Volume 21 Friday, May 15, 1998 Number 10 - fnal.gov

Volume 21 Friday, May 15, 1998 Number 10

Good ν‘sNews from studies of solar

neutrinos and neutrinos incosmic rays points to a strong

suggestion— some may even say aconclusion—that neutrinos oscillatefrom one flavor to another and thushave mass. Would such a discoverybring the study of fundamentalproperties of neutrinos to a close?On the contrary, much as Watsonand Crick’s deciphering of the DNAmolecule closed a chapter in geneticcoding but opened a book inmolecular biology, this discoverycould mark the beginning of thegolden age of neutrino physics.

fINSIDE

2 Booster Shielding

4 Missing Energy

5 Shadow

6 Dirac Monopoles

8 Wetlands

10 Neutrinos

In a story on page 10,physicist StanleyWojcicki, spokesmanfor the MINOSexperiment, surveysthe field of neutrinophysics and the roleof MINOS in thecontext of worldwideneutrino experiments.

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By Mike Perricone, Office of Public Affairs

P reparing for the worst on his inspectiontour, Dixon Bogert laced up hisworkboots. Over them, he pulled

on mud-crusted rubber boots that buckled up to near his knees.

“There’s mud, and then there’s mud,” he said, setting off past thick rolls of blueprintsrubber-banded into close formation near thedoor of his office.

All those precise drawings translate intodigging in the mud below one of the twoBooster towers. Wearing one of his many BeamsDivision hard-hats, Bogert directs this intricateproject to slip 1,450 tons of steel underneath abuilding whose support has been transferred toa series of piles that have been sunk nearly 70feet beneath the surface to reach bedrock.

The tower (incongruously, just two storieshigh) follows the curve above a segment of theBooster, the 475-meter ring that accelerates or“boosts” the energy of protons from 400million electron volts (400 MeV) to eightbillion electron volts (8 GeV).

In the old days, protons were extractedfrom the east side of Booster (as it’s called bythose closest to it) and transferred by an 8 GeVline to the now-defunct Main Ring. For Run II,protons will be extracted from a new point inBooster’s northwest quadrant and transferred by a newly-constructed 8 GeV line to the Main Injector.

At the extraction point, protons get a jolt ofenergy from a kicker magnet, and jump across ametal gateway called a septum, into the 8 GeVline. Even the most accurate and efficienttransfer will produce low-level radiation losses.

The old extraction point was under theshielding of an earthen berm. The new point isdirectly beneath a corner of the continually-occupied tower. With increased demands fromthe Tevatron and Main Injector, Booster will besending more pulses through the 8 GeV line,meaning more total losses even with the rate of loss remaining constant.

“Laboratory rules in general try to keepradiation exposures well below Department ofEnergy and legal standards,” Bogert said. “TheLab set its goal as not exceeding 100 milliremsper year based on continual loss. If you dividethat by the number of working-hours in a year,we should not be exceeding 50 microrems perhour—that’s fifty one-millionths of a rem. Lastspring, when we began to extract beam fromBooster and run it to the temporary abort inthe middle of the new 8 GeV line...wediscovered that, indeed, we exceeded 50microrems.”

An average person who never goes near anaccelerator can expect to absorb approximately360 millirems a year (3.6 times the Lab’s self-imposed limit) from the sun, soil, buildings,dental x-rays, smoke detectors and other facetsof 20th-century life.

If the towers hadn’t been added in the1980s, the original earthen berms probablywould have offered sufficient shielding. But thebuildings are there to stay. And the top of theBooster tunnel is only 12-14 feet below thesurface, compared to 22 feet for the Tevatrontunnel and 24.5 feet for the Main Injectortunnel (the 2.5-foot increase is a consequence ofthe greater expectation for beam intensity in theMain Injector than from the Main Ring). Theclearance between the tunnel and the Boostertower is akin to that of a crawl space in construction terms.

Inserting the shielding also means someconnections to Booster must be reroutedaround the steel, forming an s-shape instead of a

Booster Digs In For AnotherWorkhorse Role In Run II

Not your ordinaryconstruction site, thetwo-story tower sitsabove the BoosterRing, which will takeon a new profile aspart of Run II.

Below the building, 1,450 tons of steel will be inserted as shielding.

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FermiNews May 15, 1998 3

straight line. Offices have been closed in areasabove the construction site. Two electricaltransformers were removed and their precisely-aligned concrete pads ripped out; electricalservice to the building was maintained througha temporary parallel system. A restraining, orsecant, wall had to be added to keep thebuilding from sliding into the excavation.

“This is not just a simple project,” Bogert said.

Nor is it a cheap one, beginning with a$1.25 million construction contract. Includingdesign work, electrical work, and the cost ofsteel, Bogert estimates the price as more than$2 million.

Whitaker Excavating of Earlville, Ill., ishandling the digging, concurrently with projectsat CZero and FZero. TCDI of Lincolnshire, Ill.,brings the expertise for the project’s signaturecomponent: drilling down to bedrock, sinking14 steel piles, building bridges between thepiles, and permanently transferring the load of the building onto those bridges and piles.The piles are three concentric tubes, from 7.5 to 10 inches in diameter, designed to preventshallow groundwater from leaking into the subterranean aquifer. Among TCDI’scredentials is constructing a new roof over the old roof during renovations to Chicago’srenowned Orchestra Hall.

With the Booster tower supportedpermanently on its stilts, the earth will beexcavated between the building and tunnel; thetunnel also is being reinforced to carry extrashielding. Steel slabs are being collected in aparking lot near the Meson Assembly Building,some reclaimed from old experiments, andabout 650 tons of what Bogert calls “boat-anchor steel” purchased at bargain prices fromUS Steel in Gary, Indiana. The slabs will have tobe trimmed, numbered and fitted together inshapes conforming to Booster’s configuration.

Workers deal with mudat every stage of theBooster shieldingproject. The building’sbeam supports will becarried on “stilts” thatare sunk down tobedrock.

A run-of-the-mill slab is nine inches thick andweighs 18-20 tons.

The schedule calls for the first steel slabs tobe slid into place early in July. The earth willthen be filled in and brought back up to grade.The concrete transformer pads will be pouredand cured, then the transformers will bereplaced and full power restored so Booster canbe turned on—the primary milestone.

