoNeuT will collect tens of thousands of neutrino events within six months. Scientists plan to build a larger detector using this technology.

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extremely rare interactions that do occur, phys-icists build accelerators to generate intense beams of neutrinos, and large, heavy detectors to record the collisions of those neutrinos with atoms. The largest detector to date is the 50-kilo-ton Super-Kamiokande in Japan, located deep underground in a cylindrical cavern about 40 meters high and 40 meters wide. The cavern is full of water and its walls are covered with light-sensitive devices that register Cherenkov radiation, the faint glow emitted when neutrinos collide with water molecules.

While the interest in even larger neutrino detectors is high, the cost of building these cut-ting-edge experiments has reached hundreds of millions of dollars. Hence physicists are looking for better, more cost-effective methods. The challenge is to record neutrino interactions at the right energy, in sufficient numbers, and with the most accurate identification of the particles that emerge from the collisions.

“When you embark on a big, expensive proj-ect, you’d better evaluate your options carefully,” says physicist Regina Rameika, of the Fermi National Accelerator Laboratory near Chicago, who works on ArgoNeuT as well as on plans for much larger neutrino detectors. “We need to find something that is cheap per kiloton.”

Liquid-argon neutrino detectors, pioneered by Nobel laureate Carlo Rubbia and his ICARUS collaboration, might be the solution.

Better and cheaper?Instead of recording light emitted by particles traveling through water, as Super-Kamiokande does, liquid-argon detectors record signals from electrons knocked loose by passing particles.

Rameika thinks a liquid-argon detector could identify three to five times more neutrino collisions than a water Cherenkov detector of the same size. It potentially would better differentiate among the three types of neutrinos, a crucial require-ment for the next generation of neutrino experiments.

So far, nobody has built a large, multi-kiloton neutrino detector based on liquid argon, and sci-entists don’t know yet how much this would cost.

The real test for this type of detector will be “to use one to do an important physics experi-ment. Then you can see what the problems are,” Mike Shaevitz of Columbia University says. “The physics community would want to see a physics result before they put money into a large one.”

Jason and the ArgonautsThe ArgoNeuT project began in 2006 when Fleming secured a National Science Foundation CAREER grant to study the liquid-argon

technology. Soon she and her collaborators at Fermilab and other institutions were looking for a catchy name for their project.

“We had a contest,” Fleming says. “Rich Schmitt, a cryogenic engineer at Fermilab, came up with the name in a play on Jason and the Argonauts.”

According to Greek mythology, the Argonauts were adventurers who sailed across the Mediter- ranean Sea in their ship, the Argo, to retrieve the Golden Fleece. Led by Jason, the crew braved fire-breathing oxen and sleepless dragons.

Fleming and her ArgoNeuTs face more modern challenges in their quest to develop a small liquid-argon neutrino detector that could eventu-ally be scaled up to the size of a 20-story office building.

Not for time travelersArgon is a noble, non-toxic gas that constitutes about one percent of air. It exists as a colorless liquid in the narrow temperature range of minus 186 to minus 189 degrees Celsius.

In the early 70s, William Willis and Veljko Radeka, of Brookhaven National Laboratory, built the first detector to use layers of steel immersed in liquid argon to measure the energies of charged particles emerging from collisions. Today, high-energy collider experiments such as the DZero experiment at Fermilab and the ATLAS experi-ment at the European laboratory CERN rely on similar detectors to record the energies of particle events.

But these sandwich-type detectors, known as liquid-argon calorimeters, cannot reveal the details of a neutrino collision.

“You don’t have the picture of the event and you don’t know what particle caused the event. You only know the energy,” says Flavio Cavanna, professor at the University of L’Aquila in Italy, who works on ICARUS and ArgoNeuT.

Hence neutrino physicists are exploring a type of detector known as the liquid-argon time pro-jection chamber, or TPC.

“My sister loves the name,” Fleming says. “It’s totally sci-fi for her. She often calls it a time capsule.”

