A joint Fermilab/SLAC publication

volume 02dimensions of particle physics

issue 04

may 05

A joint Fermilab/SLAC publication

volume 02 | issue 04 | may 05

Office of ScienceU.S. Department of Energy

3 Commentary: Fred GilmanCommunication of 21st-century particle physics: Will the United Statescontinue to be among the world leaders in the field?

4 Signal to BackgroundReturn of the bubble chamber; bouncy bison babies; neutrino papers with top citations; a building that breathes; letters.

8 The Elusive NeutrinoExperiments are beginning to unravel the secrets behind a mind-bogglingquantum effect: neutrino oscillations.

14 Searching for the Neutrino’s IdentityNeutrinos are different from other matter particles. Could they even betheir own antiparticles?

18 Virtual StructureYou don’t have to relocate to join Barry Barish and his global team thatwill manage the design of the International Linear Collider.

20 Springtime at DaresburyA laboratory in the north-west of England transformed itself into a power-house of accelerator physics and technology.

24 Gallery: Chris HenschkeThe exhibit HyperCollider explores the extremes of the General Theory of Relativity in many ways, including with a pinball machine.

28 Deconstruction: Soudan MuralArtist Joseph Giannetti created a large mural to honor neutrino physicistsand their groundbreaking experiments.

30 Essay: Aaron FreemanCan a stand-up comedian and physics groupie get in touch with his inner particle?

ibc Logbook: Solar NeutrinosRay Davis’ experiments in a gold mine led him to solve the solar neutrinopuzzle and win the 2002 Nobel Prize in Physics.

bc 60 Seconds: Neutrino OscillationsNeutrinos are able to change from one “flavor” to another as they travelthrough space because of their wavelike nature.

On the CoverThree different neutrino types (ν1, ν2, and ν3) with distinct masses are mixtures of the three different neutrino “flavors” (νe , νµ, and ντ). Neutrinos of a particular flavor change to other flavors as they travelthrough space. Photos: Sandbox Studio, Chicago

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from the editor

SymmetryPO Box 500MS 206Batavia Illinois 60510USA

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

(c) 2005 symmetry All rightsreserved

symmetry is published 10 times per year by FermiNational AcceleratorLaboratory and StanfordLinear Accelerator Center,funded by the USDepartment of Energy Office of Science.

Editor-in-ChiefDavid Harris650 926 8580

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Neutrinosare complicated little beasties–far more so than physicist Wolfgang Paulicould have imagined. He introduced them in 1930 as a theoretical hack

to save the law of conservation of energy, which appeared to be violated in some newly observedparticle interactions.

Despite such an inauspicious beginning, the neutrino has risen to the status of particle physics’wonder-child. Nine of the thirteen most-cited papers in experimental high-energy physics concernneutrinos. Physicists have learned much about these creatures but the mysteries only seem to deepenwith each new finding.

It should be no surprise that there is so much activity surrounding neutrinos. After all, they fracturethe Standard Model of particle physics and interactions. The Model did not predict flavor changeand non-zero masses, for example. Fortunately, neutrinos are accessible for study by new, albeitchallenging, experiments.

The recent American Physical Society study, The Neutrino Matrix, provides a thorough analysisof the current state of neutrino physics, and makes a set of three specific recommendations onwhat would best advance the field.

This issue of symmetry focuses on aspects of neutrino physics, including experiments that dove-tail with two of the Neutrino Matrix recommendations. These experiments attempt to answer: “Whatkind of particle is the neutrino?” and “How can neutrino masses be characterized?”

The promise of neutrinos is enticing. Their as-yet-unrevealed secrets could provide solutions towhy there is more matter than antimatter in the universe, how mass comes to exist in our universe,and the origin and future of the sun’s energy. Neutrinos are also driving more speculative ideasabout the nature of dark energy and extra dimensions.

Having broken the Standard Model, can neutrinos also provide seeds for its next evolution? Thatseems likely. But, for now, theorists have more ideas than they know what to do with, and needexperimental results to direct them toward resolution.

It is clear that neutrino physics has much to teach us about the universe. And these lessons farsurpass the original promise of fixing a perceived accounting problem in the energy balance sheetof fundamental interactions.

David HarrisEditor-in-Chief

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commentary: fred gilman

Communication inchallenging timesThe question before the high-energy physicscommunity in the United States at this momentis nothing less than whether we will continue to be among the world leaders in this field. To ensure a long-term future, we must start fromthe extraordinary science that lies ahead andour plan to explore that science. The High EnergyPhysics Advisory Panel (HEPAP) has an impor-tant role in communicating these scientificopportunities for 21st-century particle physicsclearly and effectively.

At the HEPAP meeting in mid-February, therewas intensive discussion of the tough prioritychoices necessitated by the constraints onfunding in the federal budget proposal for fiscalyear 2006. Even worse, the 2006 proposal isembedded in the context of a projected declineover the next five years of the budget of theprimary supporter of the physical sciences, theDepartment of Energy’s Office of Science. If anything like this projection is actually imple-mented, longstanding US leadership in manyareas within the physical sciences will be lost.

This dire result is not set in stone. As acommunity we will do all that we can to makethe case by communicating the significance and excitement of the scientific opportunitiesthat are at hand, our prioritized plans for realiz-ing the science, and what doing this science in the United States brings to the nation.

HEPAP is acting first in its traditional role ofpresenting advice from the scientific communityto the Department of Energy and the NationalScience Foundation. In the past, HEPAP has dealtwith many specific charges from the agenciesand responded by forming a series of subpanels.Such a subpanel, chaired by Jonathan Baggerand Barry Barish, produced the twenty-year planfor our field in 2002. There are currently five

HEPAP subpanels of this type; some are finishingup, others are just being formed.

In the last few years HEPAP has been askedto produce a different type of report, addressed to policy-makers who are not necessarily familiarwith the detailed science of particle physics butwho want to understand the central scientificquestions that particle physics seeks to answer. Inthat vein, one of HEPAP’s most importantachievements of the past year has been theQuantum Universe report. It presents the revo-lutionary changes in particle physics at thebeginning of the 21st century and the excite-ment of seeing how we will begin to answer the most compelling questions confronting our field. Quantum Universe was written for a broad audience and has been a tremendoushit, not only in this country, but abroad.

For high-energy physics, the science questionsthat would be answered by the InternationalLinear Collider (ILC) are so compelling that theparticle physics community worldwide has madethe linear collider our top scientific priority afterconstruction of the Large Hadron Collider (LHC)at CERN. This year has seen good progresstoward an ILC with the choice of a single technol-ogy, and the choice of a leader, Barry Barish, for the Global Design Effort. In parallel with theefforts of the physics community, governmentrepresentatives from Europe, Asia and NorthAmerica—the FALC, or Funding Agencies for theLinear Collider—are holding discussions to try tounderstand how to make the ILC a global reality.

A new HEPAP subpanel is currently at workto produce a report in the style of QuantumUniverse that defines and communicates thescientific questions that the ILC will answer in synergy with the LHC. In responding to thecharge from the Department of Energy andNational Science Foundation, the report will alsoanswer clearly and convincingly the physicsquestions posed to HEPAP by the NationalAcademies’ decadal review of particle physics,EPP2010. The report of the EPP2010 panel, due late this year, is expected to have broad andsignificant influence on the future of US particlephysics. The time is now to communicate thechallenge and excitement of the science of 21st-century particle physics and the role thata vibrant US program can play.

Fred Gilman is Buhl Professor of Theoretical Physics andHead of the Department of Physics at Carnegie MellonUniversity. He is the current Chair of the High Energy PhysicsAdvisory Panel (HEPAP).

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signal to background

Bubble chamber technology, at its prime in the 1960s and 1970s, is back in

business; bouncy bison babies are a sign of spring; reports on neutrino

experimental results earn top citations in the last 10 years; synchrotrons breathe

in the sun; letters.

Roger Hildebrand in 1955, holding a bubble chamber. Source: University of Chicago Magazine, April 1955

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Bubble chambersare backBubble chambers, once at theforefront of particle detectionand then relegated to the his-tory books, are coming back.On March 28, 2005, researchersat Fermilab and the University of Chicago lowered the first of a new generation of bubblechambers into the MINOSgallery at Fermilab in an effortto detect elusive dark matter.Juan Collar and AndrewSonnenschein of the Universityof Chicago, in associationwith Fermilab’s Mike Crisler,designed the compressed,CF3I-filled chamber, which is

about the size of a bowling ball(photo above). Giving encour-agement along the way wasRoger Hildebrand, a pioneer of bubble chamber technologyin the early 1950s (left).

The first bubble chamber,filled with highly volatile ether,was made by Don Glazer of the University of Michigan.