All this by mid-August, when the schedulecalls for Booster to begin “off-hours” operation,with full-time running slated for mid-September. This is the critical path forcirculating beam in the Main Injector, whichcan’t be commissioned unless Booster providesbeam. The old workhorse of Lab acceleratorswill have to meet new demands.

“And this old workhorse has gotten olderin the past 30 years,” said Bob Webber ofBeams Division.

For Run II of the Tevatron, Booster willproduce slightly less than one pulse of protonsper second; for NuMI (Neutrinos at the MainInjector), it will produce three pulses persecond. The MiniBooNE (Mini BoosterNeutrino Experiment) proposal has requestedseven to eight pulses per second. The numberof protons per pulse expected from Booster willrise by 20 to 25 percent, from about 4.2x1012

protons per pulse, to 5x1012 protons per pulse.A longer term goal will be to raise that numbereven higher.

“Historically, Linac (the linear accelerator)and Booster have had a fairly low profile in theLab as a whole,” said Webber. “They did whatthey needed to do and people kept themrunning smoothly. Now they’re being asked to do new things, and that’s going to raise the profile of these machines in the Lab’slandscape.”

Booster’s new profile will brandish its mudstains as a badge of honor. ■

Information on the Boosteris available athttp://www—bd.fnal.gov/proton/booster/booster.html

May1998

June1998

July1998

August1998

September1998

October1998

November1998

December1998

Booster

Main Injector

Recycler

Accumulator

Tevatron

ACCELERATOR SCHEDULE 1998

Civil Construction Start-Up & Beam to Main Injector

Ready For Beam (7/31) CommissioningIntermittentCommissioning

IntermittentCommissioning

ShutDown

VacuumBakeout

InstallDebuncher

Cooling

Ready For Beam (8/22) Proton Commissioning

Intermittent Commissioning

Ready For Beam (10/15)

Shut Down


critical density problem will be profound. The missing component of the critical densitywill have to exhibit a property called “negativepressure” that tends to push the universe apart,rather than pulling it together.

In his opening talk, Turner summed up thestate of the field at the moment.

“Current observations tell us that most ofthe universe is funny energy whose pressure isnegative, and little more.”

Candidates for Turner’s “funny energy,”the missing two thirds of the critical energydensity, include the cosmological constant, abackground energy density, first proposed byEinstein, that remains the same over space andtime. Or it could come from something moredynamical that changes and interacts withmatter as it evolves.

“Matter is the stuff in the universe thatclumps,” explained University ofChicago/Fermilab astrophysicist Josh Friemanto a group of science journalists over lunch. “To distinguish the missing energy from theclumpy stuff, we talk about a smoothcomponent. The smooth stuff could be thecosmological constant, that is an energy thatremains the same. Or there could be somethingelse that is not constant but changes over spaceand time. It could have a negative pressure thatwould cause the universe to accelerate. Evidenceis building for a smooth component withnegative pressure. An accelerating universe is a smoking gun for a smooth component.”

And why, asked a reporter, do we care?After a rare moment of stunned silence

among the assembled experts, University ofPennsylvania cosmologist Paul Steinhardt gave a response to gladden a physicist’s heart.

“This is a monumental issue,” Steinhardtsaid. “Understanding it is important forunderstanding the fundamental laws of physics,whatever form it takes.” ■

By Judy Jackson, Office of Public Affairs

For the universe, density is destiny. Thevery shape the universe takes depends onthe amount of “stuff” it contains, in the

form of matter and energy. A universecontaining more than a certain critical energydensity would curve positively, like the surfaceof a baseball. A universe with less than thecritical amount would curve negatively, like theseat of a saddle. But a universe with neithermore nor less than the critical density of matterand energy would be geometrically flat.

Many cosmologists, including several atFermilab, are not shy about predicting which ofthese shapes will prove correct.

“We live in a flat universe,” said Universityof Chicago/Fermilab cosmologist MichaelTurner, during a recent workshop organized byFermilab’s Theoretical Astrophysics Group on“The Missing Energy of the Universe,” held atFermilab May 1-3. Turner was among severaldozen cosmologists gathered to try to makesense of an influx of astrophysical datasuggesting that something funny is going on in the universe.

In particular, the cosmological books don’t balance. Adding up all the matter, bothluminous and dark, in the universe yields onlyabout a third of the critical density required toflatten the universe. If the universe is indeed flat— it might not be, but persuasive theoreticalmodels and some experimental evidence suggestthat it is—then something must be making upthe other two-thirds of the critical density. That“something” is the so-called missing energy thatdrew cosmologists, astrophysicists, particlephysicists and science journalists to Fermilab, ifnot to find it, at least to explore the most likelyplaces to look.

Among workshop participants weremembers of two research teams that recentlypresented startling evidence that the expansionof the universe is not only not slowing down, aseveryone thought it should, but in fact appearsto be speeding up. If they prove right and theuniverse really is accelerating, the effect on the

Cosmologist ScottDodelson of theFermilab TheoreticalAstrophysics Group,which organized themissing EnergyWorkshop. “The natureof the missing energy inthe universe hasprofound implicationsfor particle physics,”Dodelson said.

Department of (Missing) EnergyMuch of the energy of the universe is unaccounted for.It must be around here somewhere, cosmologists say.

MISSINGENERGYIN THE

UNIVERSE

CURIA II2nd Floor

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Information on MissingEnergy is available athttp://www.physics.upenn.edu/~www/astro-cosmo/caldwell/workshop/index.html


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By Kurt Fenner, Batavia Middle School

M y day at Fermilab was very exciting,but also rather exhausting. I had toget up at 6:30 a.m. to get there by

8:30. Just getting there was exciting. The firstthing that happened was that I saw a group ofgeese; but when we drove by, one bent theantenna on my mom’s car.

Well, we finally got to the Public AffairsOffice, where I met the scientist I wouldshadow, Peter Mazur. From there, we went toDr. Mazur’s office. We had nothing to do until9:00. It was 8:30, so he explained many thingsto me. First, he explained what our basicschedule would be for the day. Then he toldme how all the gadgets in his office worked andwhy he got them. They were all really neat.

