At 12:58 p.m. local time last Tuesday, the Large Hadron Collider, a mammoth particle accelerator buried 100 metres beneath Geneva, Switzerland, finally began smashing subatomic particles together at record-high speeds.
Though the LHC’s first successful particle collisions occurred in November, on Tuesday physicists at the accelerator recorded the first collisions at the energy level – about seven trillion electron volts (TeV) – at which the collider will operate for about the next year and a half. Collisions recorded in early December had broken the previous speed record of 1.96 TeV, held by an accelerator at Fermilab, located near Chicago.
Whether they were in the control room at the European Organization for Nuclear Research (CERN) in Geneva or halfway around the world, physicists watched last week’s collisions with intense excitement.
“When the LHC finally started, people at CERN were simply ecstatic,” said Marc-André Dufour, a fourth-year McGill PhD candidate who has spent over a year working on the LHC. “Others who were not fortunate enough to physically be at CERN for that event, including me, were following from their computer screens.”
The LHC, which straddles the border between France and Switzerland, is the world’s largest particle accelerator, with a circumference of 27 kilometres. The physics behind the massive machine, however, is relatively simple.
“You’re starting with a bottle of hydrogen gas,” said Steven Robertson, an associate professor of physics at McGill who was one of the first Canadians to work on the LHC. “All the scientists do is inject the gas into something that strips off the electron. You’re left with a bunch of protons floating around. You apply voltage to them and off they go.”
Like race cars navigating a circular track, the particles are then steered around the collider by powerful magnets. The larger a given particle accelerator and the more powerful the magnets, the faster the particles can be whipped around the collider.
Several McGill professors and graduate students have worked on the collider and are looking to use the data generated by the LHC in their research. Physicists from institutions around the world are each responsible for different aspects of the LHC’s operation, and those from McGill worked with the high-level jet trigger, which attempt to identify the most interesting particle collisions that occur.
“These particle interactions happen at an enormous rate, and the vast majority of them are very mundane,” Robertson said. “We’re trying to pick out individual events out of literally millions of less-interesting ones. The trigger system is almost like taking a snapshot of a particle interaction.”
Though exciting for physicists, the collisions recorded last week are of mostly symbolic importance. Any actual discoveries that may be made will require months’ worth of data generated by the collider.
“The first interactions aren’t going to tell you anything,” Robertson said. “It’s really exciting when these events appear, but you have to accumulate a fair number of them before you can actually say anything about it.”
Once they accumulate the necessary amount of data, physicists have several ideas of what they might discover. A popular one is the Higgs-Boson, a theoretical particle that would fill the last remaining gap in the Standar Model of particle physics.
Another possible discovery involves a theory known as supersymmetry, which attempts to describe the behaviour of particles at energy levels above one TeV – a point at which the mathematical model breaks down. To envision supersymmerty, imagine a very intelligent fish able to measure pressure. Such a fish would be able to tell that underwater pressure decreased the closer it got to the surface, but it wouldn’t know what kind of environment exists above the surface. In theory, the LHC should enable physicists to examine the behaviour of subatomic particles beyond this threshold.
Any discoveries, however, are unlikely to have immediate practical applications.
“If we were to discover supersymmetry, it tells us something very fundamental about the universe, but we’re not likely to taking these particles and making a better iPod with them,” Robertson said.
It is possible, however, that the LHC may aid in developing spin-off technologies. When they needed a more efficient way to share large amounts of information decades ago, physicists working at CERN played a key role in the development of the internet.
“Over the long term, the LHC will very clearly dominate as the primary source of particle physics discoveries worldwide,” wrote Andreas Warburton, an associate professor of physics at McGill, in an email to the Tribune from Switzerland. “We at McGill are excited to be playing an important role in that program.”