Issue 03 Volume 06 July 09 Dimensions of Particle Physics A

dimensions volume 06 of particle physics symmetryA joint Fermilab/SLAC publication

issue 03

july 09 volume 06 | issue 03 | july 09

2 Editorial: Diversity and Mentoring in Particle Physics A consultant hired to look at diversity issues at Fermilab found no evidence of bias. But he did find a lack of support and mentoring for some symmetryA joint Fermilab/SLAC publication visiting scientists at the lab. This observation is important for any institution with a large proportion of visiting students, postdocs, and scientists, and addressing it will require a coordinated approach.

3 Commentary: Karin Fornazier Guimares “If more scientists start to use it, Twitter can be a tool for developing new relationships, networks, collaborations, and communities. I believe it can help us send messages and get unexpected answers, talk to different kinds of people, get instant feedback.”

4 Signal to Background Shooting down UFO rumors; growing a physics family tree; driving an eco-trend; feeling a mine’s deep, earthy vibes; baby detector on board; quake-shaken lab reaches out to neighbors

On the cover: 8 symmetry breaking For some reason, Brookhaven National A summary of recent stories published Laboratory has always attracted more than its online in symmetry breaking, share of UFO buffs. So it was that the crew www.symmetrymagazine.org/breaking of UFO Hunters, a weekly TV show on the History Channel, went to the lab recently to film an episode about an alleged 1992 UFO crash nearby. The burning question: Had the lab shot down a UFO with a particle beam? The answer: Of course not. There was no UFO, and particle beams from the lab’s accelerator can’t be used as weapons.

Illustrations: Sandbox Studio 24 18 10

to livewithoutit. thispreciouscommodityorlearn to preserve stepsparticle physicscommunitymusttake the dwindles, supply world’s the As ators. Helium isthelifeblood oflargeparticleacceler- Helium’s ShrinkingBubble out what’sgoingon. inChile,theyhopetofind from amountaintop light fromhundredsofmillionsgalaxies the recording By work? at is force mysterious What faster. ever expanding is universe intospace,scientistswonderwhytheGazing Dark Energy Camera Scans Ancient Skies level. the problematevery Fermilab, atthreenationallabs— of science.Staffers particle physicslagsfarbehindotherfields minorities, ethnic of members and women When itcomes totraining,hiring,andretaining Growing aDiverseWorkforce SLAC , and Brookhaven—are tackling tackling Brookhaven—are and ,

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metal partsof metal original purpose,which istoensurethatallthe These exquisite testsamplestranscendtheir Accidental Beauties Gallery: mining gold,butscience. be about mining. Now, however, we are no longer mining,andwillcontinueto always beenabout The has Dakota communityofLead, South TomEssay: Nelson solving themysteriesofuniverse? and particles, detecting accelerators, building for elements important most the are What Periodic TableDeconstruction: are flawless. particles—in measurableways. charged two between force electric the or cle physical quantities—such asthemassofaparti- cannot bedirectlydetected, butwhich affect Virtual particlesareshort-livedthat Particles seconds:Virtual 60 the universe. in mysteries ofthehighest-energycosmicrays array ofdetectors designedtounravelthe was eagertoseetheconstructionofalarge physics. Cronin, a Nobel Prize winner in physics, to visitAlanWatson, anexpert oncosmic-ray In 1991, James Cronin traveled to Leeds, England, Logbook: PierreAuger Observatory SLAC accelerators and detectors

symmetry | volume 06 | issue 03 | july 09 from the editor

Diversity and mentoring in particle physics

Women and minorities are significantly underrepresented in physics. There are many possible reasons for the imbalance, and understanding the causes is a challenging task. In this issue of symmetry, we look at how particle physics laboratories and the science community are tackling parts of the problem and trying to create a more diverse workforce (see page 10). Fermilab recently commissioned an independent consulting firm to study issues that influence diversity at the lab. The firm convened a series of focus groups consisting of randomly selected participants, whose identities were withheld from laboratory leadership to encourage honest feedback. On the positive side, the consulting group reported that discrimination against women and minorities was not a contributing factor to lack of diversity. On the other hand, participants revealed a number of general management weaknesses among line managers, potentially due to lack of training and mentoring, and some significant issues for visiting scientists from outside Fermilab. The visitors, typically graduate students and postdoctoral fellows, often do not have mentors and have trouble getting the support they need to do their work effectively. This observation is important for all institutions that have a large proportion of visiting students, postdocs, and scientists. Because people tend Photo: Reidar Hahn, Fermilab to learn institutional processes better from other people than from an abstract handbook or set of rules, mentoring is vital. Good mentoring would certainly help institutions in many ways, quite likely helping to create a more diverse workforce. But the issue of mentoring young visiting scientists also reveals that no institution can solve by itself the challenges of changing a culture within a scientific discipline. Cultural change is needed to improve workforce diversity throughout physics. There is so much mixing of people among institutions in particle physics that cultural change will need a coordinated approach. This is a serious challenge but we think it is worth the invest- ment of time and resources. To begin the process, it is definitely worth more discussion.

Symmetry Editor-in-Chief Publishers Print Design and Production PO Box 500 David Harris Rob Brown, SLAC Sandbox Studio MS 206 650 926 8580 Judy Jackson, FNAL Chicago, Illinois Batavia Illinois 60510 Deputy Editor Contributing Editors Art Director USA Glennda Chui Michael Branigan 630 840 3351 telephone Roberta Antolini, LNGS 630 840 8780 fax Managing Editor Peter Barratt, STFC Designers/Illustrators [email protected] Kurt Riesselmann Romeo Bassoli, INFN Andrea Butson Stefano Bianco, LNF Aaron Grant For subscription services go to Senior Editor Tona Kunz Kandice Carter, JLab Web Design and Production www.symmetrymagazine.org Lynn Yarris, LBNL Staff Writers Xeno Media symmetry (ISSN 1931-8367) James Gillies, CERN Oakbrook Terrace, Illinois is published six times per Elizabeth Clements Silvia Giromini, LNF year by Fermi National Calla Cofield Youhei Morita, KEK Web Architect Accelerator Laboratory and Kathryn Grim Tim Meyer, TRIUMF Kevin Munday symmetry | volume 06 | issue 03 july 09 SLAC National Accelerator Kelen Tuttle Perrine Royole-Degieux, IN2P3 Web Design Laboratory, funded by the Rhianna Wisniewski Yuri Ryabov, IHEP Protvino Karen Acklin US Department of Energy Interns Yves Sacquin, CEA-Saclay Justin Dauer Office of Science. (c) 2009 Kristine Crane Kendra Snyder, BNL Alex Tarasiewicz symmetry All rights reserved Tia Jones Boris Starchenko, JINR Web Programmer Lauren Schenkman Maury Tigner, LEPP Mike Acklin Michael Wall Ute Wilhelmsen, DESY Tongzhou Xu, IHEP Beijing Photographic Services Gabby Zegers, NIKHEF Fermilab Visual Media symmetry Services

2 commentary: karin fornazier guimares

Twitter: micro which other interested people, such as a PhD blogging for a macro student from another science network university, did not know anything about. As From the beginning, science and communication you have only 140 char- have been connected. Writing is a good exer- acters with which to cise for inquiring minds; this is not just a saying, deliver your message, but a fact. If you look at scientific biographies, you will just point it out, you probably will find mention of a notebook in and your “followers” which the scientist writes down ideas, questions, will decide to read and quick observations. Those notes give us a or re-tweet (re-broad- perspective on what the scientist was doing at cast to their followers) the time. your post. Today we have not only notebooks, which are If more scientists usually used to jot down private thoughts, but start to use it, Twitter can be a tool for developing also blogs in which we can make public all of our new relationships, networks, collaborations, and work, our ideas, and our opinions. Examples communities. I believe it can help us send mes- of communities of blogs are Science Blogs, sages and get unexpected answers, talk to Quantum Diaries, US LHC blogs, Nature Network, different kinds of people, and get instant feedback. and Discover blogs. Some of these were set up This makes Twitter a very useful tool. It can as experiments in scientific communication. These allow scientists to make unexpected connections blogs are a powerful tool for divulging and both with other scientists and with other people discussing scientific research, as discussed a few who are valuable to know and work with.

months ago at ScienceOnline09. But not enough In my own case, I have used Twitter to meet Guimares Photo courtesy of Karin Fornazier scientists have taken up blogging. other scientists, to find out about useful physics Many more of us could be using this tool information I wouldn't have seen otherwise, and to bring science to a different public, in different also to practice writing in other languages. How countries, and across social levels as an oppor- you use Twitter would be up to you, but you tunity to understand what scientists do day to day. might also find it useful for building a network That would translate to more adults interested of colleagues around the world who share in science, more high school students interested interests and information, and help make the in science, more girls interested in science, scientific world better connected. and more people learning the latest news about science from real scientists. Karin Fornazier Guimares is a PhD student in particle physics at Instituto Tecnológico de Aeronáutica, SP Brazil. You can However, science blogging is not an easy task; follow her as @charmqgp on Twitter. She met the editor-in- not everyone is comfortable with writing at chief of symmetry, and they decided to publish this article, such length and in a relatively formal way. To link through conversations on Twitter. You can read Fornazier Guimares’ tweets at twitter.com/charmqgp. symmetry people who don’t want to write so much but tweets as @symmetrymag, and the editor as @physicsdavid. still want to share their ideas, why not consider Twitter? It allows a sort of micro blogging in which you describe what you’re doing in 140 characters or fewer. How you use this tool is entirely up to you. You can just talk about your life, your tasks, etc., or you can project and promote yourself and your work, letting ideas, insights, difficulties, and achievements flow in a very easy, rapid way. You can point out scientific papers, lectures,

and proceedings you find interesting or relevant, symmetry | volume 06 | issue 03 july 09 as well as blogs with relevant science news and high-level discussion. In this way you can indirectly help a science teacher or novice physicist find the appropriate references for improving their knowledge, tackling school work or demys- tifying particular issues. You could also point out some workshop or summer/winter school Web sites that your regular network of colleagues might know about but

3 signal to background

Shooting down UFO rumors; growing a physics family tree; driving an eco-trend; feeling a mine’s deep, earthy vibes; baby detector on board; quake-shaken lab reaches out to neighbors.