Despite its curious name, a time projection chamber has nothing to do with time travel. The term refers to the time it takes for electrons, knocked loose by charged particles, to drift through liquid argon to an array of high-voltage wires that record their arrival time and location. Just as rays of light cast the shadow of a moving object onto a wall, the electrons set free by a moving particle project its trajectory onto the array of wires.

“Many particles come out of a collision, and the TPC traces all the particles and their

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interactions,” producing images almost like those from a video camera, Cavanna says. Scientists then select the images that are of interest. “You can measure for each track the energy associated with this track, and you can identify the particle that created the track.”

Because electrons can drift long distances through liquid argon, a relatively small number of wire arrays, placed a few meters apart, could capture neutrino collisions across a large volume and possibly reduce the cost of a large neutrino detector.

Drifting through an argon seaRubbia, spokesperson of the ICARUS collaboration and CERN director general from 1989 to 1993, recognized the potential of large liquid-argon TPCs more than 30 years ago. He hoped to use them to track rare subatomic processes, such as neutrino collisions and elusive proton decays that some theories predict. He has pursued this idea ever since.

“Carlo Rubbia is the father of the long-drift technique for liquid-argon detectors,” says Willis, now a professor at Columbia University. “Many people had the idea of building a long-drift detector; Carlo had the strength to do it. He could work on many things at once. He had a number of smart and brave people to work on this.”

In 1997, the ICARUS-Milano collaboration recorded neutrino events with a 50-liter liquid-argon detector exposed to a high-energy neutrino beam at CERN. In 2001, the ICARUS collaboration assembled a detector 20 meters long in the INFN-Pavia laboratory and filled one of its two modules with about 300 tons of liquid argon to record cosmic rays, showers of particles created in the Earth’s atmosphere.

“We had five months of operation,” Cavanna says. “We collected millions of cosmic-ray events. We were satisfied with our physics results, but we were not completely satisfied with the cryogenics system.”

After making improvements to the detector, the collaboration moved the two modules under- ground to Gran Sasso National Laboratory. This fall, ICARUS will begin recording neutrinos from a powerful muon neutrino beam originating at CERN, about 730 kilometers away. The neutrinos travel straight through the Earth—no tunnel needed. The collaboration expects to record about 1300 neutrino interactions with argon per year when the CERN-Gran Sasso beam reaches full strength.

For their part, ArgoNeuT scientists expect to collect tens of thousands of neutrino events within six months.

“The Europeans have solved many problems, in particular in issues related to argon purity and the actual detection of particle tracks,” Fleming says. “We owe them a huge amount because of their incredible push to advance this technology over the last 20 years.”

Fighting scavengersIn April 2007, a prototype liquid-argon detector, developed at Yale University, recorded its first cosmic-ray tracks. It was the first crucial step in bringing US physicists up to speed with this technology.

“We call it technology transfer,” says Fermilab physicist Stephen Pordes.

Pordes works on the US effort to find the best way to fill a time projection chamber with ultra-pure liquid argon. If there is too much air in the vessel, it will stop the electrons before they can reach the readout wires.

“The purity of the argon is really the main point of the technology,” says Cavanna, who will spend the summer at Fermilab to help with the startup of the ArgoNeuT detector. “Impurities are like scavengers. If the argon is not pure enough, it practically eats the signal that we would detect with our wires.”

The level of impurity inside a liquid-argon detector must be less than 50 parts per trillion. ICARUS achieves this by pumping the air out of the detector before filling it. This approach, how-ever, is impractical for detectors that might reach the size of a 20-story building. So Pordes and other physicists are exploring the possibility of pushing the air out of the detector vessel by repeatedly flushing it with argon gas before filling it with liquid argon. Then they further reduce impurities by filtering the liquid argon as it circulates within the chamber.

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Mitch Soderberg works on the ArgoNeut detector at the Proton Assembly Building. Photo: Reidar Hahn, Fermilab

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ArgoNeuT records a “video” of the charged particles emerging from the collision between a neutrino or cosmic ray entering the detector and an argon nucleus. The charged particles knock loose electrons, which then travel through the argon to an array of high-voltage wires. The wires record the location and arrival time of the electrons, which reveal the various particle trajectories.