Then, finally it was 9:00, and it was timefor the first experiment. We had to test somewater that they deionized. This distilled waterwas more distilled than the distilled water thatyou buy in the store. What they did was takesome of the water and placed it in differentnutrients to see if any bacteria grew. Wefinished that, and then went back to the officeand Dr. Mazur made some phone calls.

By 10:00 we went into the acceleratortunnel and looked at the stainless steel pipes.See, most people think that if you have stainlesssteel pipes no bacteria will do any harm, butthey are wrong. The bacteria that grew actuallyate through the pipes and there were leaks. Sothey rewelded the pipes, and cleaned them outwith a new invention. It was a bunch ofsandpaper attached to a spinning device toclean the pipes. This was so that, hopefully, nomore bacteria would grow.

When we finished that we went into theindustrial area and looked at all the differentmagnets they had. One even weighed 50 tons!We saw how they looked and then saw theliquid helium tester they were building. Then at11:30, we went back to the office. There wasreally nothing to do until 12:15 when westarted to walk to lunch. (That is how we gotour exercise.) We met up with other physicists

and an engineer and ate lunch. It was providedby Fermilab. Then at about 1:15, after lunch,we started to walk to a meeting. When we gotthere, they talked about how their water tankswere working. I didn’t really understand, andafter lunch I was tired, so I almost fell asleep,but I didn’t.

Finally, the meeting was over and welooked at the water tanks. By then it was 3:30,and the day was almost over, so we took a tourof the main building. We went to the top floorand could actually see the top of the SearsTower and John Hancock building. When itwas 4:30, we went to the administration officeand met my mom. We said our good-byes andleft. I couldn’t believe it was over so soon.Someday I hope to go back and actually have a good understanding of what they are talking about. ■

Fermilab physicist PeterMazur and eighth-grader Kurt Fennerdiscuss installation ofcomponents ofFermilab’s new MainInjector accelerator.

The Shadow KnowsHow does a Fermilab physicist spend the day?

Eighth-grader Kurt Fenner, an aspiring physicist, describes the day he spentshadowing Peter Mazur, a physicist in Fermilab’s Technical Division

By Greg Landsberg, DZero

P eople have known about electricity andmagnetism for centuries. The ancientGreeks noted that pieces of amber, when

rubbed, would attract light objects. The word‘electricity’ comes from the Greek word foramber: “elektron.”

In time, observers found that there are twotypes of electric charge, (Benjamin Franklinnamed them positive and negative) and thatopposite charges attract. In the twentiethcentury Robert Millikan showed that theelectric charge is quantized: all electric chargesare multiples of the elementary electric chargefound on the electron.

The ancient Greeks also knew aboutmagnetism. They saw that certain mineralsattracted iron and other pieces of the samemineral. About a thousand years ago, theChinese noticed that a magnetized needlealways points in the same direction and thuscould be used for navigation. However, unlikeelectric charges, which can be isolated,magnetic materials always have two “poles,”called north and south for the directions theypoint to on Earth. Break a compass needle intwo, and each will again have both north andsouth poles. It appears impossible to isolate asingle magnetic pole; only the combination ofnorth and south poles (a “dipole”) seems toexist. This absence of a single magnetic charge,or monopole, makes the laws of electricity andmagnetism different, and this difference hasbothered symmetry-loving physicists for years.

In 1931 one of the founders of quantummechanics, Paul Dirac, showed that if amagnetic monopole existed, it could help toexplain the puzzling fact that electric charge is quantized. The existence of a magneticmonopole is one of the few theoretical ways to explain the quantization of electric charge.In fact, the existence of only one magneticmonopole in the entire universe would do the trick! Naturally, physicists would like to find one.

Dirac found that the product of the electriccharge (e) and a magnetic monopole charge (g) is necessarily an integer multiple of thefundamental constant in quantum mechanics, 2hc (where h is Planck’s constant, which relatesthe energy and the frequency of a photon, and c is the speed of light). Given the values ofh, c, and e, the minimum monopole charge gmust be at least a few thousand times larger


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Polar ExpeditionDZero experimenters explore their data for evidence of a lone magnetic pole.

The absence of a

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Paul Dirac (1902-1984) won the Nobel Prize in 1933 forhis work on antiparticles and wave mechanics. Diracshowed that a magnetic monopole could help explainthe quantization of electric charge.

than e. This implies that light would scatter offthe monopoles like billiard balls struck by a cueball—much more strongly, in fact, than offordinary electrically charged particles. Themonopole could exist with intrinsic angularmomentum (spin) of 0, 1/2, or 1. Forcomparison, the spin of the electron is 1/2.

Recently, I. Ginzburg and A. Schillercompleted theoretical calculations of thescattering of photons at the Fermilab Tevatronfor heavy pointlike magnetic monopoles. (A pointlike particle, such as a quark or anelectron, has no discernible size.) Thecalculation gave a large scattering probabilityfor photons from monopoles of masses of up toabout 1000 GeV/c2, a thousand times the massof the proton. (However, we should note thatit is still unknown if pointlike monopoles arefully consistent with current theory at thesemasses.)


Theory in hand, a group of DZerocollaborators performed a search for evidenceof these signature scattered photons using dataaccumulated in the 1994-1995 Tevatron run.We did find evidence for the production of twoor more photons, but the scattering we foundcan be fully accounted for by a sum of twobackgrounds involving ordinary interactions of quarks on the one hand, or detectormisidentification of parton jets or electrons as photons on the other. We found no excess of photon scattering beyond these backgroundsthat would point to the presence of amonopole.

Converting our measurement into limitson monopole mass, we can say that pointlikemagnetic monopoles do not exist with masses

DZero collaborators set out to look for thehypothetical creature called the Dirac MagneticMonopole, combing through the data fromRun I for signs of this theoretical particle. Theydidn’t find it. Does that mean their search wasa failure? Most physicists would say no, for anumber of reasons.

First, from their search, the experimenterslearned more about what kind of creature themonopole will be if it does exist. They learnedmore than anyone had known before about itsmass and cross section. This new informationwill give the next group of searchers a betteridea of where to look and what to look for. Itwill also kick the ball back to the theorists, toincorporate the new information into theirtheoretical picture of the monopole.