Nope, no UFOs at Park, about five miles from the they would dissipate as soon Brookhaven Lab lab. UFO buffs tell of the lab’s as they interacted with air. The spotlight caught Todd fire department responding With its history of operating Satogata. The camera zoomed in. to the crash and extinguishing research reactors and particle “Did your particle beam massive brush fires. accelerators, Brookhaven has shoot down a UFO?” the TV Brookhaven lab Fire Chief long been a focus of UFO host asked. Chuck La Salla showed the film fans; a Google search of the

Photo-illustration: Sandbox Studio The accelerator physicist at crew a logbook entry for that two brings up 4620 postings. RHIC, Brookhaven National evening, which noted nothing Brookhaven scientists hope that Laboratory’s Relativistic Heavy out of the ordinary and no if they show UFO buffs what Ion Collider, smiled. off-site response by firefighters. the laboratory really does, alien Of course not. Later versions of the tale tales will carry less weight. With a friendly countenance claim that firefighters brought During the TV crew’s visit, and confident tone, Satogata parts of the wreck back to the RHIC was delivering protons kept steering the dialogue back lab, where scientists analyzed to the STAR and PHENIX detec- to physics concepts and giving alien tissue. They even have the tors. Satogata, interviewed in the hosts of UFO Hunters, laboratory’s Alternating Gradient the main control room, found

a weekly series on the History Synchrotron, which injects par- time during tape changes symmetry | volume 06 | issue 03 july 09 Channel, a reality check on their ticles into RHIC, shooting down and sound checks to teach the extraordinary claims. the spacecraft with a high- crew about the science going Each week, UFO hunters Bill power plasma beam. on in the background. Birnes, Kevin Cook, and Pat But the sci-fi-like sniper “It’ll be interesting to see Uskert travel to the sites of pur- attack couldn’t have occurred. how it’s edited and how it turns ported alien encounters. They The beams that circulate in RHIC out,” Satogata said after the visited Brookhaven in April to and other particle accelerators crew wrapped up. probe an alleged UFO crash are confined to a prescribed Mona Rowe Nov. 24, 1992 in South Haven path. Even if they did escape,

4 Detectors shipped Germanium Detector Array, in cooking pots or GERDA. Located deep under- Looking for an inexpensive and ground in the Gran Sasso safe way to transport delicate mountains in Italy, GERDA will particle detectors? Try pressure search for the existence of cookers and child safety seats. the nuclear process known as When researchers at the Max neutrinoless double beta decay

Planck Institute for Physics in to gain more information on Photo courtesy of James Volk Munich drive fragile germanium neutrinos, elusive particles pro- crystals across Europe, they duced in the center of the resort to conventional house- sun. Scientists want to deter- hold equipment to keep the mine the masses of neutrinos crystals safe. and find out whether neutrinos The fist-size crystals have to are their own antiparticles. remain under clean-room The first crystals have already the world’s deepest under- conditions to keep their particle made the trip from Strasbourg ground lab. detection prowess. Pressure to Munich, a distance of about In January, Fermilab physicist cookers, normally used to cook 400 kilometers. Later they Jim Volk (photo, right) helped food and steam vegetables, will travel to the Gran Sasso Larry Stetler (left), a geologi- are the perfect solution. The MPI National Laboratory. Fortunately, cal engineer from the South Mechanics Division has out- border controls have disap- Dakota School of Mines & fitted seven pots with connec- peared in most of Europe. Technology, and a few graduate tors and pressure gauges. Imagine how difficult it would students install 12 of the ground After placing the crystals in the have been to explain to officers sensors at the 2000-foot level pots, researchers pump the the transport of these precious of Homestake Mine, future air out of the pressure cookers GERDA “babies.” Just in case, home of DUSEL. to protect the crystals from the drivers carry with them doc- They lugged cables, wires contaminants. The team then uments to prove that the and water lines through puddles straps the pots into child safety pressure cookers are tested of muck in 75-degree heat with seats, creating a low-tech transport containers. 95 percent humidity. More sen- solution for the transportation Silke Zollinger sors will go in at the 4100-foot of high-tech equipment. level this summer and at the The crystals, produced at The DUSEL cavern 4850-foot level later this year. Canberra France, are prototype is getting restless “It was hot and dirty,” Volk detectors developed for the You can’t feel it. Yet the moon’s says. “That brown iron ore dust,

Photos: Max-Planck-Institut für Physik, Munich Photos: Max-Planck-Institut gravitational pull shifts the it gets in everywhere.” ground ever so slightly, creating After the South Dakota “earth tides” that rhythmically gold mine closed in 2001, the raise and lower the ground. pumps were turned off and That’s enough to throw off groundwater submerged half delicate scientific equipment, of its 8000-foot depth. such as the systems used to aim As that water is pumped two hair’s-width particle beams back out, the ground shifts. into a head-on collision. Monitoring those movements, And that’s not the only slow, as well as earth tides and subtle movement going on. shifts in the rock triggered by At Fermilab, for instance, the excavation, will be key to spring thaw shifts the magnets calibrating research equipment. that focus particle beams. So “It is not pure high-energy the lab developed sensors physics, but it is useful science,” that track ground tilt to within Volk says of his work in

1/14th the diameter of a hair the mine. “We are helping those symmetry | volume 06 | issue 03 july 09 over a distance of 30 feet, guys get data and understand allowing them to correct for the what is going on with the rock.” motion at one-tenth the pre- As a bonus, he says, he’s vious cost. learning a lot of geology that will Now those sensors are come in handy for other projects. offering a new way to cheaply Despite the discomforts monitor the effects of sucking of working deep underground, seven megatons of water out “I can’t wait to get back there.” of granite caverns that will house Tona Kunz

5 signal to background

It’s cute! It’s clean! For some of the older vehi- It’s a SLACmobile! cles “a lot of repair parts are Plugged into a weatherproof not available any more,” says outlet behind SLAC’s Test SLAC Transportation Manager Laboratory, what looks like an Ken Rubino, so workers sal- oversized green-and-silver go- vage parts from others that are cart waits with its load of tools beyond repair. and paint supplies. It’s part As SLACmobiles go out of of a fleet of pint-sized econo- service, the fleet changes com- mobiles that have carried position. At one time, Rubino people, materials, and equip- says, scores of mopeds zipped ment around SLAC National around SLAC. Now the balance Accelerator Laboratory since the has shifted in favor of small- lab’s early days. appetite gas vehicles and It all started with trikes. electric carts. The fleet’s users “The linac was full of three- treat their wheels with some wheeled bicycles way back affection. One cart’s cab sports when,” says SLAC fleet services a pair of bull’s horns. Volunteers garage supervisor Al Manuel. spruced up a second with In the mid-60s, he says, SLACers removable flame stickers and This family tree has pedaled tricycles up and a set of fuzzy dice for founding physics branches down the Klystron Gallery that SLAC Director Pief Panofsky, Who is the grandfather of par- serves the lab’s two-mile who died in 2007. ticle physics? Some might argue linear accelerator. “Pief loved it,” says Ellie Lwin, he is Otto Mencke, a German Over time the trikes gave way Panofsky’s assistant at the philosopher and scientist who to three-wheeled Cushman time, who spearheaded creation received his doctorate from

carts, former US Post Office of the Piefmobile—even paying Leipzig University in 1688. Photo-illustration: Sandbox Studio vehicles powered by gasoline. for the materials herself—as In the SPIRES HEPNAMES By the early 1980s, electric a surprise for him. database, Mencke has the four-wheelers began to appear. SLAC’s 15 gas-powered mini- largest number of traceable aca- More than 50 of those jaunty pickups and vans get up to demic descendents in the field. flatbeds and microvans, some 50 miles to the gallon, thanks His 1228 physicist descendents painted orange, red, or purple, to their three-cylinder engines include 30 at Fermilab, 20 carry ladders, mail, or library and light weight. But most of at SLAC, and 19 at Brookhaven books across the site and today’s fleet runs on electricity. National Laboratory. around the mile-long PEP Ring If the United States plays its The worldwide directory of Road. Manuel’s group keeps cards right with solar and names allows particle physicists them running, alongside the wind power, more SLACmobiles and astrophysicists to trace mopeds and low-speed gas could run on sunshine and their scientific genealogies in vehicles that have since joined fresh air in the years to come. much the same way that peo- the fleet. Shawne Workman ple track their family trees. In Photos: Brad Plummer, SLAC symmetry | volume 06 | issue 03 july 09

