dimensions volume 05 of particle physics symmetryA joint Fermilab/SLAC publication

issue 03

august 08 volume 05 | issue 03 | august 08

2 Editorial: Positive News for Particle Physics 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.

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.” symmetryA joint Fermilab/SLAC publication 4 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.

On the cover 10 New Tools Forge New Frontiers Battered or shiny, personalized license plates are a US particle physics is pushing forward on three frontiers. whimsical part of physics culture. On one level they’re Each has a unique approach to making discoveries, inside jokes, told with a wink to those in the know; on and only by pursuing all three can scientists address key another, an invitation to approach and learn more. In questions about the laws of nature and the cosmos. response to a call from symmetry, readers sent dozens of their favorites. “It’s a memento from one of the 16 Bonnie and the ArgoNeuTs most intense times I’ve been through,” one wrote. “It’s Inspired by heroes of Greek mythology, physicists are on a treasure from that great time.” a quest to find a cheaper, more efficient way to capture neutrinos—one of the strangest and most fascinating par- Inside front cover ticles in the universe. Liquid-argon detectors may hold According to Greek mythology, the Argonauts sailed the key to discovering whether neutrinos are the reason across the Mediterranean Sea to retrieve the Golden that stars, planets, and people exist. Fleece. Scientists of the ArgoNeuT project use an argon-filled particle detector to explore the interactions 22 A Bumper Crop of Physics Plates of the neutrino, one of the most abundant particles in In our October/November issue, we asked readers to the universe [see story, p. 16]. share stories and photographs of physics-related license plates. Here are the responses. 28 Day in the Life: Mr. Freeze His 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 Chamber Scientists retool a classic technology for a modern quest: In March 2008 we launched our blog, symmetrybreaking. the search for dark matter. Here are some highlights of the stories we have posted to date. You can read more at www.symmetrymagazine.org/breaking/. 34 Essay: Elizabeth Wade “The cyclotron was an artifact of an age before the atomic Physicists discover the bottom-most “bottomonium” bomb when excitement, wonder, and hope outweighed the July 9, 2008, 4:30 pm: Bottomoniums are particles that contain fear that is so familiar today. It was an artifact of decades both a bottom quark and an anti-bottom quark but are bound of tunnel spelunking, Columbia’s most public secret. It was together with different energies. Now researchers have an artifact of my college experience, bringing me closer detected and measured the lowest-energy particle of the family. to the people who shared my first Columbia adventure and setting the tone for all the rest that followed.” Code crackers wanted! May 15, 2008, 5:12 pm: A little over a year ago, the Fermilab C3 Logbook: Z Boson Office of Public Affairs received a curious letter in code. In May 1983, physicists working on the UA1 detector You can read partial solutions of the top and bottom sections in for the Super Proton Synchrotron accelerator at CERN the comments. However, the middle section remains unsolved. made the first definitive observations of the Z boson. Are the laws of physics the same throughout C4 Explain it in 60 Seconds: Z Boson the universe? The Z boson is a heavy particle that is one of the carriers June 19, 2008, 6:32 pm: Observations of a quasar about 6 of the weak force. Its discovery completed the Standard billion light years away have shown that one of the funda- Model of particle physics and allowed physicists to probe mental properties of physics is the same there as here: the characters and interactions of many of the other protons there are 1836.15 more massive than electrons. fundamental particles. Mariah Carey vs. Albert Einstein April 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 complete July 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.”

Office of Science U.S. Department of Energy Illustration: Sandbox Studio from the editor

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

Symmetry Editor-in-Chief Publisher Print Design and Production PO Box 500 David Harris Judy Jackson, FNAL Sandbox Studio MS 206 650 926 8580 Chicago, Illinois Contributing Editors Batavia Illinois 60510 Deputy Editor Art Director USA Roberta Antolini, LNGS Glennda Chui Peter Barratt, STFC Michael Branigan 630 840 3351 telephone Managing Editor Romeo Bassoli, INFN Design Assistant 630 840 8780 fax Kurt Riesselmann Stefano Bianco, LNF Jared Grodt www.symmetrymagazine.org Kandice Carter, JLab [email protected] Senior Editor Illustrator Tona Kunz Lynn Yarris, LBNL Aaron Grant (c) 2008 symmetry All rights James Gillies, CERN reserved Staff Writers Silvia Giromini, LNF Web Design and Production Elizabeth Clements Xeno Media symmetry (ISSN 1931-8367) Youhei Morita, KEK Kelen Tuttle Tim Meyer, TRIUMF Hinsdale, Illinois is published 6 times per Rhianna Wisniewski year by Fermi National Perrine Royole-Degieux, IN2P3 Web Architect symmetry | volume 05 issue 03 august 08 Accelerator Laboratory and Copy Editor Yuri Ryabov, IHEP Protvino Kevin Munday Stanford Linear Accelerator Melinda Lee Yves Sacquin, CEA-Saclay Web Design Center, funded by the Interns Kendra Snyder, BNL Karen Acklin US Department of Energy Calla Cofield Boris Starchenko, JINR Maury Tigner, LEPP Web Programmer Office of Science. Matt Cunningham Mike Acklin Jennifer Johnson Ute Wilhelmsen, DESY Zoë Macintosh Tongzhou Xu, IHEP Beijing Photographic Services Gabby Zegers, NIKHEF Fermilab Visual Media symmetry Services

2 commentary: seth zenz

persistently adding unsourced nonsense to Wikipedia Wikipedia and harassing other users; he responded needs by sending a letter to one of the high-level admin- istrators on my real-life experiment to complain that more I was suppressing The Truth about how Relativity physicists is false. I ultimately had to explain the situation to Wikipedia, the popular my PhD advisor, and of course the decision was online encyclopedia, made to ignore the letter, but it was certainly jarring has often been criti- to have personal volunteer work interfere with cized as having misin- my real job in that manner. formation and inadequate references. By allowing One frustration for many academics is that any user to edit, it runs the risk of having “truth” no Wikipedia user has special authority because defined by majority vote or a persistent vocal of personal experience and knowledge. Editors minority; it has the potential to deliver the have to back up what we know—even some- public’s perception of science into the hands of times the most seemingly obvious facts—by includ-