Second, the scientific search process itselfoften produces new and unexpected results.Consider the famous example of the centuries-long attempt to prove Fermat’s Last Theorem,inspired by the notorious marginal note thatFermat scribbled in his father’s copy ofDiophantus’s Arithmetica around 1630. Formore than 350 years, mathematicians tried, andfailed, to prove the FLT. In the process, anumber of great mathematicians significantlyadvanced the knowledge of number theory.

In fact, in quite early stages, it became apparent that themathematics of the FLT is closelyconnected to other fields, such ascomplex number theory, and isrelated to fundamental propertiesof space. When the mathematicianAndrew Wiles first announced theproof of FLT in 1993, and completedit in 1995 with the help of RichardTaylor, the proof required the entiremathematical apparatus accumulatedover three and a half centuries sinceFermat’s margin-scribbling: numbertheory, complex analysis, Galois groups,Riemann’s hypothesis, elliptic functions and more.

In the same way, the 18-year search for the topquark produced countless advances in acceleratorand detector technology, data storage and analysis,networking and particle theory.

Just because you don’t find what you’relooking for doesn’t mean the search wasn’tworthwhile.

On the other hand, as Fermilab theorist ChrisQuigg has pointed out, for years physicists failed tofind the top quark at Fermilab—but we didn’t havea party until they found it.Judy Jackson and Greg Landsberg

“450 Physicists Fail to Find....”

below about 600, 900, and 1600 GeV/c2 formonopole spins of 0, 1/2, and 1, respectively.These are the most restrictive limits on themonopole mass to date. The sensitivity of ourexperiment in the low monopole mass region islimited by the requirement on the minimumphoton energy and by theoretical assumptionsused in the calculations. We are sensitive to amonopole mass as low as a few hundredGeV/c2. Combined with the previousmeasurement by the L3 experiment at theLarge Electron-Positron Collider at CERN,which explored a lower monopole mass range,our measurement excludes the existence ofpointlike magnetic monopoles in a broad massrange from few dozen GeV/c2 to our newexperimental limit. ■

PROTON ELECTRON

ELECTRIC CHARGES

MAGNETIC

MONOPOLES?MAGNETIC DIPOLE

+ – S NS N

Information on the Dirac Monopoleis available athttp://d0server1.fnal.gov/www/gll/Monopole_PE.htm


Time and Fate: The Past and Future of Fermilab’s Wetlands

By Sharon Butler, Office of Public Affairs

T ime is supposed to heal all wounds, but scientist are beginning to doubtwhether newly created wetlands can ever

compensate for the loss of those destroyed by road and building construction. Restoredwetlands, they say, may never equal the real ones.

The Fermilab site was once virtually allwetlands, according to resident ecologist RodWalton. But in the middle of the 1800s, aspioneers eyed the fertile land for grain, theydug an efficient drainage system composed of clay field tiles that ran the water off theirproperties to the nearby Ferry and Indiancreeks.

The land dried up, enabling farmers toplant corn and wheat crops, creating acres ofrich farmland. In the process, though, they losta valuable resource. Once dismissed as fetid,insect-ridden swamps, wetlands are now

recognized as vital ecosystems. They processnutrients, store floodwaters and shelter anamazing variety of plants and animals.

When Fermilab took over, the landscapereverted in part to its former self. Thelaboratory broke the field tiles that the farmershad laid, creating a ring of cooling water forthe heat exchange system needed for theaccelerator. Without maintenance, the drainagesystem was deteriorating anyway, helped by theconstruction of roads and facilities that brokethe underground tiles.

As a result, Fermilab now has 225 acres ofwetlands stretching across the southern andeastern sections of the site. According toWalton, the property now is closer to its naturalstate than it has been in years.

The best wetlands are located at the centerof the Main Ring, where Fermilab once tried tocreate lakes in the shape of the laboratory’s

Main Ring wetlands show a healthy mix of vegetation with good perching.


logo. This time of year, the great cottonwoodsturn into a heron rookery, with nesting greatblue herons, great egrets and sometimes evencormorants.

The youngest wetlands lie on a 10-acreplot in the center of the Main Injector ring.They were created to compensate for the lossof 6.5 acres of forested wetlands borderingIndian Creek when the tunnel for the newaccelerator was constructed. Under the CleanWater Act, Section 404, the federal governmentrequires that “compensatory” wetlands becreated, in the same floodplain and preferablyresembling the original. Since 1982, accordingto Science magazine, about a million acres offresh- and saltwater wetlands have beenrestored or created

But the fate of these kinds of reconstructedwetlands, and whether they can ever resemblethe wetlands they were meant to replace, isnow in question.

A recent study of a reconstructed marsh inthe Sweetwater National Wildlife Refuge inCalifornia found that the marsh had failed toattract light-footed clapper rails, as it wassupposed to. The problem was, thetransplanted Spartina cordgrass didn’t grow tothe height the birds require. To make it grow,the researchers added nitrogen fertilizer to thesandy soil. But then pickleweed overtook thecordgrass.

The researchers also found that the marshaccumulated fewer nutrients and produced lessorganic matter than comparable naturalwetlands.

Mike Becker, of the Roads and GroundsDepartment, expects that it will take at least acentury to bring Fermilab’s reconstructed

wetlands in the Main Injector area to a naturalstate. Certain plants typical of wet prairies aredoing well: rattlesnake master and some of thetall grasses like big blue stem, switchgrass andspecies of sedges. The Roads and Grounds crewroutinely seeds the area, using seeds of nativeplants obtained from the state’s forest preserves.But woody vegetation, as expected, is a constantproblem. Box elders and cottonwoods, whilenative to the area and hence desirable,nevertheless claim ground before othervegetation has had a chance to root. Regularburns each year check these unwanted plants,but until there is enough plant material for fuel,the fires don’t get hot enough to destroy thetougher woody species. Deer have also been aproblem, damaging the young oak trees plantedto recreate a forested swath of wetlands.

Eventually, this restored wetland may turnaround. But it will take time, and the magichand of chance. ■

A World Wide Web search under “wetlands”turns up many interesting sites.

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Preserved wetlands inthe Nelson Lake Roadarea of Bataviaillustrate the ideal.