6 this case, each senior scientist Beacom. HEPNAMES also can the physics department on- trains successive waves of help prevent bias in peer site. With the village of Assergi graduate students and postdocs, review: Beacom makes sure he in rubble, the laboratory offered who become siblings of sorts doesn’t send students’ papers to shelter the villagers’ tent city as they work together and go to their advisors for review, and inside its boundaries. When on to train descendents of vice-versa. villagers chose instead to stay their own. Beacom has been using close to their damaged homes, John Beacom, a physics pro- HEPNAMES regularly since the laboratory came to them. fessor at Ohio State University, SLAC started it in the early 1980s. Chairs, tables, and just about says looking at a colleague’s “It’s interesting and fun just to anything moveable that could scientific relatives is helpful in understand how long and how improve life in the camps understanding his or her school slow the scientific process is,” he was toted to the nearby village. of thought. “There is some family says. “What we are doing today Lab Director Eugenio Coccia resemblance,” he says. “It’s resembles what scientists were and other staff visited the really about understanding the doing hundreds of years ago.” camp regularly to offer a lifeline context of who someone is.” Kristine Crane of aid and support. HEPNAMES is part of the Photo: Francesco Arneodo, LNGS-INFN Photo: Francesco SPIRES service, which is jointly operated by DESY, Fermilab, and SLAC. HEPNAMES itself is managed by Fermilab. It gets about 2000 hits per day, mostly from people combing through its 80,000 individual monikers to find current contact information for colleagues, says Heath O’Connell, Fermilab’s head of information services. Enrico Fermi has 27 Fermilab physicists in his family tree, including Winslow Baker, Norman Gelfand, King-Yuen Ng, Jim Strait, and Gong Ping Yeh. Ten Fermilab physicists had Unharmed in quake, Physicist Roberto Aloisio, Nobel Prize winners as advisors. Gran Sasso lab who fled the collapse of his own Jim Strait, project manager goes to the rescue home in L’Aquila, spent the for US participation in the Large When an earthquake flattened days after the quake searching Hadron Collider, has three buildings in a number of towns the rubble for survivors and Nobel Prize winners in his phys- across central Italy, physicists then, with the help of friends, ics family. turned their focus from research installing free wireless Internet Beacom primarily uses the to rescue and rebuilding. access for all of the town’s database to get background The 6.3-magnitude earth- tent camps. on students. “When I’m trying to quake on April 14, 2009, killed Other Gran Sasso employees judge letters of reference, and more than 300 people and left who lost their homes found professors say a student was towns near Gran Sasso National temporary shelter in towns out- their best student, I can look Laboratory, a particle physics side the earthquake zone, up their other students,” says research center studying neu- commuting 120 miles or more trinos and dark matter, nearly to work. obliterated. With the laboratory The faculty of the university symmetry | volume 06 | issue 03 july 09 itself mostly unscathed, scien- physics department will remain tists and engineers rushed to the at Gran Sasso for the rest aid of villagers and the physics of the year. The laboratory man- department of L’Aquila University. agement continues to discuss A laboratory building was other ways of helping the uni- quickly converted into a guest versity and the villages. house for employees and users Tona Kunz who had lost their homes, and space was made to relocate

7 symmetry all the gory details. details. all thegory today andyoucandigthrough interim update was just released particle physicists.The 2009 particlesstudiedbyobserved the all about data best-of the compiling been has Group 50 years,theParticle Data Every second year for more than June 8,2009 particles greatest latest, The Highlights from our blog work byresearchers at thanks torecenttheoretical observed in future experiments, but never-seen atom, might be True muonium, a long-theorized May 29,2009 to “true muonium” reveal Theorists path ATLAS a miniature etched image of the denly camefacetowith Turning overtheblocks, Isud- June 1,2009 alphabet blocks scientist’s first A youngmad small dot. small which isetched withjusta the whimsical Nanotechnology, Experiment, Bioengineering, and Other facesincludeInvention, face QforQuantumPhysics. Hadron Collider. Itsatonthe and observed. by which itcould becreated an unambiguous method Until now no one had uncovered University.and ArizonaState experiment attheLarge breaking SLAC

the Internet. virtual computing resources over on-demand, provides which Elastic ComputeCloud,or their computingwithAmazon’s supplementing considering are particle physics and process of Peering at the people painted ontherock wall. mural soaked 25-by-60-foot through theblinds atacolor- gaze them of many desks, clouds roll by as they sit at their cannotwatch the Laboratory Underground Soudan the of employees the if Even May 20,2009 mile underground The muralahalf- at Collaborators community. research academic ing to pique the interest of the the commercial world, it is - start popular computingsolutionin As the cloud becomes a more May 21,2009 your grid,ma’am? with cloud of side A the of research groupsworkingon and workofonethehundreds trend, delvingintothelives Colliding Particles follows a new The series online documentary scenarios. doomsday or goals, struction challenges, scientific project’s engineeringandcon- documentaries focused on the For years, Large Hadron Collider May 26,2009 LHC experiments. 8 KEK in Japan

EC2 , done it. for ChicagoPublic Radio,has Well, Gabriel Spitzer, reporter powerful particleaccelerator? most world’s the and nos, mentions thesun,bison,neutri- in sevenminutesorlessthat Have you ever tried to tell a story May 14,2009 seven minutes Fermilab in breaking ceremonyforthe in aspeech attheground- off his comedy stand-up chops turned-Congressman, showed a Fermilab-particle-physicist- Foster, Bill Rep. Illinois May 13,2009 address breaking humorous ground- for from history draws Foster Rep. address. Lincoln’s famousGettysburg own take on President Abraham neutrino experiment withhis

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symmetry | volume 06 | issue 03 | july 09 xenon—10 atom inthe10 need tofinda single barium what they’re looking for, they will sions inthegalaxy. the mostcommonstellarexplo- bursts, X-ray understand to easier it make may Theresults surements offoursuch nuclei. have madeprecisemassmea- Universityresearchers State nuclei are similarly coy. Michigan much theyweigh.Rareatomic No one likes to say exactly how May 6,2009 a hair’s precision measured towithin Nuclear masses at www.symmetrymagazine.org/breaking Read the full text of these stories and more Observatory, or Xenon Enriched the facing achallengetackle of thekind quantities, butrarelydothey smallwith rare events and very Physicists areusedtodealing May 3,2009 000,000,000,000 000,000,000,000,000, Finding 1atomin10, power.staying some ofthemhavemuch more Space Telescope showat least data from the Fermi Gamma-ray a few short minutes. But new thought to last mere seconds or verse sincethebigbang,are powerful explosions intheuni- Gamma-ray bursts, the most May 5,2009 previously thought than longer last may Gamma-ray bursts 28 atoms. -ton bath of liquid EXO . To . find with accelerators The do stuffyoucan large numbersofhigh-energy seemstobeproducing borhood Something in our galactic neigh- May 2,2009 cosmic electrons source of high-energy matter mightbethe Pulsars or dark the protoncomesfromthissea. of mass the of percent 99 fact, “bare” upanddownquarks. In and gluons that surround the a seething seaofquarkpairs make up the proton, it is actually quark you might have heard down one and quarks up two plicated object.Far fromthe The protonisasurprisinglycom- May 2,2009 of theproton Making 3Dimages area ofscience. have applications in nearly every a small fraction of them but they and neutron sources are just where aretheyall?Synchrotrons those numbersarecorrect!So accelerators in the world. Yes, There are 15,000-17,000 particle May 2,2009 9

agreement between the cooperative a under Fermilab ManagedbyMinnesota. innorthernphysics laboratory on Construction begins this month May 1,2009 experiment neutrino advanced world’s most the for ground break Officials nearly aquarteroftheuniverse. material thoughttomakeup dark matter, the elusive, invisible could be a longed-for signal of from nearbypulsars—orthey The electrons couldbecoming Telescope. Space Gamma-ray gatheredbytheFermidata electrons, accordingtonew gram distribution ofalerts. a Web evolution of actual tele- Astronomer’s Telegram service, the research communityvia the as thisisdistributedamong pected astronomical events such last summer. Newsofunex- flared that object astronomical gamma-ray perspectiveonan released a paper giving the Telescope has collaboration Telescope’s LargeArea Space Gamma-ray Fermi The 2009 April 30, blazar on dazzling light cast Telegram Astronomer’s signature, Gamma of theuniverse. called neutrinosintheorigin the roleofsubatomicparticles detector thatwillinvestigate it willhousea15,000-ton particle and the University of Minnesota, NO ν A , acutting-edge DOE

symmetry | volume 06 | issue 03 | july 09 Photo-illustration: Sandbox Studio

Percentage of PhDs earned by women

Source: National Science Foundation 10 Growing a diverse workforce When it comes to training, hiring, and retaining women and members of ethnic minorities, particle physics lags far behind other fields of science. Staffers at three national labs— Fermilab, SLAC, and Brookhaven—are attacking the problem at every level. When Cherrill Spencer started at SLAC National Accelerator Laboratory as a postdoctoral researcher in 1974, she was one of only three female physicists there. “I wanted to have more women around me, enough so that we could get our own bathroom,” Spencer says. “I could see no good reason why more women weren’t becoming scientists.” Today Spencer, who designs magnets that focus and steer beams of particles in accelerators, has many more female colleagues. But she still works hard to encourage the next generation of female scientists. In 1978, Spencer became involved with the Expanding Your Horizons Network, which works to motivate middle school and high school girls to pursue careers in science, technology, engineering, and math.

The group’s conferences give girls a chance to interact with female scientists symmetry | volume 06 | issue 03 july 09 and engineers and complete hands-on scientific activities. In a typical year, about 26,000 girls, including 10,000 members of ethnic minority groups, participate in more than 80 conferences in 31 states. “In just a day-long program you can actually change someone’s mind,” Spencer says. “You can go into a workshop led by a marine biologist and come out wanting to be a marine biologist.”