“How he didn’t blow himself upI’ll never know,” said Hildebrand,who took the first photographof a nuclear reaction via hispencil-case-sized bubble cham-ber. Hildebrand’s team at theUniversity of Chicago built ever-larger chambers as particledetectors, until the use of spark

chambers and other devicesbecame widespread in laterdecades.

Now 83 years old and withfour grown children, eightgrandchildren, and two great-grandchildren, Hildebrand isinvestigating far-infrared astron-omy and has no plans on slow-ing down. Is he trying to outdohis father, a renowned chemistwho worked though his 90s?

“I haven’t set that as a goal,” hechuckled. “I’m just curious abouthow nature works, and I’m trying to do the best job I can.”Eric Bland

Frolicking bisonAs spring arrived, so did thekids. Their knees wobbly andeyes wide open, they stayedclose to their moms. Dad,weighing more than 2500pounds, made sure that noharm came the babies’ way.

Fermilab’s herd of bisonwelcomed its first new familymember before crocuses

broke the ground and daffodilsopened their flowers. By theend of April, about 25 calveswere born. Within a couple ofdays of birth, the little beastswere brave enough to runaround, while the adults slowlywandered across the pasture.Looking at the massivegrownups, who would haveguessed that the little onescould be so bouncy?

Fermilab has been home to bison for more than 30 years. Founding director RobertWilson introduced the firstseven animals from Wyomingand Colorado, bringing a symbol of 19th-century Illinois back to the grounds. Today,the buffalo, as they are com-monly called, are as much a part of Fermilab as WilsonHall and the tall-grass prairie.

Every year, thousands ofvisitors come to see the ani-mals. But the fling with youthonly lasts through the summer.By fall, the calves’ hair will

have turned dark brown, mark-ing the transition into adult-hood, and their frolicking willhave stopped. For many ofthem it will also be the time tosay good-bye: farmers fromacross the Midwest will be bid-ding for the animals at a silentauction.

In 1889, only 600 bison re-mained in North America.Today, more than 200,000 roamthe continent.Kurt Riesselmann

The decade of theneutrinoSpeaking experimentally, thepast decade has been the

“Decade of the Neutrino.” It pro-duced neutrino experimentsacross three continents, goingfrom the lab, to the nuclearreactor, to the atmosphere, tothe sun, and back to thenuclear reactor. Along the waythe experimental results modi-fied the Standard Model ofparticle interactions, opened a window to “new physics,” and broke (and then fixed) theStandard Solar Model. Perhapsno other particle has led us onsuch a rich and varied journey.

spires, the high-energyphysics literature database,identifies 13 scientific paperswith over 500 citations in thehigh-energy physics experimente-print archive, hep-ex. Nine* ofthe 13 papers have been aboutneutrino experiments. (The

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others include three papers onthe discovery of the top quarkat Fermilab, and one on themeasurement of the muonanomalous magnetic moment at Brookhaven NationalLaboratory.) Neutrino papersalso account for all five* of thetop-cited nuclear physics experi-ment (nucl-ex) publications.

Of all neutrino experimentpublications (hep-ex and nucl-ex), the top-cited paper belongsto the Super-Kamiokande collaboration, based in Japan.Cited more than 2300 times, the paper presents evidence forthe oscillation of atmosphericmuon neutrinos. Second placegoes to the Sudbury NeutrinoObservatory (SNO) in Canada. It rescued the Standard SolarModel by finding evidence formuon and tau solar neutrinos,which were essentially unde-tectable by Super-Kamiokande.Third place belongs to theCHOOZ collaboration, basedin France, for its report onseeing no mixing for electronantineutrinos in a reactor-based experiment. Other top-cited experiments includeKamLAND (Japan) and LSND(Los Alamos).Heath O’Connell, Fermilab

* Full details of the papers are online.

Breathing acceleratorAs the sun rises each day,warming the grounds and build-ings of the Stanford LinearAccelerator Center, the entirespear3 synchrotron facility(photo) expands in response.The change is minuscule, on the scale of a few microns—far too slight to observe withthe naked eye. But this expan-sion doesn’t escape thewatchful gaze of the spear3feedback regulation system. In fact, the system responds by

“breathing” in time with dailyfluctuations in temperature.

As the infield area and theshielding tunnel of spear3 heatup and expand radially, the lattice of magnets that keepsthe beam focused expands withit. Hence the beam becomesslightly displaced in relation tothe magnets.

In order to keep the beamcentered, the beam must be expanded in circumference.To achieve this, an array ofbeam position monitors (BPMs)precisely measures the dis-placement of the beam andrelays the information to afeedback system.

“The BPMs signal that thebeam is not where it’s sup-posed to be,” explains JeffCorbett. “The beam circumfer-

ence is set by radiofrequency,so the feedback system adjuststhe radiofrequency to keep thebeam centered in the BPMs.”

The feedback signal fromthe BPMs cycles every sixseconds. While the sun is ris-ing and spear3 is expanding,the radiofrequency drops byabout half a hertz. Then, astemperatures begin to cool offin the early afternoon, theradiofrequency rises again asthe building contracts.

Recent plots of the dailyfrequency shift confirm the pat-tern. Corbett expects to see a similar effect in response tothe change in seasons over an annual time scale.

“The effect is roughly propor-tional to the circumference ofthe machine,” Corbett says. With a bigger machine, a biggershift in frequency is generallyobserved. According to Corbett,the LEP ring at CERN, Geneva,and the Advanced PhotonSource, Illinois, have even beenobserved to breathe in cir-cumference due to gravitationaleffects of the moon.Matthew Early Wright

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Letters

Don’t forget the universitiesGreat article on the LHC and the US involvement(April 2005)—very complete and well presented.As usual, a nice job with the symmetry issue.

I’d like to comment on the sentence, “TheUnited States contributes high-tech acceleratorand detector components, developed and builtby US national laboratories with some help fromindustry.” While very true, we don’t acknowledgehere—as part of these projects—the incrediblyimportant US university contribution! I have foundmyself guilty at times (inexcusably) of having

“DOE National Lab” blinders on when talkingabout this project, but the efforts of approxi-mately seventy US universities across the coun-try on ATLAS and CMS, in collaboration with the four DOE national labs involved, needs to beclear. Aside from being most of the end “users”(doers, really) of the experiments, the universitiesare much more (as we and they know). Pick your state or region and you’ll find a universitythat has contributed directly through their physics,engineering and technical staffs to the CMS or ATLAS detector design, development, fabri-cation, and testing at their institutions, and nowin the detector installation and pre-operationswork at CERN.

As part of the Federal oversight of the USLHC Project, I have been both privileged andimpressed in my visits to a number of theseuniversities during the construction work to seefirst-hand the facilities, capabilities and resultsfrom this effort. Scientists and students at everypossible career stage (from high school/under-grad to senior scientist) have made the overallcollaborations and detector construction possible.There are unique and important stories associ-ated with many of these institutions, for example,from the work of students at Hampton University(a historically black college) building ATLAS transition radiation tracker modules, to the con-version of a pasta noodle shop near Notre DameUniversity into a lab for processing fiber opticcables and waveguides for CMS hadroncalorimeter read-out.Pepin T. Carolan, DOE/NSF US LHCProject Office, Batavia, IL

North vs. SouthEditor’s note: Our error regarding the location of the Homestake mine elicited the followingresponse.

In your March 2005 article about deep under-ground labs you write “…negotiations over thetransfer of [Homestake] mine ownership to the state of North Dakota foundered…”I writeto point out the obvious reason why thisoccurred. Your map correctly shows the locationof the Homestake mine in South Dakota. Myexperience as a North Dakota native suggeststhat North and South Dakota exist in differentparallel universes between which exchange ofmatter, energy, or information is extremely rare.Don Langenberg, College Park, MD

Smoking mouse chased bySchrödinger’s cat?After reading “The Smoking Mouse” in the Marchissue of symmetry, I believe I may be able tooffer a viable theory to explain how the creatureobtained entry into a seemingly impregnable H-spool magnet. While scampering throughFermilab, the mouse performed an observationthat collapsed the wave-function of Schrödinger’scat, determining with 100 percent certainty thatthe cat was alive (since it had given up playingwith a bit of string theory and was preparing topounce). In the ensuing chase the mouse calcu-lated that the probability of escape was so slimthat, in desperation, it resorted to quantum tunnel-ing, thus penetrating the steel box and ending upsafely inside. Later, mistaking the technician forthe cat, it tunneled out, and so was never directlyobserved. Admittedly, the matter of the chewedbird head isn’t explained by this theory, but until a larger set of mouse evidence is gathered I think it can safely be dismissed as an observationalartifact or anomaly.Chris Paul, Sackville, New Brunswick, Canada

Editor’s note: Despite the suspicions of manyreaders, The Smoking Mouse was not an April Fool joke. The story has spread through theworld thanks to additional distribution bynewswire services.

