Issue 10 Dimensions of Particle Physics Volume 04 a Joint Fermilab

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dimensions volume 04 of particle physics symmetryA joint Fermilab/SLAC publication

issue 10

december 07 symmetryA joint Fermilab/SLAC publication

On the cover The ALICE Time Projection Chamber Photo: Antonio Saba, CERN

Inside front cover Model of a superconducting quadrupole magnet for the Large Hadron Collider project. These magnets are used to focus the beam by squeezing it into a smaller cross-section, similar to the way a lens focuses light. However, each magnet focuses the beam only in one direction so alternating magnet arrangements are required to produce a fully focused beam. Photo: CERN

Office of Science U.S. Department of Energy volume 04 | issue 10 | december 07

2 Editorial We are on the eve of one of the greatest experiments in the history of physics. The Large Hadron Collider is pushing the frontier of exploration into the fundamentals of our universe.

3 Commentary: Lyn Evans “ Although the majority of the LHC was produced in Europe through collaboration between CERN and industry, a walk through the accelerator tunnel tells an international story.”

4 Signal to Background Not just about aliens anymore; life among physics tribes; Spartan software; connecting with Africa; the LHC by mail; penguins and particles; two new directors.

8 Voices: Dennis Overbye What’s in a name? Parsing the ‘God Particle,’ the ultimate metaphor.

10 Across the Ocean, Yet Close to Home Among the 10,000 people working on the Large Hadron Collider, 1000 hail from universities and national labs in the United States.

14 Entering Higgs Habitat The LHC will allow scientists to explore the territory where the long-sought Higgs particle—or maybe even a whole family of them—resides.

18 Protecting the LHC From Itself While human safety is always the first concern at the Large Hadron Collider, the machine also needs shielding from its own proton beams, which pack the energy of high-speed trains.

24 Gallery: In the Labyrinth It’s heavy, dusty, dirty work: Deep in the bowels of the LHC detectors, workers are connecting a rat’s nest of cables.

28 Q&A: James Gillies Hollywood directors, time travelers, journalists, school kids—CERN’s press office sees them all.

30 Essay: Peter Steinberg “The fascination with the LHC should not just be in the results, but in the false starts, inevitable stumbles, and occasional flashes of insight about the physics. Stay tuned to the bloggers, both official and not, as the LHC and its detectors rumble to life.”

ibc Logbook: CMS Cosmic Challenge Scientists working on the Compact Muon Solenoid test the detector using particles that rain down from space.

bc Explain it in 60 Seconds: Terascale The Terascale is an energy region named for the tera—or million million—electronvolts of energy needed to access it. Physicists are standing at its threshold, poised to enter this uncharted territory of the subatomic world. from the editor The LHC: The greatest physics experiment of history We are on the eve of one of the greatest experiments in the history of physics. The Large Hadron Collider, a 27-kilometer ring straddling the Swiss-French border, is pushing the frontier of exploration into the fundamentals of our universe. The machine is currently being prepared for first injection of the high- energy proton beams, due in the next few months. Soon after, the largest detectors ever made will be peering into the debris of collisions, a tangle of data that physicists will dissect, examine, and probe in their journey to reveal long-sought secrets of nature. In recent years, particle physics has been revolutionized with the discovery that 95% of the universe is missing. The Large Hadron Collider will answer many significant questions about the part of the universe we know and start to reveal critical information that will guide our exploration of the rest. The LHC will answer much, but it will raise just as many new questions for the ongoing scientific enterprise. Projects like the LHC are almost indescribably complex, requiring many tens of thousands of person-years of effort. Experiments on this scale need a long-term, consistent commitment to make them feasible. CERN has built an outstanding structure for managing large-scale, interna-

Phioto: Reidar Hahn, Fermilab tional collaboration, and the pursuit of scientific goals through this means has brought many additional non-scientific benefits to the partners and society as a whole. This issue of symmetry is dedicated to the imminent switch-on of the Large Hadron Collider. It can only skim the surface but presents views of the science, technology, international collaboration, and humanity of the LHC. Although not a CERN member state, the United States has one of the largest contingents of scientists working on the LHC. In the fiscal year 2008 federal budget, the United States fully honors its commitment to the LHC program. However, last minute cuts to the science budget, made as a consequence of political tussles, seriously threaten the future health of high-energy physics (and other sciences) in the United States. Whether the US government is able to justify its claim to support the physical sciences, and whether it will be able to generate confidence in itself as a good partner in international scientific projects, hangs in the balance. However, science goes on, and the promises and opportunities of particle physics are now greater than at any time in the past few decades. David Harris, Editor-in-chief

Symmetry Editor-in-Chief Publishers Print Design and Production PO Box 500 David Harris Neil Calder, SLAC Sandbox Studio MS 206 650 926 8580 Judy Jackson, FNAL Chicago, Illinois Batavia Illinois 60510 USA Deputy Editor Contributing Editors Art Director Glennda Chui Roberta Antolini, LNGS Michael Branigan 630 840 3351 telephone Peter Barratt, STFC 630 840 8780 fax Managing Editor Romeo Bassoli, INFN Designer www.symmetrymagazine.org Kurt Riesselmann Stefano Bianco, LNF Aaron Grant [email protected] Senior Editor Kandice Carter, JLab Web Design and Production (c) 2007 symmetry All rights Tona Kunz Reid Edwards, LBNL Xeno Media reserved Suraiya Farukhi, ANL Hinsdale, Illinois Staff Writers James Gillies, CERN symmetry (ISSN 1931-8367) Elizabeth Clements Silvia Giromini, LNF Web Architect is published 10 times per Heather Rock Woods Youhei Morita, KEK Kevin Munday

year by Fermi National Kelen Tuttle Marcello Pavan, TRIUMF symmetry | volume 04 issue 10 december 07 Accelerator Laboratory and Rhianna Wisniewski Perrine Royole-Degieux, IN2P3 Web Design Stanford Linear Accelerator Yuri Ryabov, IHEP Protvino Karen Acklin Center, funded by the Copy Editor Yves Sacquin, CEA-Saclay Alex Tarasiewicz US Department of Energy Melinda Lee Kendra Snyder, BNL Office of Science. Web Programmer Interns Boris Starchenko, JINR Mike Acklin Haley Bridger Maury Tigner, LEPP Lizzie Buchen Ute Wilhelmsen, DESY Photographic Services Amber Dance Tongzhou Xu, IHEP Beijing Fermilab Visual Media symmetry Gabby Zegers, NIKHEF Services

2 commentary: lyn evans

multipole corrector magnets made in India, and support structures from Pakistan. Collaboration of this kind has long been the norm in particle detectors, but the LHC is the first major particle accelerator to be built with substantial contributions from beyond the host laboratory. What has made this possible is the long history of collaboration among particle physics laboratories around the world. When CERN was founded in the 1950s, Brookhaven was probably the new European lab’s main competitor—and also its best friend. Both labs were building new machines. A development at Brookhaven opened the road to higher energies, an advance that Brookhaven immediately shared with CERN. As a result, CERN could build the proton synchrotron as a 28 GeV machine instead of a 10 GeV machine and briefly hold the world energy record before Brookhaven switched on the Alternating Gradient Synchrotron. In my younger days, I spent many hours in the control room of Fermilab’s Tevatron, always dur- Photo: Reidar Hahn, Fermilab ing those beautiful Chicago months of January and February when the CERN machines were shut down for maintenance. The experience I A truly international gained there on the world’s first superconducting accelerator synchrotron served me well in later years. Every time I take visitors to see the Large Hadron For our part, CERN has never hesitated to Collider, I’m reminded of the extent of the inter- share the results of our own accelerator innovation. national collaboration that has made this project Inviting partner labs to join in the construction of possible. Although the majority of the LHC was the LHC was a natural next step in this long tradi- produced in Europe through collaboration between tion of cooperation. CERN and industry, a walk through the acceler- We at CERN are all looking forward to switch- ator tunnel tells an international story. ing on the LHC in 2008, an event that will be The 27-kilometer-long LHC consists of eight closely tracked in the United States via Fermilab’s arcs joined by straight sections. These straight Remote Operations Center. That event will launch sections, each about 200 meters long, highlight the next level of our global collaboration: a new era the contributions from nations that are not CERN of discovery at the high-energy frontier. member states. Entering the tunnel at access point 1 next to the ATLAS experiment, for example, Lyn Evans is the LHC project leader at CERN. the first thing you see are the Japanese and American flags on the final-focusing inner-triplet magnets. The magnets are powered through a feed box made at the Lawrence Berkeley National Laboratory in California and are sitting on precision jacks from India. Next come six magnets made in Novosibirsk, Russia. They bring the beam trajectories together for collision. A little farther on, there’s a neutron absorber from Berkeley and a superconducting magnet from Brookhaven National Laboratory in New York symmetry | volume 04 issue 10 december 07 that puts the beams on parallel trajectories. After that come the quench resistors and main arc feed boxes, also from Russia. In the next three kilometers of arc are more than 150 superconducting magnets built by European industry. Less visible are the pulsed electronic systems and quadrupole magnets from Canada, the

3 signal to background

Not just about aliens anymore; life among physics tribes; Spartan software; connecting with Africa; the LHC by mail; penguins and particles; two new directors.