Liquid argon

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Next: scaling upThis summer, ArgoNeuT scientists will place their detector into a high-intensity beam of muon neutrinos generated by Fermilab’s Main Injector accelerator and begin to take data. They will measure the cross section, or probability, of neutri-nos colliding with argon nuclei in the detector. This is an important piece of information for the analysis of data from ICARUS and other, future experiments, Cavanna says.

“We need to know the neutrino-argon cross sections with very high precision,” he says. “It is not Nobel Prize physics, but it is important to understand the exposure of a liquid-argon detector to a neutrino beam at low energies. It will show that this technology is suitable for extracting neutrino physics information when implemented in the next generation of experiments.”

Fleming and other neutrino physicists are already tackling the next step. They plan to build a bigger detector at Fermilab containing 170 tons of liquid argon. It would catch muon neutrinos

from a beam generated by the lab’s Booster accelerator, and rely on the new method of removing impurities. If approved, the Micro Booster Neutrino Experiment, or MicroBooNE, would be about one-third the size of the ICARUS detector, cost about $6 million in materials and clarify mysterious low-energy neutrino sig-nals seen in an earlier experiment.

“MicroBooNE would be a step beyond ICARUS 600,” Fleming says. “If it is built, we would be able to do important physics measurements using a liquid-argon detector that could be scaled to even larger sizes.”

Eventually, neutrino physicists hope to build experiments with five kilotons and, ultimately, 100 kilotons of liquid argon to find out whether neutrinos are the reason we and the matter around us exist.

“It’s a long haul,” Fleming says. “I think the liquid-argon technology will revolutionize the field of neutrino research if we can make it work for very large detectors.”

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A bumperof phy

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In our October/November issue, we asked readers to share stories and photo- graphs of physics-related license plates. Here are the responses.

by Matt Cunningham

sics platescrop

Tune KamaeStanford Linear Accelerator CenterMenlo Park, CaliforniaI acquired my plate from a visiting postdoc. He was fascinated to learn that one can customize license plates in the United States. I bought his car when he went back to Japan, mostly because of the GLAST (Gamma-ray Large Area Space Telescope) license plate. Later, I sold the car to another postdoc and kept the plate. Jonathan Ormes also had a GLAST plate when he was director of research at Goddard Space Flight Center in Maryland. Jonathan moved to Denver, so I don’t know what’s happened to it, but at one time there were an East Coast and West Coast GLAST.

Jeff GeraciAnaheim, CaliforniaI had applied for this plate with the notion that I could get my life a bit more organized, provided there was a constant metaphorical reminder close at hand. The plate DELTA S is the term for the change in entropy, and was intended to be a reminder to keep up on maintenance, exercise, eat the right foods, keep organized files, de-frag-ment my hard drive, yada, yada, yada... My wife, Karen, agreed that this would be a noble gesture, and we did eventually bring some order to our nest. Nearly four years have passed since mount-ing that plate. Now we have a two-year-old son, Ronnie, who has done a fine job of restoring entropy in our household. Perhaps we can take some comfort in the fact that the term is variable.

Chris QuiggFermilabBatavia, IllinoisBack in the days of the Superconducting Super Collider Central Design Group, my family pre-sented me with license plates signifying the 20-TeV on 20-TeV collisions we planned for the SSC. It was a private source of pleasure for my colleagues and me. The world at large didn’t notice. It was on an ancient Volvo, which blended in with all of the other ancient Volvos in Berkeley. The plate hangs in my garage now. It’s a memento from one of the most intense times I’ve been through. It’s a treasure from that great time.

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These clever combinations of numbers, letters, and symbols are a mixed bag of inside jokes, conversation-starters, a way of recognizing like-minded people, and tangible reminders of the sweat, toil, and joys of research. They reflect not only their owners’ gusto for science, but also

the desire, and need, to share it. Taken together, they present a much broader story than when viewed alone. They are the shorthand of proud scientists who wish to invite interaction. We hope you enjoy them as much as we did; please continue to send us your photos and stories.