Letters can be submitted via letters@symmetrymagazine.org

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Illustrations: Aaron Grant

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Life on Earth depends on light and heat provided by the sun. But the nexttime you are sitting outside, catching some rays, take a moment to think of some of the invisible particles emitted by the sun: neutrinos. As you readthis sentence, hundred trillions of neutrinos pass through your body, doingno harm and leaving no trace.

Neutrinos are capable of traversing the entire Earth in the blink of aneye. At close to the speed of light, these particles travel straight throughrock and space, and nothing stops them. Well, almost nothing. Once in a blue moon, a neutrino will come across a nucleus and they will interact.

“Neutrinos are always referred to as ghostly particles, as if they are of little interest and have to be apologized for. Nothing could be furtherfrom the truth,” says Michael Turner, the National Science Foundation’sAssistant Director for Mathematical and Physical Sciences. “Neutrinosaccount for as much of the mass of the universe as do stars, and theymay well explain the origin of the neutrons, protons and electrons that arethe building blocks of all the atoms in the universe.”

In 1930, theorist Wolfgang Pauli introduced the neutrino as a theoretical“remedy” to account for an energy imbalance in nuclear reactions. Heworried that scientists might never be able to detect this seemingly invisibleparticle. But a quarter century later, a Nobel Prize-winning experimentobserved the first signs of neutrinos, recording their occasional collisionswith matter. Later experiments revealed that nature provides for at leastthree different types of neutrinos.

Scientists think that the abundance of neutrinos—they outnumber allother known matter particles by far—may have played a key role in theshaping of the early universe. For decades, most physicists assumed theparticles to be massless as experimenters found no hint for neutrinomass. In the 1990s, new and improved measurements provided the firstevidence for neutrinos to have mass, putting a huge crack into the the-orists’ Standard Model of particles and interactions.

Neutrino scientists must be patient. Observing neutrino interactionsrequires large detectors weighing thousands of tons, preferably builtdeep underground to shield them from other cosmic particles bombard-ing the Earth. Building these detectors takes years and they can cost one hundred million dollars each. When operational, the experiments needto run for a long time: a lot of neutrinos must cross a particle detector to produce a single “neutrino event,” either its deflection off a nucleus orits destructive collision. The latter produces a detectable tell-tale signal in form of an electron or one of its heavier relatives, the muon and the tau.

Nobel Prize winner Ray Davis and his team needed 30 years to “catch”2000 solar electron neutrinos in a mine in South Dakota. His count wasmuch lower than predicted by theoretical calculations. While some scien-tists began to question the validity of the Standard Solar Model, other

Not only are neutrinos hard to catch, but theyalso change form as they travel throughspace. New experiments hope to understandtheir chameleonic nature.

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scientists began to wonder whether electronneutrinos could “disappear” by transforming intoother particles, avoiding their detection in Davis’experiment. The disappearance of neutrinosseems to be tied to a rather mind-boggling be-havior of these elusive particles: neutrinooscillations. As neutrinos travel through matterand space, they transform from one type intoanother, either appearing as electron neutrinos,muon neutrinos, or tau neutrinos.

When a car becomes a vanCompletely unknown in the macroscopic world,neutrino oscillations are a quantum effect. Theyare equivalent to a sports car changing into aminivan or a bus, and then, many miles fartherdown the road, reappearing as a sports car. Ifinitially there were only sports cars on a highway,the road would soon be populated with a mix-ture of all three types of vehicles.

Only neutrinos with non-zero mass can per-form this trick, and measuring the details of the oscillation process allows scientists to deter-mine the mass difference among the threeneutrino species. (Measuring the absolute massrequires different, more challenging experiments.)Over the last ten years, a number of experimentshave looked for neutrino oscillations studyingeither neutrinos created in the sun, the Earth’satmosphere, nuclear reactors, and—more recently—particle accelerators. In each case, scientistsknow the particular types of neutrinos that thesource (sun, atmosphere, reactor, or accelera-tor) produces, and they examine the types ofneutrinos they find away from the source.

The probability with which neutrinos transforminto each other depends on the energy of theinitial particles (“horsepower of the sports cars”),

the differences in mass among the three neu-trino types (“weight of the vehicles”), the mixingangles that are characteristic for transitionsbetween two neutrino types (“a number assignedto each pair of vehicle types”), and the distancethe initial neutrinos have traveled from theirpoint of creation (“miles driven on the highway”).

Ups and downsThe idea of neutrino transformation gained sig-nificant support in 1998, when the Super-Kamiokande collaboration improved on earlierexperiments and announced that some muonneutrinos produced in the Earth’s atmospherealso “disappeared” before traversing the Super-Kamiokande detector, 2000 feet undergroundin an old zinc mine in Japan. In particular, adeficit was observed for atmospheric neutrinosoriginating on the opposite side of the Earth,traveling the largest distance.

Today, scientists agree that a neutrino canindeed transform into a different one, and faithin the Standard Solar Model has been restored.But do neutrinos really oscillate? Or is the trans-formation a one-way street? The ultimate answerrequires the reconstruction of the full oscillationcurve—including the reappearance part—not justthe observation of neutrino disappearance.

In the last four years, the Sudbury NeutrinoObservatory (Canada), the KamLAND experi-ment (Japan), and the CHOOZ experiment(France) have yielded good information on thetransformation of electron neutrinos. The exper-imental data fit the oscillation predictions, but Fermilab theorist Boris Kayser notes thatthe final clincher is still missing.

“We haven’t seen a lot of wiggling yet,” saysKayser, referring to the ups and downs of

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5a typical oscillation curve. “Ideally, you want theexperimental observations to determine theshape of each curve. That is not yet the case.There is a pretty strong suggestion of a wig-gle in KamLAND’s observation of electronneutrinos from reactors, but it’s not definitiveyet. Super-Kamiokande measures atmospheric[muon] neutrinos, and it sees only a hint of anoscillatory dip.”

A new type of experimentScientists have now set out to conduct a newgeneration of neutrino experiments, studyingthe elusive particle under laboratory-controlledconditions. The new experiments probe high-intensity neutrino beams produced by particleaccelerators with a finely tuned energy range.The beams travel hundreds of miles through theEarth—no tunnels needed—to large under-ground detectors that measure changes in thecomposition of the neutrino beam. These long-baseline experiments will either reveal the missingpieces of the sought-after oscillation curves, orthey will provide evidence for the true mechanismresponsible for the neutrinos’ Jekyll and Hydesyndrome.

In November 2004, the 130 scientists of theK2K collaboration, including members from sevenUS institutions, finished the first long-baselineexperiment with a muon neutrino beam. The proj-ect began in the mid-1990s when researchersadapted an accelerator already operating at theJapanese laboratory KEK to send a neutrinobeam 156 miles through rock to the existingSuper-Kamiokande neutrino detector. In four and a half years, the K2K experiment recorded107 neutrino events, 44 fewer than expected in the absence of neutrino transformation. The

experiment confirmed the neutrino deficitobserved for atmospheric neutrinos. But the ini-tial hopes of measuring the oscillation curvewere dashed.

“Super-Kamiokande’s atmospheric neutrinoresult in 1998 had a big impact on the K2K goal,”says KEK scientist Kenzo Nakamura, a memberof the K2K Executive Committee. “When wedesigned the K2K experiment and started con-struction of the neutrino beamline and neardetector, we knew the old Kamiokande’s atmos-pheric neutrino result. If this [had remainedunchanged], K2K could have confirmed muonneutrino oscillation with more than five sigmasignificance,” a statistically compelling level ofcertainty.

Instead, the 1998 results shifted one of thecrucial parameters in the muon neutrino oscilla-tion function, the neutrino mass difference, andthe K2K experiment lost most of its sensitivity tooscillations. “Unfortunately, with a given protonaccelerator and a given far neutrino detector, wehad no means to recover the sensitivity,” saysNakamura.

The most powerful beamIn early 2005, Fermilab celebrated the start-up ofits long-baseline experiment (see page 13). TheMain Injector Neutrino Oscillation Search(MINOS) uses a high-intensity muon neutrinobeam traveling 450 miles through the Earth to a detector in an old iron mine in Soudan,Minnesota. Every two seconds, Fermilab’s MainInjector accelerator slams a pulse of high-energyprotons into a graphite target, producing theworld’s most intense neutrino beam. About twothousandths of a second later, the neutrinoscross the 6000 tons of steel and scintillating

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plastic of the MINOS detector, half a mile under-ground. Every day, the steel stops on averagethree neutrinos, each one creating a muon easilyrecorded by the detector.