As a volunteer’s computer cranks out calculations for LHC@home, it displays a screensaver with an artist’s impression of the evolving particle beam. Images courtesy of LHC@home

Computers take on at CERN, the European particle data warehouses with newer more than aliens physics lab in Switzerland. In this data sets. They started out scanning the case, all that number crunching Users can also organize into cosmos for signs of extrater- helps scientists determine how teams and compete for top restrial intelligence with SETI@ to position the magnets that ranking. SwissTeam.net holds home. They’ve plotted chess control the proton beam. the lead with nearly 5.5 million moves, battled malaria, and Since 2004, when LHC@ “credits”—a measure of CPU folded proteins, all from their home hit the Internet, 40,000 power donated to LHC@home. home computers. Now, volun- users have registered, log- Team founder Dominique teers are tackling particle ging in from more than 100 Bugmann, an IT specialist in physics with LHC@home. countries. Combined, they Baden, Switzerland, manages It’s one of a number of dis- have put in 3000 years’ worth more than 100 computers run- tributed computing projects that of computer time. But they’re ning LHC@home and other allow you to download scientific still hungry for more data. distributed computing projects. data for your computer to ana- “We have very eager users “One of the great things lyze when it would otherwise be who want to be running their about LHC@home is that what sleeping. The Search for computers red-hot 24/7,” says we do directly helps the scien- Extraterrestrial Intelligence Alex Owen, manager of the tists,” Bugmann says. “I can help launched the first @home proj- project, which recently moved the world just by running soft- ect in 1999 with screensaver from CERN to Queen Mary, ware on some PCs.” software that searched for University of London. Amber Dance signs of life amid radio signals To feed the volunteers’ symmetry | volume 04 issue 10 december 07 from space. Today, users can voracious appetites, Owen Life among the choose from more than 20 and co-manager Neasan physics tribes @home options. O’Neill plan two new projects Meeting in CERN’s Restaurant The LHC@home software for LHC@home in early 1, anthropologist Arpita Roy simulates particles cruising 2008. The Garfield program of the University of California, along the Large Hadron Collider will test drift chambers, and Berkeley is quick to declare ring, currently under construction Rivet will compare online that she will not be having any

4 Schwarz on Fermilab’s CDF experiment. “Joey chose that name just to goad me,” Schwarz says jokingly. Part of the credit for develop- ing SpartyJet goes to yet another Spartan—Michigan State undergraduate student Kurtis Geerlings.

Photos courtesy of Arpita Roy “It is unusual for an undergraduate to be able to create cutting-edge software like this, physicists to predict the signa- and it bodes well for him,” says tures of collisions that might Huston, who invited Geerlings produce new particles. If they to join the team, along with post- chose different signatures, doctoral researcher Pierre- they would record a completely Antoine Delsart from the French different set of events. laboratory LAPP. In an experience common Last year, he says, Geerlings to anthropologists around the presented his work at a CDF world, Roy struggles to find meeting, and “everyone was members of the tribe who take sending me e-mail asking if an interest in her work and Kurtis had committed to a more coffee today. She has are willing to help, and is grate- graduate school yet, and could begun drinking multiple cups ful to physicists who spare an they interest him in theirs.” per day as she meets with hour or two to talk with her. Her Geerlings says that as an CERN physicists to learn about research, like the Large Hadron undergraduate not burdened their work. “Going native” over Collider project itself, offers lit- with PhD research, he actually the last two months, she has not tle in the way of immediate gain had more freedom to pursue yet acclimated to her increased to those who have invested in his interest in SpartyJet. caffeine intake. Nevertheless, it. Rather, it serves primarily As for the name, he says she intends to stick it out until to enrich our understanding of it’s a good thing: “I got sick of she has observed experimenters how scientists measure and referring to it as ‘the anony- taking data, even if it takes describe the world. mous program’ or ‘the program another year. Katie McAlpine, CERN which must not be named.’” “I’m interested in how social Haley Bridger convention or custom enter Spartan software the objective world of physics,” Every time Fermilab scientist Roy says. For example, the Tom Schwarz starts up SpartyJet, use of “right-handed” and “left- he inwardly grimaces. handed” to describe the parity The computer program of particles can be seen as a link works well. It does a fine job from concrete, observed reality of finding and recording jets— to the abstract workings of the sprays of subatomic particles mind. To study this topic more that emerge from collisions closely, she plans to work with involving protons. physicists from the LHCb exper- But as a graduate of the iment, since parity is one of the University of Michigan, Schwarz key topics they will investigate. finds one thing irritating: The Roy also examines the software was named for Sparty, assumptions made by particle a Spartan warrior and the mas- physicists and the effects of cot of rival Michigan State those assumptions on their University. The two universities symmetry | volume 04 issue 10 december 07 results. She is interested, for battle for student enrollment, instance, in the criteria that the academic prowess, and success ATLAS Trigger Data Acquisition on the football field. group use for deciding which The software was created particle collisions are interesting last fall by a group led by enough to record, and which to Michigan State professor Joey throw out. The choice requires Huston, who collaborates with

5 signal to background

This summer, three graduate want them to find some specialty students from the University that will make them visible.” of Witwatersrand in South Africa Kendra Snyder, Brookhaven came to the United States for National Laboratory a 10-day tour and a workshop on the Open Science Grid, which The LHC by mail will help US scientists analyze Each year the European labo- the huge amount of data col- ratory CERN welcomes tens lected by the ATLAS experiment. of thousands of visitors. Now Photo: Brookhaven National Laboratory At Brookhaven NationalNational the lab can visit them back. Laboratory on Long Island, New Last summer, the French York, Claire Lee,Lee Norman(photo, from Ives, postal service of the Pays de left),and Martin Norman Cook Ives, met and with Martin Gex issued a set of pre-paid Cookphysicist met Keteviwith physicist Assamagan Ketevi envelopes featuring the labo- Assamaganand his colleagues and his (photo).colleagues. ratory, which straddles the Brookhaven isis the the central central hub hub French-Swiss border. A sec- University of Witwatersrand graduate students for distributingdistributing ATLAS ATLAS data data ond set of 10 envelopes, pro- (bottom, from left) Martin Cook, Norman Ives, among USUS physicists.physicists. duced in collaboration with and Claire Lee, with (top, from left) US ATLAS “Prior to this trip, all we really the laboratory and this time Deputy Research Program Manager Howard Gordon, Columbia University physicist Jeremy knew about the Grid is that highlighting its Large Hadron Dodd, Brookhaven physicist Ketevi Assamagan, it’s a bunch of computers put Collider, went on sale at five and US ATLAS Research Program Manager together,” says Cook. At the Grid post offices on November 12. Michael Tuts. workshop in Nebraska, he and Each envelope in the new his fellow students learned how series focuses on a technical Connecting with Africa to install software back at their aspect or spin-off of the LHC. ATLAS, a particle physics home university and how to use Some sets even contain a small experiment at CERN’s Large various data analysis techniques. sample of the superconducting Hadron Collider, boasts 2000- They also talked with scien- cable used in the LHC magnets. plus members from 35 coun- tists about how their university If you are not lucky enough tries. But on a map showing might fit into the ATLAS collab- to receive one of the envelopes where those members come oration. So far it includes just in your mailbox, don’t despair. from, one continent is almost one African country—Morocco. You can learn more about the mark-free: Africa. “We don’t want them to just LHC at the Web address printed Leaders of ATLAS are trying disappear in this massive collab- on the envelopes, www.cern.ch. to change that. oration,” says Assamagan. “We Kurt Riesselmann Image: CERN symmetry | volume 04 issue 10 december 07

6 Penguins and New directions, Heuer spent 14 years at CERN. particles new directors For four of those years he was ‘Tis the season for science at Two labs on the brink of launch- spokesperson for OPAL, one of the bottom of the Earth. ing major projects have one the major experiments on the Researchers are flying to the more thing in common: new Large Electron Positron collider. South Pole from all over the directors named in December. While the LHC should be globe to take advantage of the Persis S. Drell (top photo) running by the time Heuer is “warm” summer months, when was named director of the handed the baton by current temperatures average minus 35 Stanford Linear Accelerator Director General Robert degrees Fahrenheit. Center in California—only Aymar, his main concerns will This year, San Francisco’s the fourth director in the lab’s be getting the machine to Exploratorium brings their tales 45-year history. operate smoothly and seeing of science to the Internet with And the CERN council that data analysis is handled Ice Stories, a series of Webcasts elected its next director general, efficiently. highlighting Antarctic research. Rolf-Dieter Heuer (bottom “This is a very exciting time Among the tuxedoed birds and photo). He will begin his five- for particle physics,” Heuer said. climatologists, particle physicists year term at the European “To become CERN’s director are building a neutrino detector particle physics lab near general for the early years of called IceCube. Geneva on January 1, 2009. LHC operation is a great “Neutrino telescopes are Drell joined SLAC in 2002 honor, a great challenge, and weird; they’re not what most after 14 years as a professor probably the best job in physics people think of as telescopes,” of physics at Cornell University research today.” says Mary Miller, Ice Stories in New York, and served in a Glennda Chui, SLAC, and project director. “It’s almost number of senior positions there. Katie McAlpine, CERN

mysterious and magical.” But her roots at SLAC are much and CERN Photos: SLAC Viewers can join the dozens deeper: Her father, Sidney Drell, of workers using hot water to was a deputy director of the lab. drill through 2.45 kilometers of She’s already launched a ice to place sensors in an array major reorganization and that will fill one cubic kilometer. established her vision of SLAC The sensors detect the blue as “one lab,” in which all flashes generated when neutri- research programs are united nos collide with ice molecules. under one management sys- The South Pole is the prime tem and benefit from multidis- location for the instrument ciplinary collaboration. Drell because of the vast depths of will also guide the lab through pure ice. a major transition in which the Neutrinos may fly in from two-mile-long linear accelera- sources such as supernova tor, after more than 40 years explosions and black holes, of providing beams for particle and scientists plan to match physics, will in 2009 become neutrinos with their origins to the injector for the Linac better understand extra-galac- Coherent Light Source, the tic events. But project leader world’s first hard X-ray free Francis Halzen, a physics pro- electron laser. fessor at the University of “The science delivered by Wisconsin, Madison, says other the LCLS, along with programs applications are possible and in particle physics, photon it’s too early to know exactly science, and particle astrophys- how IceCube will contribute to ics and cosmology, will ensure science. frontier science from the labo- “We will build it; we will ratory for decades to come,” see what will come,” he says. Drell said. “Hopefully it’s exciting.” Heuer will take his new post Tune in to www.explorato- at CERN just months after the rium.edu/icestories for start-up of the Large Hadron symmetry | volume 04 issue 10 december 07 archived Webcasts about Collider, by far the world’s most IceCube and the rest of the powerful particle accelerator. science at the coldest place Currently research director for on Earth. particle physics at DESY labo- Amber Dance ratory in Hamburg, Germany,

