Nuclear research

THE WORLD OF PHYSICS HAS ITS EYES RIVETED ON GENEVA: THE LHC PARTICLE ACCELERATOR IS DUE FOR START-UP IN LATE 2007. THE GREATEST SCIENTIFIC EXPERIMENT OF ALL TIME COULD REVOLUTIONIZE OUR VIEW OF THE WORLD.

So this is where they’re trying to find God. A hundred meters beneath the ground in a ring-shaped tunnel 27 kilometers long, the world’s finest physicists are searching for answers to the mystery of life. The tunnel penetrates the rock mass of the Jura mountains, passes hard by Geneva airport, reaches out towards the lake and crosses the border with France—and inside it is the greatest scientific experiment of all time: the Large Hadron Collider (LHC), the largest particle accelerator in the world, accelerates atomic particles almost to the speed of light and causes them to collide. Each proton circulates 11,000 times around the tunnel—per second. In towering detectors built into the ring, the atomic particles crash into one another. From the traces of these collisions, scientists at the European Organization for Nuclear Research (CERN) hope to learn more about the building blocks of the world.

To scientists, rocks and trees, animals and people are nothing more than a sophisticated assembly of minute building blocks. Atoms gang together to form all matter. But why do they combine? That is the question that physics is trying to answer by imitating the conditions of the Big Bang 14 billion years or more ago, when theory has it that the universe expanded at lightning speed and energy was turned into matter. “It is this condition of creation that we are replicating,” says physicist Hans Falk Hoffmann.“We are recreating energy conditions in the accelerator which prevailed a split second after the Big Bang.”

GIANT MACHINES IN SEARCH OF MINUTE PARTICLES
Detectors are installed in the annular accelerator, some of which are bigger than the Tower of London. “To see the smallest things, we need the biggest machines.” Hans Falk Hoffmann is standing in front of one of the detectors located somewhere deep beneath a French field. Its high-tech components are arranged like wedges of cake around a beryllium tube five centimeters in diameter in which the particles collide with one another. Inside is a vacuum like that in outer space. Bundles of protons are set in motion by high-frequency resonators, held on course by powerful magnets, and then compressed shortly before the point of collision into an area smaller than the cross-section of a hair. A proton, one of the components of an atom, is so small—500 billion of them would fit on the dot of an ‘i’ in this article— that only a fraction of the particles actually collide in the LHC.

“The magnetic field inside the accelerator is 100,000 times stronger than the earth’s magnetic field,” reports Dr. Vinod Chohan, head of CERN’s Magnet Test Facility. To maintain such a phenomenal field, the colossal magnets—each up to 15 meters long—are cooled with 96 tons of liquid helium to a temperature lower than that of the universe. The super-cold temperature of minus 271 degrees Celsius is needed for the coils to become superconductive and the finger-thick cable to handle the 13,000 amp current without resistance. By comparison, normal domestic cables carry about ten amps of current.

RIDDLE OF THE UNIVERSE
By mimicking the conditions of creation, it is hoped that the LHC will shed light on the great issues eluding mankind: what holds the world together? Where does the material, the substance of life originate from? Why is space expanding faster than mass and gravity actually permit? One of the puzzles perplexing physicists is why elementary particles should even have mass, and why this is sometimes small and sometimes great.

“We believe that there is an omnipresent field, the Higgs field, mediated by a new particle, the Higgs boson”, explains Dr. Jörg Wotschack, a physicist at the ATLAS Detector. “The mass of a particle becomes greater, the more intensively it interacts with the Higgs field. So it could be that it is the Higgs particle which confers mass on all other particles.” Some physicists call it the “God particle,” the missing building block in the so-called “standard” theory that attempts to explain the fundamental components of matter and their reciprocal relationships. If the theory is correct, the Higgs particle should turn up in the LHC. On the other hand, it is highly elusive: physicists expect to record just one Higgs particle for every 1013 collisions. “It’s like multiplying the whole of humanity by a thousand and then trying to find one individual person,” says Dr. Jörg Wotschack.

HUNDREDS OF MILLIONS OF COLLISIONS PER SECOND
Giant, super-sensitive devices known as detectors are used to track down these particles.The largest among them is ATLAS, a 25-meter tall giant measuring 46 meters in length. It employs precision electronics in the form of millions of sensors to sort through the traces of particle collisions.

Over a billion particles per second crash into one another in the detectors and splinter into subparticles. The detectors are so sensitive that they can record a petabyte of data per second. A petabyte—that’s a quadrillion packets of data. “Most of our efforts have gone into figuring out how to separate the wheat from the chaff in this avalanche of data,” says Hans Falk Hoffmann, team leader at the CMS detector. “Of a billion events per second, we retain only 100.We are unable to analyze more than that.” In order to master the volume of data, the scientists harness a worldwide network of megacomputers.

THE WHOLE WORLD IS JOINING IN
Physicists, engineers and fitters, institutes and companies have come from every continent to help build the LHC. The 1,232 dipole magnets that keep the particle stream on course were built in Germany, France and Italy. In Germany, the contract was awarded to Babcock Noell GmbH (BNG), a subsidiary of Bilfinger Berger Power Services specializing in magnet, nuclear and environmental technology. “This is one of our most prestigious projects,”says Michael Gehring, manager of the Magnet Technology division of BNG. The 15-meter long dipoles weighing 32 tons had to be manufactured to an accuracy of 20 microns—that’s the width of a hair. “We need this degree of precision to direct the particle beam and ensure that the magnet remains superconductive, otherwise it could even burn out,” explains Michael Gehring. Babcock Noell’s success in delivering its magnets more than seven months ahead of the contractual deadline earned the company the Golden Hadron Award, a prize awarded by CERN for outstanding cooperation.

LIKE THE VOYAGE OF COLUMBUS
“CERN is like an orchestra.” Lucio Rossi sits in his office, waxing lyrical about a Beethoven violin concerto in which the solo violin vies with the orchestra before finally merging in harmony with it. An apposite metaphor for the interplay between top scientists, institutes and industry at CERN, the man in charge of acceleration technology believes:“Everyone here gives their best, the art lies in putting it all together. We must never forget how many individuals have contributed their intelligence,” says the professor.

When the accelerator is started up as planned in November 2007, it won’t be running at top speed. “It’s like getting into a Ferrari for the first time,” Lucio Rossi continues. You don’t immediately drive a sports car to its limit.“It will be 2011 before we can make optimum use of our Ferrari,”he explains. “But we’ll need hundreds of drivers.”

But what would it mean for physics if the greatest particle accelerator of all time were to find nothing? What if the Higgs particle doesn’t show up? “That in itself would be a revolution,” says Hans Falk Hoffmann. His colleague Lucio Rossi agrees, and explains this strange optimism: “The LHC is like the voyage of Columbus.To find something entirely different than what was expected—that in itself would be a realization for physics.”

(Text: Kirsten Wörnle, Photos: Cira Moro)