Like the K2K experiment, MINOS will observethe disappearance of muon neutrinos. But thelonger distance and the higher neutrino beamenergy should allow MINOS scientists to map a significant stretch of the oscillation curve, too.The neutrinos crossing the MINOS detectorhave an energy spread from less than 1 GeV toabout 30 GeV (gigaelectronvolts). Mapping the entire range should reveal the dip in the curveas theoretical predictions indicate the disap-pearance to be greatest at 2 GeV.

“For the first time, physicists will explore awide band of neutrino energies,” says MINOSco-spokesperson Stan Wojcicki of StanfordUniversity. “We will trace out the oscillation curve.”

Where do they go?But some scientists believe the MINOS experi-ment will not provide all the answers. YvesDesclais is the spokesperson of the OPERAexperiment (Oscillation Project with Emulsion-tRacking Apparatus), currently under constructionat the Gran Sasso underground laboratory inItaly. For him, the measurement of muon neutrinodisappearance and reappearance is only halfthe equation. He and his 150 colleagues of theOPERA collaboration would like to observe the particle that the muon neutrinos presumablyoscillate into: the tau neutrino.

The OPERA experiment will utilize a high-intensity neutrino beam traveling 450 milesstraight through the Earth from the European par-ticle accelerator laboratory CERN, in Switzerland,to the Gran Sasso cavern. The energy of theneutrinos leaving CERN will be higher than theneutrinos leaving Fermilab, reflecting two differ-ent experimental strategies.

“To observe tau neutrino appearance, you needto run at higher energy, above the tau produc-tion threshold,” explains Desclais. “But then youare not in a good position to do a disappear-ance experiment. The two types of experimentscannot be done at the same beam.”

OPERA scientists expect to install half thedetector by June 2006, coinciding with thelaunch of the first high-intensity neutrino pulsesfrom CERN to Gran Sasso. The second half of the detector will be finished by the end of2006. Capturing a few tau neutrinos per year—achallenging task—will be enough to settle animportant question.

“We want to check that the [anticipated]MINOS results are not related to neutrino decayto sterile neutrinos,” says Desclais.

According to the Standard Model, there arethree types of neutrinos with very similar prop-erties. The French CHOOZ experiment has ruled

out any significant transformation of muon neu-trinos into electron neutrinos. Hence muon neutrinos can only morph into tau neutrinos—ifthe Standard Model is correct.

But history has taught physicists that theobvious answer is not always the correct one. Inthe case of neutrinos, there is even corroborat-ing evidence. In the 1990s, the LSND experimentat the Los Alamos National Laboratory madeobservations that—in connection with resultsfrom other experiments—indirectly suggest theexistence of a fourth type of neutrino, dubbedthe sterile neutrino because it must be evenless reactive then the three “ordinary” neutrinos.Results from the ongoing MiniBooNE neutrinoexperiment at Fermilab may confirm or refute theLSND results before the end of the year.

The quest continuesQuestions about neutrino oscillations and a fourthneutrino are only some of many neutrino puzzlesyet to be solved. Exactly how heavy is a singleneutrino? What do neutrinos tell us about the origin of mass? Are neutrinos connected to extradimensions? Do neutrinos violate the matter-antimatter symmetry or other fundamental sym-metries of the universe? Are neutrinos their own antiparticles, unlike any other matter particle?

With its new muon neutrino beam line,Fermilab is in an excellent position to confrontthese questions. Japan has begun the con-struction of a new 184-mile high-intensity neu-trino beam line, which will be operational in2009, and US laboratories are contemplating a similar project. Ultimately, physicists hope to build a neutrino factory based on muons circling in a ring-shaped accelerator. Turning thisdream project into reality will require years ofresearch and development to overcome thetechnological challenges—nothing new for neu-trino physicists, who have seen the need forpatience when unraveling the mysteries of theuniverse is their goal.

“Ideas like transformations from one neutrinokind to another, proposed some 50 years ago,seemed then a far-out and unlikely concept tomost physicists. But today this phenomenonappears to be a reality,” says Wojcicki. “Thereare a number of other far-out ideas being pro-posed today about neutrinos. Will any of themturn out to be reality?”

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At a dedication ceremony on March 4, 2005,Speaker of the US House of RepresentativesDennis Hastert officially started the MINOSneutrino experiment at Fermilab. Tapping on acomputer keyboard, he launched the graphicdisplaying the live signal of Fermilab’s new neu-trino beam line on a large screen.

“Now we have a date with the future and des-tiny,” said Hastert shortly before launching theexperiment. “This bold, innovative project will keep Fermilab on the cutting edge of physicsresearch for years to come. It highlights theimportance of the work done day in and dayout at national laboratories such as Fermilab.These projects keep our nation at the forefrontof scientific discovery.”

Every two seconds, Fermilab now sends apulse of neutrinos from Batavia, Illinois, to theMINOS detector in Soudan, Minnesota, 450miles straight through rock. Located half a miledeep in the Soudan Underground Laboratory,the detector will record a sample of the beam,unveiling changes in its composition.

“In time, the MINOS project will be viewedas a landmark event in the history of physics.This world-class research is a bold, visionaryinitiative, which will have profound implicationsfor our understanding of the structure and evolution of the universe,” said CongressmanJames Oberstar, Minnesota. “The billion-year-oldrock formations in the Soudan Undergroundmine have provided some of the world’s richestiron ore. Now the mine may help unlock mysteriesabout the origins of the universe.”

The MINOS collaboration includes over 200 scientists from six countries: Brazil,France, Greece, Russia, the United Kingdomand the United States. The US Department

of Energy provides the major share of the$180 million funding of the NuMI/MINOS proj-ect, with additional funding from the USNational Science Foundation, the UK’s ParticlePhysics and Astronomy Research Council, the State of Minnesota, and the University ofMinnesota.

“I would like to offer congratulations on thesuccessful start for this new experiment andthe beginning of an exciting new age of physicsdiscoveries for Fermilab,” said Raymond Orbach,director of the DOE Office of Science, at thededication ceremony. “Neutrinos are fascinatingparticles. What Fermilab is doing today is thefirst step in long-baseline studies that will openup untold excitement as we learn more aboutthe properties of these mysterious particles.This lab and those of you who work here havea very bright future.”

MINOS co-spokesperson Doug Michael,Caltech, added a unique and emotional perspec-tive to the ceremony. His schedule of chemo-therapy treatment for recently-diagnosed multiple non-Hodgkin’s lymphoma required himto stay in California, hence MINOS colleagueStan Wojcicki, Stanford University, read someremarks on his behalf.

In his letter, Michael thanked the Americanpeople for funding basic research, pointing out that “basic scientific research proves to bea wise investment for the future through cre-ation and development of new technologies towhich it invariably leads…In my recent diagnosisand treatment, I have frequently found myselfmarveling at the technology that is available for21st-century medical care. It is very gratifying to me to know that many of the basic ideas andtechniques for modern imaging equipment wereeither first developed in our own field of high-energy physics or by people trained in our field. I have gotten a first-hand view of the remarkableachievements in the engineering, technology,chemistry, and medicine which enable us toeffectively treat diseases like the one that I have.”

Official Startupof MINOS

Tapping a key on a laptop, House Speaker Dennis Hastert (left)unveils the beam signal, with Fermilab Director MichaelWitherell, Rep. James Oberstar, and DOE Office of ScienceDirector Raymond Orbach looking on. Photo: Reidar Hahn, Fermilab

450 miles

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Fermilab

Soudan

Neutrinos are like no other particle in the universe. The more we learn about these “little neutral ones,” the less we seem to understand them. Physicists do not even yet know what type of particle the neutrino is. But experiments looking for a rare decay process might soon provide the answer.

Neutrinos should have no mass and come inthree unchanging “flavors”. At least that’s how theStandard Model, physicists’ most completedescription of fundamental particles, tells it. Butrecent experiments have revealed that neutrinosdo not play by these rules: they have mass andthe flavors morph into one another as they travelthrough space.

As a result, more questions tug at the mindsof neutrino researchers than ever before: Whatare the exact masses of the neutrinos? Is it possible that neutrinos are their own antiparti-cles? Do neutrinos really oscillate between flavors? Do they break the standard matter-anti-matter symmetry?

Several experiments seek answers to the

first two questions by searching for a rare typeof nuclear decay called neutrinoless doublebeta decay. Theorists suspect these decaysoccur, and a Heidelberg-Moscow experimentalgroup has claimed evidence for them based on a controversial analysis. But so far no experi-ment has been able to unambiguously docu-ment neutrinoless double beta decay.