Newly created wetlandsin the Main Injector areaare far from resemblingthe real thing.

An egret gracefullysurveys wetlands createdinside the Main Ringnearly 30 years ago.

The past 20 years have taughtus much about the quarks. Now,the leptons are beginning to catch up.

By Stanley Wojcicki, Stanford UniversityThe fundamental particles of matter, the

quarks and the leptons, are cousins. Each groupcontains six of the 12 fundamental fermionsthat are the building blocks of our universe.The three flavors of neutrinos, together withtheir charged partners, electron, muon, andtau, are the six leptons. Many parallels existbetween quarks and leptons; by looking at whatwe have learned about quarks, we cananticipate some of the lepton characteristics.

We can describe both the quark and leptonfamilies by 10 fundamental parameters, ornumbers. Currently, we have no idea wherethese numbers come from; we rely onexperiments to measure them. In the future, anas-yet-unformulated theory may explain theirvalues. These 10 numbers are the six masses ofthe quarks (or leptons) and four moreparameters that describe how different quarks(or leptons) “mix,” or transform from one toanother.

If the solar and atmospheric neutrino data demonstrate the existence of neutrino

oscillations, our knowledge ofleptons will not even approachour knowledge of the quarksector as of 20 years ago. Weknew then that strange andbottom quarks existed and that they decay, in a processanalogous to neutrinooscillation. We knew five of thesix quark masses and one mixingangle reasonably well, but ourknowledge of the other four

quark parameters was only

10 FermiNews May 15, 1998

rudimentary. Neutrino oscillation results wouldgive us the first inkling about neutrino massstructure and the first crude equivalentinformation about neutrinos. The last 20 yearshave witnessed an intense and largely successfuleffort to complete the knowledge of the 10quark parameters. Neutrino physics has a longway to go to catch up with the quarks.

In another telling historical analogy, ourinitial information about the quark sector camefrom cosmic rays. Particles like pions, kaons,lambdas and charged sigmas and xis werediscovered in cosmic rays. But systematic studyof these particles required acceleratorexperiments with experimental conditionscontrolled and optimized for specific goals.There are no knobs to turn off cosmic rays orthe sun, to change the energy or nature of thebeam. Clear understanding of the neutrinos willalso require controlled accelerator experiments.We are now entering that phase.

There are other reasons to understandneutrinos besides their fundamental nature.Neutrinos played an important part in theevolution of the universe immediately after theBig Bang. They are still all around us, the relicsof that distant past, with 300 neutrinos percubic centimeter everywhere in the universe.We are also constantly bombarded by neutrinosfrom outside the Earth: from the sun, fromcosmic ray interactions in the atmosphere, from distant supernovae, from every violentastrophysical event. Neutrinos, because of theirextremely weak interaction, may offer us a newwindow on the outer edges of the universe.And finally, neutrinos may contribute to theunseen dark mass in the universe.

Changing flavorsConsider next the oscillation situation.

Oscillation is a phenomenon that causesneutrinos of one flavor to change intoneutrinos of another flavor as a neutrino beampropagates through space. A most generalneutrino beam can be described as asuperposition of the three neutrino flavors: νe,νµ, ντ. From studies of Z0 decays, at SLAC andat CERN, we have reason to believe that thereare only these three neutrino flavors. It is aquantum mechanical property of neutrinos thatif they have mass, then one flavor can changeinto another flavor. An initially pure νµ beamcan acquire a νe or ντ component.

An analogy with light might illustrate thisphenomenon. A beam of light of any color canbe thought of as composed of the threeprimary colors: red, green and blue. Imagine abeam that starts out as pure red slowlyacquiring a green or bluish tinge as it shinesthrough space.

The good news: Neutrino physics is entering a new era in experiments around the world—and at Fermilab.

Good ν‘s

STANDARD MODEL

I II III

electron neutrino muon neutrino tau neutrino

W boson

gluon

photon

tau

Z boson

muon electron

Three Generations of Matter

top charm

strange down

up

bottom

electron neutrino muon neutrino tau neutrino


There are two general kinds of experimentsto look for neutrino oscillation: appearance anddisappearance. In appearance experiments, wedirectly detect the presence of an initially absentneutrino flavor, at a distance from the source.In disappearance experiments, we measure thenumber of neutrinos of the initial flavor to seeif they are fewer than expected. In the light-beam analogy, an appearance experiment woulduse a filter that blocks the red light (if the initialbeam was red) and transmits perfectly one ofthe other primary colors, such as green. Adisappearance experiment would use a filterthat transmits only red light, and we wouldmeasure whether the light intensity diminishedat some distance from the source. Appearanceexperiments are more sensitive and are ideal to look for small effects. But sometimescircumstances do not allow us to perform such experiments.

HintsCurrently, there are three classes of

experimental hints for the existence of neutrinooscillations. The oldest comes from themeasurement of the number of solar neutrinosstriking the Earth. From the standard solarmodel and the measured intensity of the solarelectromagnetic radiation striking the Earth wecan predict the number of expected neutrinointeractions in a detector. Experiments seefewer than predicted. The theoretical

interpretation of these disappearanceexperiments is difficult. The sun emits electronneutrinos; if they oscillate into νµ’s or ντ’s, thenumber of detected νe’s would be lower thanexpected. Unfortunately, the energy of solarneutrinos is so low that the generated νµ’s orντ’s are below the threshold for creating muons or taus and cannot be detected. An appearanceexperiment is hence impossible; we cannotdirectly identify a new neutrino flavor.

Solar neutrino experiments are truly heroicventures, because the interaction rate of solarneutrinos is very low. They require massive detectors and ingenious techniques. The

The Mass Squared DifferenceStudying neutrino oscillations is a powerful method to learn about the10 fundamental lepton constants. We already know three of themwell: the masses of the electron, muon and tau. Oscillations can teachus about the other seven, the three neutrino masses and the fourmixing parameters. Specifically, the wavelength associated with theoscillations (how far a neutrino of a given energy has to go before itchanges from one flavor to another and back again) is inversely relatedto the difference of mass squared of two neutrino mass states. Moreprecisely, the wavelength is proportional to Eν/∆m2. Thus if the masssquared difference is small, we must go far away from a neutrinosource to observe the oscillations. The amplitude of the oscillation(what fraction of one flavor converts into another flavor at theoptimum location) teaches us about the four mixing parameters.