7 voices: dennis overbye

Last year, I described the onset five billion years What’s in a name? ago of dark energy, the mysterious force that Parsing the ‘God seems to be accelerating the expansion of the cosmos, with the words “as if God had turned particle,’ the ultimate on an antigravity machine.” metaphor More people than I had expected wrote in By Dennis Overbye wanting to know why I had ruined a perfectly good article by dragging mythical deities into it. We need to talk about the “God particle.” My guide in all of this, of course, the biggest Recently in The New York Times, I reported on name-dropper in science, is Albert Einstein, who the attempts by various small armies of physi- mentioned God often enough that one could cists to discover an elementary particle central to imagine he and the “Old One” had a standing date the modern conception of nature. Technically for coffee or tennis. To wit: “The Lord is subtle, it’s called the Higgs boson, after Peter Higgs, an but malicious he is not.” English physicist who conceived of it in 1964. It Or this quote regarding the pesky randomness is said to be responsible for endowing the other of quantum mechanics: “The theory yields much, elementary particles in the universe with mass. but it hardly brings us closer to the Old One’s In a stroke of either public secrets. I, in any case, am convinced that He does relations genius or disaster, not play dice.” Leon M. Lederman, the former With Einstein, we always knew where he stood director of the Fermi National in relation to “God”—it was shorthand for the Accelerator Laboratory, or mystery and rationality of nature, the touchstones Fermilab, referred to the of the scientific experience. Cosmic mystery, Higgs as “the God particle” Einstein said, is the most beautiful experience we in the book of the same can have, “the fundamental emotion that stands name he published with at the cradle of true art and true science.” the science writer Dick “He who does not know it and can no longer Teresi in 1993. To Dr. wonder, no longer feel amazement,” he continued, Lederman, it made met- “is as good as a snuffed-out candle.” aphorical sense, he If we didn’t already have a name for the object explained in the book, because of Einstein’s “cosmic religion,” we would have the Higgs mechanism made it possible to invent one. It’s just too bad that the name has to simplify the universe, resolving many different been tainted and trivialized by association with seeming forces into one, like tearing down the the image of a white-bearded Caucasian-looking Tower of Babel. Besides, his publisher complained, creature who sits in the clouds attended by harp- nobody had ever heard of the Higgs particle. strumming angels. In some superficial ways, the Higgs has lived If Einstein were around today, he would likely up to its name. Several Nobel Prizes have been be scolded every other time he opened his awarded for work on the so-called Standard Model, metaphor-laden mouth for giving aid and comfort of which the Higgs is the central cog. Billions to the creationists. Indeed, the architects of intelli- of dollars are being spent on particle accelerators gent design have not been shy about interpreting and experiments to find it, inspect it, and figure his aversion to divine dice playing, and a remark out how it really works. wondering if God had any choice in creating the But physicists groan when they hear it world, as support for an intelligent designer. referred to as the “God particle” in newspapers Einstein didn’t mean it that way, of course. He and elsewhere (and the temptation to repeat it, was only using a metaphor to wonder if it given science reporters’ desperate need for color- was possible to build more than one logically ful phrases in an abstract and daunting field, is consistent universe. That’s a question that irresistible). Even when these physicists approve still provokes hot debate. of what you have written about their craft, they As it happened, Dr. Lederman’s book came out grumble that the media are engaging in sensation- about the time that creationism was on the rise symmetry | volume 04 issue 10 december 07 alism, or worse. in this country, and “my colleagues gave me hell,” Last week a reader accused me of trying to as he put it in a recent e-mail message. attract religiously inclined readers by throwing out Neither time nor criticism seems to have “God meat” for them. dimmed Dr. Lederman’s taste for metaphor or It was not the first time that I had been accused sense of humor. Only two weeks ago, he titled of using religion to sell science. Or was it using an article about particle physics “The God Particle, science to sell religion? Et Al.” Well, OK, he had a book to sell.

8 irreverent way. and familiar a such in nature personify to able being by intuition his in aided universe—was the called “a feeling for the organism”—in this case man with what the geneticist Barbara McClintock prove it, but I can’t help wondering if Einstein, a had Einsteinfigurativelyonhisknees.Ican’t it is a piece of the sublime beauty of nature that creationists andreligiousfundamentalists. to metaphor powerful a such yield to scientists for mistake a be would it think I likewise and ful symbol of patriotism—to the war’s supporters, toyieldtheflag—apower- movement ofthe1960s suggested that it was a mistake for the antiwar to applaudDr. Lederman’s spirit.Historianshave the Higgs particle reaches a climax. But I have couple of years as the generation-long hunt for we arelikelytohearagainandinthenext the top as the one that Dr. Lederman used—one The Higgs particle is not God, but as theorized It’s not easy to stand up for a moniker as over

9 with permission. Reprinted 2007, The NewYorkreserved. rights TimesAll . which publishedthisessayonAugust7,2007.Copyright Dennis Overbye is a correspondent for metaphorical tools. metaphorical or rhetorical her or his of Einstein future any against it. betting advise wouldn’t I and is, it as optimistic and bold presumption, that on founded been Intellectual empiresfromPlatotoEinsteinhave Absolutely. ultimatelyexplicable? Isthatmystery and evenabhorrentidea. sparrow?Einsteinsaidthatwasanaïve of every Not tomentionmyself. In the meantime, I wouldn’t dream of depriving Do Ibelievetheuniverseisamystery? theflight Is thereaGodwhoworriesabout The New York Times ,

Photo courtesy of Dennis Overbye

symmetry | volume 04 | issue 10 | december 07 Across the ocean, yet close to home By Katie Yurkewicz

Among the 10,000 people from around the world who are working on the Large Hadron Collider, 1000 hail from universities and national labs in the United States.

The Large Hadron Collider is the world’s next-generation and students from almost 60 nations. More than 1000 of particle accelerator. Arguably the most ambitious scien- these hail from 93 universities and national laboratories tific endeavor ever undertaken, the $8.7 billion project at in the United States. Researchers from US institutions have CERN, the European particle physics lab in Geneva, made vital contributions to all aspects of LHC construction, Switzerland, has been in the works for more than two and are now looking forward to the next phase, when they decades. When it begins operating in mid-2008, scien- will see collisions begin, watch data start flowing, and spend tists predict that its very-high-energy collisions will yield many a sleepless night searching for the tracks of particles extraordinary discoveries about the nature of the whose existence would transform our understanding of the physical universe. universe. The LHC project has two equally important aspects: the collider itself and its six particle detectors, each one a Putting the C in LHC self-contained experiment. The collider, nearing completion The heart of the LHC project is the collider itself, and the in a 27-kilometer ring deep below the Swiss-French border, heart of the collider is a series of thousands of super- will accelerate two beams of protons in opposite directions conducting magnets. They create the extremely high to a whisker below the speed of light. For most of their magnetic fields needed to accelerate particles to high split-second journey around the ring, these hair-thin beams energies, guide them in circles, and focus them for collision. will travel in separate vacuum pipes; but at four points, Such fields are possible today only with superconducting in the hearts of the main experiments, they will collide at technology, which requires that the magnets be cooled to energies of 14 trillion electronvolts. These massive experi- nearly absolute zero—colder than outer space—by super- ments—huge both in size and in worldwide participation— fluid helium. are known by their acronyms: ALICE, ATLAS, CMS, and The LHC’s particle collisions will reach energies LHCb. They are the tools physicists will use to turn particle seven times higher than those achieved at Fermi National collisions into scientific breakthroughs. Accelerator Laboratory’s Tevatron, the most powerful par- Building the LHC and its experiments has required the ticle collider operating to date. Building a machine capable efforts of some 10,000 scientists, engineers, technicians, of reaching those energies has proved a formidable task;

10 US Participation in the LHC symmetry

Arizona University of Arizona, Tucson California California Institute of Technology, Pasadena KEY California Polytechnic State University, ALICE ATLAS San Luis Obispo CMS California State University, Fresno Indiana LHC Lawrence Berkeley National Laboratory, Berkeley Indiana University, Bloomington LHCb LHCf Lawrence Livermore National Laboratory, Livermore Purdue University, West Lafayette TOTEM Stanford Linear Accelerator Center, Menlo Park Purdue University Calumet, Hammond University of California, Davis University of Notre Dame, South Bend University of California, Irvine Iowa Minnesota University of California, Los Angeles Iowa State University, Ames University of Minnesota, Puerto Rico University of California, Riverside University of Iowa, Iowa City Minneapolis University of California, San Diego Kansas Mississippi South Carolina University of California, Santa Barbara Kansas State University, Manhattan University of Mississippi, Oxford North Carolina University of South Carolina, Columbia University of California, Santa Cruz University of Kansas, Lawrence Nebraska Duke University, Durham Tennessee Colorado Louisiana Creighton University, Omaha Ohio Oak Ridge National Laboratory, Oak Ridge