Because of immense interest in the topic, a range of new experiments, prototype detectors,and experiment proposals are under con-sideration. Some of these include the EnrichedXenon Observatory (EXO), the CryogenicUnderground Observatory for Rare Events(CUORE), the Molybdenum Observatory ofNeutrinos (MOON), and the Majorana experiment.

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Sea Level

Salado Formation

Rustler Formation

Dewey Lake Redbeds

Surficial Sand

“Observing this type of decay would be aClass I discovery, the highest goal achievable,”says Stanford University physicist and EXOproject leader Giorgio Gratta. “It would be an important step toward understanding naturein general.”

The physics community at large agrees withGratta. In a 60-page report, The NeutrinoMatrix, published in November 2004, members ofthe American Physical Society (APS) Multi-Divisional Study on the Physics of Neutrinos out-lined the most compelling areas of study. Thereport placed a high priority on experiments toobserve neutrinoless double beta decay, statingthat it “is the only practical way to discover ifneutrinos are…a new form of matter.”

Gratta and his collaborators from StanfordUniversity, Stanford Linear Accelerator Center(SLAC), and eight other institutions believeEXO is a nearly ideal tool to see these elusivedecays. According to the APS report, com-bining the results of experiments similar to EXO offers the best strategy to answer many of theperplexing questions surrounding the neutrino.

Of particles and antiparticlesTheorist Paul A. M. Dirac predicted that everytype of fermion should have an antimatter partnerof equal mass but opposite electric charge.These particles with distinct antimatter counter-parts now carry his name. Neutrinos, whichconspicuously lack a charge, do not obviously

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EXO, an experiment designed to discover the nature of neutrinos, is buried deepbelow the New Mexico desert at the Department of Energy’s Waste Isolation Pilot Plant. The experiment is protected from external sources of radiation by largesalt beds in the geologic strata.

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nor necessarily fit this pattern in the same wayas quarks and other Dirac particles.

Assuming that neutrinos and antineutrinosare distinct particles, experiments have seenboth of them where expected: antineutrinos indecays that also produce electrons, and neutri-nos in decays that also produce positrons.

However, the lack of charge allows for the pos-sibility that an antineutrino is the same particle as the neutrino. Italian theorist Ettore Majoranaproposed this idea, and the phenomenon of a particle being identical to its antiparticle isnamed after him.

The discovery of neutrino mass has pushedthe issue to center stage. In order to reconcilemassive neutrinos with the Standard Model,theorists must first know whether neutrinos areDirac or Majorana in nature.

The easiest approach to this problem is tolook for neutrinoless double beta decay. A formof nuclear decay that occurs rarely at best, it can only happen if neutrinos are Majorana innature. But as Gratta says, “even if neutrinosare massive and Majorana, we might not see double beta decay happen too often. It’s a lot like looking for a needle in a haystack.”

Standard double beta decay, in which twoantineutrinos are released from the decayingnucleus, has already been observed. In this pro-cess, two neutrons convert to protons, releasingtwo electrons in addition to the two antineutri-nos. Experiments can detect the electrons whilethe antineutrinos escape without leaving a trace.

Neutrinoless decay is a different matter.Single beta decay can occur with either theemission of an antineutrino or the absorption ofa neutrino. If neutrinos are Majorana, an anti-neutrino is the same as a neutrino. Hence the antineutrino emitted in one beta decay canbe absorbed as a neutrino by the second one, resulting in neutrinoless double beta decay (see figure).

In this case, only two electrons will be re-leased, and they carry as much energy as the

four particles emitted in standard double betadecay. As a result, the two electrons emitted inthe neutrinoless decay have slightly more energythan the two electrons in the standard decay.

“The only experimentally measurable differ-ence between two-neutrino decay and zero-neutrino decay is the energy of those electrons,”says EXO project scientist Martin Breidenbachof SLAC. “We must measure this energy differ-ence with good resolution. There’s no other way.”

If EXO observes neutrinoless double betadecay, physicists will have a strong case toargue that neutrinos are their own antiparticles.And they’ll be well on their way to answering a second key question: what are the neutrinos’masses?

Weighing the unweighable“There are experiments that limit how large theneutrino mass is,” says EXO project scientistCharles Prescott, also at SLAC. But below thispoint, it’s anyone’s guess what the actual massis. “It’s open territory. EXO is a true experiment.We don’t know what to expect.”

Results from past experiments suggest theneutrinos’ masses are tiny. At such small massscales, scientists prefer to express mass in unitsof energy. The upper limit on neutrino mass that Prescott refers to is around one electronvolt(1 eV). This number is supported by acceleratorexperiments, data on supernovae, and other linesof evidence, he says.

Neutrino oscillation experiments have madesome progress toward understanding the differ-ences in mass between pairs of neutrinos.However, absolute mass values remain elusive.For example, the lightest neutrino could have a mass almost anywhere between exactly zeroand the 1 eV ceiling.

Experiments like EXO can explore massranges below 1 eV, either by discovering theabsolute mass scale if neutrinoless double betadecay is observed, or by pushing the upper limitof neutrino masses lower and lower if it isn’t. The key to success is the relationship betweenthe rate of neutrinoless decay and neutrinomass: If neutrinos are heavier, decays should beseen more often. Turning this around, rarerdecays mean lighter neutrinos.

EXO will look for neutrinoless double betadecay in heavy liquid xenon, starting with a rela-tively small, 200 kg detector capable of seeingdecays if they occur at a high rate. This prototypedetector, now in development, will be sensitive to masses as low as 100 meV (millielectronvolt).

“But if we see nothing, it doesn’t mean nothing is happening,” Gratta explains. “It might be thatwe need to build a larger detector.”

Left: Standard double beta decay. As the nucleus (N ) decays into a newnucleus (N’ ), two neutrons convert to protons, releasing two electrons(e- ) and two antineutrinos ( ν ). The decay energy is split between theelectrons and antineutrinos. Right: Neutrinoless double beta decay. Ifneutrinos and antineutrinos are Majorana, an antineutrino can be emittedfrom the first neutron (A), then absorbed as a neutrino by the second(B). Only the two electrons will be released, carrying all the decay energy.

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If the prototype fails to find neutrinolessdecays within three to five years, a larger, oneto ten ton detector can be used to probe down to 20 meV or lower. And if, after continuedefforts, no neutrinoless double beta decay isseen, physicists will have to consider that neu-trinos might not be Majorana, but Dirac, parti-cles. In that case, theories that attempt toexplain the extremely light mass of the neutrinosbased on their Majorana nature will need to beabandoned.

The search is onThe EXO prototype, due to begin operation inlate 2005, will use “enriched” xenon, consistingof 90 percent of the relatively rare isotope xenon-136, the only xenon isotope that could undergoneutrinoless decay.

Xenon offers advantages over other nucleisuch as germanium and tellurium, which arebeing used in other experiments. It is a noblegas, and therefore easy enough to purify andenrich, as long as suitable facilities are accessi-ble. To obtain enough enriched xenon for theprototype, the EXO collaboration relied on col-leagues at the University of Moscow.

“The infrastructure in the US is optimized foruranium separation,” Gratta explains. “TheRussian infrastructure is more generic andlends itself well to separating xenon.”

If neutrinoless double beta decay occurs in theEXO tank, it will cause a faint flash of light andleave behind an ion of barium-136. Both can beused as evidence that a decay has occurred.However, the prototype will detect only the flashof light; the challenge of identifying barium will beleft for a future upgrade. The EXO team hasalready made significant progress toward engi-neering a system to pluck the occasional singlebarium atom from a large tank of xenon.

The EXO team has another hurdle to jump.Any neutrino observatory must be buried deepunderground to avoid false signals from bom-bardment by cosmic rays. But going deep isn’tenough, since metals and minerals in the sur-rounding rock can also contain radiologicallyactive materials. For this reason, physicists lookfor subterranean areas where radiologicalinterference is low.

The EXO prototype will be installed deepbeneath the New Mexico desert at theDepartment of Energy’s Waste Isolation PilotPlant (WIPP). It may seem strange to install an experiment that hopes to escape radiationin a large nuclear waste repository. But thesalt walls of the facility provide shielding fromall sorts of radiation, including the waste in the adjoining chambers. In fact, according to

Breidenbach, “WIPP is one of the more radiolog-ically quiet places on Earth, as long as we’reupwind of the plutonium.”

But since EXO’s threshold of sensitivity is soincredibly low, the team has to protect itself froma seemingly unlikely source: background inter-ference can also come from the detector itself.

“The shielding and the materials surroundingthe detector have to be very pure, and free ofradiological contaminants like uranium, thorium,and potassium,” Prescott says.