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Solar neutrinoexperiments, like theSudbury NeutrinoObservatory in Canada, are heroic ventures.U.S. physicists,supported by DOE, arecollaborators in SNO.


GALLEX experiment, for example, on theaverage observes one gallium->germaniumnuclear transformation per day, in a tank of 30 tons of gallium, due to solar neutrinointeraction. Experimenters have the challengeof identifying the one germanium atom in abatch of 2.5 x 1029 other gallium atoms. Now results from four different solar neutrinoexperiments all show a deficiency of observedνe’s but cannot detect the postulated neutrinosof different flavors.

The second hint is the “atmosphericneutrino anomaly.” The Earth is constantlybombarded by energetic cosmic rays, mainlyprotons and heavier nuclei. As they enter theatmosphere, they interact with oxygen ornitrogen nuclei, typically some 20 km abovethe Earth’s surface. These interactions producesecondary particles, which in turn also interactor decay, and so on. The resulting cosmic rayshower contains both electron and muonneutrinos resulting from pion and muondecays. We can calculate their ratio from ourknowledge of how these particles decay andfrom the knowledge of muon and pionlifetimes. Thus the cosmic ray neutrino “beam”striking the earth is a well-defined mixture ofνe’s and νµ’s. In the light analogy, we canpredict exactly what the color should be. Thegoal of the experiments is to measure that color— the νµ / νe ratio — to see if it agrees withthe prediction.

The pioneering and currently most precisedata in this area come from large undergroundwater Cerenkov counters. When chargedparticles go through a medium with velocitieslarger than the velocity of light in that medium,they emit light (Cerenkov radiation), like asonic boom as an airplane breaks the soundbarrier. Thus a tank of very pure water linedwith photodetectors on its inner walls can

identify charged particles resulting fromneutrino interactions in the water and, from thepattern of the Cerenkov light, determine theflavor of the interacting neutrino. The mostambitious of these detectors, now taking datafor two years, is the Super-Kamiokande inJapan. It is a cylindrical underground cavern,42 m high and 39 m in diameter, filled withwater, its inner surfaces lined with 11,200 20" photomultiplier tubes, deep undergroundto shield it from the non-neutrino cosmic rayparticles.

The Super-Kamiokande results, as well asthe results of other large experiments studyingthis problem, detect fewer νµ’s than expected.The most likely interpretation of the data is νµ -> ντ oscillations; as in the solar neutrinocase, appearance experiments for this mode are not possible here. Most of the atmosphericneutrinos have too little energy to produce tausdirectly.

However, these experiments can teach usabout the mass squared difference of oscillatingneutrinos. Neutrinos arriving at different zenithangles have traveled different distances fromtheir creation in the atmosphere to theirdetection points. For example, a typical pathlength for downward-going neutrinos will beabout 20 km or less; for upward-goingneutrinos, those from cosmic rays interactingon the other side of the Earth, the path lengthwill be about 12,000 km, the Earth’s diameter.Evidence suggests that the muon neutrinodeficit varies with different zenith angles,allowing deductions about the wavelength ofthe oscillation and hence the mass squareddifference.

The third experimental hint for neutrinooscillations is the only one from an acceleratorexperiment. An experiment at Los Alamosfound evidence for the existence of νe’s in an

Neutrinos

120 GeV PROTONS PIONS & KAONS

0 meters 360 meters

TargetProton beam from Main Injector Pion/Kaon decay region

Proposed NuMI Beamline

The MINOSexperiment willsend a beam ofmuon neutrinos toMinnesota. Willthey change flavoron the trip?


initially pure νµ beam. This evidence is stillsomewhat controversial, because otherexperiments that might also have been able tosee this effect have reported null results.However, the Los Alamos experiment is theonly one that covers a certain small region ofneutrino parameter space, so the otherexperiments do not absolutely contradict theLos Alamos results.

The jury is outWhen we look at these three sets of results,

a difficulty emerges. The mass squareddifference indicated by the three experiments— about 10-5 for solar neutrinos, 10-3 - 10-2

for atmospheric neutrinos, and about 1 for LosAlamos (all in units of eV2) are not compatiblewith originating from only three differentmasses, which could give only two independentmass squared values. At least one of theexperiments is wrong, or the observed effect is not neutrino oscillations, or there is someexotic theoretical possibility. For example, afourth, sterile neutrino could exist that doesnot interact with the matter in our universe atall and thus would not be seen in the Z0 decays.In other words, the jury is still out on neutrinooscillations. New, more powerful experimentswill have to resolve the controversy.

What are the most productive ways topursue these issues? More refined solar neutrinoexperiments are planned, and more data willcome from the existing solar and atmosphericneutrino detectors. But if history is any guide,we will need accelerator experiments to resolvethe possibilities put forth by the nonacceleratorexperiments. The mass scales, and henceoscillation wavelengths, suggested by the solardata are such that they cannot be probed withterrestrial accelerator experiments; the Earth issimply too small. MiniBooNE, a proposed

Fermilab experiment, would use the FermilabBooster to improve the sensitivity of the LosAlamos experiment and verify or contradict itsresults. And an experiment with neutrinos fromthe Fermilab Main Injector, to be detected inthe Soudan mine in northern Minnesota some730 km away, is being designed to study andunderstand theatmospheric anomalyquestion. This articleconcludes with a discussion of that effort.

UONS & NEUTRINOS NEUTRINOS

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Hi-intensity absorber MINOS near detector

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Cosmic rays (above)have given inklings ofnew neutrino physics,but it will requireaccelerator experimentslike the NuMI project atFermilab to resolve thequestions raised.

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International CollaborationThe MINOS (Main Injector Neutrino

Oscillation Search) experiment is an inter-national collaboration of scientists from 23 institutions, 13 of them from the U.S. andthe rest from China, Great Britain, and Russia.It will use the Fermilab Main Injector toprovide an unprecedented flux of neutrinos in the energy range suitable for generalinvestigation of neutrino oscillations. Its initialgoals were to explore as large a domain ofneutrino parameters as possible; as theatmospheric results become more reliable anddefinite, the collaboration will optimize thebeam and the detector for studying neutrinoparameters in the region of the atmosphericneutrino anomaly. The source-to-detectordistance, coupled with the GeV range of theMain Injector neutrinos, is well suited toexplore the 10-3 to 10-2 eV2 mass squareddifference region.