Photo courtesy of Seth Zenz fringe groups with an ax to grind. ing citations for our statements. Although this However, as a physics graduate student and may seem irritating and time-consuming, these Wikipedia editor and administrator, I argue that policies ultimately help experts because our Wikipedia’s rules for reliable sourcing of articles knowledge can be supported by reliable sources. are stronger than is often believed, and that aca- There are examples of scientists having tre- demics can play a very positive role in improving mendous influence over Wikipedia articles in and expanding Wikipedia. their areas of expertise and creating excellent, Using Google is enough to see why we are well-sourced articles. stuck with Wikipedia as a major source of popu- One can ask if it is possible to create a better lar knowledge and we ought to make the best version of Wikipedia by giving experts special of it: Wikipedia articles turn up among the first authority, as does Wikipedia co-founder Larry hits for most physics topics. For most people of my Sanger’s new project, Citizendium. But ultimately generation, a Google search is now the first stop the question is moot, because replacing Wikipedia in almost any search for information. This means simply isn’t practical. Wikipedia’s willingness to that if an undergraduate is trying to get a quick accept any warm body gives it vast armies of refresher on a topic for her physics exam, or a contributors, while Citizendium’s requirement worried member of the public is trying to get an that the most trusted editors be faculty members independent assessment of whether the Large or equivalent means that that project has very Hadron Collider will really make black holes that few. Wikipedia’s strategy of appealing to non- eat the Earth, they will end up reading Wikipedia. experts’ desires to make a difference, chaotic The quality of those articles will ultimately determine though it is, has so far proven far more empirically whether thousands of searchers come away successful; it has about a thousand times as informed, confused, or misled. many articles as Citizendium, and Citizendium’s One of the main sources of the misinformation sixty-eight officially approved articles so far is the author who has no formal training in physics do not appear to me to be much better sourced but an enthusiasm for the subject, and who or better written than the equivalent topics promulgates their own theories with no credibility on Wikipedia. in the scientific community. On Wikipedia, such For a scientist, then, editing Wikipedia may people have the same ability to contribute as prove to be a difficult experience, but ultimately anyone else, and they do. They try to reinterpret a successful one. As things stand now, though, the Wikipedia policies to have their edits accepted, the physics articles are rather understaffed, but those policies are actually quite strict about resulting in longer delays in removing rubbish using verifiable and reliable sources. These individ- and very little time to improve content. A relatively uals are persistent and editors spend a significant modest number of expert contributors could make

fraction of their time holding the line against them, a big difference in the quality and scope of symmetry | volume 05 issue 03 august 08 often simply by watching articles and reverting Wikipedia’s physics articles. As measured in the unsupported edits. This makes article improvement number of people reached, such an effort may on Wikipedia more like a random walk than a be a more important form of outreach and edu- steady progression, but at least Wikipedia policy cation than almost any other. makes sure that the random walk goes in the right direction. Seth Zenz is a University of California, Berkeley, graduate stu- dent, working with the Lawrence Berkeley National Laboratory These individuals can also fight dirty. I once group on the ATLAS experiment at CERN and living in Geneva, blocked from editing someone who was Switzerland. He is a contributor to the US/LHC Blogs.

3 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 Photo courtesy of Circuit Global Sports Management

Call of the bike prairie-powered winds that After breaking his leg in a colli- As Reid Mumford pedals, some- sometimes threaten to topple sion with a van during practice, times he thinks about how strollers at the laboratory. On he had to work even harder to to break away from the pack. the most blustery days, wind recover and reclaim his position. Other times he thinks about speeds average 26 mph and His Johns Hopkins profes- how the smallest bits of the gusts blow nearly 80 mph. sors and co-workers from the universe break apart in high- “The wind makes training lab’s CDF experiment support energy collisions. here hard, which is a good his bid for bicycling fame, Mumford, who studies rare thing,” Mumford says. “Most helping him fit training—and subatomic particles at Fermilab, of the people I race against weekend races all over the is a rarity himself: a particle live in high altitudes. If I didn’t country—into grueling grad- physicist who is also a profes- have the wind, it would be student hours of data analysis. sional bicycle racer. Riding hard to get faster.” Mumford is wrapping up his gives him a physical workout; He practices 17 hours a PhD thesis and plans to take analyzing data from the world’s week, even in the snow, using a break from physics in the fall highest-energy particle accel- the time to recharge and work to focus full-time on racing. erator, the Tevatron, exercises out complex theories in his head. But once that challenge runs

his mind. Mumford started racing as its course, he hopes to return symmetry | volume 05 issue 03 august 08 “Cycling is a tough sport. a graduate student at Johns and tackle the new energy fron- You don’t win much, but the Hopkins University. In 2007 he tier at CERN’s Large Hadron one day that everything works joined Kelly Benefit Stategies/ Collider. is a beautiful thing,” he says. Medifast, a Minneapolis-based You can find Mumford’s “Just like high-energy physics professional team. In a sport team bio at www.symmetrymag. research.” that requires half the team fall org/bikeracer/. The 32-year-old finds a under age 27, Mumford had to Tona Kunz grueling physical trainer in the work extra hard to secure a spot.

4 All aboard barriers affect the flow of mph before the front wheel Jason Steffen waited to board cars per second—a topic of starts to wobble, and it’s been a plane in the Seattle airport. special interest in Illinois, a known to out-race a Harley He waited to get his boarding land of nearly perpetual road Davidson. But along the way pass scanned. Then he walked construction. the car became more than a a few steps down the jet way, “I would look at how they test of engineering—it turned and waited some more. His minimize the number of cars into Jones’ personal canvas frustration grew. through per second,” he says. “That car is me,” he says. “It’s a “I thought, I’ve got to be “That seems to be the goal—not little different; I’ve always able to do something about to maximize the flow.” been a little different. I made this,” Steffen says. To read Steffen’s paper, myself my car.” After brooding for 18 months, visit www.symmetrymag.org/ Looking closely, one can Steffen, a physicist in the Particle boardingstudy/. see symmetric designs drilled Astrophysics Center at Fermilab, Rhianna Wisniewski and into the rusting doors and came up with a mathematical Tona Kunz hood—Jones’ own handiwork. solution. It would allow passen- Antique Coca Cola serving gers to board four to 10 times Rat rod trays function as floor boards, faster, depending on the size Parked between a shiny green an oversized bullet plugs the of the airplane. Camaro and a remodeled ’63 overflow tank, and safety pins The secret: load passengers Mustang, a 1929 Ford Model A keep the spark-plug wires in groups, spaced two to three pickup-turned-hot rod is a together. The cable bracket is rows apart, so they can simul- mosaic of rust and rot. A rag a silver spoon. “I had the stock taneously stow their luggage. plugs the radiator, and ancient bracket,” he says with a shrug. Steffen posted his method wooden slats border the truck “It was just too normal.” The in the Physics and Society bed. The car looks fresh from words “Straight 2 Hell,” bor- section of arXiv.org, a Web site the junkyard, and hardly at home rowed from the title of a Hank where physicists share results. with such classy competitors Williams III album, are fading In the 3 1/2 months since, at the Stanford Linear from the doors, but are still bold he’s been contacted by dozens Accelerator Center’s Hot Rides enough to proclaim the car’s of media outlets all over the Car Show. attitude. globe. But guess who hasn’t But the car’s owner, Jeff The Rat Rod has won three called? The airlines. Steffen Jones, stands self-assured car-show awards, most notably says he heard from a friend of next to what is known around the Chrome and Suede Award a friend of a friend who works SLAC as the Rat Rod. To him, at a Good Guys show, where at Boeing that the airline manu- the car is exactly what he wants it was the only car in the winners’ facturer has taken note of it to be. He proudly declares, circle without a paint job. the study, but his phone has “It’s a work of art.” To Jones, the car is complete. yet to ring. Jones is the precision sheet “People still ask me what color Since posting his results, metal engineer at SLAC. Two I’m going to paint it,” he laughs, Steffen has learned that four years ago he pulled the truck “but it’s done.” Then he pauses or five other groups, including body out of a friend’s yard, and adds, “Except for front

one in Arizona and one in planning to turn it into a hot rod. brakes. And seat belts. It should symmetry | volume 05 issue 03 august 08 Belgium, had also done airplane The Rat Rod has certainly met have seat belts.” boarding studies. Only one that expectation: It can go 120 Calla Cofield 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 Photo: Calla Cofield 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