University of Colorado, Boulder Louisiana Tech University, Ruston University of Nebraska, Lincoln Case Western Reserve University, Cleveland Vanderbilt University, Nashville www.symmetrymagazine.org Connecticut Maryland New Jersey Ohio State University, Columbus University of Tennessee, Knoxville Fairfi eld University, Fairfi eld Johns Hopkins University, Baltimore Princeton University, Princeton Ohio Supercomputer Center, Columbus Texas Yale University, New Haven University of Maryland, College Park Rutgers State University of New Jersey, Piscataway Oklahoma Rice University, Houston Florida Massachusetts New Mexico Oklahoma State University, Oklahoma City Southern Methodist University, Dallas Florida Institute of Technology, Melbourne Boston University, Boston University of New Mexico, Albuquerque University of Oklahoma, Norman Texas A&M University, College Station Florida International University, Miami Brandeis University, Waltham New York Oregon Texas Tech University, Lubbock volume 04 | issue 10 december 07 Florida State University, Tallahassee Harvard University, Cambridge Brookhaven National Laboratory, Upton University of Oregon, Eugene University of Texas at Arlington University of Florida, Gainesville Massachusetts Institute of Technology, Columbia University (Nevis Laboratory), New York Pennsylvania University of Texas at Austin Illinois Cambridge Cornell University, Ithaca Carnegie Mellon University, Pittsburgh University of Texas at Dallas symmetry | volume 04 issue 10 december 07 Argonne National Laboratory, Argonne Northeastern University, Boston New York University, New York Penn State University, University Park Virginia Fermi National Accelerator Laboratory, Batavia Tufts University, Medford Rockefeller University, New York University of Pennsylvania, Philadelphia Hampton University, Hampton Northern Illinois University, DeKalb University of Massachusetts, Amherst State University of New York at Albany University of Pittsburgh, Pittsburgh University of Virginia, Charlottesville Northwestern University, Evanston Michigan State University of New York at Buffalo Puerto Rico Washington University of Chicago, Chicago Michigan State University, East Lansing State University of New York at Stony Brook University of Puerto Rico, Mayaguez University of Washington, Seattle University of Illinois at Chicago University of Michigan, Ann Arbor Syracuse University, Syracuse Rhode Island Wisconsin University of Illinois at Urbana-Champaign Wayne State University, Detroit University of Rochester, Rochester Brown University, Providence University of Wisconsin, Madison US Participation in the LHC symmetry

CMS TOTEM LHCb CERN ATLAS LHCf ALICE Large Hadron Collider

CMS TOTEM LHCb CERN ATLAS LHCf ALICE now, with LHC construction almost complete, focus has Frequent fliers turned to testing, cooling, testing again, and preparing to With their part in LHC construction almost complete, US accelerate beams. scientists from institutions in 30 states and Puerto Rico, “The LHC is ten times bigger than the Tevatron,” says supported by the US Department of Energy’s Office of LHC Project Leader Lyn Evans from CERN. “Every step of Science and by the National Science Foundation, pre- the way has been challenging: getting it approved, getting pare to play key roles in the discoveries to come. These the hardware solid, getting through budget crises, handling scientists and students may make their contributions technical difficulties, and now getting the whole thing to from the United States, travel to CERN for short periods, work together.” or live at CERN full time. “US particle physicists want to do the best science, no Solving mysteries matter where the facilities may be,” says Fermilab’s Joel Physicists hope the LHC’s experiments will reveal new Butler, program manager for US participation in CMS. worlds of unknown particles and explain why those parti- “Institutions in the US will further increase their level of cles exist and behave as they do. Scientists will also search involvement over the next few years, and pretty soon the for the origins of mass, study the universe as it existed LHC could be what most US particle physicists will be shortly after the big bang, and try to uncover hidden sym- working on.” metries of the universe and extra dimensions of space. During the last dozen years, US scientists have helped The two biggest LHC experiments are ATLAS and build the LHC experiments’ complex detectors and their CMS. ATLAS, measuring 148 feet long, 82 feet wide, and intricate computing systems. They are now focused on 82 feet high is the largest, while CMS, weighing in at testing and preparing for startup, and will soon be oper- 13,000 tons, is the heaviest. Each involves approximately ating the detectors and analyzing the data as it emerges. 2000 physicists from some 35 countries. These scientists Graduate students play a vital role; they often spend will search for new particles and phenomena, measure several years doing research at their home universities the properties of previously discovered quarks and bosons before moving to CERN to gain hands-on experience. with unprecedented precision, and be on the lookout for “There are probably about 100 people from US ATLAS completely unexpected physics. institutions at CERN now,” says Columbia University’s “The most exciting discoveries are the ones you don’t Michael Tuts, project manager for US ATLAS. “We expect anticipate,” says CERN theoretical physicist John Ellis. that to ramp up, but it depends on the reality of funding “People looked into the first microscope and saw a whole and budgets. It’s more expensive to send people to CERN, new world of bacteria that they didn’t know existed. It and institutions have had to adjust budgets at home.” could be that way again.” One way to increase international collaboration while The 1000-member ALICE collaboration will use colli- keeping costs down is through remote monitoring and sions of lead ions to study the quark-gluon plasma, a state operations. This year saw the opening of the LHC@FNAL of matter that existed just after the big bang. The ALICE Remote Operations Center, through which scientists at detector may also provide vital information about run-of- Fermilab can monitor conditions at the CMS experiment the-mill proton collisions in the early days of LHC operation, and the LHC accelerator and participate in high-definition paving the way for physicists with the ATLAS and CMS videoconferences with colleagues at CERN. experiments to identify unusual collisions that may reveal “We’ve been pioneers in remote operations,” says Butler. new physics. “We’re separated from CERN by many thousands of miles The aim of the LHCb experiment is to measure rare of ocean and six to nine time zones. This will keep a part decays of B mesons—particles containing a bottom quark. of the US community that can’t easily go to CERN—due Such decays happen very rarely in the familiar world of to funding limitations or academic, professional, or family observed particles, but more frequently in scenarios such responsibilities—more engaged in the experiment.” as supersymmetry, in which every particle has a heavier The US contributed to the construction of the LHC superpartner. If LHCb’s 600 scientists find these decays, accelerator through a $200 million project funded by the it could be the first evidence of new physics phenomena. DOE’s Office of Science. More than 100 accelerator sci- “If you compare the LHC to an earthquake, ATLAS entists are already involved in research and development and CMS may produce something that shatters our for future LHC upgrades. understanding of the universe—a really big earthquake,” The detectors are nearly complete, the global comput- explains Ellis. “But earthquakes often have tremors ing system is almost ready, and parts of the collider are that precede them and tell you something big is coming. already cooled to nearly absolute zero. After more than LHCb could generate such tremors.” two decades of preparation, the LHC will produce its first On a much smaller scale are the LHCf and TOTEM proton collisions in 2008. Excitement is growing among experiments. Built around the ATLAS and CMS collision US scientists, their colleagues, and the rest of the world. symmetry | volume 04 issue 10 december 07 points, respectively, these experiments have very specific “I would like to be in the ATLAS control room at the right aims. The 21-member LHCf experiment will contribute to the time to see that very first collision,” says Columbia’s Tuts. understanding of ultrahigh-energy cosmic rays that bom- “Seeing everything finally working together will make all bard the Earth. The 80-member TOTEM experiment will those plane trips worth it.” measure particles flying off at very small angles from the LHC’s proton-proton collisions, allowing scientists to study physical processes that can’t otherwise be explored.

13 Entering Higgs habitat By Heather Rock Woods A powerful new collider will allow scientists to explore the territory where the long-sought Higgs particle—maybe even a whole family of them—resides.

They sound like Zen koans: The Higgs field bestows mass on other particles, but its own mass is unknown. It pervades the universe, but no one has seen its physical manifestation, the Higgs particle. It’s the only missing piece of the Standard Model of particles and forces, but the model accounts for just four percent of the universe. Less puzzlingly, but just as important, physicists think the Higgs field is responsible for giving mass to some particles but not others. It acts like a gooey, universe-sized bucket of molasses. As particles travel through the field, some interact with the molasses more strongly than others. Those that interact most become heaviest, while those that don’t interact at all are left without mass. Without this fundamental phenomenon, the world would be a different place: heavy atoms wouldn’t hold together; all elementary particles would be massless, zipping around at the speed of light; the reactions that stoke stars would go faster, slower, or not at all.