Gratta likes to use a tangible example: “Thechair you’re sitting on is very radioactive on thescale that we care about.”

Despite such challenges, Gratta, Breidenbach,Prescott, and their collaborators are confidentthat EXO will work and is worth the effort.

The neutrino is shaking the Standard Modelto its foundations. Yet the secret identity of thismysterious little particle might help to lay thefirst bricks in a new edifice of particle physics.

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Schematic of the WIPP underground site, more than 600 meters underground. EXO will be separated from the waste disposal chambers by a wall of salt over 300 meters thick.

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The DOE’s WIPP nuclearwaste repository nearCarlsbad, NM. The EXO prototype will begin opera-tion here in late 2005.

VirtualStructure

Photos: Diana Rogers, SLAC

As the newly-appointed Director of the GlobalDesign Effort (GDE) for the proposedInternational Linear Collider (ILC), Barry Barishwill lead teams of scientists worldwide in theresearch and development projects advancingthe design of the next-generation discoverymachine in high-energy physics. But in doing so,no one will have to change addresses.

Barish will soon be extending invitations tojoin the GDE’s Central Management Team. Theteam will consist of an anticipated 15-20 FTEs(full-time equivalents) drawn from a total staffof perhaps twice that number—all working from their home laboratories. The GDE will bemodeled on the experiment collaborationapproach, with its work spread across the threeregions forming the basic ILC infrastructure:Asia, Europe and North America. Barish wantsthe best people, not just the best people whoare willing to relocate.

“I am collecting suggestions from the commu-nity, from the ILCSC [ILC Steering Committee],from the laboratory directors,” he says. “I am plan-ning to use that to form the core group for theGDE and then to round it out with other memberswith the missing skill needs. The talent in HEP is spread across the globe, and we must provideaccess and ways to enable participation for sci-entists from all countries.”

Barish chaired the ILC International TechnologyRecommendation Panel (ITRP), which recom-mended superconducting radiofrequency technol-ogy as the basis of the collider’s main linearaccelerator design. That recommendation wasendorsed by the International Committee forFuture Accelerators (ICFA) at a meeting in Beijingin August, 2004. The GDE appointment cameon March 18, 2005, during the Linear ColliderWorkshop at Stanford University. The choicewas announced by Jonathan Dorfan, Director ofStanford Linear Accelerator Center (SLAC) and chair of ICFA. Dorfan described Barish as

“one of the most respected personalities in particle physics.”

Barish immediately made communication atop priority. “As one moves further from personsworking in this area of physics,” he said, “Ibelieve we still have a big challenge to convinceour colleagues of the science case and thatthis machine should be built. The science argu-ments must be honed and the design and plan must be understood so that it can becomea common goal to fit this new facility into thelong range program for high-energy physics. I believe that the communications must involvea very proactive effort to provide information,keep the communities and policy makers informed,and make our case. This must be done on a scale beyond what we are accustomed to in HEP.”

Barish models International Linear Collider team on worldwide experiment collaborations.

by Mike Perricone

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The next steps in R&D, in Barish’s plan,involve agreeing on a baseline configuration forthe ILC. The first efforts will take place at theILC Snowmass (Colorado) conference in Augustand at follow-up meetings, with the goal ofdeveloping a Conceptual Design Report (CDR)before the end of 2005. Barish also hopes todefine a small set of candidate ILC sample sitesin the three regions during that time, enablingsite-dependent designs for the CDR—which hewants produced by the end of 2006. Barish seesthe longer-range R&D guided first by the CDR, and then by the Technical Design Report,which would come out 2-3 years later. There will also be a well-defined R&D program on alter-natives in design that could improve cost and performance, as well as R&D on the process ofbuilding the machine, stressing the importanceof technology transfer to industry.

In taking on the GDE role, Barish is resigninghis position at Caltech, where he is LindeProfessor of Physics and director of the LaserInterferometer Gravitational Wave Observatory(LIGO). He will report to the ILCSC, with hissalary supported through the Department ofEnergy, the same arrangement for otherAmerican scientists joining the team. His experi-ences on several US and international advisorycommittees tell Barish there is broad support forthe Linear Collider within the particle physicsfield. They also tell him there are concerns aboutcosts, and about the impact on the rest of thefield and on other areas of the physical sciences.As a result, Barish sees the need for a “delicatebalancing act over the next few years:” first, find-ing a robust and affordable design, withoutunduly affecting the rest of the field; then redi-recting the program to accommodate buildingthat machine.

It’s a challenge, but Barish says he sees theresources to meet it. “Clearly, there is a lot to do,”he says, “and I invite physicists of all persuasionsand all nations to join the ILC design effort.”

Global reach of ILC showsearly results

The distributive ILC infrastructure, stretch-ing through Asia, Europe, and the Americas,is demonstrating its effectiveness.

“There have already been two significantaccomplishments as an international body,” says Michael Witherell, Director of Fermilab and member of the US Linear ColliderSteering Group. “The main success was theappointment of the International TechnologyRecommendation Panel, which Barry Barishchaired. The second and most recent is theselection of Barry Barish to direct the GlobalDesign Effort. The search committee wasinternational in its makeup, and its recom-mendation was endorsed by the InternationalLinear Collider Steering Committee.”

The key Linear Collider groupsand their current chairs

International Committee for FutureAccelerators (ICFA)Chair: Jonathan Dorfan, Stanford LinearAccelerator Center

International Linear Collider SteeringCommittee (ILCSC)Chair: Maury Tigner, Cornell University

US Linear Collider Steering Group(USLCSG)Chair: Satoshi Ozaki, Brookhaven NationalLaboratory

Asian Committee for FutureAccelerators (ACFA)Chair: Dilip Devidas Bhawalkar, Centre forAdvanced Technology, India

European Committee for FutureAccelerators (ECFA)Chair: Brian Foster, Oxford University

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by Judy Jackson

How a quiet, unassuming laboratory in thenorthwest of England transformed itself into a powerhouse of accelerator physicsand technology.

Scotland

EnglandWales

Daresbury

Springtime at Daresbury

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Daresbury Laboratory lies in the green and pleas-

ant countryside of Cheshire, about a 40-minute

drive west from Manchester, not far from the Welsh

border. Lewis Carroll was born in Daresbury. The

Bridgewater Canal, the first canal built in England,

flows past the laboratory, and on a day in mid-

February, the daffodils were blooming. So was the

accelerator physics.

That was not always the case. Although Daresbury began life in 1962 asa high-energy physics laboratory, the 1972 decision of the UK govern-ment to pull back from building independent accelerators in Britain in favorof collaboration with Europe’s CERN and DESY laboratories quashed the laboratory’s plans to build a forefront superconducting proton machine.For years after that, Daresbury was a laboratory that knew its place. It was home to the world’s first dedicated synchrotron light source, theSRS, which began operating in 1980 and has chugged steadily along,with here and there an upgrade, for the last 25 years.

Daresbury is one of two laboratories in the United Kingdom that workon accelerator physics. Together with its sister laboratory, the RutherfordAppleton Laboratory in Oxfordshire, Daresbury is operated by the mouth-numbingly-named Council for the Central Laboratory of the ResearchCouncils. The CCLRC and the Particle Physics and Astronomy ResearchCouncil (PPARC) are the funding agencies that support the majority ofthe United Kingdom’s high-energy physics and related research.

In the 1990s, Daresbury scientists began work on the design for a pro-posed new third-generation synchrotron light source, Diamond, in theconfident expectation that, if approved, it would be built at Daresbury, toreplace the aging SRS and ensure a predictable light-source future forthe laboratory. Imagine Daresbury’s surprise on awakening one morningin March 2000 to find that the UK government had agreed to fund theconstruction of Diamond—at Rutherford. Suddenly, Daresbury’s future didn’tlook so predictable. Some believed the laboratory would close.

In fact, the decision to build Diamond at Rutherford was the spark forDaresbury’s reinvention of itself as a laboratory at the forefront of accel-erator technology, said Daresbury accelerator physicist Susan Smith.

“We were shocked,” Smith said. “We had never considered that Diamondwould be built anywhere but here. Looking back, though, it was probablythe best thing that could have happened. Before the Diamond decision,everybody took us for granted, including ourselves. Then, overnight, allthat changed.”