5 signal to background

Pécub’s Cup A 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 Dark matter music data into light and sound. Lawrence Berkeley National The search for dark matter “I spent a lot of time program- Laboratory and held at Lake strikes a new note with a multi- ming it,” Cushman says. “I had Tahoe in early May. In keeping media art work that turns data to get CDMS files in the proper with the workshop’s theme— from an underground experi- format and figure out what the challenges of beam diag- ment into colored light and sounds good.” Her neighbor’s nostics—Suren Arutunian, head Photos: Reidar Hahn, Fermilab musical tones. 10-year-old nephew helped film of the Low Temperature Physics Karl Ramberg’s creations the musical model and post it Laboratory at Armenia’s Yerevan often blend sound and visuals; on YouTube. Physics Institute, won the award one of his most recent works, Cushman translated the for inventing a beam-diagnostic for example, combined art made energy of each incoming “vibrating wire scanner” for the from musical scores with the particle into a musical note, and Yerevan Synchrotron. music they contained. But a trip the point where it struck the Second trick: the Faraday with his brother, Fermilab physi- detector into color. In addition, Cup Award isn’t a cup at all. cist Erik Ramberg, took his work each type of particle got a It’s a work of art. In 1981 the in a more scientific direction. unique instrumental voice. Italian Swiss artist Pierpaolo Their destination was a mine Midway through the perfor- Pugnali, better known as Pécub in Soudan, Minnesota, where mance, Cushman had the model (“P cubed”), illustrated some Erik was scheduled to work play the familiar six-note melody ads in the CERN Courier for in the control room of the from Close Encounters of the a new company, Bergoz Cryogenic Dark Matter Search Third Kind and a snippet of Instrumentation. Pécub and experiment. “When You Wish Upon a Star.” the company’s founder, Julien “The whole notion of being (“That is a little joke,” she Bergoz, became friends, and at the bottom of an abandoned confesses in the comments fol- in 1992 Bergoz asked him to iron mine—there is something lowing the video clip. “I couldn’t design the certificate for a new

kind of romantic or mysterious help myself.”) Image courtesy of Pierpaolo Pugnali about it,” Karl says. The end result, Karl says, The Cryogenic Dark Matter is that “you get an experience, Search detects particles such aurally and visually, of sub- as neutrons, electrons, and atomic effects. You get a better cosmic rays that rain in from understanding of what the space. It hasn’t recorded any data is saying.” dark matter particles yet, but Cushman says she and the scientists are hopeful. Rambergs would eventually After spending the better like to display the model, or one part of a week in the mine, Karl just like it, at a science or uni- built a full-scale plastic model versity museum. of the detector with the help of “This could be a great out- symmetry | volume 05 issue 03 august 08 his brother and CDMS collabo- reach tool,” Cushman says. “It rator Prisca Cushman, a physics has a lot of potential to spark professor at the University of people’s interest.” Minnesota, who translated the Rhianna Wisniewski

6 Photo courtesy of NASA

award his company was spon- debut at the June 9 pre-launch soring. Voilá. party in Cocoa Beach, Florida. “You can’t tell Pécub what The piece can be rhythmically he should draw,” says Bergoz. complex when evoking the “You tell him what you want to wavelengths of the electro- communicate; he listens intently, magnetic spectrum, or simple then draws four or five sketches and beautiful when depicting on a large sheet of paper­—less GLAST’s elegant orbit. A video than two minutes per sketch.” created by the NASA Goddard Once a sketch is chosen, “he Television and Multimedia gets his set of seven or eight Group accompanies the music. small pots of colored ink, dips “The visuals,” Gasser explains, his fingers in a few... Another “allow for that rare mix of an four minutes and it’s done.” aesthetic experience with Bergoz thinks of Pécub as scientific appreciation and both an artist and a philoso- education.” pher of science: “I am always The gamma-ray telescope, amazed how he can imagine designed and constructed in things I have not told him.” It part at Stanford Linear was Bergoz who introduced Accelerator Center, will be the Pécub, who has a scientific first to survey the entire sky background in pharmaceutical every day searching for the research, to high-energy physics. most energetic form of radia- Says Pécub, “The invisible tion in the universe. Until about in biology and the invisible of a year ago, Gasser knew basic matter are closely con- almost nothing about the sci- nected. Bridges to put imagi- ence related to GLAST. He is nation into the big bang... Your a classically trained composer atomic world is so infinite in and artistic director of the questions.” Classical Archives, an online Although there’s no poster classical music site. Then his this year, Pécub has drawn friend and Classical Archives a handsome certificate for CEO Pierre Schwob, a science the winner. enthusiast who is one of the Paul Preuss, Berkeley Lab major donors to the Kavli Institute for Particle Astro- Gamma-rays inspire physics and Cosmology, com- brass quintet missioned him to compose When you hear the descending a piece for the GLAST launch flurry of 16th notes in the trum- and mission. pets, you know the gamma Gasser spent months rays are coming. They speed immersing himself in scientific toward the detector in the literature. He traveled to the Gamma-ray Large Area Space NASA Goddard Flight Center Telescope in chromatically har- to meet with the mission’s monized notes. The rays split project scientist, Steve Ritz, with a sharp accent, and an and deputy scientist, Neil electron and positron speed Gehrels, and learn about the away from each other in the history, mission, and expecta- GLAST detector, their move- tions of GLAST. ment conveyed by short bursts The art, Gasser says, is an of notes sliding in opposite invitation to the science, a directions along the scale. doorway through which the That’s how Nolan Gasser public, and hopefully the press interprets the science of GLAST and the government, will enter in his original composition the world he has become so GLAST Prelude for Brass passionate about. Quintet, op. 12, which made its Calla Cofield symmetry | volume 05 issue 03 august 08 7 signal to background

Letters

The Big Bang Theory Jennifer 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 boson I 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 symmetry | volume 05 issue 03 august 08 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]