11 Many more women and members of minority went to blacks, 504 to Hispanics and 43 to Native groups work at Department of Energy laboratories Americans, “it has a startle effect,” Czujko says. now than 30 years ago. In fact, Asians are In addition, large percentages of physics represented in far greater numbers than their per- students and researchers in the United States centage in the population, mostly because of an are foreign. American citizens earned 75 influx of immigrant engineers and scientists. But percent of physics PhDs in 1973, but only 40 women, blacks, Hispanics, American Indians, percent in 2006, according to the National and Pacific Islanders are still vastly underrep- Science Foundation. resented. Statistics compiled from Brookhaven As opportunities in their home countries National Laboratory, Fermi National Accelerator increase, an increasing number of foreign scien- Laboratory, and SLAC, for instance, suggest tists are expected to go back, and not enough that 22-32 percent of their employees—everyone Americans are being attracted into the workforce from cafeteria workers and technicians to to replace them. administrative staff and scientists—are members With the United States on track to become of underrepresented minority groups, and 20-28 a majority-minority nation by 2042, it needs to percent are women. Among lab physicists, the attract more American women and minorities into percentages are far smaller. science to ensure a robust scientific workforce National laboratories are working with educa- in the future and boost the country’s competitive- tors to change that—offering training for science ness, security, and defense, says Ernestine teachers, employing college students during the Psalmas, senior program officer for the National summer, and mentoring students. Academy of Sciences. They’re also working to recruit already-molded As Bill Valdez, director of the US Department minds and to create a workplace culture that of Energy’s Office of Workforce Development entices them to stay. for Scientists and Teachers, puts it, “We have At Fermilab, a major effort is under way to boost a stewardship responsibility to ensure that diversity in the workforce by attracting a broad the next generation of physicists exists out there.” range of job candidates and creating a welcom- ing environment for people of all backgrounds. Barriers persist The laboratory recently held a series of focus On paper, there are no reasons why women and groups to examine the lab’s climate, and is minorities shouldn’t be rapidly gaining represen- adding cultural programs and creating task forces tation in science, engineering, and technical fields. and committees to address diversity issues. Legal, academic, and governmental actions “When you have done your homework, hopefully within the past few decades have addressed you’ll end up with people who represent differ- open discrimination. ent cultures and a good gender mix,” says Sandra But experts taking a closer look have found Charles, equal opportunity specialist at Fermilab. cultural, societal, and academic factors that “That requires the entity to take a look at including hamper the pursuit of science by these groups. all people in a respectful workplace environment.” Ted Hodapp, director of education and diversity at the American Physical Society, believes Progress steady but slow physics carries a stigma. Women and members of underrepresented “We don’t market physics,” Hodapp says. “You minorities have gained ground in scientific fields. tell people, ‘I am a physicist’ and they are put From 1966 through 2006, the percentage off. You tell them what you’re working on and it of PhDs earned by women in all science and becomes interesting.” engineering fields increased from 8 percent However, the problem goes far beyond a nega- to 38 percent. But while women were earning tive reputation. 34 percent of all chemistry PhDs by 2006, Math and science, historically, were categorized they were awarded only 17 percent of physics as male fields. According to New Formulas PhDs that year, according to the National for America’s Workforce: Girls in Science and Science Foundation. Engineering, a report published by the National As for minorities, their numbers are still Science Foundation in 2003, biases persist in so low that Roman Czujko, director of the sta- schools, and teachers may offer more encour- tistical research center at the American agement to male students in science and math Institute of Physics, does not like to state them than to female students. Female students in percentages. were also encouraged to pursue the less math- “To tell you the truth, when I produce reports ematical sciences. that say that the numbers have grown by 0.4 “One thing seems pretty evident: Females are percent, people read right past it,” he says. “That’s more pervasive in the biological and life sciences,” the kind of thing we’re talking about here.” says Ken White, manager of Brookhaven’s But when people learn that of the 41,446 PhDs Office of Educational Programs. “There is a much granted in physics from 1973-2005, only 303 smaller population of female students in physics,

12 JoAnne Hewett symmetry | volume 06 | issue 03 july 09

Photo: Brad Plummer, SLAC 13 Duane Doles

Photo: Reidar Hahn, Fermilab 14 chemistry, engineering, and computer science.” in a variety of hair styles and attire. Although high school students are required Providing role models and mentors is another to take science classes, they don’t always have approach. access to physics. It’s offered in only about 45 per- Some national lab scientists, like Spencer, cent of New York City high schools, according reach out to young people through non-profit to Angela Kelly, assistant professor and coordina- groups. Others participate in lab-sponsored tor of the Graduate Program in Science Education education and outreach programs, such as lab at Lehman College, City University of New York. open houses, science bowl competitions, and “At least 75,000 students in New York City attend field trips. schools where physics isn’t an option,” Kelly Nearly 100 high school students come to SLAC says. “In urban areas with a very high under- each February for the DOE’s regional science represented minority population, the numbers bowl, an academic competition that tests students’ are even lower. Only 31 of 82 Bronx high schools knowledge of mathematics and science. offer physics.” Brookhaven brings in faculty members from Whether physics is offered depends on many historically black colleges and universities to factors, including the school’s size and ethnic conduct science at the laboratory. makeup. When she asked school administrators “These faculty from minority-serving institutions why they don’t offer physics in their schools, develop strong relationships and collaborations Kelly says the response was often, “Our kids can’t with researchers at Brookhaven,” says White. They do it.” They thought physics would be too bring students with them, and take their science difficult for most of their students to pass, and experience and enthusiasm back to the classroom. were unwilling to spend money to take that risk. Fermilab also offers teachers three consecutive Instructor attitudes also play a role, says summers of training as part of Academies Sharon Fries-Britt, an education researcher at Creating Teacher Scientists, a DOE-funded pro- the University of Maryland at College Park. gram. They do scientific research the first year, She and her students conducted a four-year study learn teaching techniques the second and focus on minority high achievers in the classroom on reaching out to other teachers during the third. as part of a project by the National Society for Michael Johnson, a former electronics engi- Black Physicists and National Society for neer, switched to teaching in 2003. He entered the Hispanic Physicists. program to learn how to teach science at the In interviews with 100 undergraduate students Robert Emmet Academy in Chicago, one of the who were members of underrepresented minori- lowest-scoring schools on the LSAT in 2006. ties, Fries-Britt says she saw clear evidence of “This program is making me look at science verbal and non-verbal behaviors discouraging from a whole new perspective,” Johnson says. “I’m the students from pursuing physics. learning leadership skills and other skills that I can Minority students said they felt as if they had to take back to other teachers and other schools. prove themselves in every situation. Their instruc- I’d like to teach teachers how to teach science.” tors often called their work into question, criticizing sub-par work while speculating that students Building momentum through mentoring who turned in excellent work were cheating. This Of full-time freshmen at American four-year led some students to aim for mediocrity. colleges who said in a 2006 survey that they would “Long-term coping is a challenge for these probably major in physics, 21 percent were women, students,” Fries-Britt says. according to the Higher Education Research Institute at the University of California, Los Angeles. Stoking a passion for science That’s a dramatic increase from 1973, when To produce more female and minority scientists, only nine percent were women. educators and laboratory staff members know But while 21 percent of bachelor’s degrees and they have to start by making science attractive. 23 percent of master’s degrees in physics went “We have to introduce science to children in to women in 2006, they earned only 17 percent junior high and high school,” says Shirley Kendall, of the physics PhDs that year, according to the diversity manager for Brookhaven. “We have to get National Science Foundation.

them at the very beginning and we have to sell To plug leaks in the educational pipeline for symmetry | volume 06 | issue 03 july 09 science as a cool, integrated part of their future.” women and minorities, laboratories are trying to An activity at Fermilab reveals stereotypes engage and mentor college students such as elementary school children have about scientists. Duane Doles. Before visiting the lab, students are asked Growing up in a predominantly black neighbor- to draw their impressions of what a scientist looks hood in northwest Washington DC, Doles like. Most often, they draw white male scientists was always interested in life’s big questions, and in white lab coats. After touring Fermilab and traveled across town to attend a public high meeting with scientists, students tend to draw both school specializing in math and science. But until male and female scientists of varying ethnicities he met Fermilab scientist Herman White at

15 Brianna Stephens

Photo: Reidar Hahn, Fermilab 16 careers in the sciences. Another pursue vating studentswhomaynototherwise Internship Program, which isdedicatedtomoti- in to studyandworkatFermilab. paid part of Doles’ tuition, enabling him to continue science andengineering.The programhas minorities whoarepursuingmasters’degreesin fellowships tomembersofunderrepresented in Engineering and Science, knownas in EngineeringandScience, Consortium forGraduateDegreesMinorities graduate level,” hesays. undergraduate levelandcontinuetobeatthe physics project. where he is simulating the design of a new astro- Fermilab, at working University Howard from says. Today, he is a third-year graduate student becoming atheoristwascareeroption,” Doles andTechnologyin Science program. intheStudents sophomore yearatthelaboratory Fermilab that year, andspentthesummerafterhis could becomeacareer. meeting in 2004, he never knew that his interests forBlack Physicistsannualthe NationalSociety inclusive, andacceptingculture. inclusive, pay, clearcareer paths,andawelcoming, theirskillstoprivate companies. take they oftenseeemployeeswho trainedatthelab more challenging; sheandKendall notethat Fermilab’s diversity officer. Retention can be even often lose the salary war, says Dianne Engram, against businesses in private industry, national labs there yet.” organizations are in a similar position, which isMost not environment. work inclusive and force groups forthepurposesofhavingadiversework- fromallthe samegoal—toattracttoptalent Kendall says. efforts, outreach and recruiting of focus primary candidates for jobs in the basic sciences is the Expanding the pool of strong female and minority Attracting andkeeping workers remain inschool. to them motivate and expenses education their 18-22 with full-time summer jobs to help offset Program peopleages providesdisadvantaged grams. For instance, after transferring tofour-yearinstitutions. students tocontinuepursuesciencemajors Community CollegeInitiatives,encourages DOE Many of the national laboratories participate participate laboratories national the of Many For graduate studentslikeDoles,theNational “The scientists here were mentors for me at the that know didn’t I internship, the “Before Doles appliedforasummerinternshipat Two committees oftheAmerican Physical To prevent this, the lab must offer competitive Unfortunately, whenitcomestocompeting slow,” very is “Wehave “Progress all says. she In addition,individuallabshavetheirownpro- ’s Science Undergraduate Laboratory UndergraduateLaboratory ’s Science SLAC ’s Youth Opportunity DOE GEM program, program, , offers , offers