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L.N. BlancoMiami, FloridaI’ve had the custom license plate SOLITON for 30 years. I transfer it from one car to the next. In many ways a car behaves like a soliton: It is a wave localized in a certain region of space, it keeps its shape when traveling, and it interacts with other solitons (cars) emerging unchanged, most times, perhaps with only a small phase shift.

About 28 years ago, I was attending a con-ference at a hotel in Fort Lauderdale. During the meeting, an employee interrupted to find the owner of a car parked in a restricted spot. The employee spelled the tag S-O-L-I-T-O-N and then pronounced it. I stood up to tell the employee that I was the owner, right as a physicist in the audience said something like, "A soliton at rest, parked outside? Don’t worry, it will prob-ably collapse and disappear rapidly." Everyone burst into laughter. As we walked toward the park-ing lot, I tried to explain the meaning of the word soliton to the puzzled employee.

Jamie SantucciFermilabBatavia, IllinoisI have Illinois license plate PHYSICS on my 2005 Toyota Camry. I believe that it cannot get more physics than that! The story is simple, unlike Tom Nash’s (Oct/Nov 07). I work at Fermilab and I used to have a Toyota pickup truck with 900 GEV plates (the TeV ring energy at that time). When I traded my truck in for a Camry, I had to get new plates because Illinois does not allow truck plates on cars. I applied for PHYSICS as my first choice and, much to my surprise, I got it.

Steve AxelrodLos Altos, CaliforniaMy license plate was originally suggested a year ago by my two young daughters. The plate, XRAY BMR, is on a BMW 330 convertible. It applies to both the car and me, since I’m helping to develop a new miniature X-ray tube to treat breast cancer. My colleagues think it’s cute, but I haven’t got many questions outside of work. Maybe people are scared that the car emits X-rays.

Richard JanesBellevue, IowaWhen I visited my hometown in Wisconsin, rela-tives and friends kept calling me “the scientist” because I worked at Argonne National Lab and later Fermilab. I responded, in time, with this vanity plate.

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Leon HellerLos Alamos National LaboratoryLos Alamos, New MexicoIt’s a lot of fun and a great conversation starter using aspects of my work as a physicist on license plates. Friends are quick to spot whenever a new one goes on the car, and invariably ask what it means. For some I provide a brief expla-nation, but for my weekly hiking group there is ample time to also give some background about the significance of the research. Those not familiar with Los Alamos National Laboratory are pleasantly surprised to learn that there is basic research going on in addition to work on nuclear weapons.

I try to come up with a new license plate every year. I am proudest of the very first one: NUCLEON, because it contains my first name. On the other hand, one wag suggested it was an invitation to nuke Leon.

The operation of a high intensity proton linear accelerator at Los Alamos yielded large fluxes of pi mesons and led to PION. The advent of the quark revolution and development of a gauge theory based on the color degree of freedom, involving different flavors of quarks interacting with glue, led to a long research period and many license plates: COLOUR, FLAVOUR (British spellings), GAUGE, UP, DOWN, and GLUE. At MIT a bag model of the interaction of quarks and glue was developed, and led to BAG.

QBARQ represents a meson made of a quark and anti-quark. DIMESON signifies a particle composed of two quarks and two anti-quarks. OMEGA-* is a particle comprised of three strange quarks. (An excited state is normally denoted with an asterisk, which is not available in New Mexico, but the Zia symbol is close enough.)

I have about 30 plates in my basement. I’ve kept every one, with one exception. A local res-taurateur, who is also a scientist at the laboratory, recently decided to turn a portion of his restau-rant into a bar, which is a place for people to meet and talk science. He named the bar Quark. I told him I had a plate by the same name and let him borrow it.

A strange thing happened involving that plate back in 1975. I was driving home, and in my rear view mirror I noticed the car behind me was uncomfortably close. I could easily make out the QUARKS California plate on the front of the car. I had no doubt that the car belonged to Murray Gell-Mann, who had earlier proposed such frac-tionally charged particles and gave them the name that stuck. He was visiting Los Alamos that summer, but was not in the car at the time; I think his wife was behind the wheel. I was con-cerned about a possible collision of quarks, but fortunately no accident occurred.