MINOS will measure the neutrino beamand its properties at two widely separatedlocations, using the same beam, and detectors as similar as possible, so that uncertainties willcancel and even small differences will show upin the event characteristics at the two locations.In our light analogy, we are measuring the

Neutrinos

color of our beam both at Fermilab and atSoudan to see if the color has changed.Experimenters will perform a variety ofdifferent and redundant measurements, withdifferent potential systematic errors, to helpexperimenters draw accurate conclusions from the data.

How MINOS worksTo produce the neutrino beam,

experimenters will extract the 120 GeV protonbeam from the Main Injector and direct it to a carbon target downstream. The pions andkaons produced in the resulting interactions arethen focused with pulsed current devices calledmagnetic horns. They act like lenses for a beamof light and make the resulting particle beamparallel, like a light beam from a flashlight.These secondary particles will then travel in an 800 m long evacuated decay pipe; theirdecays produce the neutrinos of interest,predominantly νµ’s. The beam is aimed at theSoudan mine; because of the Earth’s curvature,it must be directed downward at about a three-degree angle. The first detector is located about350 m downstream of the end of the decaypipe. Neutrinos interact so weakly (at theseenergies, if 10,000 neutrinos strike the earth,only one will interact) that they can travel to Soudan through the Earth without anysignificant loss of intensity. But the flip side ofthis low interaction rate is that the detector inthe Soudan cavern must be massive, to detect a significant number of interactions.

The current design of the MINOS fardetector is an 8-kiloton magnetized ironspectrometer, consisting of 730 octagonal steelplates, 8 m in diameter and an inch thick.Interleaved between the steel plates are planesof scintillator bars, 4 cm wide. When a neutrinointeracts in a steel plate, the resulting secondaryparticles will travel through a number ofdownstream iron and scintillator layers. Thecharged particles traversing the scintillator willproduce visible light, which will be trapped bywavelength-shifting fibers embedded in thescintillator and transported to photodetectors atthe edges of the steel plates. The differentflavors of neutrinos produce characteristicpatterns of light from their interactions. Muonneutrinos produce muons, which lose energyslowly and light up many consecutivescintillators. The patterns of light for electronand tau neutrinos typically extend a far shorterdistance. By separating events into “short” and“long,” we can distinguish on average the νµ’sfrom the νe’s and ντ’s. MINOS works bymeasuring the neutrino flavor content in two places, Fermilab and Soudan, and lookingfor a change—proof of oscillation. The

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Octagonal steel plates, like slices in a loaf of bread, will alternate withscintillator in the MINOS far detector (inset).

MINOS far detectorlayout, showing thevertical mine shaft andthe detector caverns.


Lunch served from11:30 a.m. to 1 p.m.

$8/personDinner served at 7 p.m.

$20/person

For reservations, call x4512Cakes for Special Occasions

Dietary RestrictionsContact Tita, x3524

-Lunch

WednesdayMay 20

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DinnerThursdayMay 21

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LunchWednesday

May 27Booked

DinnerThursdayMay 28Antipasto

Grilled Stuffed Veal ChopsOven-Roasted Vegetables

with HerbsLemon Cake

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MAY 20Wellness Works presents: Health & Fitness Day!

MAY 22Potluck Supper at Kuhn (Village) Barn. Drinks and appetizers at 6 p.m. Dinner at 6:30 sharp.Everybody either brings a main dish serving 6-8; or a dessert for 12; or contribute $3. Soft drinksprovided, pizza for the kids and wine for adults.Babysitting is available. Questions? Call AngelaJöstlein (630) 355–8279.

Fermilab International Film Society presents:Microcosmos. Dir: Claude Nuridsany & MariePerennou, FRANCE (1996). Admission $4, in Ramsey Auditorium, Wilson Hall at 8 p.m. For more information (630) 840-8000 orhttp://www.fnal.gov/culture/film_society.html.

CALENDARJUNE 27Fermilab Art Series presents: Tommy Makem withJohn Forster, $16. Performance begins at 8 p.m.,Ramsey Auditorium, Wilson Hall. For reservations or more information call (630) 840-ARTS.

ONGOINGNALWO coffee mornings, Thursdays, 10 a.m. in the Users’ Center, call Selitha Raja, (630) 305–7769.In the Village Barn, international folk dancing,Thursdays, 7:30–10 p.m., call Mady, (630)584–0825; Scottish country dancing Tuesdays,7–9:30 p.m., call Doug, x8194.

Conversational English classes, 9–11:30 a.m.,Thursdays, in the Users’ Center.

http://www.fnal.gov/faw/events.html

experimenters expect to see and measure about30,000 neutrino events per year. Furthermore,unlike the case in the atmospheric neutrinobeam, the energy of MINOS neutrinos will be high enough so that tau leptons can beproduced if νµ -> ντ oscillations occur.

The MINOS far detector will beconstructed in three supermodules so that data-taking can start before the full detector iscomplete, using the first supermodule. Thisapproach allows experimenters to reexaminehow to proceed as more information becomesavailable. One possibility is to substitute forpart of the MINOS main detector thin layers oflead and emulsion sheets to allow identificationof taus (and hence tau neutrinos) one by one,by observing their characteristic decay kinks.

For FY1998, Congress has appropriatedthe first funds for the design and study of theneutrino beamline for MINOS. For the nextfiscal year, FY1999, the President’s budgetrequests $14.3 million for the start ofconstruction. If Congress appropriates thesefunds, construction of the experiment can startin the fall, with the first neutrino interactions inthe year 2002.

Plans around the worldThe question of neutrino oscillations is

important enough that other laboratories haveplans (definite or tentative) to pursue this topic.In Japan, KEK is building a neutrino beamline

from the accelerator to the Super-Kamiokandedetector about 230 km away. The properties ofthat accelerator, however, cannot guaranteeexploration of the full suggested region of parameter space. Nature could chooseparameters that allow this experiment to see a significant effect, but the statistical power ofthe experiment is insufficient for the detailedstudies that MINOS can perform. There is alsointerest in Europe to build a beam at CERN tothe Gran Sasso Laboratory. The Europeancommunity has not yet decided whether theyshould pursue that ambitious undertaking.