The Bridgewater Canal, thefirst canal built in England,flows past DaresburyLaboratory, whose signaturetower, once used for nuclear physics experi-ments, now houses R&D fora fourth-generation lightsource now under develop-ment at the laboratory.Photo: Daresbury Laboratory

The Diamond light sourcenow under construction inOxfordshire. The main build-ing is due to be completedin fall 2005, with the start ofoperation planned for early2007. Photo: Diamond LightSource Ltd

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Straight to the fourth generationThe surprise decision to send Diamond toRutherford Appleton outraged local universities,Members of Parliament, and regional govern-ment in the United Kingdom’s north-west.Outrage soon turned to action, spurring anintense campaign to preserve and strengthenaccelerator science in the region. LancasterUniversity and the Universities of Liverpool andManchester joined forces with the NorthwestRegional Development Agency and Daresburynot only to save the laboratory but to make the area a center of excellence in acceleratorphysics and technology.

Results followed quickly. By December 2001,Daresbury scientists had submitted a proposal for 4GLS, a fourth-generation energy-recovery,free-electron, up-to-the-nanosecond laserlight source to be designed at Daresbury, forDaresbury. Elaine Seddon is manager for the 4GLS project.

“Diamond was not a cutting edge machine,”Seddon said. “The 4GLS design is truly revolu-tionary. When it is built, the 4GLS will be the most advanced light source in the world.”

Currently, 4GLS is moving steadily ahead. A prototype of the project’s energy-recovery linearaccelerator is under construction in Daresbury’slandmark Nuclear Structure Facility, a 230-foottower mothballed since 1993, when the labora-tory’s nuclear physics program shut down. TheUnited Kingdom’s most recent science budgetprovides enough additional funding over the next two years, says Seddon, to allow the groupto solve the remaining technical challenges.Scientists plan to seek final approval for 4GLSin late 2006 and hope to start construction in 2007.

The 4GLS effort has brought Daresburyrecognition from throughout the acceleratorcommunity.

“Diamond went to Rutherford,” said accelera-tor physicist Shane Koscielniak, of Canada’sTRIUMF nuclear physics laboratory. “Daresburyscientists were forced to think further over

the horizon, and now they’re prototyping com-ponents for a fourth-generation source. They’reable to profit from all the R&D they have donefor other proposed accelerators, and that’s a smart plan. They are the right team for thisproject.”

New life for accelerator scienceA cutting-edge light source was not the onlynew trick up Daresbury’s sleeve. The labora-tory’s historic capabilities in accelerator physicsand technology, long devoted mainly to the care and feeding of the SRS, now came to newlife. The timing was right.

“Accelerator science and technology had been undervalued for a long time,” said MichaelPoole, director of Daresbury’s AcceleratorScience and Technology Centre, ASTeC. “Butbeginning in 2000, PPARC and CCLRC re-cognized the value of building an academicbase in accelerator physics in order to position the United Kingdom to win major shares in the construction of future particle physics facili-ties wherever they are built in the world.”

The creation of ASTeC by CCLRC in 2001,with its two sites at Daresbury and RutherfordAppleton, was a clear indication of resurgencein accelerator R&D. Today Daresbury’s ASTeCgroup is a hotbed of accelerator physics andtechnology, with R&D in accelerator physics,beams, insertion devices and magnets, vacuumscience, and radio frequency technology—thebedrock technologies of particle acceleration.The staff of 40 physicists and engineers is atwork on key areas of accelerator physics for theInternational Linear Collider and other high-profile global accelerator efforts.

Last year, PPARC announced the creationand funding of a new university center forAccelerator Science and Technology—theCockcroft Institute, named for Nobel laureateSir John Cockcroft, a son of the north-west and a founding father of accelerator research.A joint venture of Lancaster University, theUniversities of Liverpool and Manchester,CCLRC, PPARC, and the Northwest Regional

Daresbury scientist Elaine Seddon, leader of the4GLS energy-recovery free electron laser light sourceproject at Daresbury. Right: 4GLS logo.

Photo: Daresbury Laboratory

“When it is built, the 4GLS will be the most advanced light source in the world.”

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Development Agency, the Cockcroft Institutewill have a staff of 40 and will be built atDaresbury on land owned by the DevelopmentAgency.

“Together with the new John Adams Institutebased at the University of Oxford and RoyalHolloway, University of London,” said physicistKen Peach, recently appointed director of theJohn Adams Institute for Accelerator Science,“the aim of the new center is to allow the part-ner universities to expand their expertise in thisfield, working closely with ASTeC to create a world-leading accelerator science capability inthe UK at both the Daresbury and RutherfordAppleton sites.”

The plan appears to be working. Daresburyscientists are making their mark on acceleratorscience, winning recognition from collaboratorsand colleagues worldwide. Physicist TorRaubenheimer is leader of the ILC design teamat Stanford Linear Accelerator Center.

“It is great working with the Daresbury group,”Raubenheimer said recently. “They are activelyinvolved in the design of the ILC beam deliverysystem. They are one of the groups working on the layout of the small crossing angle inter-action region, the performance of the beam collimation system, and the design of the ‘crabcavities’ that would be used to rotate the particlebunches just before collision so that they fullyoverlap. It is fascinating accelerator technologyand an example of the worldwide collaborationthat is making real progress on ILC design.”

As the season advances in Daresbury, thedaffodils may have faded but the acceleratorphysics continues to flower.

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Women at Daresbury

In every area of particle physics, from theory toexperiment, men outnumber women. And when itcomes to the physics and technology of the accel-erators themselves, the demographics are evenmore lopsided. There is never a line for the ladies’room at an accelerator physics workshop.

So what is going on with Daresbury Laboratory’sAccelerator Physics Group, where a third of thescientists, including the group leader, Susan Smith,are women? Daresbury scientists themselvesseem somewhat at a loss to explain.

“The presence of so many women acceleratorscientists at Daresbury is not the result of anydeliberate policy,” said Michael Poole, ASTeC direc-tor. “Hopefully it is the reflection of an attitude that there is no difference in professional capabil-ity if we put prejudices aside.”

Some credit Smith’s 20-year leadership roleand strong personality with making Daresbury afemale-friendly environment. Others cite theabsence of an “old boy” hiring network in acceler-ator science; the laboratory’s willingness to hireaccelerator scientists with nontraditional aca-demic backgrounds; and the fact that acceleratorscientists are sometimes hired at a less seniorgrade than other scientists, attracting younger, lessestablished applicants, including women.

“Accelerator physics is not part of the embed-ded academic culture,” Smith said, “which maymake it more flexible and open to women. RecentUK science funding has made high-energyphysics a high priority, so professional opportuni-ties are there.”

Whatever the reason, women are playing majorroles in Daresbury’s accelerator physics renaissance.

Michael Poole, Susan Smith (middle)and Deepa Angal-Kalinin with a part ofthe beam transport system for theenergy-recovery linac prototype project(ERLP).

Photo: Daresbury Laboratory

gallery: chris henschke

HyperCollider In 1905, Albert Einstein published his Special Theory of Relativity andoverthrew the notions of absolute space and time. His later General

Theory of Relativity was so revolutionary that even he had trouble accepting its full implications.HyperCollider explores the extremes of relativity and how they disturbed Einstein’s own cosmo-

logical philosophy of a balanced, logical, and eternal universe. It also plays with the unease thatexists between the macroscopic worlds of relativity and the ultramicroscopic quantum universe,and the difficulties Einstein had with his colleagues’ theories on quantum mechanics and its

“uncertain” implications.

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Text and art by Chris Henschke

Explore HyperCollider online at www.symmetrymagazine.org

Smolin Multiverse Vortex, 2004 (detail). This image is inspired by Lee Smolin’s theory thatwithin each black hole a new universe is born, each with its own laws of physics, creating a “multiverse” of cosmoses that evolve toward optimum black hole production.

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HyperCollider exhibited in a former convent infirmary converted into a gallery space, Daylesford(Victoria, Australia), November 2004.

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Top left: “Particle View,” showing “Tone-arm,” “Action Bumpers” (with diagrams of classical versusrelativistic space-time), and gravity well. Top right: Interface of the online version.

HyperCollider, top view showing the “Geometrodynamic Vortex,” “Observer Time” clock, “ParticleTime” counter (measured in Planck time units), and particle-launching “Accelerator Ring.”

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A collage of Einstein’s relativity papers, handwritten notes, pressure graphs, and star charts is com-bined with a computer display running a simulation within a remade 1920s German pinball machine to make the HyperCollider exhibit. A hybrid of pinball game, gramophone player, and “particle accel-erator,” HyperCollider lets players launch various matter particles into a “theoretical universe.” Theparticles collide with each other and get pulled into a black hole, which displays spatial contractionand temporal dilation effects. By bouncing particles into the black hole, players can move throughtime into an increasingly uncertain future, accompanied by a “pop-science-pop-music” soundtrack.