17 a systemic pattern of bias within the laboratory. laboratory. the within bias of pattern systemic a whether thereport’sfindingsstemmedfrom examine to groups focus 25 ran who facilitator regarding decision-makingprocessesandresults. and increasecommunicationtransparency improve trainingamongleadersatthelaboratory; and userstotreateach otherwithrespect; ment acodeofethics requiringalllabemployees leadershiponhowtoimproveinclusiveness. tory closely relatedfieldsandtoadvisethelabora climate forwomenandminoritiesinphysics Society visited Fermilab in May 2008 to assess the But they’redetermined toget there. and inclusive. is working to create a future that is open, inviting sity officers throughout the national lab system, toback down.She, alongwithotherdiver- about initiatives. diversity office’s her of awareness increase to wants and employees, full-time for started program mentoring a get to hopes employees andusers. of ethnicities andbackgrounds oflaboratory number ofeventscelebratingthedozens the boosted also has pair The Office. Diversity diversity issuesandactasliaisonswiththe program. inclusive more and comprehensive more a Engram and Charles are leading an effort to create ture andwerenotcondoned.” as aresultofFermilab’s currentpoliciesandcul- absolutely happened,buttheydidn’thappen women,” “These and says. he students graduate have learnedtohandlethisdiversityreallywell.” aspectofthelab.Fermilabin every employees many internationalculturesworkingtogether the of because workplace normal the beyond Sarno says.“Theisdiversewell laboratory fields. all from users and staff laboratory interviewing employees toparticipate,andspentweeks focus groups. Perspectives ofthe Group,Inc.andfacilitator it seriously,” saysDougSarno,principalof allegations andthelabwantedneededtotake committees dididentifyrealproblems. “The In response, Fermilab hired an independent They concluded thatFermilab needstoimple- They acknowledge itwon’tbeeasyorquick. Although theclimbissteep,Engramisn’t More needs to be done, Engram says. She They’re committeestoaddress establishing Fermilab, at diversity Toincrease further At thesametime,Sarnosaysthat “What we didn’t find was a systemic condition,” lab of section cross random a invited Sarno “The APS APS heard some individual stories from heardsomeindividualstoriesfrom reportpresentssomeserious

APS

symmetry | volume 06 | issue 03 | july 09 The Fermilab team that will use the Dark Energy Camera to peer deep into the dark includes, from left, physicists John Peoples, Brenna Flaugher, Juan Estrada, and Tom Diehl.

18 By Kristine Crane out what’sgoingon. Chile, theyhopetofind in mountaintop a from of millionsgalaxies the light from hundreds work? Byrecording mysterious forceisat ing ever faster. What the universeisexpand- scientists wonder why Gazing intospace,

symmetry | volume 06 | issue 03 | july 09 Imagine a camera that takes pictures of the A fateful conversation universe not only as we see it today but back In the summer of 2003, former Fermilab director through time, closer to when the universe began, John Peoples and University of Chicago capturing images of roughly 300 million galaxies. physicist John Carlstrom shared a cab on their At Fermilab in Batavia, Illinois, Brenna Flaugher way back from an astrophysics conference and her colleagues are building such a device. in Seattle. The subject of dark energy was already Called the Dark Energy Camera, it will survey the on Peoples’ mind, and Carlstrom was working skies of the Southern Hemisphere and peer far on the South Pole Telescope, whose construc- back in time, allowing scientists to see galaxies tion would soon begin in Antarctica. Since as they were when the universe was only a few 2007, the telescope has recorded the microwave billion years old. background radiation left over from the The goal is to search for signs of dark energy— big bang, looking for distortions that mark giant the ubiquitous, invisible substance believed clusters of galaxies. But the telescope is to make up 70 percent of the universe. unable to determine how far away, and hence For Flaugher, who spent 15 years studying how old, galactic clusters are—information subatomic physics, the prospects were so intrigu- crucial for connecting its observations to dark ing that she changed the focus of her career. energy calculations. “I have gone from studying the smallest known What they needed, the two physicists agreed, things in the universe—quarks—to galaxy was a project that would fill the gap by deter- clusters, the biggest things we know,” she says. mining how far these clusters are from Earth. “The thing that makes both fun is that you get “The prospect was exciting,” Peoples recalls. to think about the origins of the universe.” At the time, he had just finished directing the Sloan Digital Sky Survey. The project, which makes A mysterious force observations from a telescope in New Mexico, has Eighty years ago, Edwin Hubble discovered that provided three-dimensional maps of nearly our universe is expanding, with galaxies becoming one million galaxies and 120,000 quasars in the increasingly distant from each other. Scientists Northern Hemisphere. Combined with data reasoned that the gravitational attraction among recorded at other observatories, the measure- galaxies must slow this expansion. But then ments indicate that 96 percent of the universe in 1998, two independent teams of scientists dis- is composed of dark matter and dark energy. covered a perplexing change in the expansion rate of the universe: for the first eight billion years Is gravity the problem? after the big bang, gravity indeed had slowed the Mounted on a telescope in Chile, the Dark Energy expansion, as predicted. Then, roughly five billion Camera will peer deeper into the sky and years ago, the expansion began to speed up. unveil more galaxies at greater distances than What caused this acceleration? any previous project, including the Sloan Digital The preliminary answer is dark energy, Sky Survey. It will collect data on the distances a mysterious “antigravity force.” When the universe of supernovae from Earth; the large-scale was young, gravity was the dominant force. But clustering of galaxies; the abundance of mas- over time, matter spread out enough to significantly sive galaxy clusters; and the bending of diminish the gravitational attraction between light caused by galaxies and clusters of galaxies. galaxies. Dark energy, a repulsive force, began Scientists use these four methods to deter- to overpower the gravitational force and push mine how fast the universe has been expanding the galaxies ever faster apart. and the rate at which galaxies and clusters Confirming the existence of dark energy and formed over cosmic time. Two of those methods understanding its origin would have profound will yield answers that are independent of implications for our understanding of the universe. the role that gravity played in the evolution of the But an even more radical outcome would universe. The other two will provide answers emerge if scientists discovered that dark energy that depend on the theory of gravity. does not exist. Instead, some theoretical models “If all four measures show the same result, it suggest that an extra spatial dimension causes means that our current ideas about dark energy the universe to expand ever more rapidly, are correct; if they differ, there is either a problem unraveling Einstein’s general theory of relativity. in our understanding of gravity or some other The Dark Energy Survey, scheduled to be up explanation,” says Flaugher, who is spearheading and running in 2011, might reveal which explanation the camera’s construction. The $50-million is correct. Dark Energy Survey involves 120 scientists from “It’s throwing the tools of the digital age onto 13 institutions in the United States, Brazil, Spain, the old question of where we are,” says Craig and the United Kingdom. University College Hogan, the director of the Center for Particle London is responsible for polishing the five lenses Astrophysics at Fermilab. that make up the optical system of the camera.

20 The Expansion of the Universe

Galaxy Formation

Over billions of years, gravity draws matter together into a web of structure. The bright spots are where galaxies form.

Size of the Universe

Not to scale symmetry | volume 06 | issue 03 july 09

Matter dominates: Dark energy dominates: Expansion slows Expansion speeds up

Big Today Bang

Time 0 1.0 9.5 13.7

Not to scale; In billion years

Energy Dark 1% 50% 73% and Energy Matter

Content symmetry | volume 06 | issue 03 july 09

Dark Matter 84% 43% 23% Ordinary Matter 15% 7% 4%

Simulations and visualization of galaxy formations by Andrey Kravtsov, The University of Chicago, and Anatoly Klypin, New Mexico State University

21 The Spanish groups provide the electronics Joe Mohr, physics and astronomy professor at that will process faint signals of light that traveled the University of Illinois, Urbana-Champaign. billions of years across the universe before landing in the “eyes” of the Dark Energy Camera. Reviving an old scope Crafting the CCDs requires a unique process Traveling back in time developed by engineers at Lawrence Berkeley At the forefront of Fermilab’s construction team National Laboratory. The final steps of the manu- is physicist Juan Estrada, who joined the project facturing process take place in a clean room as a Fermilab Wilson Fellow in 2004. Estrada inside a dome-shaped building at Fermilab. The was a postdoctoral researcher studying the top lab’s technicians were already familiar with quark at Fermilab’s DZero experiment when he the assembly of silicon detectors used in parti- became attracted by the prospect of working on cle physics experiments; now they produce an the Dark Energy Camera. average of four CCDs per week for the camera. As an undergraduate in Argentina, Estrada had Once all the CCDs are ready—a milestone studied the properties of the vacuum, and he the team expects to reach next year—technicians was eager to re-visit an issue that he considers the will finish assembling the camera and ship it biggest problem in physics: the mysterious to the Cerro Tololo Inter-American Observatory energy that seems to come from empty space in Chile, where it will be placed atop a four- in our universe. meter telescope called the Blanco. To do that, he first had to learn astronomy. The Dark Energy Camera will give new life to “Fermilab gave me the opportunity to learn the 40-year-old telescope, which met the something I had never done before,” Estrada says. survey’s criteria beautifully, according to Peoples: He learned how an astronomical camera works “It was a marriage made in heaven.” from a retired Fermilab engineer, Tom Droege, who practices astronomy from his home observa- From Chile to Illinois tory. By taking apart and reassembling Droege’s The Dark Energy Survey collaboration will use the camera, Estrada learned the basic steps of build- telescope for five years between September ing a camera, valuable lessons for the construction and February, taking images on 105 nights each of the Dark Energy Camera. year and sending a few hundred images When complete, the Dark Energy Camera will per night to the University of Illinois, Urbana- be the size of a Smart car. What makes it so Champaign. Each image comprises 520 powerful are 74 delicate detectors, called charge- million pixels, equivalent to about 1 gigabyte coupled devices or CCDs, each three by six of data, with information on the redshifts centimeters in size and 0.250 millimeters thick. and brightness of about 200,000 galaxies and As in an ordinary digital camera, they are the other celestial objects too faint to be seen camera’s “film” that records incoming light. The by a simple household camera. CCDs will sit on a plate about half a meter in A supercomputer, which Mohr calls the diameter, located a few centimeters behind the “mother ship,” will store all these images and auto- camera’s set of lenses. matically detect the objects they contain, Cooled to minus 100 degrees Celsius to reduce producing a catalog of galaxies with their bright- background noise, the Dark Energy Camera’s nesses, positions on the sky, and other superb CCDs will record longer wavelengths properties. The science team will analyze and of light than other optical cameras do. This will interpret this information, searching for clues allow it to see light from fast-receding galaxies that might help explain cosmic acceleration. that has shifted to longer wavelengths, toward the So what will scientists find out? red end of the spectrum, in the same way “None of us is a prophet,” says Ofer Lahav, chair a siren drops in tone as it moves away. The fast- of astrophysics at the University College est-moving galaxies are also the farthest away, London, who co-chairs the scientific committee as Hubble discovered. What’s more, the light we of the Dark Energy Survey collaboration with see from the farthest galaxies is the oldest Fermilab’s Josh Frieman. Lahav says the findings because it has taken longer to reach us. And so will lead to a more complex view of dark energy, through this chain of inferences from reddest or perhaps a modified version of gravity. to fastest to farthest to oldest, the Dark Energy Especially if it’s the latter, revisiting Einstein’s Camera will be able to see distant galaxies as theory of relativity would be “a big shake-up they looked billions of years ago, closer to the to the foundations of physics,” says Lahav. “Either universe’s infancy. way it’s exciting.” “We are mapping the distribution of the galaxies While future surveys aim to probe even deeper from what the local universe looks like now into the sky for answers about dark energy, to a time when the universe was just a few billion the Dark Energy Survey will be the first to take years old,” says Dark Energy Survey collaborator a stab at solving the mystery, says Lahav.