8 letters travels. withphotographic evidenceofthemagazine’s to sendphotosofplacestheircopiessymmetryhavebeen.Herearethree went!InAugust2007,Oh, theplacesyoursymmetry weaskedreaders results… Contest after a 28-day flight circling after a28-day flightcircling down came it where Shelf, Ice fromtheRoss after itsrecovery instrument ing uptheCREAM abreakfrompack- while taking reading mysymmetry magazine found me Antarctica, Station, McMurdo at day beautiful A Amber Jones Abacos vacation“sailed”by! tles, andrumpunches, our Between black holes,seatur- and waitforthetidetorise. stereo, the on Buffett Jimmy us—raidthecooler,faze put didn’t sandbars on aground Cay.Elbow Evenrunning basedinHopeTown,sailboat sion onachartered 31-foot foranexcellent excurJanuary - thou? Two friends joined me in mask andfins,acoolone, a steamy climate)thanaboat, and sun intense the from offallingintolethargy hazard the mind(therebyavoiding explore natureandexercise to means better What torso. thesizeofahuman starfish beaches, snorkelingreefs, and sandy houses, bougainvillea, oped anddesertedcays,pastel tion ofturquoisewater, devel- eastern Bahamasisadestina- Abacos archipelago innorth- wise restfulvacationdays!The stimulatedme even on other crews), the from quotes and quips (and news physics particle est I amsofascinatedbythelat- symmetry keeps - and I had to wait for two two for wait to had I and has beenpretty poorthisyear, covered thatday. The weather although itwasabitcloud- photo, distant more the of in theworld,background southernmost activevolcano You can see Mount Erebus, the are preparedandlaunched. where theballooninstruments area the in itself, shelf the out onthepermanenticeof isbuilt.Iam McMurdo Station which upon Island, Ross background the glacier-covered instruments into,andinthe recovered and equipment been puttingthesupport can seetheseacratesIhave Inthephotos,you unbeatable. my wait.The viewhereis on severalback issuesduring brethren, andhavecaughtup touch withmyearth-bound on asmallerbudget. but done in a smaller space and really high-energy experiments, are experiments cosmic-ray Balloon speak. to so pieces, the up pick to out go then come back down to earth and to it for wait to was January andmyjobsinceearly Station, from the ice shelf near McMurdo launched on December 19th was umd.edu/cream). CREAM mic rays(seehttp://cosmicray. acceleration mechanism ofcos- thesupernova questions about nent in its quest for answers to conti- theAntarctic high above to stay in I get symmetrytostay 9 metrymag.org/lateshowclip/. Carpet Ride,” isatwww.sym- Scientist segment,titled“Magic part oftheFebruary 27Kid Editor’s note:Avideoclipof Lee Marek Bardeen. Marge and Fermilab of Friends with programsfor20years cation edu Fermilab with I “worked” becausemetry magazine kids atDave’sdesk.Iget sym- withsymmetry taken and the picture a had 27.I February on appeared Scientists Kid The science. the doing area Illinois, Naperville, the from but forthelast10Ihadkids The first eight were me alone, years. 18-plus Lettermanfor the LateShowwithDavid I havebeendoingscienceon Scott Nutter antarctic-scott.blogspot.com. through viamyblogathttp:// have been doing here and going was availabletogoget it. came downbefore aplane instrument the after weeks You canseemoreofwhatI

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Photo-Illustration: Sandbox Studio 10 symmetry | volume 05 issue 03 august 08 ergy Fr En ont he ie T r New tools forge new frontiers US particle physics is pushing forward on three frontiers.

T r h Each has a unique approach to making discoveries, e e i t and all three are essential to answering key questions In n o te r about the laws of nature and the cosmos. n F s it ic By Elizabeth Clements y F sm rontier The Co

11 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: “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.” 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 Scientific questions approaches to particular 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?

12 Diagram courtesy of P5 nergy Fron e E tie Th r

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Matter/Antimatter Dark Matter symmetry | volume 05 issue 03 august 08 Asymmetry

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Energy, intensity and cosmic dark energy. A combination of underground exper- At the energy frontier, scientists build advanced iments and telescopes, both ground- and space- particle accelerators to explore the Terascale. based, will explore these mysterious dark phenom- There, in this new scientific territory named for ena that constitute 95 percent of the universe. the Teravolts of energy that will open it up for All of these approaches “ultimately aim at the discovery, they expect to encounter new phe- same transformational science,” the report says. nomena not seen since the immediate aftermath “We need a diversity of approaches to these of the big bang. Subatomic collisions at the questions—a mix of projects both on different tim- energy frontier will produce particles that signal escales and with different scientific reach,” says these new phenomena, from the origin of mass P5 Subpanel member Josh Frieman, a theoretical to the existence of extra dimensions. astrophysicist at Fermilab and the University of At the intensity frontier, scientists use accel- Chicago. erators to create intense beams of trillions of Some questions are unique to a single frontier: particles for neutrino experiments and measure- Only at the cosmic frontier, using highly advanced ments of ultra-rare processes in nature. Measure- instruments to observe the evolving universe, ments of the mass and other properties of the can scientists directly explore the mystery of dark neutrinos are key to the understanding of new energy. In contrast, shedding light on dark mat- physics beyond today’s models and have critical ter requires a combination of astrophysical implications for the evolution of the universe. observations and experiments at high-energy Precise observations of rare processes provide particle accelerators. For example, physicists a way to investigate energy scales at the Terascale anticipate that experiments at the Large Hadron and beyond. Collider, soon to begin operating near Geneva, At the cosmic frontier, astrophysicists use the Switzerland, may identify dark matter particles in cosmos as a laboratory to investigate the funda- high-energy collisions. The Cryogenic Dark mental laws of physics from a perspective that Matter Search, an experiment half a mile under- complements experiments at particle accelerators. ground in Minnesota, uses a sensitive detector Thus far, astrophysical observations, including to search for naturally occurring dark matter the bending of light known as gravitational lens- particles. Gamma-ray detectors in space, such ing and the properties of supernovae, reveal as the recently launched GLAST satellite, may a universe consisting mostly of dark matter and see the glow created when dark matter particles