The project was created during Chris Henschke’s time as the inaugural “online artist-in-residence”with the National Gallery of Australia in 2004 and was supported by the Film Victoria Digital MediaFund. HyperCollider is currently touring Australia and will be exhibited internationally in 2006. Visitwww.topologies.com.au for details.

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deconstruction: soudan mural

This mural in the Soudan Underground Laboratory, located inMinnesota half a mile underground, was designed by

artist Joseph Giannetti. Its theme is matter and energy, and—more specifi-cally—neutrino physics. The mural is in the same cavern as the MINOS experi-ment, which in March began to record neutrinos sent to the mine straightthrough the Earth from Fermilab in Illinois—no tunnel needed.

“When I started to create this image, I was feeling something about energy,something about universal language, something that was abstract and yet soclear,” says Giannetti. He views the image as a graphic representation of energyas it changes from one form to another. “Accepting that all things are inmotion—you, me, the world, the universe—from the subatomic level to the uni-versal level, there is then only one constant: change. If one person sees thismural, and it changes the way he or she looks at the world, if it makes achange in their life for the better, I would consider this painting to be a ravingsuccess.”

The mural, 59 feet wide and 25 feet tall, highlights the history of neutrinophysics, particle symbols and interactions, the connection of the mine toFermilab, and the contributions of neutrino experiments at other mines. Thebackground of the mural was inspired by an image of the Carina Nebula.

The mural is next to the 6000-tonMINOS detector.

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51. Physicist Enrico Fermi,originator of the name“neutrino” (“little neutralone”)

2. Austrian theoristWolfgang Pauli, originator of the con-cept of the neutrino

3. Fred Reines and ClydeCowan, the first scien-tists to experimentallyidentify neutrinos

4. Ray Davis, the first per-son to observe neutri-nos from the sun usingtanks with dry-cleaningfluid in South Dakota’sHomestake gold mine

5. The headframe locatedat the top of the Soudanmine shaft

6. Bats at the Soudan lab(the face of the artist is hidden in the bat atthe bottom)

7. Wilson Hall at FermiNational AcceleratorLaboratory, Batavia,Illinois

8. The Linear Acceleratorat Fermilab

9. Neutrino interactiondetected in the historicSoudan 2 experiment(sited in a cavern adja-cent to MINOS)

10. Representation of aneutrino interactioncausing tracks in thescintillator strips of the MINOS detector

11. Rings of light created by neutrino interactionsin Japan’s Super-Kamiokande detector

12. The MACRO experi-ment at the Gran Sasso laboratory in Italy

13. Fish-eye image of theinterior of the SudburyNeutrino Observatory(SNO) in Ontario,Canada

14. Light produced by acosmic-ray muon in the SNO detector

15. Minnesota Departmentof Natural Resources,which offers tours of themine.

Mural artists: JosephGiannetti, Leila Giannetti, Mick Pulsifer. Funded by a grant from the University of Minnesota.

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essay: aaron freeman

My inner particleA lot of us physics groupies look to quantumphysics as the coolest theory. We believe the physicists who say classical ideas don’t cutit when you go nuclear. We get that quantumstuff is so weird the only way you can convinceanyone you’ve really studied it is to endlesslyrepeat, “I don’t know.” We, the civilians, acceptthat a rock is really a cloud composed mostly of empty space and sprinkles of tiny particles.

But what exactly are we supposed to dowith the knowledge that everything we knowfrom everyday life is different at the subatomiclevel? How should evidence of extra six orseven dimensions inform our days? Where inmy head and worldview am I supposed to putantimatter?

I want to get in touch with my inner particleand let it point the way.

Particle logic—mysterious, counterintuitive,seemingly insane—pretty much describes life asI live it. And since we are so mind-numbinglysmall compared to the rest of the universe itmakes sense to me to think of individuals as particles.

I want to reason like an electron, to be allover any task from every direction at once. Iwant to philosophize like a meson, yin and yang,opposites contained in a unified whole. I want to dream like a neutrino, limitless, unstoppable.

As individuals we display a kind of wave-particle duality. While the positions of our bodiesare measurable with a high degree of accuracy at any given time our images—audio, video andphotographic—spread out around the world via the Internet, existing everywhere at once. Formillions of people appearing on TV, broadcast television images spread out, wave-like, acrossthe galaxy in all directions at the speed of light.

Like quarks we are attracted to one anotherby a strong force: love. We are kept within oursocial shells by weaker but still potent bonds ofcommerce and culture. Geography attracts us,like gravity, in ways that are destiny-producingacross the vastness of time. Civilizations rearedamid bountiful and fertile soil are destined forone kind of history. Peoples arising on land that

happens to contain oil will chase another fate.But like gravity acting on a gluon, the effect of geography on individuals is difficult to measure.

Race is an artificial and misleading socialconstruct. My skin is not actually black nor is my wife’s genuinely white. Physics might helpus categorize populations more usefully. Maybewe’d be well served by a Standard Model ofParticle Humans. Top humans, for example, arethe leaders of the industrial west. They’re certainlymassive in terms of their ability to warp globalresources. Tops are produced by powerful col-lisions and often decay quickly. Bottom humanswould be the other ninety-nine percent of us.

Charm humans include athletes, politicians,performers—folks who make us believe. Thestrange ones are artists, academics and scien-tists—those who sit alone pursuing queer gods.

Folks in uniforms and guns certainly are the equivalent of force carriers. Though we mayhave to check whether some cops are morebozos than bosons.

My late father and sister have gone off tojoin our ancestors among the neutrinos. It’sunlikely that I will see them again in the visibleparticle world.

We humans are perhaps most particle-like in our slavish submission to the principle ofuncertainty. Everyone who’s ever sat down towrite a letter knows you can form in your mindprecisely what you want to say, yet still be sur-prised by what you ultimately write. Uncertaintyis what makes every day an adventure.

I believe accessing my inner particle willhelp me deal with the uncertainty of my life. Myinner particle does not know how the worldshould be and is thus untroubled by how it is. It desires neither certainty nor comprehension.Thus my inner particle is far wiser than I.

Perhaps my inner particle will grant insightsinto all manner of human phenomena. Maybe I’ll be a faster cyclist by embracing my photonself. Maybe I’ll start to see the womb as ahuman Higgs field wherein eggs, like particles,acquire mass.

Then again, if the string theorists are right,maybe all I’ll get from my inner particle are somegood vibrations.

Aaron Freeman is a journalist, stand-up comedian and sought-after humorous speaker. He frequently performs with thefamed Second City Theater, and his commentaries have beenbroadcast on National Public Radio and Chicago PublicRadio. His second comedy CD Confessions of a Hebro willsoon be released.

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logbook: solar neutrinos

Deepin the Homestake Gold Mine in Lead, SouthDakota, during the early 1970s, Ray Davis

monitored a 100,000-gallon tank of perchloroethylene, a chlorine-rich dry-cleaning chemical. The experimentwas designed to detect solar neutrinos, using the theorythat an incoming neutrino would produce radioactiveargon by interacting with a chlorine nucleus.

Davis was successful, but detected just one-third of the expected number. This “solar neutrino puzzle”inspired a series of experiments that eventually confirmedneutrinos change flavors. For his work, Davis won the2002 Nobel Prize in Physics.

This page from his notebook captures a piece of thatwork. Davis discusses the “tank cars”—500-gallon tanksmounted on rail cars—used to measure the production rateof one type of background particle, neutrons, at differentdepths of the mine. The tanks (he sketched one in the lower left) contained a solution of calcium nitrate, a common fertilizer. The results helped Davis determinethe cosmic ray background in the 100,000-gallon tank. Laura Mgrdichian, Brookhaven NationalLaboratory

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explain it in 60 seconds

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

Office of ScienceU.S. Department of Energy

Neutrino MixingWaves describesome of the most

extraordinary phenomena in the world. Waves can besimple–the sound of a flute playing a sustained, singlenote–or they can be complicated mixtures–a musicalchord, for example, which is a combination of many soundwaves. Combining two waves of similar tones produceswhat physicists call beats. Listen to two flutes playing thesame note, one flute slightly mistuned. You’ll hear a

“wah-wah-wah” effect as the sound comes and goes, be-cause the sound that you hear is a mixture of theslightly different waves from the flutes interfering witheach other.

Waves also govern the character of neutrinos as theyfly through space. Interference between the waves produces regular beats, much like the combined notesof the flutes. We detect the resulting “wah-wah-wah” in properties of the neutrino that appear and disappear.For example, when neutrinos interact with matter theyproduce specific kinds of other particles. Catch the neu-trino at one moment, and it will interact to produce anelectron. A moment later, it might interact to produce adifferent particle. “Neutrino mixing” describes the originalmixture of waves that produces this oscillation effect.Janet Conrad, Columbia University