A cluster of galaxies imaged by the Canada-France-Hawaii Telescope is superimposed with a false-colour map showing the regions of the cluster (blue) where dark matter is mostly abundant based on its gravitational effects. (NASA, ESA, CFHT, CXO, M.J. Jee (University of California, Davis), and A. Mahdavi (San Francisco State University)) The curiosity machine

Asimina Arvanitaki was just a small child growing up in Greece when plans were first being drawn up for the Large Hadron Collider. By the time its powerful proton beams were switched on for the first time in 2008, she had a newly minted PhD from Stanford University.

But only now, as a 35-year-old faculty member at the Perimeter Institute for Theoretical Physics in Waterloo, Ont., is Dr. Arvanitaki about to access a realm she has been waiting to explore her entire academic life.

This month, the Large Hadron Collider – the LHC – comes into its own.

By the numbers $5-billion Cost to build the Large Hadron Collider 27 Kilometres circumference 50 to 175 Metres below ground 22 000 Number of times per second a proton will cross the French-Swiss border while moving around the ring

As the world’s most powerful particle accelerator, the LHC is already famous. The collider, located near the foothills of the Jura Mountains west of Geneva, Switzerland, is where scientists finally chased down the long-hypothesized particle known as the Higgs boson. That achievement, announced in 2012, effectively completed the Standard Model of particle physics, the most formidable description of the basic constituents of nature that humans have ever devised. It was the culmination of a quest that began more than a century earlier with J.J. Thomson’s discovery of the electron in 1897.

Yet even while physicists were hungering for the Higgs, it was only ever meant to be an appetizer for the LHC. “In a sense, the Higgs was a sure bet,” Dr. Arvanitaki said. “We knew it had to be there.”

Now comes round two and all bets are off. After a lengthy hiatus and a complete overhaul, the LHC is about to switch back on with its power nearly doubled. This time the goal is to push onward into the unknown. It means the curtain is about to rise on a period of raw discovery that is relatively rare in science. And after decades of work by thousands of researchers and many billions of dollars spent, it’s Dr. Arvanitaki’s generation that now find itself in the midst of the action.

Switches are pictured in the Control Centre of the Large Hadron Collider (LHC) at the European Organisation for Nuclear Research (CERN) in Prevessin near Geneva March 11, 2015. (Reuters)

A NEW MACHINE

The LHC is mind-bogglingly complex, but at its heart lies a simple idea: Smash particles together at high speeds to concentrate as much energy as possible, and then watch how that energy dissipates through processes that can involve the spontaneous creation of new particles.

Like a miniature Niagara, each collision resembles a waterfall – an energy-releasing cascade that pours over a precipice and tumbles onto the rocks below. In this metaphor, there are any number of possible pathways that water can take along the way down. And the higher you start, the more pathways there are to explore, which is why physicists are so keen to see the LHC running at higher energies.

“This is the machine that is at the frontier of what can be done,” said Tiziano Camporesi, spokesperson for one of the LHC’s giant particle detectors.

It was all supposed to have happened well before this. The LHC is made up of two opposing beams of protons that race around a 27-kilometre-long ring guided by superconducting magnets. Wherever the beams cross, protons can collide and the products of those collisions can be carefully measured.

Early on as the LHC was ramping up to full operations in 2008, a faulty electrical connection triggered a massive failure that partly tore some of the accelerator’s giant magnets from their concrete moorings. The hobbled machine was shut down for two years. When it was finally back online, it was only able to run at half its design energy.

That still proved enough to find the Higgs boson, vindicating a decision by the LHC’s managers that it was better to get some science done sooner rather than later. In 2013, with the Higgs in hand, they switched off the beams and set about rebuilding the collider.

“It’s practically a new machine,” said Rolf-Dieter Heuer, general director of the CERN, the sprawling pan-European research facility where the LHC is based.

A view of the Large Hadron Collider in its tunnel at CERN. The head of the world's biggest atom smasher discovered the long-sought Higgs boson particle, which is believed to give all matter in the universe size and shape. (The Associated Press)

A SHOT IN THE DARK

As early as March 23, protons will again be flying around the LHC ring as systems come back online, with the first collisions expected in May. With higher energy and more particles in the beams, it will certainly find the Higgs again. The questions is whether it will find anything else.

But while it’s possible nothing will turn up, there are good reasons to think there is something more for the LHC to discover.

Chief among them is the fact the universe is known to be full of a mysterious substance called dark matter that cannot be explained by the Standard Model. There are other possibilities too, including signs of extra-dimensions or the production of microscopic black holes that evaporate in a flash of particles. Alternatively, nothing so direct may emerge. Instead, the presence of new physics may be inferred, through unexpected quirks in the behaviour of the Higgs boson. There could be more than one kind of Higgs.

“The most important thing we can do as part two of this search is to ask is this really the Higgs we expected, or is this something else,” said Manuella Vincter, a physicist at Carleton University and a member of ATLAS, the LHC detector with which Canada has partnered.

The only way to be sure, of course, it to look and see.

“It will be great to be in the data-taking business again,” said Robert McPherson, an experimental physicist at the University of Victoria and co-spokesperson for ATLAS.

As a theorist, Dr. Arvanitaki agrees. “Basically,” she says, “experiments are the language by which nature speaks to us.”