13 and their opposites collide. Thus a clue from one By defining scientific opportunities for the frontier sheds light on another. field’s existing experiments and future proposals, “You need to pursue all three frontiers to make the report attempts to make a balanced plan that progress in particle physics,” P5 Subpanel Chair maintains the nation’s leadership role in world-wide Charlie Baltay, a physicist at Yale University, says. particle physics regardless of funding levels. “The scientific priorities have not changed in Facing new realities the last few years, but the context has,” Baltay In the United States, the field of particle physics says. “The present P5 Subpanel has developed is in a time of transition. In a year or two, Fermilab’s a strategic plan that takes these new realities Tevatron, the world’s highest-energy particle into account.” accelerator, will turn off. The energy frontier will move to Switzerland, where the Large Hadron The lure of cutting-edge science Collider is about to turn on at the European par- Because the United States will soon shut off the ticle physics lab, CERN. More than 1200 US Tevatron and doesn’t have plans to build another scientists, the largest contingent of CERN massive accelerator any time soon, the energy experimenters from a single nation, will collaborate frontier is likely to remain in Europe for 20 years in experiments at the LHC. or more. However, significant discoveries are New budget realities, however, cloud the within reach at the intensity and cosmic frontiers, future of particle physics in the United States. leading to proposals for new projects that fit The proposed International Linear Collider within the new budget realities. figured as the centerpiece in previous plans In the immediate future, the physics of neu- for the future of US particle physics. A large trinos and the study of rare processes offer cost estimate for the ILC made it likely that unique opportunities to address basic questions a delay in the proposed schedule would occur of particle physics. and led the US particle physics community to At the time of the big bang, nearly equal re-examine the scientific opportunities ahead. amounts of matter and antimatter existed. Since In December 2007, the Omnibus Funding then, however, the antimatter has vanished. Stars, Bill delivered an unexpected blow, eliminating people and everything else that exists consists of $90 million in funding for particle physics from matter. What happened to the antimatter? the expected budget level for FY08. The Physicists believe that neutrinos may be the diminished funding had a powerful impact on only particles with mass that are their own anti- US particle physics, stopping work on several particles. If so, they follow a different set of rules projects, including Fermilab’s NOvA neutrino from other particles regarding the symmetry experiment, SLAC’s B-factory, and all ILC R&D, between matter and antimatter. Hence, neutri- and leading to layoffs and furloughs. nos have profound implications for the evolution “This is a pivotal point in the US program,” says of a universe made of matter. Physicists are Dennis Kovar, acting associate director of the eager to build intense proton sources to make US Department of Energy’s Office of High Energy unprecedented numbers of neutrinos for experi- Physics. “We need to think harder about how ments that will illuminate their unique properties. to get at the key science questions with the Physicists can also use intense proton resources that we have.” sources to observe rare processes in nature. Rare The DOE and the National Science Foundation particle decays can peek into a higher-energy asked P5 to recommend priorities for the future regime—far in excess of the energies the LHC of US particle physics under four budget scenarios: can directly reach. By observing the decay pat- terns of particles with long lifetimes, such as • Constant level of effort at the FY08 muons and kaons, scientists may catch glimpses funding level of $688 million of heavy new particles whose brief cameo • Constant level of effort at the FY07 appearances can alter normal decay processes. funding level of $752 million • Doubling of budget over ten years starting in FY07 • Additional funding above the previous level, associated with specific activities needed to mount a world-leading program.

14 Physicists must sift through billions of particle DUSEL is also a collaboration, in this case decays to find these rare events that could between DOE and the NSF. At 2400 meters below answer questions about the nature of matter and ground, DUSEL would provide more shielding energy, the evolution of the universe and the from cosmic rays and other surface “noise” than subtle differences between matter and antimat- any previous underground particle physics envi- ter. High-intensity accelerators can create the ronment. At the cosmic frontier, DUSEL would immense numbers of particles they need. make an ideal spot for directly detecting dark “The more, the better,” says P5 subpanel mem- matter particles. At the intensity frontier, it could ber Robert Tschirhart, a physicist at Fermilab. “The host neutrino experiments. The P5 report calls currency here isn’t energy. It’s intensity.” for sending a high-intensity neutrino beam from At the cosmic frontier, physicists observe Fermilab to Homestake Mine, where a large naturally occurring particles such as gamma rays detector would record any changes that occurred symmetry | volume 05 issue 03 august 08 to investigate the nature of the universe. High- during the particles’ 1300-kilometer journey. energy gamma rays are photons, or particles of “Experiments at DUSEL would address many light, that are millions to hundreds of billions issues, including neutrino physics, proton decay, more energetic than the light people see. They dark matter, and neutrinoless double beta decay,” are typically emitted from powerful astrophysical Baltay says. “DOE and NSF should define clearly phenomena such as supermassive black hole sys- the stewardship responsibilities for such an exper- tems and rapidly spinning neutron stars, revealing imental program.” fundamental physical processes that are impossi- ble to investigate in terrestrial laboratories. “Helps for the eye” Gamma rays may also be emitted when mas- At the dawn of the era of modern science, the sive particles interact weakly with their surround- extraordinary power of early microscopes and ings—the same weak interactions that are a telescopes to reveal the nature of the world hypothesized property of dark matter particles. The around them gave 17th–century scientists a sense recently launched Gamma-ray Large Area Space of nearly limitless scientific opportunity, and they Telescope, or GLAST, a NASA/DOE collaboration foresaw future generations of increasingly pow- with international partners, hopes to find these erful tools for discovery. dark matter signatures, among other intriguing “Tis not unlikely,” Hooke wrote in Micrographia, phenomena. Stanford Linear Accelerator Center “but that there may be yet invented several other managed the construction project for the pri- helps for the eye, as much exceeding those already mary instrument, the Large Area Telescope, or found, as those do the bare eye, such as by which LAT, and played a key role in the instrument we may perhaps be able to discover living assembly. Scientists based the LAT on accelerator- Creatures in the Moon, or other Planets, the figures based particle detector technology adapted for of the compounding Particles of matter, and the use in space. particular Schematisms and Textures of Bodies.” As 21st-century physicists contemplate the Where frontiers converge power of such “helps for the eye” as next-generation The intensity and cosmic frontiers could meet in accelerators, detectors, telescopes, and cameras, the Homestake Mine in South Dakota. There they have a similar sense that these tools at the the proposed Deep Underground Science and frontiers of particle physics are about to change Engineering Laboratory, or DUSEL, presents their view of the universe forever. 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.

Photos courtesy of CERN and NASA

15 Illustration: Sandbox Studio 16 Bonnie and peopleexist. whether neutrinos are the reason that argon detectorsmayholdthekey todiscovering stars, planets, most fascinatingparticlesintheuniverse.Liquid- way tocaptureneutrinos—oneofthestrangestand are on a quest to find a cheaper, more efficient Inspired by heroes of Greek mythology, physicists by KurtRiesselmann the ArgoNeuTs 17 and

symmetry | volume 05 | issue 03 | august 08 hen Bonnie Fleming graduated with that neutrinos have no mass, experiments have a bachelor’s degree in physics from shown, to the surprise of many scientists, that W Barnard College, a small all-women’s they do have a tiny mass. college in Manhattan, she wasn’t sure she wanted Neutrinos come in three types that transform a career in research. She worked as a particle into each other as they travel. Physicists think beam operator at a Department of Energy labo- even more types of neutrinos may exist. Short- ratory for three years before deciding to go to lived, ultra-heavy neutrinos may have been pres- graduate school. ent in the early universe, and might have played “All my bosses were accelerator physicists,” a crucial role in determining that everything we she says of her time at Brookhaven National know today would be made of matter rather Laboratory. “I decided I wanted to get a PhD and than antimatter. do research, too.” So, are neutrinos the reason we exist? Today, Fleming is a junior faculty member at “It’s such a compelling question,” Fleming says. Yale University and principal investigator of the “People are made of matter; they can relate to that.” Argon Neutrino Test project, or ArgoNeuT. With physicists from six institutions, she works on a Catching neutrinos technology that could be the key to unveiling Despite their abundance, neutrinos are hard to the role neutrinos played in the early universe. detect. They can easily travel all the way through Neutrinos are one of the most abundant the Earth without interacting with the atoms that particles in space, and one of the most peculiar. make up matter. They emerge from nuclear reactions inside “Hold out your hand and count to three,” stars and from other nuclear processes, such as Fleming says with a smile. “A trillion neutrinos radioactive decays. Although the Standard just went through your hand.” Model of particles and their interactions predicts To increase the likelihood of observing the

