It was one of the greatest moments in physics history and Bryan Caron missed it.
It's 1 p.m. Geneva time, March 30. Two proton streams hurtle through a vacuum-sealed tube underneath the border of France and Switzerland and smash together at just under the speed of light. Millions of explosions result, sending subatomic shrapnel everywhere.
Scientists in a packed control room nearby erupt with joy. Hands clap. Corks pop. "WE HAVE COLLISIONS!" researcher Jim Degenhardt posts on the ATLAS Experiment Blog seconds later. After 16 years and $10 billion, the Large Hadron Collider (LHC), the world's biggest particle accelerator, was finally working.
And Caron, one of the many researchers who helped build it, was just getting out of bed. He'd meant to catch the big moment, he says, but he was at home in St. Albert at the time, where it was 5 a.m. He had to settle for the replay online.
"It was obviously quite jovial," he says, as well as a great relief. Tinged with that relief is a growing excitement — after more than a decade of patience, he can now start using the collider to probe the secrets of the universe itself. "The future is now."
The great machine
Caron walks into a card-locked room on the University of Alberta campus. The room is a long way from Switzerland, but it's technically part of the LHC. The roar of cooling fans fills the room as he approaches one of many caged black obelisks covered with flickering green lights.
This is one of the many data centres around the world that handles the data coming out of the LHC, he explains, as he pulls a foldout terminal out of the black server tower. This particular centre is hooked to the ATLAS Experiment, one of the main detectors at the LHC. ATLAS collects enough data to fill 100,000 CDs a second — enough to make a tower 150 meters high and more than enough to crush any normal network. It's been his job to design a global computer system to handle the data.
The LHC is big — really big. You can think of it as a 27-kilometre-long racetrack for hadrons (protons or ions) big enough to circle St. Albert and most of Big Lake. It's the most powerful particle accelerator in the world and has been in the works for 16 years.
Caron is one of around 3,000 physicists working on ATLAS, the biggest of the six detectors in the LHC. ATLAS resembles a pop can that's as long as three Greyhound buses, as tall as Rexall Place, and as heavy as the Eiffel Tower (7,000 tonnes).
In the middle of the can is a vacuum-sealed tunnel just a few centimetres wide down which subatomic particles flow. Around it are layers of sensors ranging from about a meter wide to the width of the collector designed to observe collisions in the tunnel. Surrounding the whole mess are eight huge magnets shaped like stretched donuts that propel particles through the detector.
Big questions, small answers
Researchers built the LHC to answer big questions about the universe, according to Roger Moore, a physics professor at the University of Alberta who worked on the data collection system for ATLAS.
Physicists have a theory called the Standard Model that explains the universe through particles — particles of matter (such as protons) and particles of force (such as photons). The model works well, Moore explains, but falls apart when it comes to gravity: it says electrons should not have mass, yet they do.
Researcher Peter Higgs came up with a possible solution in the 1960s called the Higgs boson — a particle that would create gravity. If you move a ball through water, Moore says, the water causes drag and makes the ball seem heavy. The Higgs boson is thought to create a field with a similar effect on everything — it gives inertia and mass to all particles that move through it.
Physicists have yet to see the Higgs, but are pretty sure it will fall out of atoms if they bash them hard enough. "If you hit water hard enough, you make waves," Moore says, which lets you see the water. "We have to hit the universe hard enough to make a wave of the Higgs field."
World's biggest crash course
Hence the LHC. The collider's main goal in life is to accelerate particles to ludicrous speeds and smash them together so scientists can look at the bits of physics that spill out.
The collider starts by sending two proton beams through three separate magnetic accelerators to get them up to speed — one clockwise, one counter-clockwise. They eventually take the off-ramp to the LHC, where giant superconducting magnets boost them to 99.99 per cent of light-speed (about 11,245 collider laps per second).
These beams have as much energy as a 400-tonne train going 200 kilometres an hour, Moore says — enough to explode concrete and melt through the walls of the collider.
Some people were worried that these beams were strong enough to blow up the Earth, Moore notes, but researchers have ruled out that possibility. "Nature produces particles that have far higher energy than the LHC," he says, in the form of cosmic rays. Those rays hit the Earth all the time, and it hasn't blown up yet.
When they're ready, Caron says, researchers tweak the beams so they collide inside one of the detectors — ATLAS, for example. Protons smash into each other every 25 nanoseconds, producing millions of tiny, silent explosions similar to the Big Bang. "Your detector lights up electrically," he continues, as the numerous sensors — like a crowd of paparazzi — start taking pictures of each event.
Computers crunch the data and spit it out as pictures for the people in nearby control rooms. Lines on the pictures represent sturdy particles such as muons, which, like hubcaps, are so massive that they fly through most of the detector intact. Cones show less stable ones that, like car radios, decay into a spray of smaller bits as they move. By looking at the pattern of lines and cones, Caron says, researchers can identify the particles that flew out of the collision — including Higgs particles, should they exist.
Let physics begin
These collisions should produce a whole bunch of particles that physicists have never seen before, says Doug Gingrich, a University of Alberta physicist who designed some of the electronics in ATLAS. He's personally hoping for a miniature black hole, as it would point towards the presence of extra dimensions.
The LHC should produce a lot of antimatter through its collisions, Caron says, which, if studied, would help us determine why the universe is made mostly of matter and not antimatter.
It could also crank out dark matter or dark energy — the mysterious stuff that's thought to make up 95 per cent of the universe. (The rest is regular matter.) "We don't really know what it is," Gingrich explains, but we suspect it's really heavy, meaning we need high-energy collisions to knock it out of matter.
But the Higgs is the big prize, say physicists. "If the Higgs exists, everything is great," Gingrich says: the Standard Model works and we can teach it with confidence. "If we don't see the Higgs, it really says we're on the wrong track."
A Higgs-less universe would overturn decades of scientific thought, Moore says, which is why he personally hopes they don't find it. "It'd be even more exciting if we don't find the Higgs and we find something else because it'd open up a whole new realm of possibilities as to what the universe might be doing."
Whatever the LHC produces, Moore, Gingrich and Caron are eager to be there when it happens — all three are dashing to the LHC this month to do research. "It's new territory for everyone," Caron says.