22 In a Fermilab clean room, Ken Schultz and Kevin Kuk check the alignment of the prototype camera's front window. symmetry | volume 06 | issue 03 july 09

“It is among the surveys that will push the sub- The Dark Energy Survey collaboration hopes jects of dark energy and modified gravity to to be equally successful. Its survey of the a new level,” he says. southern sky will cover an area smaller than the But that is not all. Sloan survey of the northern sky, but it will go deeper, further back in time. The big payoff “It’s a small project for a really big scientific The Dark Energy Survey collaboration expects payoff,” says Flaugher. Most importantly, it might that its data on stars, quasars, and galaxies will answer what she and her colleagues consider lead to hundreds if not thousands of scientific “the biggest question out there.” publications. The collaboration will make its Although Flaugher won’t wager a guess on data public a year after it has been taken, an whether the findings will confirm or deny the approach also used for the data collected by existence of dark energy, she is certain about the Sloan Digital Sky Survey and the Hubble one thing. Space Telescope. “I don’t want to argue about it anymore,” The Sloan survey, which mapped a quarter Flaugher says. “We need data, data, and of the sky, has generated more than 2400 scientific more data.” publications so far. Its results have been cited In a few years, she’ll have it. more often than those from any other observatory, including the Hubble.

23 Photography by Reidar Hahn, Fermilab

24 symmetry | volume 06 | issue 03 july 09

Helium’s shrinking bubble Helium is the lifeblood of large particle accelerators. As the world’s supply dwindles, the particle physics community must take steps to preserve this precious commodity or learn to live without it.

By Calla Cofield

25 At a couple of degrees above absolute zero, far colder than any living organism can survive, liquid helium stirs to life the largest particle accelerators in the world. It pulses through the veins of the Large Hadron Collider, following thousands of dipole superconducting magnets around a 27-kilometer ring. Flowing through magnets in Fermilab’s Tevatron, it helps jump-start subatomic particles on their way. These and other vital organs at dozens of labs around the world depend on helium to help them thrive. Hot air balloons, blimps, car airbag systems, welding, leak detection, scuba breathing mixtures, and NASA space shuttles all use helium. Cryogenics, which includes cooling for particle accelerators and detectors, consumes 28 percent of helium in the United States, with half of that chilling tens of thousands of Magnetic Resonance Imaging, or MRI, machines. And the market is growing. At the turn of the 20th century, natural gas miners found helium coming from underground, produced by the radioactive decay of uranium and thorium. It appears in pockets of natural gas in small portions, with three percent helium considered a good ratio. Although helium is relatively easy to extract, it falls on the natural gas companies to capture the gas or let it go. Lighter than air, helium released from the Earth escapes the atmosphere into space. As the second- smallest atom in the universe, the cunning gas finds its freedom through almost any opening, joint or crack, eventually leaking out of party balloons and even passing through some types of glass. Like oil, coal, and natural gas, Earth’s supply of helium will inevitably run out. While the physics community is aware of this impending problem, says Fermilab cryogenic engineer Tom Peterson, “we’re just not sure what to do.”

The coldest liquid “Helium,” says Serge Claudet, “is a very nice gas.” Claudet is head of the Large Hadron Collider’s cryogenics operation team, and he has a very specific set of qualifications for a “nice gas.” Placid helium is non-flammable, a big bonus for facilities storing large quantities of it. A noble gas, it is also easy to keep clean since it doesn’t tend to bond to other elements. Helium is the only element that is liquid at nearly absolute zero, and even at that frigid temperature solidifies only under pressure. Helium’s ultra-cool nature makes it the perfect option—the only option—for many superconducting applications. At super-cold temperatures, certain materials— such as copper, aluminum, and niobium titanium—lose all resistance to electricity. This allows electrons to flow uninhibited, delivering current with 100 percent efficiency. Wrapped into coils, superconducting wires become electromagnets that substantially out- perform conventional magnets in the strength of their magnetic fields. With this strength, scientists can steer particle beams around circular tracks, as the particles move at nearly the speed of light.

26 To maintain these cold temperatures, superconducting magnets require a liquid coolant that will flow over them, pick up excess heat, and carry it away. The helium refrigeration system at Fermilab rumbles with the get-up of 10,000 horsepower, cooling 10,000 liters of liquid helium—a little more than enough to fill two double-decker buses. Helium exits the refrigeration unit through pipes of stainless steel, one of the few materials that won’t become brittle and crack at 1.8 kelvin, or minus 456 degrees Fahrenheit. Peterson and the cryogenics team surround that pipe in a vacuum, seal it in a second pipe, box the pipes in a copper thermal shield, wrap that in another layer of shielding, and weld the whole package inside a vacuum-tight steel container. It’s the ultimate thermos, dedicated to reducing heat loss to zero. “Liquid helium is a utility in the production of the

particle beam, like power or water,” Peterson says. symmetry | volume 06 | issue 03 july 09 “When the cooling is available, experimenters don’t think much about it. It is when it goes away that you notice it.”

A knack for getting loose In theory, a system carrying helium through a facility like Fermilab should never need to replenish its supply. It should carry cold helium to its target, bring warmed helium back to the refrigeration unit, and so forth. But joints in miles of piping and hair-line cracks unseen by engineers leave helium just enough room to escape. Materials commonly used to seal up joints become brittle at 1.8 kelvin and cryogenics teams can dedicate only so much time to searching for leaks. Brookhaven National Laboratory holds 50,000 liters of liquid helium and loses 20 percent to leaks per year; after the LHC’s yearly shut-down, cooling-down, and starting up, the helium loss is about 25-30 percent. This leaked helium is rarely recov- ered. In addition, power outages cause helium to heat up and expand beyond what facilities can hold, forcing them to release it into the atmosphere. In 1925, the US government recognized helium’s limited availability and began storing it in the Federal Helium Reserve in Amarillo, Texas. In the 1990s, in an effort to keep helium costs down, the government began selling off the reserve. Debate over this decision still rages between those who would like helium costs capped, and those who worry what will happen when the supplies run out. Even so, prices have nearly doubled in the United States in the past three years. In 2007, several US helium refineries failed to come online as scheduled, due to a series of coin- cidental delays. Helium users felt the pinch. Roberto Than, a cryogenics specialist at Brookhaven, says the lab’s supplier warned of possible delays in delivery. It turned out to be a close call. “We were still able to get it on time,” Than says, allowing the lab’s Relativistic Heavy Ion Collider to start up on schedule.

27 Helium may be the second most abundant element in the universe, but on Earth it’s a non- renewable resource. Physicists and engineers are working on ways to conserve and recycle this essential gas so it doesn’t just float away.