14 Illustrations: Sandbox Studio symmetry | volume 04 issue 10 december 07

15 Discovering the Higgs particle and pinning down how The Higgs hasn’t turned up at any of the energies—up much it weighs will ultimately make or break theories to 115 GeV—that accelerators have explored so far. The that explain, for example, the nature of the dark matter LHC opens new territory to the search. It’s the first accel- that makes up nearly a quarter of the universe. erator that will provide access to the full range of habitat After more than 20 years of searching, physicists think where the Higgs can live. If the Higgs predicted by the they will finally find this elusive particle at the Large Standard Model exists—and the Standard Model has been Hadron Collider, now being set up in an underground right about everything it has predicted so far—it will be tunnel near the Geneva, Switzerland, headquarters of CERN, seen at the LHC. In fact, the LHC might even observe five the European particle physics lab. or 12 kinds of Higgs, if closely related theories like Why is this omnipresent entity so hard to find? What supersymmetry are also correct. makes the search different this time? Finding the Higgs “will not be easy. We have to suffer,” says CERN physicist Fabiola Gianotti, deputy spokesper- Cranking up the energy son for the LHC’s ATLAS detector collaboration. “But that One reason the Higgs particle is hard to find is because way, the satisfaction will be even bigger.” nobody knows how much it weighs, which means no one knows exactly where to look. While the Standard Model Not empty-handed is clear about what roles the Higgs fulfills, it doesn’t offer While the Higgs remains unseen for now, physicists have very practical parameters for conducting the search. some idea of where to look. One direct search took Thanks to Albert “E=mc2” Einstein, physicists recognize place at LEP, the Large Electron-Positron collider, which that energy and mass are interchangeable. Particle used to inhabit the tunnel where the LHC is now being masses are expressed in terms of energy, usually in units commissioned. That expedition saw teasing hints of a of GeV, or billions of electronvolts. Physicists create Higgs particle at 115 GeV, the upper limit of LEP’s power. new particles by packing more energy into particles that The signal, however, was too weak to rule out random are traveling at nearly the speed of light. When these fluctuations. Reluctantly, after keeping the collider running particles collide, they free all that energy, which coalesces an extra month to take more data, CERN shut down the into new particles. The heavier the particle you want experiments in 2000 to begin LHC construction. to create, the more energetic the collision needs to be. Indirect searches also support the idea of looking at The Higgs could have any mass up to about one trillion the lower end of the range of possible masses—closer electronvolts, or TeV—about 1000 times heavier than a to 100 billion electronvolts than to a trillion. Experiments at hydrogen atom. If it’s on the lighter side, the Higgs could be two colliders, the Stanford Linear Collider in California within the scope of today’s most powerful accelerator, the and LEP at CERN, put boundaries on the possible mass Tevatron collider at Fermi National Accelerator Laboratory of the Higgs by making extremely precise measure- in Illinois; scientists at two experiments there are racing ments of the Z particle. to find its footprints. The Z and W particles mediate the weak force, the driver of radioactive decays that power the sun. Thanks to the Higgs, both are heavy, with masses of 91 and 80 GeV, respectively. (In contrast, the Higgs field does not confer mass on other types of particles that transmit fundamental forces, such as the strong force that binds atoms and the electromagnetic force that radiates light and heat.) Precise measurements of the Z made with LEP and the Stanford collider detected slight perturbations that were consistent with the presence of a Higgs particle. This data, combined with other precision measurements from all over the world, points with high probability to a Higgs mass no greater than 144 GeV.

16 the Higgsisn’taseasilyproduced. top quarks, which are quite possibly heavier than the Higgs, “We aredoingallofthese.Will itbeenough?” who hasbeenapartoftheHiggshuntforalmost20years. improved triggering, and better analysis,” says Conway, fluctuation. random another away, just melted had bump the data, more percent GeV. 80 150 with around at fall, last by But a stir by describing in a blog the “bump” his group saw saw group his “bump” the blog a in describing by stir a caused Davis California, of University the of Conway John searcher Higgs GeV.long-time 2006, December In could besensitivetoHiggstracks inthevicinityof160 luminosity, todiscovertheHiggsfirst. fingers, hopingforluck andenoughparticlecollisions,or their crossing are Fermilab at Tevatron collider the from data analyzing Scientists 2008. in on switches LHC There’s still a chance that the Higgs will turn up before the and luminosity Luck a much rarerHiggsdecay. for thelessdistinctamuch signaloftwophotonsgenerated in rarerHiggs decay. look to have will researchers Instead, static. by whelmed for thelessdistinct signaloftwophotonsgenerated in look to have will researchers Instead, static. by over- would beinaudible,likeafavoritewhelmed radiostation over- collisions willmakesomanybquarksthattheHiggssignal wouldbeinaudible,likeafavorite radiostation mon decayistoapairofbcollisionswillmakesomanyquarksthattheHiggssignal quarks. Unfortunately, LHC light, themostcom- ButiftheHiggsisvery at theLHC. mondecayistoapairofb quarks. Unfortunately, LHC light, themostcom- ButiftheHiggsisvery muons. ThisattheLHC. wouldbetheeasiestwayto findtheHiggs of Z muons. This wouldbetheeasiestwayto findtheHiggs pair a into decay predominately will it predict, surements of Z pair a into decay predominately will it predict, GeV, 190 Higgs isabout surements heavierthantheindirectmea- the if Forexample, masses. different of GeV,particles 190 Higgs isabout heavierthantheindirectmea- the if Forexample, masses. different of particles have tousedifferentHiggs techniques topick upthesignalsof sweep acrossincreasingfrequencies,searchershavetousedifferent techniques will topick upthesignalsof sweep acrossincreasingfrequencies,searchers will different asslugslimefrombear scat. microscopes andtelescopes,fortracksthatcanlookasdifferent as thatcanlookasslugslimefrombearscat. searchbinoculars, butwithmicroscopesandtelescopes,fortracks notjustwiththeequivalent ofbinoculars,butwith Higgs,physicistsneedto patterns leftphysicistsneedtosearch bythetransitory not justwiththeequivalentof Tovarying the routes. spot rarer as well as paths decay To patterns left Higgs, spot the varying by the transitory preferred has it way; same the in disintegrate always way; it has preferred decay paths as well as rarer routes. not would particle Higgs the mass, its whatever addition, the Higgs particle would not always disintegrate in pattern willbecompletelydifferentthe differentthanifitislight.Inaddition,whateveritsmass, thanifitislight.In same they leaveindetectors.IftheHiggsisheavy, IftheHiggsisheavy, itsdecaypatternwillbecompletely itsdecay tracksin thiscase,thedecaypatternstheyleavedetectors. inthedirt—or, in this case,thedecaypatterns their find to have Scientists savanna. treeless flat, a savanna. Scientists have to find their tracks in the dirt—or, Higgs particleswon’tjustappearlikeaherdofzebraon TeV, 14 to up energies with particles of numbers huge offersWhile tremendousenergyreach, creating theLHC dirt inthe Tracks Even thoughtheTevatron routinelyproduces175 GeV To maximize the Tevatron’s odds, “We need more data, The Tevatron can’t cover the full Higgs habitat, but it it but habitat, Higgs full the cover Tevatron The can’t So ratherthan twistingthedialonananalogradioto So ratherthan twistingthedialonananalogradioto So particles that in turn make four electrons or four four or electrons four make turn in that particles four or electrons four make turn in that particles

17 preparing to track the Higgs’s first tangible footprints. preparing totrack theHiggs’sfirst cleaning their binoculars, weatherproofing their boots, and ing. In the meantime, physicists are building their nets, ofall,”the biggestdiscovery saysSuDong. the moreyoucanpindownunderlying story.” of The theoristandco-author Brookhaven NationalLaboratory ities. That’s the exciting thing,” says Sally Dawson, a collisions atahighenoughrate. Higgs couldsurfacefirstatthe Tevatron, ifitproduces There’s andthe supersymmetry evenachance thatboth exciting. more and crowded more both universe our may wellbeoneofthecollider’sfirstdiscoveries,making at which particles theyareproduced,supersymmetry goals of the LHC experiments; and thanks to the rapid rate than oneHiggsfield. correct, therecouldbemultipleHiggsparticlesandmore Modelhasaheavierpartner.Standard is Ifthetheory supersymmetry, particleinthe which suggeststhatevery scenarios. uncover oneofthosemorespectacular will something justlikeit,they’rereallyhopingtheLHC and experimentalists clearly expect to see the Higgs, or experiment hasruledouttheseconcepts.While theorists percentoftheuniverse. make up96 doesn’t accountforthedarkmatterandenergythat it as itis,themodelisclearlyincomplete; forinstance, handy theoretically. it making energies, high very at Model Standard the the Higgsseemstosolveproblemsthatcropupwith on some lists of new particles to be discovered. Moreover, Higgs hasbecomesoacceptedthatitdoesn’tevenrank the of existence the Model, Standard the of success the on Based Dong. Su asks unknown?” an or particle physics. “The Higgslivesontheboundary. Isitaknown The of Higgs occupiesastrangeplaceinthetaxonomy More thanone? everywhere,”everywhere,”SLACSLAC theoristJoAnneHewett. theoristJoAnneHewett. affirms affirms decaydecay usingusing multiplemultiple analyticalanalytical techniques.techniques. “You“You havehave toto looklook atLHC. atLHC. detectordetector collaboration collaboration Linear AcceleratorCenter’sparticipationintheATLASLinear AcceleratorCenter’sparticipationintheATLAS cornerscorners forfor thethe LHC,”LHC,” sayssays SuSu Dong,Dong, headhead ofof thethe StanfordStanford Such aconundrumwouldhastenthepaceofnewthink- What if the Higgs doesn’t show itself? “That would be “There areamillionmodels,somanydifferent possibil- main the of one is particles supersymmetry Finding called theory a in occurs scenario multi-Higgs The No Higgses. multiple or Higgs, no be might There Modeliswrong?Successful But whatiftheStandard “If naturechose“If naturechose 115GeV, 115GeV, it’soneofthemostdifficult it’soneofthemostdifficult Physicists willhavetomonitorallthesechannelsPhysicists willhavetomonitorallthesechannels of of . “The more you can measure, Higgs Hunter’sGuide.“The moreyoucanmeasure,

symmetry | volume 04 | issue 10 | december 07 When particles collide, a spray of new particles is created; this simulation shows what happens when lead ions collide in the Large Hadron Collider’s ALICE detector. While each particle carries only a tiny puff of energy, the combined energy of particles in the beam is that of a speeding train.

