Large hadron collider: A revamp that could revolutionise physics

Large hadron collider: A revamp that could revolutionise physics

Deep underground amidst the Alps, scientists are barely able to contain their excitement.

They whisper about discoveries that would radically alter our understanding of the Universe.

“I’ve been hunting for the fifth force for as long as I’ve been a particle physicist,” says Dr Sam Harper. “Maybe this is the year”.

For the past 20 years, Sam has been trying to find evidence of a fifth force of nature, with gravity, electromagnetism and two nuclear forces being the four that physicists already know about.

He’s pinning his hopes on a major revamp of the Large Hadron Collider. It’s the world’s most advanced particle accelerator – a vast machine that smashes atoms together to break them apart and discover what is inside them.

It’s been souped up even further in a three-year upgrade. Its instruments are more sensitive, allowing researchers to study the collision of particles from the inside of atoms in higher definition; its software has been enhanced so that it is able to take data at a rate of 30 million times each second; and its beams are narrower, which greatly increases the number of collisions.

What all this means is that there’s now the best chance ever of the LHC finding subatomic particles that are completely new to science. The hope is that it will make discoveries that will spark the biggest revolution in physics in a hundred years.

As well as believing that they may find a new, fifth force of nature, researchers hope to find evidence of an invisible substance that makes up most of the Universe called Dark Matter.

The pressure is on the researchers here to deliver. Many had expected the LHC to have found evidence of a new realm of physics by now.

Atlas detector
Image caption,The Atlas detector comprises 7,000 tonnes of metal, silicon, electronics, and wiring, intricately and precisely put together. It is now more powerful than ever

The LHC is part of the European Organisation for Nuclear Research, known as Cern, on the Swiss-French border, just outside Geneva. As one approaches, it seems an unremarkable complex – blocks of 1950s office buildings and dormitories, sprawling across a two and a half square mile site of manicured lawns and winding roads named after revered physicists.

But 100 metres underground, it is a cathedral to science. I was able to go into the heart of the LHC, to one of the giant detectors that made one of the biggest discoveries of our generation, the Higgs Boson, a subatomic particle without which many of the other particles we know about would not have mass. The Atlas detector is 46m long and 25m high. It is one of the LHC’s four instruments that analyse the particles created by the LHC.

It is 7,000 tonnes of metal, silicon, electronics, and wiring, intricately and precisely put together. It is a thing of great beauty. “Majesty” is the word used by Dr Marcella Bona from Queen Mary University of London, who is one of the scientists who uses the Atlas detector for her experiments.

I am awestruck by the view, as Marcella tells me about the improvements to the detector during the LHC’s three-year shutdown.

“It is going to be two to three times better, in terms of the ability for our experiment to detect, collect and analyse data,” she tells me. “The whole experimental chain has been upgraded.”

Infographic of CERN

Amid the clanking and banging of the engineers finishing off Atlas’s refurbishment, I find it hard to imagine that something so large is needed to detect particles that are many times smaller than an atom.

The LHC has four such detectors, each one doing different experiments. It is right in the centre of these gigantic detectors that particles known as protons, which are found in the core of atoms, are crashed together after being accelerated close to the speed of light around a 17-mile circumference ring.

The collisions create even smaller particles that fly off in different directions. Their path and energy are tracked by the detector systems, and it is this trail that tells the scientists what kind of particle it is, rather like determining the species and characteristics of an animal from its footprints.

Particle collision
Image caption,The collisions create particles that fly off in different directions. The trail tells the scientists what kind of particle it is.

Nearly all the smaller particles arising from the collisions are already known to science. What the physicists here are after is evidence of new particles, which may arise from the collisions but are believed to be created extremely rarely.

It is these undiscovered particles that physicists believe hold the key to unlocking a completely new view of the Universe. Their discovery would create the biggest shift in physics thinking since Einstein’s theories of relativity.

Engineers have spent the past three years upgrading the LHC to produce more collisions in a shorter space of time. The refurbished machine has a much greater chance of creating and finding the rarely created new particles. Much of that work has been led by Dr Rhodri Jones, who rejoices in his title of “Head of Beams”.

I meet Rhodri in Cern’s magnet assembly area, which resembles a vast aircraft hangar. Here, engineers are revamping the 15 metre-long cylindrical magnets that bend the particle beams around the accelerator. This is precision work with absolutely no margin for error.

Magnet assembly area
Image caption,The LHC’s magnet assembly area. They have been revamped to make the beam narrower and so increase the number of collisions

Rhodri tells me that his team has made the beams narrower, so that more particles are squeezed into a smaller area. This greatly increases the chances of particles crashing into each other.

“We are looking at very rare processes, so the greater the number of collisions, the greater the chance of actually finding what is going on and seeing small anomalies,” he says.

“The improvement in the beam means that for all the physics that we have done since the start of the years the LHC has been in operation, we’ll be able to get the same amount of collisions in the next three years as we did in those ten years.”


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