Making recycling pay Many small particle physics facilities don’t use Although experts know helium isn’t as rare as xenon enough helium to make recovery cost-effective. nor as abundant as nitrogen, they have difficulty Refrigeration machines need frequent maintenance assessing just how much helium is left underground, and eat up a significant amount of power. So used and they can’t tell how much of that will be captured helium is often released into the atmosphere. by natural-gas miners. It is possible that in as But a new technology may change that. The little as 30 years, world helium production could peak. Soudan Mine in Minnesota hosts the Cryogenic While there is no direct concern for tomorrow, Dark Matter Search, CDMS, in a laboratory a half mile Claudet says the particle physics community does underground. There, protected from cosmic rays, have a focus on helium conservation, and notes physicists hope to identify the passage of dark matter that over the past 30 years helium recovery efforts particles. To reduce thermal noise, they cool their have improved significantly. Large facilities likeCERN , germanium and silicon detectors with liquid helium. Fermilab, and DESY have always liquefied their In May 2009, Soudan scientists carefully lugged own helium and have increased efforts to recapture a new type of helium refrigerator, called a “cryo- it. At SLAC National Accelerator Laboratory, cooler,” down a 12-foot-wide, 2341-foot-deep mine workers built a custom recycling unit to purify contam- shaft that provides the only entrance to the labora- inated helium from the PEP-II accelerator when it tory. These small helium liquefiers, about the size was running. of a household refrigerator, cost less than one-fifth “ A t CERN we’re working on diminishing losses,” the price of a traditional liquefier. Bauer, who manages Claudet says. “We’re trying to increase storage the CDMS project, explains that the lab’s 60-liter- and become less dependent” on the helium market. per-day helium usage wouldn’t justify the cost of

28 symmetry | volume 06 | issue 03 july 09

a traditional liquefier, especially since the older units be used as coolants. Nitrogen is cheaper than usually need maintenance every few weeks. But the helium, represents about 80 percent of the air we cryocoolers are a perfect fit for Soudan, and need breathe, and isn’t flammable or explosive like maintenance only every year or two. hydrogen. However, at this time there are no high- Bauer says he learned about the cryocoolers less temperature superconductors that could fill the than two years ago and made a move to obtain needs of particle accelerators. them right away. With helium prices climbing the way While the particle physics community must do its they are, the coolers should pay for themselves in part to preserve the world’s helium supplies, in less than two years. some ways its hands are tied. Although facilities like Fermilab and CERN use helium on a larger scale Pressing ahead than most, they represent only a very small percent- Peterson is now working on designs for the age of overall helium consumption. For that International Linear Collider, which would rely on liquid reason, their conservation efforts alone won’t stop helium as well. But by the time it is built and a helium shortage. running, physicists may already need to be on the But that hasn’t stopped them from trying. lookout for alternatives. Conservation efforts at large facilities continue to High-temperature superconductors present one improve and grow, while physicists and engineers possibility. Scientists are working doggedly to press ahead to create new technologies that could cut understand the mechanics of superconductivity, helium usage across the board. Slowly but surely, and hope to achieve it at temperatures where high-energy physics is preparing for a possible helium elements such as nitrogen are still liquid and can shortage. Only time will tell if it is acting fast enough.

29 gallery: accidental beauties

These exquisite test samples transcend their original purpose—ensuring all the metal parts of SLAC accelerators and detectors are flawless. By Lauren Schenkman symmetry | volume 06 | issue 03 july 09

30 symmetry | volume 06 | issue 03 july 09

31 gallery: accidental beauties

1 A gas tungsten arc weld, in 2 Gazing through a micro- 3 Copper, especially oxygen- 4 These may look like tools which electricity arcs from scope, metallographers free electronic grade, for a toy soldier, but they’re a tungsten electrode to looked for imperfections is used heavily in klystron actually cross-sections of the metal within an envelope radially along the thickness fabrication. Any tiny amount screws that were machined, of inert gas, was used to of this stainless steel of oxide can cause failures. rather than made by roll- join these square flanges vacuum pipe. ing thread onto a post, to pieces of stainless which can trap contami- steel tubing. nants inside. 1

There is something undeniably appealing about would slice off a small chunk with a diamond these baubles, which were rescued by the saw, place it in an epoxy mold, and bake it at boxful from the salvage yard at SLAC National high temperature and pressure. Then he’d begin Accelerator Laboratory. Each gemlike piece is at the slow, painstaking work of polishing the once simple, playful, and eloquent. One resembles sample’s surface with five different grit sizes, then an assortment of minuscule wrenches, another with three progressively finer grades of diamond a face cracking a geometric grin. They seem to slurry, and finally an incredibly fine 0.05 micro- mean or symbolize something, to tell a tale in meter alumina polish that left the surface as their glint and sparkle. Each one is unique, and smooth as a mirror. Then Glesener would dab uniquely compelling. But what are they? the mount with a cotton swab dipped in an The answer, it turns out, is everything. etching chemical, removing the smooth layer, “Every project that came through SLAC sent and the sample would be ready for viewing. stuff through us,” says former SLAC metallographer “It was very time consuming, but the whole Will Glesener. Now a metallurgist with a company purpose was to get beyond this and then look in New York, Glesener spent five years at SLAC at the microstructure, which is what you’re after. inspecting the quality of materials that eventually Then the story begins,” says Jean Francis, who found their way into particle detectors and accel- began working as a metallographer at SLAC erators. He would take snippets of every batch in 1964, during the early days of accelerator of metal SLAC purchased, whether it came from construction. “After all the heating, pounding, and the United States, Finland, or Japan, and process cutting, the challenge is to maintain what was them into these metallographic mounts, which he done to [the metal], without altering the story.” then examined under a microscope. In her 40 years at SLAC, Francis made To the trained eye of a klystron engineer or thousands of samples, inspecting the raw materials accelerator physicist, the tiny wrenches become for components ranging from the original machined screws, a zigzag of copper and stain- accelerator cavities to flanges for the B-meson less steel becomes an electron-beam weld, two factory of the late 1990s. Viewing the samples eyes and a nose become vacuum tubing. through a specialized microscope called a metal- lograph, Francis could read the tale of a poorly Finer and finer executed braze or a flawless vacuum tube. She Crafting a mount is an art, a meticulous process especially loved looking at extremely pure with many steps. “It usually took, from start to copper, whose microstructure held the story of the finish, a couple of days for the whole procedure,” smelting and extraction processes. Glesener says. To sample a bar of copper, he “Copper to me is prettier than gold,” says

32 5 These are pieces of wave- 6 The sharp points of these 7 The tiny hitch in this 8 These white clips were guides that are used welds are a tell-tale sign flange allows it to form a employed to keep slender in klystrons. Microwave- that an electron beam fused perfect vacuum seal with pieces of metal upright frequency signals are these copper and copper its mate. during the sample-making deflected by the guide’s con- nickel pieces. process. ducting walls, bouncing along in a zig-zag path.

5 7

Francis, who now lives in rural Utah. “It has this “If you have enough it will turn it into Swiss pink cast to it. The purity that we were handling cheese, and it no longer meets the requirements was outstanding, and I always remember that this of being a nice vacuum material,” says Erik is not what the material was before extraction Jongewaard, head of SLAC’s klystron department. from nature.” To think of the process this material went through, she says, “is truly a wonder.” Pieces of lab history As they worked, the metallographers scratched Tiny flaws, big trouble a code of letters and numbers into the back Smelting processes for copper can go slightly awry. of each mount, and kept the matching reports and Gazing into the microscope, Francis and Glesener images in black D-ring binders. hunted for specks of copper oxide in a landscape “We kept all the mounts from day one, so we resembling an aerial view of a desert crossed by could pull out a mount and retest it,” Glesener one or two lonely highways, boundary lines divid- says. “I’ve had a request from the klystron depart- ing different grains in the metal. Impurities like ment where a part they put in 20 years ago these can lead to electric arcing, which causes the broke, and they wanted to test the material that copper to warp and melt, undermining the per- part was made of.” The trays of gleaming formance of klystrons, the devices that feed micro- mounts were also a popular attraction on lab tours. wave-frequency power into the linear accelerator. When major budget cuts shook SLAC in “The klystrons are the pulse of the linear January 2008, the Surface and Materials Science accelerator, so there was really critical analysis department, of which metallurgy was a part, done,” Glesener says. “What we were actually was closed and the work contracted out. The looking for was oxygen contamination down in the department head tried to save as much of the parts per million.” scientific equipment as possible, but the large

Accelerator and klystron components are collection of mounts went to salvage. Although symmetry | volume 06 | issue 03 july 09 joined by brazing, in which two parts are placed in most have been lost, the survivors have found a furnace with a filler metal that has a lower a new home in the SLAC archives. melting point. The metal melts and capillary action The metallographic mounts are part of the pulls it into the gap between the two components; physical record of the laboratory’s history, and removed from the furnace, the metal cools and a testament to the incredible challenges that hardens. But when contaminated copper parts are were overcome in building such large-scale exper- brazed together in a hydrogen furnace, hydrogen iments. As Francis puts it, peering through a can seep into the copper to join trapped oxygen, microscope at these samples was a first-hand forming water vapor. glimpse of “man trying to do the impossible.”

33 deconstruction: periodic table

Look at the periodic table of elements, and you’d be hard pressed to find an element that is not used in physics. But what are the most important elements for building accelerators, detecting particles, and solving the mysteries of the universe? The search for answers takes us on a winding journey that includes ancient shipwrecks, trendy earrings, and the sound of dark matter. symmetry intern Kristine Crane asks Fermilab physicists about the elements they could not live without.

H 1 Hydrogen provides the protons H for proton beams. Made of 3 4 only one proton and one electron, the hydrogen atom is Li Be the lightest element. It is also 11 12 the most abundant, compris- ing 90 percent of the visible Na Mg universe by mass. 19 20 21 22 23 24 25 26 27 K Ca Sc Ti V Cr Mn Fe Co Nb 37 38 39 40 41 42 43 44 45 Niobium helps push and steer particles. Of all the elements, Rb Sr Y Zr Nb Mo Tc Ru Rh it superconducts at the high- 55 56 71 72 73 74 75 76 77 est temperature—9.2 kelvin. It is the material of choice for Cs Ba Lu Hf Ta W Re Os Ir the superconducting magnets 87 88 103 104 105 106 107 108 109 that keep beams moving in the right direction and supercon- Fr Ra Lr Rf Db Sg Bh Hs Mt ducting cavities that accelerate beams. Niobium is also 57 58 59 60 61 62 63 used for stylish earrings and superconducting magnets La Ce Pr Nd Pm Sm Eu in MRI machines. 89 90 91 92 93 94 95 Ac Th Pa U Np Pu Am W Tungsten wires as thin as a human hair span the interior Fe Pb of the outer tracker of the Iron is the most stable ele- Lead shielding protects CDF experiment at Fermilab. ment in the universe: it supersensitive particle detec- The wires record the arrival takes more energy to break tors from naturally occurring times and paths of charged apart an iron nucleus than radiation. But lead itself can particles. Thin wires are the any other type. At the be radioactive. The melting best for recording signals in European laboratory CERN, of lead ore isolates heavy iso- an electric field, but the wires an iron yoke weighing topes, but lead-210 remains. must also last. Tungsten approximately 10,500 tons Hence the best kind of lead endures more tension than its channels the magnetic field is at least 200 years old and close relative, copper. of the CMS detector. can be found, for example, in shipwrecks.