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. Photo: Reidar Hahn, Fermilab

18 extremely rare interactions that do occur, phys- technology. Soon she and her collaborators at icists build accelerators to generate intense Fermilab and other institutions were looking for beams of neutrinos, and large, heavy detectors a catchy name for their project. to record the collisions of those neutrinos with “We had a contest,” Fleming says. “Rich Schmitt, atoms. The largest detector to date is the 50-kilo- a cryogenic engineer at Fermilab, came up with ton Super-Kamiokande in Japan, located deep the name in a play on Jason and the Argonauts.” underground in a cylindrical cavern about 40 According to Greek mythology, the Argonauts meters high and 40 meters wide. The cavern is were adventurers who sailed across the Mediter- full of water and its walls are covered with light- ranean Sea in their ship, the Argo, to retrieve the sensitive devices that register Cherenkov radiation, Golden Fleece. Led by Jason, the crew braved the faint glow emitted when neutrinos collide with fire-breathing oxen and sleepless dragons. water molecules. Fleming and her ArgoNeuTs face more modern While the interest in even larger neutrino challenges in their quest to develop a small detectors is high, the cost of building these cut- liquid-argon neutrino detector that could eventu- ting-edge experiments has reached hundreds of ally be scaled up to the size of a 20-story millions of dollars. Hence physicists are looking office building. for better, more cost-effective methods. The challenge is to record neutrino interactions at Not for time travelers the right energy, in sufficient numbers, and with Argon is a noble, non-toxic gas that constitutes the most accurate identification of the particles about one percent of air. It exists as a colorless that emerge from the collisions. liquid in the narrow temperature range of minus “When you embark on a big, expensive proj- 186 to minus 189 degrees Celsius. ect, you’d better evaluate your options carefully,” In the early 70s, William Willis and Veljko says physicist Regina Rameika, of the Fermi Radeka, of Brookhaven National Laboratory, built National Accelerator Laboratory near Chicago, the first detector to use layers of steel immersed who works on ArgoNeuT as well as on plans for in liquid argon to measure the energies of charged much larger neutrino detectors. “We need to find particles emerging from collisions. Today, high- something that is cheap per kiloton.” energy collider experiments such as the DZero Liquid-argon neutrino detectors, pioneered experiment at Fermilab and the ATLAS experi- by Nobel laureate Carlo Rubbia and his ICARUS ment at the European laboratory CERN rely collaboration, might be the solution. on similar detectors to record the energies of particle events. Better and cheaper? But these sandwich-type detectors, known Instead of recording light emitted by particles as liquid-argon calorimeters, cannot reveal the traveling through water, as Super-Kamiokande details of a neutrino collision. does, liquid-argon detectors record signals from “You don’t have the picture of the event and electrons knocked loose by passing particles. you don’t know what particle caused the event. Rameika thinks a liquid-argon detector could You only know the energy,” says Flavio Cavanna, identify three to five times more neutrino collisions professor at the University of L’Aquila in Italy, who than a water Cherenkov detector of the same works on ICARUS and ArgoNeuT. size. It potentially would better differentiate among Hence neutrino physicists are exploring a type the three types of neutrinos, a crucial require- of detector known as the liquid-argon time pro- ment for the next generation of neutrino jection chamber, or TPC. experiments. “My sister loves the name,” Fleming says. “It’s So far, nobody has built a large, multi-kiloton totally sci-fi for her. She often calls it a time neutrino detector based on liquid argon, and sci- capsule.” entists don’t know yet how much this would cost. Despite its curious name, a time projection The real test for this type of detector will be chamber has nothing to do with time travel. The “to use one to do an important physics experi- term refers to the time it takes for electrons, ment. Then you can see what the problems are,” knocked loose by charged particles, to drift

Mike Shaevitz of Columbia University says. “The through liquid argon to an array of high-voltage symmetry | volume 05 issue 03 august 08 physics community would want to see a physics wires that record their arrival time and location. result before they put money into a large one.” Just as rays of light cast the shadow of a moving object onto a wall, the electrons set free by a Jason and the Argonauts moving particle project its trajectory onto the array The ArgoNeuT project began in 2006 when of wires. Fleming secured a National Science Foundation “Many particles come out of a collision, and CAREER grant to study the liquid-argon the TPC traces all the particles and their

19 “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 Mitch Soderberg works on the ArgoNeut detector at the Proton Assembly Building. Photo: Reidar Hahn, Fermilab within six months. “The Europeans have solved many problems, interactions,” producing images almost like in particular in issues related to argon purity and those from a video camera, Cavanna says. the actual detection of particle tracks,” Fleming Scientists then select the images that are of says. “We owe them a huge amount because of interest. “You can measure for each track the their incredible push to advance this technology energy associated with this track, and you can over the last 20 years.” identify the particle that created the track.” Because electrons can drift long distances Fighting scavengers through liquid argon, a relatively small number In April 2007, a prototype liquid-argon detector, of wire arrays, placed a few meters apart, could developed at Yale University, recorded its first capture neutrino collisions across a large volume cosmic-ray tracks. It was the first crucial step in and possibly reduce the cost of a large neutrino bringing US physicists up to speed with this detector. technology. “We call it technology transfer,” says Fermilab Drifting through an argon sea physicist Stephen Pordes. Rubbia, spokesperson of the ICARUS collaboration Pordes works on the US effort to find the best and CERN director general from 1989 to 1993, way to fill a time projection chamber with ultra- recognized the potential of large liquid-argon pure liquid argon. If there is too much air in the TPCs more than 30 years ago. He hoped to use vessel, it will stop the electrons before they can them to track rare subatomic processes, such reach the readout wires. as neutrino collisions and elusive proton decays “The purity of the argon is really the main point that some theories predict. He has pursued this of the technology,” says Cavanna, who will spend idea ever since. the summer at Fermilab to help with the startup “Carlo Rubbia is the father of the long-drift of the ArgoNeuT detector. “Impurities are like technique for liquid-argon detectors,” says Willis, scavengers. If the argon is not pure enough, it now a professor at Columbia University. “Many practically eats the signal that we would detect people had the idea of building a long-drift with our wires.” detector; Carlo had the strength to do it. He could The level of impurity inside a liquid-argon work on many things at once. He had a number detector must be less than 50 parts per trillion. of smart and brave people to work on this.” ICARUS achieves this by pumping the air out of In 1997, the ICARUS-Milano collaboration the detector before filling it. This approach, how- recorded neutrino events with a 50-liter liquid-argon ever, is impractical for detectors that might reach detector exposed to a high-energy neutrino the size of a 20-story building. So Pordes and beam at CERN. In 2001, the ICARUS collaboration other physicists are exploring the possibility of assembled a detector 20 meters long in the pushing the air out of the detector vessel by INFN-Pavia laboratory and filled one of its two repeatedly flushing it with argon gas before modules with about 300 tons of liquid argon to filling it with liquid argon. Then they further record cosmic rays, showers of particles created reduce impurities by filtering the liquid argon as in the Earth’s atmosphere. it circulates within the chamber.