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E PLUSBen Smith, a retired SLAC engineer, acquired his plates about 15 years ago when he was designing and installing the Stanford Linear Collider positron source.

Common questionDoes that stand for educational excellence?

E MINUSJym Clendenin, a retired SLAC physicist, also acquired his plates about 15 years ago when he was commissioning the SLC polarized electron source. He was in charge of the SLAC linac electron injector until his recent retirement.

Common commentThat’s a really poor grade!

Ben Smith and Jym ClendeninStanford Linear Accelerator CenterMenlo Park, California

Ben and Jym offer similar explanations when asked about the meaning of their plates. It goes something like this: “It stands for positron (elec-tron), which is the antiparticle for the electron (positron), both of which are accelerated by the two-mile-long SLAC linac where I work.” Generally, upon hearing the word “antiparticle” the questioner’s eyes are seen to glaze over and the conversation either ends or goes on to another subject.

SLACers, on the other hand, usually say something like: “Be sure not to run into E MINUS (E PLUS) or you’ll be annihilated!”

Both Ben and Jym plan to keep their plates for the indefinite future.

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27Photo: Diana Rogers, SLAC

day in the life: the versatile mr. freeze

Some days Jerry Zimmerman calmly follows his typical morning routine and joins

countless other suburbanites on the road to work. Then there are the other days.

Those days Zimmerman takes on an alter-persona.

He wakes up early: a little anxious, a little excited. His energy builds as he prepares for the day, mentally checking off his supplies and reviewing scenarios of the questions soon to pepper him. His mind drifts to freezing fog, explosions shoot-ing a ball 16 stories high, and children gasping in awe. A mischievous twinkle enters his eye, his step bounces, and he starts talking fast.

The studious physicist and computer expert has morphed into a charismatic showman: the third incarnation of Mr. Freeze.

Ask residents of the Fox Valley outside Chicago about Fermi National Accelerator Laboratory and most will utter a vague description, or nothing at all. But mention Mr. Freeze and adults and children alike break into grins and descriptions of their favorite science experiments. He makes the cryogenics of high-energy particle physics accessible and, well, cool.

“I’m excited about science, and this allows me to use that excitement for a good purpose,” says Zimmerman, who switched from occasionally performing loud, messy science experiments for families to performances once or twice a month for schools and scout troops after the previous Mr. Freeze retired 12 years ago.

Cryogenics is the study of how materials behave at temperatures near absolute zero. In high-energy particle accelerators, such frigid temperatures reduce the electrical resistance of wires in superconducting magnets, increasing the magnet strength and allowing faster particle acceleration. The same holds true for supercon-ducting cavities, cryomodules, and wires used in accelerators and detectors.

Initially, Fermilab management questioned the wisdom of diverting Zimmerman from a full day of work at the laboratory, where his projects

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require a mix of physics, computer programming, and mechanical engineering skills. Now manage-ment views his show as educational outreach, a vital part of running a government-funded physics laboratory in a heavily-populated area in tight economic times. The two-hour show con-nects everyday citizens with a complex scientific field where jargon often stands in the way of easy understanding.

“I feel it is the responsibility of people who work in science to do things like this because that is the only way people know what we do,” Zimmerman says. “Cryogenics provides an easy entry point. About anybody can understand hot and cold. And there are lots of things you can do—not quite limitless, but close.”

Zimmerman consistently adds new compo-nents to his show, but staple crowd-pleasers

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day in the life: the versatile mr. freeze

include mixing soap with nitrogen to create gey-sers of bubbles, using compressed gas to shoot confetti or rubber balls, shattering roses, and using a frozen banana to pound frozen rubber tubing through wood. Sometimes he “accidentally” breaks off the fingers of his safety glove as it emerges from a tank of nitrogen.

“I have had girls in the front row scream their heads off, like I just maimed myself,” he says with a slight smile.