The subject of neutrino oscillation has been the main topic of a number ofinternational conferences and workshops during the past few years, including the one atFermilab in the spring of 1997. These studiesfocused on physics goals of these experimentswith a view toward maximizing internationalcollaboration. The MINOS collaborationcontinues to explore possibilities for expandedinternational participation in MINOS.

The study of fundamental properties ofneutrinos is coming of age. Our knowledge ofthe leptons lags far behind our understandingof the quarks, but there are ample hints thatthe physics of the leptons is just as rich. In the coming years, the leptons may provideimportant clues essential to understanding the physical laws of the universe. ■

Information on the MINOS experiment is available at http://www.hep.anl.gov/NDK/Hypertext/numi.html

FOR SALE■ Chrome BMX bike GT Mach One, 1410chromalloy frame, 20" alum. wheels. Includes U-lock, exc. cond., for kids 9-14 years old; $189obo. Call x8492.■ Baby Cockatiels, hand-raised, very tame. Beautifulbirds! $50-$60. Call x3230.■ West Suburban Caged Bird Club’s annual Bird Fair, Sat. May 30, DuPage County Fairgrounds,10am-4pm, admission $2. For more information,contact Mary J., x3721.■ House - Batavia, 1.5 story, 2 bdrms, 1 bath. Well maintained updated charming farmhouse, largelot w/many trees, newer furnace, water heater,central air, 3 season sun porch & 15X16 deck.$134,900. Call Lynn Amore (630) 232-1581 or (630) 377-1855 for an appointment.■ House - 3 bdrms, 2 baths, screened porch, 2 fireplaces, large country kitchen, 2 car garage,cathedral ceiling in living room, cedar siding & shakeroof, St. Charles school district. On 2.5 acres inmature dense oak forest, private pond, cul-de-sac.$260,000. (847) 741–7539.

RENT■ NE Geneva location, lower 3-BR, spaciousliving/dining area opening to yard with patio, garage& laundry. Near bike trail & river. June 1. $950.(630) 584–1204.■ Looking for a room to rent from mid May tillmid August as a summer intern in Fermilab. If youhave a room near Fermilab for sublease for thisperiod, please contact Echo Qiu. (815) 753–1247(9am-11pm ) or e-mail: [email protected]

FRENCH LESSONS■ Je suis française. J’enseigne le français. Peggy-Henriette Ploquin. (630) 682-9048.

Published by the Fermilab Office of Public AffairsMS 206 P.O. Box 500 Batavia, IL 60510630-840-3351ferminews@ fnal.gov

Fermilab is operated by Universities Research Association, Inc.,under contract with the U.S. Department of Energy.

✩ U.S. GOVERNMENTPRINTING OFFICE: 1998--646-054/81004

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C L A S S I F I E D S M I L E S T O N E SBORN■ Riley Garret to Bob (BD/OPS) and TammieCarrier on April 23rd, at Central DuPage hospital.■ Jillian Marie, to Thom (TD/Machine Shop) andSheila Nurczyk on April 28 at St. Joseph’s Hospitalin Joliet.

AWARDED■ Paula Lambertz, a Sr. Drafter with BD/CD/Cryogenics Systems group, received an award and a$100 gift certificate for an image she created for theICCON (I-DEAS Customer Cooperative Network)Image Contest. Lambertz placed 5th among 26entries at the 1998 ICCON Users Conference inDallas, Texas. Her computer-generated solid modeland image of a connecting box for the Anti-ProtonDebuncher cryogenic upgrade is viewable on theweb at http://www-adcryo.fnal.gov/. ■ Muzzafer Atac received a patent on his photo-avalanche imaging detector. This detector can have revolutionary impact on medical x-rayimaging, nuclear research, airport security, and many other areas.

CONNECTED■ The Fermilab Amateur Radio Club, stationWB9IKJ, with station IY5PIS in Coltano, Italy, onSaturday, April 25, at 11:50 AM CDT, markingInternational Marconi Day. The station in Coltanowas set up by Luciano Ristori, a CDF collaboratorfrom INFN Pisa, on the site where GuglielmoMarconi operated one of the first intercontinentalwireless stations. For a 24-hour period onInternational Marconi Day, 40 amateur radio specialevent stations operated around the world, somelocated on the original sites of Marconi’sinternational radiotelegraph stations. For moreinformation about the club check the web site,http://www.fnal.gov/orgs/radioclub/farca.htm.LAB NOTES

Attention Fermilab Artists and Artisans:Now is the time to show us your artistic side! The biannual Employee’s Arts & Crafts Show willtake place on the 2nd Floor Gallery of Wilson Hall,July 1— July 31. All Fermilab employees, visitingscientists, retired employees, contractors and theirimmediate families are encouraged to enter theexhibit. The last exhibit featured, among otherthings, a wonderful mixture of photographs, prints,paintings, sculptures, weavings, quilts, and jewelry.Application forms for participating are available atthe Wilson Hall Atrium desk. Application deadline isJune 22, and exhibit drop-off is Monday, June 29.

Summer RecreationFor information on Fermi Coed Summer Volleyball, Basketball, Softball, and Soccer Leaguesor Children’s Swimming Lessons and Poolinformation, consult the Recreation web page:

http://fnalpubs.fnal.gov/benedept/recreation/recreation.html

Fermilab Amateur Radio Club members RobAtkinson, Lester Wahl and Kermit Carlson afterexchanging greetings with the Marconi Dayevent station at Coltano, Italy.

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Due to the Memorial Day holiday, FermiNewswill be published on a revised schedule. The next issue willappear on Friday, June 5,1998. The deadline forthis issue is Tuesday, May 26, 1998

Please send your articlesubmissions, classifiedadvertisements and ideasto the Public AffairsOffice, MS 206, or e-mail [email protected].

FermiNews welcomes letters from readers. Please include yourname and daytimephone number.

Volume 21 Friday, May 15, 1998 Number 10 - fnal.gov

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