20 Next: scaling up from a beam generated by the lab’s Booster This summer, ArgoNeuT scientists will place their accelerator, and rely on the new method of detector into a high-intensity beam of muon removing impurities. If approved, the Micro neutrinos generated by Fermilab’s Main Injector Booster Neutrino Experiment, or MicroBooNE, accelerator and begin to take data. They will would be about one-third the size of the ICARUS measure the cross section, or probability, of neutri- detector, cost about $6 million in materials nos colliding with argon nuclei in the detector. and clarify mysterious low-energy neutrino sig- This is an important piece of information for the nals seen in an earlier experiment. analysis of data from ICARUS and other, future “MicroBooNE would be a step beyond ICARUS experiments, Cavanna says. 600,” Fleming says. “If it is built, we would be “We need to know the neutrino-argon cross able to do important physics measurements using sections with very high precision,” he says. “It a liquid-argon detector that could be scaled to symmetry | volume 05 issue 03 august 08 is not Nobel Prize physics, but it is important even larger sizes.” to understand the exposure of a liquid-argon Eventually, neutrino physicists hope to build detector to a neutrino beam at low energies. It experiments with five kilotons and, ultimately, will show that this technology is suitable for 100 kilotons of liquid argon to find out whether extracting neutrino physics information when neutrinos are the reason we and the matter implemented in the next generation of around us exist. experiments.” “It’s a long haul,” Fleming says. “I think the liquid- Fleming and other neutrino physicists are argon technology will revolutionize the field of already tackling the next step. They plan to build neutrino research if we can make it work for very a bigger detector at Fermilab containing 170 tons large detectors.” of liquid argon. It would catch muon neutrinos

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.

Vessel Liquid argon

Vacuum

Neutrino

Particles emerging from collision

Array of high-voltage wires

Time projection chamber Graphic: Sandbox Studio

21 A bumper of phy

22 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

crop sics plates

23 symmetry | volume 05 issue 03 august 08 These clever combinations of numbers, letters, the desire, and need, to share it. Taken together, and symbols are a mixed bag of inside jokes, they present a much broader story than when conversation-starters, a way of recognizing like- viewed alone. They are the shorthand of proud minded people, and tangible reminders of the scientists who wish to invite interaction. We sweat, toil, and joys of research. They reflect not hope you enjoy them as much as we did; please only their owners’ gusto for science, but also continue to send us your photos and stories.

Tune Kamae Stanford Linear Accelerator Center Menlo Park, California I 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 Geraci Anaheim, California I 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 Quigg Fermilab Batavia, Illinois Back 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.

24 L.N. Blanco Miami, Florida I’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 Santucci Fermilab Batavia, Illinois I 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 Axelrod Los Altos, California My 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 Janes

Bellevue, Iowa symmetry | volume 05 issue 03 august 08 When 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.

25 Leon Heller Los Alamos National Laboratory Los Alamos, New Mexico It’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.

26 Ben Smith and Jym Clendenin Stanford Linear Accelerator Center Menlo 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 e e (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.

E PLUS E MINUS Ben Smith, a retired SLAC engineer, acquired Jym Clendenin, a retired SLAC physicist, also his plates about 15 years ago when he was acquired his plates about 15 years ago when he designing and installing the Stanford Linear was commissioning the SLC polarized electron Collider positron source. source. He was in charge of the SLAC linac electron injector until his recent retirement. Common question Does that stand for educational excellence? Common comment That’s a really poor grade! symmetry | volume 05 issue 03 august 08

Photo: Diana Rogers, SLAC 27 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. “I’m excited about science, and this allows me His energy builds as he prepares for the day, to use that excitement for a good purpose,” mentally checking off his supplies and reviewing says Zimmerman, who switched from occasionally scenarios of the questions soon to pepper him. performing loud, messy science experiments His mind drifts to freezing fog, explosions shoot- for families to performances once or twice a month ing a ball 16 stories high, and children gasping for schools and scout troops after the previous in awe. A mischievous twinkle enters his eye, his Mr. Freeze retired 12 years ago. step bounces, and he starts talking fast. Cryogenics is the study of how materials The studious physicist and computer expert behave at temperatures near absolute zero. In has morphed into a charismatic showman: the high-energy particle accelerators, such frigid third incarnation of Mr. Freeze. temperatures reduce the electrical resistance of Ask residents of the Fox Valley outside Chicago wires in superconducting magnets, increasing about Fermi National Accelerator Laboratory the magnet strength and allowing faster particle and most will utter a vague description, or nothing acceleration. The same holds true for supercon- at all. But mention Mr. Freeze and adults and ducting cavities, cryomodules, and wires used in children alike break into grins and descriptions accelerators and detectors. of their favorite science experiments. He makes Initially, Fermilab management questioned the cryogenics of high-energy particle physics the wisdom of diverting Zimmerman from a full accessible and, well, cool. day of work at the laboratory, where his projects

28 nents to hisshow, crowd-pleasers butstaple do—not quitelimitless, butclose.” can you things of lots are there And cold. and entry point. About anybody can understand hot providesaneasy Zimmerman says.“Cryogenics that istheonlywaypeopleknow whatwedo,” because this like things do to science in work easy understanding. inthewayoffield wherejargonoftenstands citizenswithacomplex scientific nects everyday tight economictimes.The two-hourshowcon- inaheavily-populatedarea physics laboratory government-funded a running of part vital a outreach, educational as show his views ment and mechanical engineeringskills. Nowmanage- require a mix of physics, computer programming, Zimmerman consistently addsnewcompo- who people of responsibility the is it feel “I