Gasps and giggles aside, the show teaches the basics of gases, liquids, and solids and the cryogenics used to run particle accelerators at Fermilab. Zimmerman brings the complicated, mammoth machines down to Earth by comparing them to everyday objects such as the television, which is a type of particle accelerator.

Such basic lessons come in handy for a nation whose average 10th grade science literacy scores lag behind 16 of 30 of the world’s richest countries, according to the latest Program for International Student Assessment. “The science demonstrations help Fermilab. They help sci-ence,” Zimmerman says. “Because now people see that science isn’t so boring. It isn’t so bad. I have run into people who remember seeing the show as a child, and then used the stuff they learned when cryogenics came up in their

college class. One man told me the show encouraged him to study science in college.”

Even in a media-saturated, short-attention-span society, the show keeps drawing new generations of fans. In 2001, during a break at a Snowmass conference in Colorado, Zimmerman performed his Mr. Freeze show for a nearby science day camp. Days later, when exiting a local movie theater, Zimmerman was confronted by a six-year-old girl yelling, “Mr. Freeze!” She had seen the show, and when he quizzed her on the science facts behind the explosions, she remem-bered it all.

In February, when Naperville, Illinois-based Brownie Troop 371 wanted to tear down stereo-types about science that limit female participation, they asked Mr. Freeze to perform. According to the National Science Foundation, women account for 20 percent or fewer of postdoctoral students in science, engineering, mathematics, and physical sciences.

“It’s an exciting opportunity for our girls and our guests, and we hope it will further spark their interest in math and science,” says parent Sue Grove.

Zimmerman may perform up to six shows back-to-back in a day. “At 4 o’clock, I’m really burnt out,” he says. “It is not just the talking; it is

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the concentration: Did I do that for this show? What were their questions?”

But after a good night’s sleep, Zimmerman is ready to return to Fermilab as just himself, a sort of physics jack-of-all-trades. He helped build the system to map the magnetic interior of the CMS detector at CERN, the European particle physics lab on the French-Swiss border, and maintains the extruder at Fermilab that produces plastic scintillator pieces for distribution world-wide; they’re used to detect passing subatomic particles. Zimmerman also created a high-speed pneumatic pressure system for COUPP, a mod-ern bubble-chamber experiment, and helped upgrade the zip track, a 3D robotic system to map magnetic fields.

“I like everything I do,” Zimmerman says. “But I get really excited about being Mr. Freeze. I love carrying on that legacy and seeing what I can add to make the show better.”

Text: Tona KunzPhotos: Cindy Arnold and Reidar Hahn

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Bubble technology bursts into 21st centuryby Tona Kunz

Donald Glaser of the University of California, Berkeley, won a Nobel Prize for inventing the bubble chamber in 1952 as a way of detecting subatomic particles. Now a University of Chicago professor, Juan Collar, is leading the charge to make the bubble chamber cool and cutting-edge again.

Collar is the spokesman for COUPP, which stands for Chicagoland Observatory for Underground Particle Physics. The heart of the experiment is a thin-walled quartz bell jar kept deep underground at Fermi National Accelerator Laboratory. It attempts to catch WIMPs, or weakly interacting massive parti-cles—leading candidates for the mysterious dark matter that makes up roughly 85 percent of the matter in the universe.

The liquid in a bubble chamber—typically hydrogen—is kept just above its normal boiling point, but under enough pressure that it will not boil unless disturbed. When a charged particle zips through the liquid it triggers boiling along its path, visible as a series of small bubbles. In the early days of high-energy physics, bubble chambers were a staple; but in the past two decades, scintillating wire and gas chambers proved more versatile and effective in particle detection, nearly relegating the bubble chamber to extinction. COUPP researchers think that with a few modifications the chamber can make a strong comeback.

The biggest limitation for bubble chambers of the past was an inability to keep the liquid in a superheated state for an extended period of time. This required operators to time short blasts of particles from an accelerator to the few milli-seconds when the temperature was just right. The COUPP collaborators got around this by finding a way to keep their liquid on the verge of boiling 80 percent of the experiment time, increasing the probability of catching dark matter particles.

deconstruction: COUPP bubble chamber

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Once the bubbles reach a millimeter in size, researchers take snapshots of the chamber with a digital camera and compare them, looking for particular changes in the rate of bubble produc-tion—the signature of dark matter—as the sensitiv-ity of the chamber is varied. After each photograph, the chamber sits idle for about 30 seconds as the heat dissipates; it is then reset and ready to record another series of bubbles.

