A big bang heard around the globe

Last week, the operators of the $10B atom smasher buried underground just west of here, got it up and running again.

U of T physicist Peter Krieger guides part of the ATLAS detector machine his department made to detect particles formed in the smash-ups produced by the Large Hadron Collider. The full detector weighs 7,000 tonnes.

GENEVA–Last week, in a dead-of-night experiment, the operators of the $10 billion atom smasher buried underground just west of here, got it up and running again.

For the 10,000 physicists who work on the Large Hadron Collider, it was a moment long awaited and nervously watched.

The collider is a 27-kilometre-long tunnel where protons will be driven against each other at unimaginable energies, creating explosions of subatomic particles that may reveal fundamental properties of nature. The first time they tried out the collider, 14 months ago, it more or less blew up.

"It was heartbreaking," said Louise Heelan, a 29-year-old Toronto PhD student in particle physics who witnessed the accident.

"There was so much excitement with the first beams, and then when it happened we didn't even know what went wrong."

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What went wrong was a failed electrical connection that caused a breach in the sealed container that keeps enormous magnets super-cooled. The coolant, liquid helium, instantly vaporized and sent a shock wave down the proton collider tunnel, unseating other magnets and wreaking havoc.

"This time around, there's a bit more caution," Heelan said of the mood this week at the Geneva facility known as CERN – the European Centre for Nuclear Research.

"There's still that sense of anticipation, but people are a bit more cautious."

The collider has taken 15 years to build. Canada has 150 physicists working on different parts of the collider and Canadians have been with the project since it began. Canadian universities and governments have spent almost $200 million on some of its gadgetry.

The collider works by accelerating billions of protons along the tunnel at 99.9999991 per cent of the speed of light. At that speed they circle the 27-kilometre ring 11,245 times a second.

Before they enter the tunnel, the protons are spun around a warm-up track until they reach an energy of 450 billion electron volts, when they are injected into the main accelerator.

Once in the tunnel, this energy is steadily increased. When the accelerator is operating at full power, the energies will be measured in trillions of electron volts.

"You are pushing the protons harder and harder," says Richard Teuscher, 43, a University of Toronto physicist and a 12-year veteran of CERN, "but they can't go any faster. According to Einstein, nothing can go faster than the speed of light, and yet you keep pushing and pushing. You might say that, since they can't go faster, they just get madder and madder. In fact, they acquire mass."

It is these massive, bulked-up protons that are then slammed into each other at points along the tunnel where the collisions can be monitored by massive particle detectors. As the protons annihilate each other, a mist of wreckage spatters outward, vanishing almost as soon as it appears.

"We need to collect a sample of several hundred collisions out of 800 million per second," Teuscher said.

Much of Canada's investment in the collider has been directed at one of the vast machines that sift this split-second blizzard of data. Called the ATLAS particle detector, it weighs 7,000 tonnes and contains as much steel as the Eiffel tower.

Most of the assembly of a critical part of the detector, called "end caps," was completed at TRIUMF, Canada's national particle physics laboratory in Vancouver, and at the University of Toronto.

"They're pretty delicate," says Peter Krieger, a 46-year-old Toronto physicist who has worked on the ATLAS detector for 11 years.

"When we shipped them to Geneva, we packed them in the same material that the U.S. military uses to pack nuclear warheads."

When protons collide, a storm of particles tears through the detector, stripping electrons from argon inside it as they go. The ATLAS tracks the path of these orphaned electrons and extracts from the maelstrom crucial information about the structure of matter.

So mountainous is the volume of data to be parsed that only the most powerful computers can handle it. The ATLAS data from CERN is fed to SciNet, a system owned by U of T and located in Vaughan. It ranks among the world's 20 fastest supercomputers.

Finally, this week it got something to chew on. CERN's controllers sent two proton streams squarely into each other's path. The particles collided at the relatively low combined energy of 900 billion electron volts. Still, it was enough to spew a fountain of subatomic bits into the detector and raise the spirits of the scientists.

"I was seeing electrical pulses in all our channels," Krieger happily confided as he walked from the ATLAS control centre into bright sunshine.

"I've been working toward this for 10 years," Krieger said. "It's hard to convey how exciting it is; so much of our lives are spent in working up to this. There was nothing like this detector before, so you just don't know. It's its own prototype."

The collider is the largest and most expensive scientific experiment ever built. It will examine fundamental questions in physics, such as why matter has mass. In this search, physicists will be looking for an elusive sub-atomic particle known as the Higgs boson, a theoretical particle never actually located but that, in the Standard Model of particle physics, accounts for mass.

They hope to find the Higgs boson coughed up in the eruption of data when the collider starts pelting protons together at the highest energy, 7 trillion electron volts. This energy last existed in the trillionth of a second after the Big Bang.

For a machine that strays so close to the majesty of creation, it has suffered its share of indignity.

Tearful callers, afraid that the collider will create a black hole that swallows the planet, regularly beg CERN staffers to call the whole thing off.

Last month, a passing bird gave the doomsayers hope when it dropped a piece of baguette onto something called a compensating capacitor, part of the surface system that delivers electricity to the machine. The collider was shut down for three days until it could be re-cooled.

Until this complex was built, the largest collider was at Fermilab, near Chicago, where the highest energies achieved were less than 2 trillion electron volts.

"I think CERN will try to beat that by Christmas," said Krieger.

Just the attempt is stirring. A proton has a diameter of one millionth of a millionth of a millimetre. One physicist said that the job of making two protons meet in the tunnel was the exact mathematical equivalent of firing a pair of knitting needles at each other from opposite sides of the Atlantic Ocean, and have then hit dead-on in the middle.

Enormous, superconducting magnets guide the protons down the collider tunnel. A sort of cloud of loose protons charges along outside the core stream, and a series of 52 11-tonne "cleaner" magnets designed by Canadian physicists and made by Alstom Canada in Tracy, Que., tidies them up.

When the protons smash together, data from the collisions are scrutinized in Toronto at breathtaking rapidity.

Three days ago, Louise Heelan was sitting at an observation desk outside the ATLAS control room. Behind the plate glass, about three dozen physicists, many of them her age, stood in groups and chatted and watched the progress of the next injection displayed on a wide screen. Like those inside, her excitement was palpable.

"In my own work," she said, "I look for a particular quark called the top quark. It's an interesting particle because to spot it all the parts of the detector have to be working. So when we see it we know – yes!"