29

symmetry | volume 05 | issue 03 | august 08 day in the life: the versatile mr. freeze

include mixing soap with nitrogen to create gey- college class. One man told me the show sers of bubbles, using compressed gas to encouraged him to study science in college.” shoot confetti or rubber balls, shattering roses, Even in a media-saturated, short-attention-span and using a frozen banana to pound frozen rubber society, the show keeps drawing new generations tubing through wood. Sometimes he “accidentally” of fans. In 2001, during a break at a Snowmass breaks off the fingers of his safety glove as it conference in Colorado, Zimmerman performed emerges from a tank of nitrogen. his Mr. Freeze show for a nearby science day “I have had girls in the front row scream their camp. Days later, when exiting a local movie heads off, like I just maimed myself,” he says with theater, Zimmerman was confronted by a six- a slight smile. year-old girl yelling, “Mr. Freeze!” She had seen Gasps and giggles aside, the show teaches the the show, and when he quizzed her on the basics of gases, liquids, and solids and the science facts behind the explosions, she remem- cryogenics used to run particle accelerators at bered it all. Fermilab. Zimmerman brings the complicated, In February, when Naperville, Illinois-based mammoth machines down to Earth by comparing Brownie Troop 371 wanted to tear down stereo- them to everyday objects such as the television, types about science that limit female participation, which is a type of particle accelerator. they asked Mr. Freeze to perform. According to Such basic lessons come in handy for a nation the National Science Foundation, women account whose average 10th grade science literacy for 20 percent or fewer of postdoctoral students scores lag behind 16 of 30 of the world’s richest in science, engineering, mathematics, and countries, according to the latest Program for physical sciences. International Student Assessment. “The science “It’s an exciting opportunity for our girls and demonstrations help Fermilab. They help sci- our guests, and we hope it will further spark ence,” Zimmerman says. “Because now people their interest in math and science,” says parent see that science isn’t so boring. It isn’t so bad. Sue Grove. I have run into people who remember seeing Zimmerman may perform up to six shows the show as a child, and then used the stuff back-to-back in a day. “At 4 o’clock, I’m really they learned when cryogenics came up in their burnt out,” he says. “It is not just the talking; it is

30 31 Photos: CindyArnold andReidarHahn Text: Tona Kunz to maketheshowbetter.” carrying on that legacy and seeing what I can add get really excited about being Mr. Freeze. I love map magnetic fields. to system robotic upgrade theziptrack, a3D ern bubble-chamber experiment, andhelped amod- pneumatic pressuresystemforCOUPP, particles. Zimmerman also created a high-speed wide; they’reusedtodetect passingsubatomic plastic scintillatorpiecesfordistributionworld- theextruder atFermilabmaintains thatproduces and border, French-Swiss the on lab physics particle European the CERN, at detector CMS the systemtomapmagnetic interiorofthe build helped He jack-of-all-trades. physics of ready to return to Fermilab as just himself, a sort What were theirquestions?” the concentration:DidIdothatforthisshow? “I like everything I do,” Zimmerman says. “But I But afteragoodnight’ssleep,Zimmermanis

symmetry | volume 05 | issue 03 | august 08 deconstruction: COUPP bubble chamber

Bubble technology bursts into 21st century by 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.

32 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- The COUPP bell jar, which is enclosed in a steel ber; the larger size increases the possibility that vessel, contains a liter of iodotrifluoromethane, the elusive WIMP will land inside. They hope a fire-extinguishing liquid known as CF3I. When to move that chamber to an even deeper tunnel symmetry | volume 05 issue 03 august 08 a particle enters the jar and hits the nucleus of whose extra layers of dirt and rock will further an atom in a CF3I molecule, it triggers the evap- reduce interference from particles that are part oration of a small amount of CF3I. The ensuing of the natural background. 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.

33 essay: elizabeth wade

the air duct my friend had just climbed over; Requiem for a Dunning had built the machine during the cyclotron Depression with salvaged parts and donated metal. Almost unbelievably, there was a start From 1936 to 2008, button on its side, along with stickers that declared Columbia University several other mysterious objects “critical space housed a physics legend: items” property of NASA. an early cyclotron. But the need for another kind of space became Columbia’s cyclotron was even more critical for the university. Late last one of the first machines year, Columbia announced plans to turn Pupin’s to split the atom, confirm- basement into a combination of lab space and ing reports from Europe infrastructure for a new building going up next that such a feat was pos- door. In the process, the cyclotron was disman- sible. It demonstrated tled and its pieces—many of which were pure that uranium-235 was copper—were sold as scrap metal. About a readily fissionable, leading to experiments aimed week before it was destroyed, George Hamawy, at harnessing the astounding energy of a nuclear Columbia’s director of radiation safety, organized chain reaction. It helped usher in the Atomic Age a funeral for the machine. His heartfelt eulogy and the subsequent promise and problems of covered the machine’s important scientific con- nuclear power and energy, the results of which tributions but also touched on its sentimental we continue to grapple with today. And in March value. From Hamawy’s tale of being drawn of this year, it was cut up and sold for scrap. Photo courtesy of Elizabeth Wade to physics after hearing about the cyclotron’s Physicist John Dunning built Columbia’s experiments to students taking advantage of cyclotron in the 1930s and it split atoms for nearly their last chance to see the fabled machine, people 30 years. After it was decommissioned in 1965, spoke of an attraction to the cyclotron that went the university sent key pieces of the machine to beyond its scientific importance, historical value, the Smithsonian Institution and left the rest in and even status as a real-life urban legend. the basement of Pupin Hall, Columbia’s physics The cyclotron was an artifact of an age before building. Then it sealed the basement off. For the atomic bomb when excitement, wonder, decades, the cyclotron was only accessible by a and hope outweighed the fear that is so familiar system of tunnels that runs under the entire today. It was an artifact of decades of tunnel university. The tunnels are off-limits to students, spelunking, Columbia’s most public secret. It although almost every self-respecting under- was an artifact of my college experience, bringing graduate has sneaked into them. In retirement, me closer to the people who shared my first the cyclotron became the university’s most Columbia adventure and setting the tone for all popular underground attraction. the rest that followed. It seemed the cyclotron I first ventured to see the cyclotron on a would always be there—in history and in adven- dark and stormy night in April 2005. Armed with tures both collective and personal. I always word-of-mouth directions, four friends and I thought I would be able to go back for a visit, descended into the tunnels through an entrance whether at graduation or my 50-year reunion. across campus and made our way toward Instead, I’ll be remembering how the cyclotron’s Pupin. After navigating a few forbidding rooms multifaceted appeal became most apparent at filled with imposing electrical equipment and the end of its life, and remembering how glad I many ignored Do Not Enter signs, we made it was to be able to say goodbye. to Pupin’s basement. We had been instructed to find the out-of-order men’s bathroom, where Elizabeth Wade recently graduated from Barnard College. one person had to climb over a wall (via an air She was a Fermilab intern in the summer of 2005 and duct) and into a hall of abandoned laboratories. continues to write about physics. Once inside, he opened the door for us and the treasure hunt began. We found the cyclotron in a room that looked symmetry | volume 05 issue 03 august 08 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

34 logbook: Z boson

physicists on the UA1 detector for the Super Proton Synchrotron accel- In May 1983, 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 Image courtesy of James Rohlf explain it in 60 seconds e- e+ is a heavy particle that is one of The Z boson 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 z z zzz

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