34 Left to right: superconducting cavities made of niobium; germanium crystal of the CDMS experiment; ATLAS silicon detector. Photos: Fermilab, CERN Photos: Fermilab,

2 He He Liquid helium cools the super- 5 6 7 8 9 10 conducting magnets that steer particles and bend their B C N O F Ne paths. It is the only element 13 14 15 16 17 18 that remains liquid at the ultra- cold temperature of 4.5 kelvin. Al Si P S Cl Ar Fermilab and CERN have two 28 29 30 31 32 33 34 35 36 of the world’s largest plants for converting helium gas to its Ni Cu Zn Ga Ge As Se Br Kr liquid form. 46 47 48 49 50 51 52 53 54 Pd Ag Cd In Sn Sb Te I Xe N 78 79 80 81 82 83 84 85 86 Liquid nitrogen cools magnets and other devices to 77 kelvin. Pt Au Hg Tl Pb Bi Po At Rn Fermilab uses about 80,000 110 111 112 113 114 115 116 117 118 liters of it each day. At six cents per liter, it’s a cheap Ds Rg Uub Uut Uuq Uup Uuh Uus Uuo commodity.

64 65 66 67 68 69 70 Ar Gd Tb Dy Ho Er Tm Yb Argon is an inexpensive 96 97 98 99 100 101 102 noble gas. Scientists are drilling wells in Texas to Cm Bk Cf Es Fm Md No find non-radioactive argon, which they prefer in their particle detectors to avoid signals caused by the decay Si Ge of radioactive isotopes. Silicon is the element that Germanium may reveal the gave Silicon Valley its existence of dark matter name. In particle physics, particles. Scientists of the Xe silicon vertex detectors Cryogenic Dark Matter Xenon is an expensive track the paths of particles. Search listen for the sound cousin of argon. A liter of symmetry | volume 06 | issue 03 july 09 At the Large Hadron Collider that a dark matter particle liquid xenon costs $1000. in Europe, the ATLAS would create if it hit an atom Xenon is used in lasers, detector includes enough inside a large germanium light bulbs, and anesthesia, wafer-thin tiles of silicon crystal cooled to ultralow as well as in the neutrino to cover the floor of a rac- temperature. research at the Enriched quetball court. Xenon Observatory.

35 essay: tom nelson

Mining a froze over on September 11, 2000. Homestake announced that the Lead property was being rich vein shut down. of science But the citizens of Lead had very little time to mourn. Within weeks, Richard Gowen of the Gold! That precious South Dakota School of Mines & Technology, metal has been a con- along with physicists from a variety of institutions, stant measure of value brought forth the idea that Homestake should to mankind. Fortunes be the site for a deep-level underground laboratory. have been made or lost, Suddenly, the folks in Lead began to learn empires have risen or about some very strange and foreign things—beta fallen, all in the pursuit decay, dark matter, and, of course, neutrinos. of the Mother Lode. The community embraced the next concept Such is the case of of what its hometown might become. The next Lead, South Dakota. February, and on the 23rd of that month every Not long after year since, Lead has celebrated the National General George Custer and his expedition to the Science Foundation’s initial visit to the proposed northern plains discovered gold in 1874 on the lab site with “Neutrino Day.” There is a “Miss western edge of Dakota Territory, prospectors Neutrino,” and school children participate in con- populated the area in hopes of getting rich quick. tests to determine exactly what they think Several of these nomadic miners made their way a neutrino looks like. to the heart of the Black Hills. The NSF’s designation of Lead and Homestake Photo courtesy of Tom Nelson Photo courtesy of Tom Californian George Hearst, who went on to as the site of the Deep Underground Science build a fortune on mining, sent emissaries to the and Engineering Laboratory, or DUSEL, took territory and began buying up claims. Thus were much longer than originally hoped. In fact, the born Homestake Mining Company, the famous journey turned out to be a roller coaster! When Wild West town of Deadwood, and the neighboring the announcement came that the pumps that company town of Lead (pronounced ‘leed’). were keeping groundwater out of the mine were For 125 years Homestake and Lead were one to be decommissioned, it seemed as though and the same. Generation upon generation the project was lost. Legal maneuvers delayed worked for and in the mine, and people were born, the inevitable, but the pumps shut down and lived their lives, and sometimes died for the com- water began filling the mine at a rate of about pany name. 300 gallons a minute. Homestake was behind much of the modern- The greatest catalyst for the project came when ization that came to Lead, and ultimately the Mike Rounds became governor of South Dakota entire region. The company needed power, lumber, in 2003. He and his staff recognized the para- water, and medical care; so it started an electric mount importance of this proposal and made it company, a sawmill, a water distribution and a priority early in his administration. His efforts to treatment system, and a hospital. The company form strategic alliances and develop a cooperative wanted culture and activities for its workers, so it consensus among government, the private sector, built an opera house and recreation center. and the scientific community demonstrated that Because of Homestake, the city of Lead boasted Homestake was just too good a site to pass by. a quality of life seen at that time only in places All that led to the formal donation of the site like St. Louis and San Francisco. from Barrick Gold Corp. to the state, the creation At its peak, Homestake’s Black Hills mine of the South Dakota Science and Technology employed nearly 4000 workers. School children Authority, a gift of $70 million from South Dakotan would learn the names of the company’s general T. Denny Sanford for infrastructure improvements managers just as they would the presidents of the and educational outreach, and finally the July

United States. The high school boasted a wood- 2007 designation of Lead as the home of DUSEL. symmetry | volume 06 | issue 03 july 09 shop and metal shop that technical schools today Lead boasts a wonderful past, an exciting would envy. present, and an awesome future. The community The 8000-foot-deep mining operation began has always been about mining, and will continue to fade in the 1990s. The price of gold was falling to be about mining. Now, however, we are no and the cost of production skyrocketing. Despite longer mining gold, but science. a major downsizing and reinvestment in the capital plant in 1998, Homestake was doomed. Tom Nelson, whose grandfather came to Lead at the age of 12 to work for Homestake Mining Company, is the mayor of Around Lead it had often been said, “When hell Lead, a state senator, and the general manager of Gold Dust freezes over or Homestake closes!” Hell finally and Four Aces Gaming in Deadwood.

36 logbook: pierre auger observatory

transmitter. The detector array would record the In 1991, James Cronin extensive showers of secondary particles produced travelled to Leeds, England, to visit Alan Watson, an by high-energy cosmic rays and transmit their data expert on cosmic-ray physics. Cronin, a Nobel Prize to a central receiver station. winner in physics who had worked on accelerator- Cronin and Watson became the co-leaders of the based particle physics experiments, wanted to proposed project. In 1995, researchers met for six discuss ideas for cosmic-ray projects. Inspired by months at Fermi National Accelerator Laboratory to a proposal by Russian physicist Georgiǐ Khristiansen, carry out a detailed design study. The design he was eager to see the construction of a large evolved: To reduce cost, researchers decided to use array of detectors to unravel the mysteries of the cylindrical, 3000-gallon tanks filled with water highest-energy cosmic rays in the universe. instead of the rectangular containers with scintillators Based on his conversations with Watson and other depicted in the sketch. scientists, Cronin combined what he considered the When scientists began to discuss names and best ideas and developed an ambitious conceptual acronyms for the project, Cronin rejected all of them. design for an array of almost 3000 detector stations Instead he chose to name the cosmic-ray observatory to be installed across an area larger than the state after Pierre Auger, who discovered air showers of Rhode Island. created by high-energy cosmic rays in 1938. “I hate To stimulate discussions with other scientists, acronyms,” Cronin says. “People relate to the history Cronin distributed his concept through an Enrico of science much better than to an acronym.” Fermi Institute preprint, also published in the pro- In 1999, scientists broke ground for the Southern ceedings of a symposium held in Zuoz, Switzerland, Pierre Auger Observatory in Argentina. Nine years in April 1992. This sketch, made by Richard Armstrong, later, the collaboration celebrated the inauguration head of the engineering group at the University of the project. Funding agencies in 19 countries of Chicago, is Figure 12 of the article. It shows one contributed to the construction. Plans for a northern of the proposed detector stations, powered by observatory in Colorado are under way. a solar collector and communicating by microwave Kurt Riesselmann

Image courtesy of James Cronin, University of Chicago, Enrico Fermi Institute Symmetry A joint Fermilab/SLAC publication PO Box 500 MS 206 Batavia Illinois 60510 symmetryUSA

explain it in 60 seconds

are short- Virtual particles lived particles that cannot be directly detected, but that affect physical quantities—such as the mass of a particle or the electric force between two charged particles—in measurable ways. The existence of virtual particles is a purely quantum-mechanical phenomenon. The particles can appear out of nothing—the vacuum—only to quickly disappear back into the vacuum. Or they can be emitted by real particles, travel a short distance, and disappear again as they interact with other particles. The Heisenberg uncertainty principle limits the duration of their fleeting existence and the distance they can travel. Virtual particles are both a curse and a blessing. A curse because their presence makes calculations of seemingly simple phenomena, such as the electric force between an electron and a proton, vastly more complicated. A blessing because their indirect contributions to subatomic processes can reveal new particles and forces that elude direct production by our highest-energy particle accelerators. Scientists have measured, for example, the contributions of virtual particles to the mass of the proton and to the attractive force between two metal plates. Experiments also have identified virtual contributions from the yet-to-be- discovered Higgs particle, which is a key to explaining the origin of mass. Hence, not only are we quite confident that the Higgs particle does indeed exist, but we have a pretty good idea of where to find it. Craig Dukes, University of Virginia