One advantage of the bubble chamber over other dark matter detection devices is the ability to switch the type of liquid in the detector with minimal effort and cost. Since WIMPs and other particles would trigger the formation of bubbles at different rates in different liquids, this allows the experiment to cross-check its own results, making sure that WIMP detection was not an anomaly.

Physicists theorize that dark matter particles interact with ordinary matter via mechanisms that are either dependent or independent of the nuclear spin of the atoms in the detector material. The chamber has shown promise for spin-dependent results but lags behind some other dark matter experiments in spin-independent sensitivity.

COUPP recently finished a year-long experiment using a one-liter chamber placed about 100 meters underground in a tunnel built for another experiment at Fermilab. The results, combined with the findings of other dark matter searches, contradict claims for the observation of such particles by DAMA, the Dark Matter experiment in Italy, and further restrict the hunting ground for physicists to track their dark matter quarry. If the DAMA result had been due to spin-depen-dent WIMPs, then COUPP researchers should have found hundreds of WIMPs. They found none.

Scientists now are testing a 30-liter cham-ber; the larger size increases the possibility that the elusive WIMP will land inside. They hope to move that chamber to an even deeper tunnel whose extra layers of dirt and rock will further reduce interference from particles that are part of the natural background.

The COUPP bell jar, which is enclosed in a steel vessel, contains a liter of iodotrifluoromethane, a fire-extinguishing liquid known as CF3I. When a particle enters the jar and hits the nucleus of an atom in a CF3I molecule, it triggers the evap-oration of a small amount of CF3I. The ensuing bubble grows and eventually become large enough for researchers to see. A WIMP is expected to leave a single bubble, similar to the one in this image, in contrast to the multi-bubble tracks left by other particles.

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Requiem for a cyclotron

From 1936 to 2008, Columbia University housed a physics legend: an early cyclotron. Columbia’s cyclotron was one of the first machines to split the atom, confirm-ing reports from Europe that such a feat was pos-sible. It demonstrated that uranium-235 was

readily fissionable, leading to experiments aimed at harnessing the astounding energy of a nuclear chain reaction. It helped usher in the Atomic Age and the subsequent promise and problems of nuclear power and energy, the results of which we continue to grapple with today. And in March of this year, it was cut up and sold for scrap.

Physicist John Dunning built Columbia’s cyclotron in the 1930s and it split atoms for nearly 30 years. After it was decommissioned in 1965, the university sent key pieces of the machine to the Smithsonian Institution and left the rest in the basement of Pupin Hall, Columbia’s physics building. Then it sealed the basement off. For decades, the cyclotron was only accessible by a system of tunnels that runs under the entire university. The tunnels are off-limits to students, although almost every self-respecting under-graduate has sneaked into them. In retirement, the cyclotron became the university’s most popular underground attraction.

I first ventured to see the cyclotron on a dark and stormy night in April 2005. Armed with word-of-mouth directions, four friends and I descended into the tunnels through an entrance across campus and made our way toward Pupin. After navigating a few forbidding rooms filled with imposing electrical equipment and many ignored Do Not Enter signs, we made it to Pupin’s basement. We had been instructed to find the out-of-order men’s bathroom, where one person had to climb over a wall (via an air duct) and into a hall of abandoned laboratories. Once inside, he opened the door for us and the treasure hunt began.

We found the cyclotron in a room that looked like a time capsule from the Atomic Age. Boxes full of official and not-so-official documents (a friend claimed to have found a shopping list that included uranium) and pieces of dusty lab equip-ment were everywhere, but nothing could distract from the main attraction. The cyclotron’s 65-ton magnet was anchored to the floor, sitting under a giant arch that didn’t look so different from

the air duct my friend had just climbed over; Dunning had built the machine during the Depression with salvaged parts and donated metal. Almost unbelievably, there was a start button on its side, along with stickers that declared several other mysterious objects “critical space items” property of NASA.