Image courtesy of the ALICE Collaboration

P rotecting the LHC frbyo Katiem Yurkewicz itself Human safety is always the first concern at the Large Hadron Collider. But the machine also needs shielding from its own proton beams, which each pack the energy of a high-speed train.

1818 symmetry | volume 04 issue 10 december 07

19 When people talk about the super-high energies While a beam of particles by itself creates very of proton collisions in the Large Hadron Collider, little heat, beam particles straying from the core it’s easy to envision a series of explosions—pop, of the beam will heat up surrounding material. pop, pop—that give off flashes of light and shake It takes just a small number of beam particles the room. hitting a magnet in one spot to raise the mag- Not so. Even though the protons are hurtling net’s temperature above a critical point, causing along at nearly the speed of light, each one is it to suddenly change from superconducting to so tiny that when it smashes head-on into another, “normal” conducting. This change, called a quench, the collision releases just a puff of energy, in releases the stored energy of the magnet and ordinary human terms—about 30 trillionths of its neighbors; it can heat a small part of the the energy a 60-watt light bulb puts out in a magnet from -271 to 700ºC (-456 to 1300ºF) in second. Still, this is so much more energy than less than one second. any collider has achieved before that scientists “If we don’t do anything, all the stored energy expect to see exciting new physics in the debris. will go into one magnet, and that magnet will But the proton beams themselves are another be destroyed,” says CERN’s Rudiger Schmidt, matter. Each beam contains 280 trillion protons coordinator of LHC machine protection. “We with the combined energy of a high-speed train have to detect a quench and take action to put going 200 kilometers per hour, squeezed into the energy somewhere that it’s not dangerous.” a stream much thinner than a human hair. They’ll When a quench begins, the beams are shut race around a circular ring 11,245 times per second, down and power to the affected magnet is imme- year after year, inside one of the world’s largest, diately cut. Then heaters fire up, quickly raising the most sensitive, and most complex machines. temperature of the whole 14.3-meter-long, 35-ton The beams throw off billions of stray particles magnet and dissipating the energy. that will heat up anything they hit, and they Each dipole magnet is connected to 153 neigh- pass within about a centimeter of thousands of bors, and their energy also has to be immediately superconducting magnets that have to be kept removed. A switch sends the energy into large colder than the vacuum of outer space. If stray resistors, where it heats eight tons of steel to a particles damage the magnets or other sensitive temperature of 300ºC (570ºF) in less than two equipment, the collider could be forced to shut minutes. down for weeks, months, or more. And if the beam The LHC isn’t the first accelerator to face veers ever so slightly off, parts of the $8.7 billion the danger of magnet quenches. Fermi National machine—by far the most powerful accelerator ever Accelerator Laboratory’s Tevatron collider, the built—would be destroyed. first to use superconducting magnets, has faced Just as scientists at CERN, the European this problem since it began operation in the particle physics lab in Switzerland, have taken elab- late 1970s, followed more recently by the HERA orate precautions to make sure the beams don’t accelerator at Germany’s DESY laboratory in harm people, they’ve also had to craft the world’s Hamburg. Scientists learned from those accel- most sophisticated machine protection system erators how to deal with quenches. The scale of to save the LHC from itself. The system shields the LHC increases the challenge significantly, the LHC’s 9000 magnets from the beams and however: each of the LHC’s eight sectors is similar from themselves; traps stray particles so they don’t in size to one Tevatron. damage critical components; and safely disposes of the beams—and their formidable energy—when The well-groomed beam necessary. Can quenches be prevented? Some, such as those caused by infinitesimal changes within the Hot versus cold magnet, are unavoidable. But many quenches are To harness the powerful beams of protons and due to the interaction of stray beam particles with steer them around the ring, scientists have to the magnets. As the beam intensity increases, so create strong magnetic fields. This requires super- does the number of quenches. conducting electromagnets, whose wire coils “It takes 30 minutes to five hours to restart the can carry large electric currents with virtually no LHC after a quench,” says Schmidt. “If we quench resistance. For the wire to become supercon- 10 times a day, it’s too much. If we never quench, ducting, the magnets must be kept very cold—in we’re being too conservative. We have to operate this case at a temperature of -271 degrees Celsius, such that we don’t quench too frequently.” close to absolute zero. But limiting the beam intensity shouldn’t be, Together the LHC’s magnets store even more and isn’t, the only solution. Keeping the stray energy than the proton beams do—a whopping beam particles from hitting the sensitive parts of 10,000 megajoules, compared to 362 megajoules the LHC is the task of the collimation, or beam for the beams. Most of this energy is contained cleaning, system. in 1232 superconducting dipole magnets, which do The beams’ tightly focused cores are sur- most of the work of beam steering. rounded by a halo of stray particles generated by

20 Planning for safety How does CERN ensure that the LHC’s proton beams are safe for those working on the accelerator—and for everyone else? First,Under under no circumstances no circumstances are people are people and beams and beams allowed allowed in the in thesame same place place at the at samethe same time. time. State-of-the-art State-of-the-art access access control control gates gateskeep everyone keep everyone out of theout beamof the areas beam while areas the while LHC the is LHCrunning. is running.If someone If someone were to break were into to break one of into those one areas of those when areas the beams when thewere beams on, an were interlock on, an system interlock would system immediately would immediately turn the beams turn FEU - FIRE theoff andbeams safely off disposeand safely of theirdispose energy. of their energy. ACCIDENT Once the LHC begins operating, some areas of the machine will remain radioactive even when the beams are turned off. Only workers with appropriate training and monitoring equipment will be allowed to enter those areas. CERN’s access and radiation control systems, developed over many years, were subject to an symmetry | volume 04 issue 10 december 07 extensive review and approval process by the French authorities. Third,Since thesince collider the collider is 100 metersis 100 meters or more or below more ground, below ground,people peopleliving and living working and working at the surfaceat the surface are well are shielded well shielded from thefrom LHC the LHCbeams beams and the and small the small amounts amounts of radiation of radiation they theygenerate. generate. The Therisk ofrisk radioactive of radioactive substances substances reaching reaching the surface the surface through through ven- ventilationtilation shafts, shafts, or spreadingor spreading through through ground ground water water or or cooling cooling water, has beenbeen exhaustivelyexhaustively studied studied by by CERN CERN scientists scientists and and by by officials from the Swiss andand FrenchFrench governments.governments. TheyThey concludedconcluded that any exposure to the public would be far below government limits—approximately one percent of the level of natural radiation in the area. FEU - FIRE

ACCIDENT

FEU - FIRE

ACCIDENT

FEU - FIRE

ACCIDENT How to stop a speeding train Each hair-thin beam of protons that races around the Large Hadron Collider contains as much 2 energy as a locomotive going 200 kilometers per hour. When it’s time to shut the machine down, that energy—so concentrated that it could drill a hole in any material—must be safely absorbed. 1 The machine protection system does the job in just 80 millionths of a second.

1 A thin wall down the middle of the septum magnet separates the two beams of protons, which are going in opposite directions.

2 When it’s time to shut down, the fast kicker magnet deflects the beam so it crosses the septum. Once on the other side, it’s free of the magnetic fields that normally force it to take a curving path around the collider, so it goes straight. 4

3 The dilution magnet spreads the beam out, diluting its intensity by a factor of 100,000.

4 The watered-down beam hits a cylinder of graphite composite eight meters long and one meter in diameter, which is encased in concrete. As it absorbs the beam energy, it becomes very hot but does not melt.

Illustration: Sandbox Studio 22 interactionsinteractions between between the the two two beams, beams, small small diffused, because in its compressed form it would imperfections in any of the LHC’s thousands of drill a hole tens of meters long in any material. sophisticated components, and a variety of So as the beams pass out of the LHC, they other sources. With the high-intensity beams spread out and hit the blocks in a shape that making 400 million trips around the LHC in a resembles a cursive “e.” The dump takes just typical 10-hour beam lifetime, more than 500 bil- eighty-millionths of a second, dilutes the energy lion particles may migrate from the core. The of the beam by a factor of 100,000 and heats energy in the halo is enough to not only quench the center of the lines that make up the “e” to magnets, but to melt them. almost 700ºC. “The parameters of the LHC beam are so high In 2003, two-thirds of the superconducting that microscopic effects can be very destructive magnets in the Tevatron’s six-kilometer ring to the machine and to the detectors,” says Nikolai quenched at the same time. The beam drilled a symmetry | volume 04 issue 10 december 07 Mokhov of Fermilab, a pioneering researcher in hole in one collimator and created a 30-centimeter collimator systems who works on the LHC’s groove in another. That accident, while serious, machine protection system. was the only one in the accelerator’s 20-year One of the first advances in machine protection history, and the machine was back up and running came in the late 1970s, when Fermilab’s Helen within two weeks. Could something similar happen Edwards placed stainless steel shielding in front on a larger scale at the LHC? of the first superconducting magnets to protect “In a bad accident, thethe beambeam couldcould gogo offoff coursecourse them from stray particles. These collimators and drilldrill a a hole hole through through one one or ortwo two magnets,” magnets,” says trapped the particles while allowing the beam’s Schmidt.says Schmidt. While Whilethis would this wouldnot destroy not destroy the LHC, the it core to pass through, and were the precursors wouldLHC, it still would require still requiretime and time money and moneyfor repair. for of today’s complex collimator systems. Replacingrepair. Replacing a dipole a dipole magnet, magnet, for which for which CERN CERN has The LHC’s 100 collimators are strategically 30-40has 30 spares,to 40 spares, would would take 30take days. 30 days.A more A more com - stationed in critical areas of the accelerator. No plicatedcomplicated repair, repair, or replacement or replacement of a of less a less common com- longer stationary blocks of steel, they are made component,mon component, would would take takelonger. longer. of graphite composites, and they open and close “The beam at the LHC is 150 times more pow- automatically or at the request of accelerator erful, so the scale of the accident could be 150 operators. times higher,” says Mokhov. “We want to guarantee Why use a light material like graphite, and that this will never, never happen at the LHC. Our not something heavy and seemingly impenetrable goal is to design a system to exclude this type of like lead? If the material were heavy, all the accident completely.” beam’s energy would concentrate inin thethe firstfirst half-half meter of the block. Combine that with the lower melting point of a material like lead, andand, inin shortshort orderorder, youryour beam-dumpbeam-dump blockblock wouldwould becomebecome aa beam-dump mess. Using a light, high-melting- point material like graphite ensures that the beam energy is distributed throughout the block, and that the block will last for the decades-long life of the LHC.

