A Beginners’ Guide to the Large Hadron Collider

Maximilien Brice/© 2012 CERN

Harder. Better. Faster. Stronger. Not just a song by a couple of French robots, it also describes the recent upgrades to the Large Hadron Collider in Geneva, an atom smasher so big that some people feared it would destroy the world. As it begins to power up again for the first time in over two years, we take a look at what the Large Hadron Collider is and what is expected from it in the future.

The Large Hadron Collider (LHC) is, as its name suggests, very large indeed. With a circumference of 17 miles, it straddles the Franco-Swiss border like a giant underground hula hoop. It needs every one of those 17 miles to be able to smash protons together at 99.9% of the speed of light, producing energy concentrations roughly equivalent to a trillionth of a trillionth of a second after the Big Bang. It’s under these conditions that new, exotic particles are produced, giving physicists an insight into how the Universe works on the smallest of scales.

In its principle of operation, at least, the LHC is relatively simple. Photon beams are first accelerated using a radio-frequency electric field before being fired around the underground loop in opposite directions. Large magnets help to keep the beams on track as they continue to accelerate, eventually circling the LHC 11,245 times per second. As the beams collide, they break up into smaller particles which are detected by specialist equipment located at six positions around the perimeter. This information is then sent back to the computer grid and analysed by teams of physicists.

The LHC has already made some ground-breaking discoveries, the most famous of which was the detection of the Higgs boson in 2012. Known in the media as the “God particle”, presumably for its importance to particle physics rather than any actual relation to the renowned deity, its discovery confirmed one of the key predictions of the Standard Model – the collection of theory and data which represents our best understanding of the fundamental structure of the Universe. With the Higgs boson, physicists were finally able to pin down what exactly it was that gives all the atoms in the Universe their mass, answering the question that has been a thorn in their side for the past 50 years.

But scientists hope that the Higgs boson is just the beginning. “Now that they’ve produced a Higgs boson, number one on their list is dark matter” said Michael Turner, Director of the Kavli Institute for Cosmological Physics in Chicago. Such a discovery would be a real game changer given how little we currently know about dark matter, a hypothesized family of particles thought to make up about 27% of everything in our Universe. While the Higgs boson was relatively well understood even before its existence was confirmed by the LHC, dark matter is nature’s shy spectator, inherently invisible and difficult to detect.

Physicists hope that the new upgrades to the LHC will help in overcoming these difficulties. For the past two years, the particle accelerator has been offline as work was undertaken to upgrade the superconducting magnets that line the interior walls of the underground ring. With these stronger magnets, the proton beams can be accelerated to significantly higher speeds than before, increasing the available energy from 8 tera-electron volts (TeV) to 13 TeV. It is hoped that this extra energy will allow new, previously unknown particles to be discovered.

One of the more obscure theories that physicists hope to see evidence for is that of supersymmetry. Somewhat like ordinary symmetry, supersymmetry predicts a partner particle for each regular particle that we currently know of. Theoretical physics requires supersymmetry as the Higgs boson is lighter than it should be – the extra particles predicted by supersymmetry would cancel out the contributions to the Higgs mass caused by regular particles. But, like dark matter, supersymmetry is still as of yet unsupported by experimental evidence.

It is these open questions that excite physicists, who wait in eager anticipation to see whether the LHC will confirm or – perhaps more interestingly – disprove their theories. With the LHC set to run until 2035, one thing is sure though – the Higgs boson was just the beginning.

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