But the need for another kind of space became even more critical for the university. Late last year, Columbia announced plans to turn Pupin’s basement into a combination of lab space and infrastructure for a new building going up next door. In the process, the cyclotron was disman-tled and its pieces—many of which were pure copper—were sold as scrap metal. About a week before it was destroyed, George Hamawy, Columbia’s director of radiation safety, organized a funeral for the machine. His heartfelt eulogy covered the machine’s important scientific con-tributions but also touched on its sentimental value. From Hamawy’s tale of being drawn to physics after hearing about the cyclotron’s experiments to students taking advantage of their last chance to see the fabled machine, people spoke of an attraction to the cyclotron that went beyond its scientific importance, historical value, and even status as a real-life urban legend.

The cyclotron was an artifact of an age before the atomic bomb when excitement, wonder, and hope outweighed the fear that is so familiar today. It was an artifact of decades of tunnel spelunking, Columbia’s most public secret. It was an artifact of my college experience, bringing me closer to the people who shared my first Columbia adventure and setting the tone for all the rest that followed. It seemed the cyclotron would always be there—in history and in adven-tures both collective and personal. I always thought I would be able to go back for a visit, whether at graduation or my 50-year reunion. Instead, I’ll be remembering how the cyclotron’s multifaceted appeal became most apparent at the end of its life, and remembering how glad I was to be able to say goodbye.

Elizabeth Wade recently graduated from Barnard College. She was a Fermilab intern in the summer of 2005 and continues to write about physics.

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In May 1983, physicists on the UA1 detector for the Super Proton Synchrotron accel-erator at CERN made the first definitive observations of the Z boson.

Its electrically charged cousin, the W, had been seen a few months earlier, and the Z would complete the set of particles that represent the weak force, providing evidence for the validity of the proposed electroweak theory of particle physics.

James Rohlf, an assistant professor at Harvard University, was based at CERN and led the analy-sis of the Z boson signals for UA1. This page from his personal logbook shows the summary of the first four events from UA1 that physicists thought represented the Z. The UA2 collaboration observed the Z soon after.

The first event is annotated with “track radiates” because the signal was an unusual, though possi-ble, way for Z to appear. The second event, based on seeing muons in the detector, provided a vital confirmation and check on the other events, which were based on observing electrons from the decay of the Z. The muon detection systems were independent of the electron detection and so this cross-check carried a lot of weight.

Rohlf comments that the notation “recorded 12 minutes apart!” was a sign of huge surprise as the first few events had been collected only over weeks of running, so one event right after another was unexpected.

The chart drawn here was reproduced in the paper in Physics Letters B in July 1983 announcing the discovery of the Z. Carlo Rubbia and Simon Van der Meer won the Nobel Prize in Physics in 1984 for their contributions to the discovery of both the W and Z bosons.David Harris

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symmetry

explain it in 60 seconds

The Z boson is a heavy particle that is one of the carriers of the ‘weak force’. It is

a partner of the W+ and W- bosons that mediate radioactive decay processes.

The Z boson was first discovered as an intermediary of a new type of neutrino reaction. This so-called ‘neutral current interaction’ was the missing piece of a puzzle in which the forces created by the W bosons fit together neatly with the force of electromagnetism, due to the photon. Together, these four par-ticles create the forces that form a beautifully unified theory of ‘electroweak’ interactions.

In the 1990s, accelerators at the Stanford Linear Accelerator Center and CERN produced 12 million of these Z bosons in a controlled setting and studied the decays of the Z in great detail. The Z decays to pairs of all types of quarks and leptons, except for the heavy top quark. These experiments made high precision tests of the electroweak theory and the properties of quarks and leptons. Quarks produced from the Z radiate gluons, and so these experiments also give some of the highest-precision information about the carrier of the ‘strong’ interactions.Michael Peskin, Stanford Linear Accelerator Center

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

Office of ScienceU.S. Department of Energy