The art of dumping Say a magnet quenches, too much beam goes off course, or—the most likely yet least dramatic “In a bad accident, the scenario—the beams have lost too many pro- beam could go off tons during normal collisions and scientists need to load a fresh set. What happens to the old course and drill a hole beams? Even at the ends of their usual 10-hour life through one or two spans they still hold 200 megajoules of energy that can't be sent just anywhere. magnets.” Rudiger Schmidt, CERN “This beam is not a danger by itself,” Schmidt says, “but the fact that it can deposit its energy in a tenth of a thousandth of a second makes it dangerous to the machine.” When the time comes, the beams are extracted, or dumped, into two hugehuge, cylindricalcylindrical blocks.blocks. EightEight meters long, one meter in diameter, and made of graphite composites encased in concrete, they are the only thing that can withstand the full power of the beam. But first the beam has to be

23 gallery: LHC cabling

It’s heavy, dusty, dirty work: Deep in the bowels of the LHC detectors, workers are rushing to connect a rat’s nest of cables.

Above: View of the CMS Tracker Outer Barrel in the cleaning room. Photo: CERN

Right: The ALICE inner tracking system measures the direction of particles produced in the collision of the two beams. Gas in the system is ionized as particles pass through. These ions then drift in a high voltage to strip electrodes where the position is read electronically. Photo: CERN

Top right: A technician for the ATLAS collaboration is cabling the ATLAS electromagnetic calorimeter’s first end- cap, before insertion into its cryostat. Photo: CERN

24 who figures that she and graduate student Jessica Leonard have installed about 1500 cables on their piece of CMS. “It’s heavy work and it’s dirty work. Some of the cables have eight copper wires, and then on top of it each pair is wrapped with metal, and then there’s metal mesh, and then more metal on top of this, and they’re heavy and they’re stiff and you have to push them into place.” What’s more, with cabling going on at a rapid clip, the guts of both detectors are pretty much packed, making it increasingly difficult to squeeze In the labyrinth in there to work—especially while wearing a hard By Glennda Chui hat with headlamp, sturdy safety boots, and layers If detectors are the eyes and ears of particle phys- of clothes to keep you warm in the chill. ics—sensory organs that pick up the faint echoes “You really have to be a gymnast to get around. of particles colliding—cables are the nerves, the It’s very tight,” says Monica Dunford, an Enrico veins, and the digestive tract that connect these Fermi Fellow from the University of Chicago who organs with their electronic brain and feed them works on the ATLAS experiment. With all the electricity. dust that’s accumulated during construction, she And nowhere is there such a grand display adds, she sometimes crawls out looking like a of cabling as at the Large Hadron Collider, the human dust ball. world’s most powerful particle accelerator. ATLAS has so little wiggle room that the crew If all you did was goggle in awe at the color- built a model cross-section of the detector ful spaghetti that sprouts from the machine’s about 15 feet high so they could figure out how two big detectors, you’d be missing most of the to fit signal cables, cooling pipes and all the rest. fun. Out of sight, beneath the floor, are multiple But fit is not the only consideration: For reasons levels of trays, racks, and towers given over almost of weight and fragility, access and maximum effi- entirely to cables, along with the pipes that carry ciency, the cables have to be laid in exactly the water and air and various gases. The official right order. name for this rat’s nest is the labyrinth; but those “Organization is very important,” says Martin who know it best jokingly call it a nightmare. Wensveen, a CERN electro-mechanical engineer “That’s where the heart of cabling lies,” says who is, as Sharma puts it, the cabling master. Archana Sharma, a CERN physicist who is part “Where do you start? Where do you end? Our phi- of the technical coordination team for the losophy was to always start with the big, heavy Compact Muon Solenoid detector, or CMS. “The cables and then go to the smaller, more delicate amount of cable and services we are laying ones, and the fiber optics at the end,” because down is on the order of supplying a small town they’re fragile and will crack if bent too far. of 10,000 inhabitants. People work there day and Crosstalk is also a problem. With cables packed night to get this task out of the way. Of course, so close together, electronic signals from one there are a lot of conflicts; sometimes we find cable can penetrate the next. “So you have to do things don’t match. You build a house, and you all sorts of tests,” says Dunford. “We have to make know the sorts of problems we have.” sure there’s no communication between them.” CMS alone contains 22,780 separate cables, Cables arrive at the detectors on big, heavy many of them with multiple strands, that put spools—thick, white cables for the control system, end-to-end would stretch 725 kilometers, or 450 red for high voltage, light blue to carry signals miles—roughly the distance from Brussels to from the control center to the detector and back. Geneva or Chicago to Pittsburgh. Each cable’s route is unique, and it’s a full-time Laying and connecting all that CMS cable job just to calculate how long each one should requires 38 people working full-time, plus two be. Workers slap a bar code on each cut-to-order special engineers who route the cable, prepare cable so it can be entered into a database. work assignments, and write the database that Should problems develop, as they inevitably will, keeps track of it all. The lab brought in teams of this will make it possible, although by no means expert cablers—people who honed their skills in easy, to trace the offending cable back through factories and power plants—from Russia, Bulgaria, the rat’s nest. symmetry | volume 04 issue 10 december 07 and China. Even so, a lot of cabling falls to experimenters Monica Dunford and Pamela Klabbers blog about their experiences at www.uslhc.us. Archana Sharma writes a weekly and their students. column, Point 5 News, for the CMS Times. “You can’t really outsource it, because you have to keep track of everything and where it goes. It requires a lot of patience,” says physicist Pamela Klabbers of the University of Wisconsin, Madison,

25 gallery: LHC cabling

26 symmetry | volume 04 issue 10 december 07

Top left: Cabling up the semiconductor tracker for ATLAS. This part consists of nine carbon fiber discs, each with 1.5 million thin silicon strip detectors, and was built at NIKHEF in The Netherlands. Photo: Peter Ginter/NIKHEF

Bottom left: Cabling the LHCb detector presented a different challenge to the other detectors. Instead of squeezing cables between the concentric layers of a typical particle detector, an entire wall of photomul- tiplier tubes in this planar detector needed to be cabled. Photo: CERN

Top right: A few members of the ALICE Silicon Pixel Detector group working on the completed first half barrel. Photo: CERN

Bottom right: Cabling work inside the ALICE Magnet. Photo: Antonio Saba, CERN

27 Q&A: james gillies

Hollywood directors, time travelers, journalists, school kids—CERN’s press office sees them all. symmetry’s Glennda Chui talks to James Gillies, head of communication, about what it’s like to handle the increasing demand for tours and information as the lab prepares to switch on the Large Hadron Collider.

Q: I hear things are really heating up there. Q: So you and the Catholic Church find In a typical year we get around 300 individual yourselves in the same position of trying to media visits. We had many more visits in 2004, correct the record on Dan Brown’s books. which was our 50th anniversary year, and since When something like this comes up, you can then the numbers have just been rising, to well stick your head in the sand and pretend it doesn’t over 1000 individual visits from more than 500 exist. You can attack it. Or you can just run along media in 2007. We’ve been telling people that if with it and have fun with it, and that’s what we you want to come and see and look around, this did. We put a fact-and-fiction page about Angels is the last chance to do it. and Demons on our Web site. We actually asked Georges Charpak, a Nobel Prize-winning physicist Q: Wasn’t 2004 also when Dan Brown’s who plays Frisbee in the book, if he ever plays novel, Angels and Demons, took off? Frisbee. He said no. But we point out that you Yes, and it made a big difference. The book is can play Frisbee with other Nobel Prize winners about a secret society that steals antimatter from and people do, out there on the lawn. CERN to make a bomb to destroy the Vatican. Before that, we were running 20,000 or 30,000 Q: Now Ron Howard, the American director, visitors per month on our Web site; just about is making a film version. overnight it went up to a quarter of a million visi- He was here last summer and I was quite tors a month and stayed there. So although the impressed, actually. He wants, as far as I can tell, science in the book is pretty much nonsensical, to do right by us in this film, to make the science in terms of raising awareness it’s done us a as plausible as it possibly can be, given the con- great favor. straints he was working with. It was quite fun, discussing the storyline and how it might be made into a movie. They were looking at filming here innex summert summer next, but , butat some at some point point in 2008 nextwe’ll yearbe running we’ll be and running then nobodyand then will nobody be going will beinto going the tunnel into the whilst tunnel that’s whilst happening. that’s happening.

Q: Captain Jack also put in an appearance. The actor who plays Captain Jack, John Barrowman, came in April to record the first of a James Gillies, head of series of podcasts set at CERN. He was hilar- communications at CERN. ious. He plays this character in Doctor Who, a Photo: CERN science fiction series that involves time travel. One of our particle detectors is called the time projection chamber, which is a very exotic name. But you cannot, of course, use it to travel back in time.

Actor John Barrowman, who plays the time-traveling Captain Jack in the Doctor Who TV series, films a podcast at CERN, above and top right. Photos: CERN

28 Q: CERN even played a role in Sunshine, Q: How will you handle the startup of which doesn’t even mention the lab. the LHC? The hero of the film is a physicist, actually, who We are committed now to an open-house week- leads a mission to reignite the dying sun. The end in 2008—Saturday, April 5th, for CERN guy who played the hero came and stayed with people and Sunday, the 6th, for the public. Hope- one of our physicists for two weeks; as a result, fully we will be opening all eight access points CERN got mentioned in the film pages of all sorts to the LHC, and inviting people in the community of newspapers. The basic message was, “The to visit the one closest to where they live. We’re hero is a physicist and he’s a really cool character. still working on what we do with media, but we’ll And OK, it’s very improbable that we’ll have to probably invite them to come on the day we try face a catastrophe like this, but the truth of the to put beam into the LHC for the first time. matter is there’s an awful lot out there in the universe that we don’t understand, and the impres- Q: Isn’t it a bit risky to invite the media sion we have of the universe as a nice benign on the actual day? Wouldn’t you normally place to live is false, and so if we wish to carry on announce the start of operations only living peacefully in the universe, we’d better under- after the fact, in case some last-minute stand it better than we do now, and the way to glitch develops? do that is through particle physics.” So it got great True, that’s the way it’s normally done. But I don’t coverage for us, in places you don’t normally think there’s ever been so much interest in the expect particle physics to be. start of a particle accelerator, so I don’t think we really have much option. And actually it will work Q: As you get closer to the opening of the to our advantage. BBC Radio 4, the premium LHC, I can imagine a collision course in talk-radio station in the United Kingdom, is bring- which the scientists who normally guide ing its whole network here, and every program tours are too busy, but there’s more and on that day will have a particle physics theme, and more demand from people wanting to they need a date to publish in their schedules. see things. We’ll bill it as a curtain raiser, a precursor to There will be, but there are also more and more news to come, but we will have to be careful scientists coming here as we get closer, so that to manage media expectations on and around will be sort of offset. The challenge is new the day. So we say this is the day that we try itineraries. There’s a lot of energy in the LHC’s to put beam into the LHC, and we explain very beams, and we can’t take people down there carefully that this is not the day when we first symmetry | volume 04 issue 10 december 07 when it’s operating. We have to find new places get collisions. I think people could understand that are every bit as exciting as going down that. People understand that when you launch a into these caverns, and I think we can do it. For rocket, you’re not getting results straightaway. instance, we’re building an exhibition point at the ATLAS experiment, overlooking the control room, so people will be able to see science happening; I hope we’ll be doing the same for CMS.

29 essay: peter steinberg

a standard part of life in modern mega-collab- No mere orations. We develop longtime professional cog: relationships with colleagues we rarely see in person. It’s strange at times, though perhaps Blogging not any stranger than other modes of electronic the LHC life we’ve accustomed ourselves to, such as Facebook or iChat. With so much work Despite all the meetings and communication

Photo courtesy of Peter Steinberg Photo courtesy of Peter to do on so many in our lives, we all know progress isn’t going to aspects of the Large happen just by talking through technical issues, Hadron Collider—the studying simulated events, or even making the accelerator, detectors, software, physics, and detector perform as designed. It’s also going to so on—it’s hard not to get a bit lost. It’s a crowded be found by looking at real data, in real time, and field with thousands of scientists, all of whom with hundreds of people looking over each others’ have staked the next phase of their careers on shoulders. This is where blogging the LHC experi- the LHC, and all trying to finish many different ence can play an interesting and novel role. things in the little time remaining until first collisions. The earliest days of a new machine and new Still, I’ve rarely found a productive physicist detector are hard to describe as they are hap- who actually feels like a mere cog in a huge pening. It is even harder to recall them in detail humming machine. Maybe the fact that most of after things become better understood, roles the major discoveries in physics are ultimately and hierarchies become well-defined, and habits attributed to individuals—however wrongly—lets start to form. Robert Crease, the science historian, us dream a bit. But it’s probably more that as a has suggested that “a scientific paper is more like practical matter, we each focus on a particular a trial lawyer’s concluding speech, recapitulating aspect of the physics at our machines. This lets the argument—not the proceedings—in summary us gain satisfaction through arriving at our own form and in the strongest way possible.” insights, which we then share with other small Thus, the fascination with the LHC should not groups of colleagues and ultimately with the full just be in the results, per se, but in the false starts, collaboration. inevitable stumbles, and occasional flashes of Of course, with the machine coming online dur- insight about the physics. Stay tuned to the blog- ing the next year and no actual physics data to gers, both official and not, as the LHC and its focus on yet, we are all taking on a wide variety of detectors rumble to life. They may well provide tasks in our working groups—two working some real-time glimpses into the practice of groups, in my case. nuclear and particle physics as it is experienced I spend most of my time these days helping by individuals, rather than by large groups. Of prepare a proposal for taking and analyzing data course, some things will never make it out of the from collisions of lead nuclei using the ATLAS (virtual) conference room—collaborations always detector at the LHC. At the same time, I’m having their own secrets, and rules about revealing involved in preparing to look at similar data from them—but intriguing details are sure to emerge. the first proton-proton collisions at ATLAS. Even the most prosaic events from the first LHC data— Peter Steinberg of Brookhaven National Laboratory in New York is one of four American physicists who are blogging those in which two protons shatter into hundreds about what it’s like to work at the Large Hadron Collider. of slow particles—give insight into basic features See what they have to say at www.uslhc.us of the strong interaction that generates 99% of the visible mass of the universe (an oft-forgotten fact!). These reactions are not easily accessible to current theoretical approaches, but they are an essential part of the heavy ion program, which is my main focus at Brookhaven. As it happens, these two aspects of my work involve entirely different groups of people at insti- symmetry | volume 04 issue 10 december 07 tutions all over the world. Yet despite “running” from meeting to meeting, I rarely leave my office chair, even on the busiest days. Instead, most groups interact via videoconference and telecon- ference. While this sounds somehow cosmopoli- tan and futuristic, it’s often quite taxing (“Can you hear me now? Now?”). However, it has become

30 logbook: CMS cosmic challenge

CMS Event Display Sun Aug 27, 2006 MTCC Run No 2605, Event 3981 Event display and e-logbook courtesy of CMS Event

scientists working As part of the test, the CMS team cooled the solenoid In August 2006, on the Compact Muon to its operating temperature of about minus 270 degrees Solenoid experiment at CERN conducted a Cosmic Celsius and powered it up. The magnet produced a field of Challenge to test components of their 12,500-ton CMS 3.8 Tesla, strong enough to bend the paths of even the particle detector. Using cosmic rays—particles that travel most energetic particles. through space and hit the Earth—CMS scientists checked For a couple of months, the CMS team recorded cosmic all of the four detector subsystems working together for the rays and reconstructed their tracks. The graphic shows first time. the curved path of a muon, a heavy relative of the electron, Stacked like a set of Russian dolls, these subsystems which traversed all four CMS subsystems on Sunday record the energies and tracks of particles traveling evening, August 27, 2006. A few hours later, Austin Ball, through the detector. A powerful superconducting mag- technical coordinator for CMS, wrote in the electronic net—a cylindrical solenoid embedded in the detector— logbook that the detector had achieved the goal of 10 mil- bends the paths of charged particles. The curvature of lion useful cosmic-ray events, give or take 50,000. these paths allows scientists to determine the electric Today, the CMS solenoid and much of the detector are charge and mass of each incoming particle. in the CMS collision hall, being assembled in time for the The goal of the Cosmic Challenge was to simultaneously startup of the LHC. In the spring of 2008, the collaboration test all the CMS detector subsystems with the solenoid will again power up the magnet, this time preparing the switched on. It was the final test before moving detector detector for the recording of particles emerging from pow- components into their final location 100 meters underground erful proton-proton collisions. in the tunnel of the Large Hadron Collider. Kurt Riesselmann explain it in 60 seconds TERA

is an energy region named for the tera, or million million, electronvolts The Terascale of energy needed to access it. Physicists are standing at its threshold, poised to enter this uncharted territory of the subatomic world. Today, the Fermilab Tevatron particle collider is cracking open the door, offering a first teasing glimpse of the Terascale. Soon, the CERN Large Hadron Collider will fling the door open and begin to explore this exciting new region. Later, the proposed International Linear Collider would zoom in to reveal its most important features. What do we expect to find at the Terascale? Certainly the Higgs particle—or whatever takes its place. Its discovery would help explain the mass of all elementary particles and the fundamental difference between the electromagnetic force and the weak nuclear force. But this would be just the beginning. Siblings of the Higgs particle might provide the dark matter that fills the universe. Its cousins might have driven the inflation that powered the big bang. More dis- tant relatives might even be responsible for the ubiquitous dark energy that drives the universe apart. The Terascale is rich with discovery opportunities, and exploring it is the next big step in understanding the universe in which we live. Jonathan Bagger, Johns Hopkins University

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