A section of the tunnel that houses the Large Hadron Collider under Switzerland and France.
Sraddling the Swiss-French border near Geneva and built into a 27km circular underground tunnel is the Large Hadron Collider (LHC) — the world’s largest and most powerful particle collider and the most complex experimental facility ever built — housing the single largest machine in the world.
It is every scientist’s dream and a facility that is truly space-age. It took 10 years for the European Organisation for Nuclear Research (CERN) to build, becoming operational in 2008. It was the result of a collaboration with over 10 000 scientists and engineers from over 100 countries, as well as hundreds of universities and laboratories.
The facility lies in a tunnel 175m beneath the border. Its first research run took place from March 30 2010 to February 13 2013, at an initial energy of 3.5 teraelectronvolts (TeV), a unit of energy used in particle physics. One TeV is about the energy of the motion of a flying mosquito.
“The Large Hadron Collider was conceived to discover, if possible, the Higgs boson, which was predicted by the standard model (SM) of particle physics — a comprehensive theory for particle physics akin to the role of DNA for the biosciences,” says Simon Connell, professor at the University of Johannesburg school of physics and team member of the A Toroidal LHC Apparatus (ATLAS), one of the seven experiments at the LHC.
“The SM seemed correct in every aspect, except that the Higgs boson predicted in 1964 had not yet been discovered. The first proposal for the LHC was in 1977, and it was to become the largest global scientific collaboration ever.
“The mega-science project took 30 years from conception to first operation. That such a massive project could be undertaken as a global endeavour was testimony to how impactful many thousands of scientists felt this quest was. The Higgs boson was indeed discovered in July 2012.”
Professor Connell says attention has moved on to precisely measuring the Higgs boson’s properties and to further studies of the standard model.
“Almost exasperatingly, the SM is holding up very well,” he says. “Exasperating, as it is known to be rather deficient. For example, it does not accommodate gravity, dark matter, dark energy or indicate why the universe has far too little anti-matter content. The SM actually explains less than 5% of the universe.
“Because of this, the LHC was also designed to take us beyond the SM (BSM), with yet more exciting discoveries. Most of the motivations for BSM physics, especially those mentioned, come from astronomical, astrophysical and cosmological considerations. The fact that the astro-sciences depend ultimately on the particulate content of the SM (or BSM physics) creates a strong link between these sciences.
“The LHC has ramped up to almost its design energy, with ever increasing luminosity. The combination of the dramatic advance in global large-scale research infrastructure in new telescopes, space platform observations and the LHC together place us in a golden age of discovery,” concludes Connell.
New subatomic particles
Just a few days ago, five new subatomic particles were uncovered by the LHC. Hiding in plain sight, they were discovered by scientists exploring what happened after the Big Bang that gave birth to the universe — the LHC experiment also known as “beauty”.
Physicists hope to gain greater insight into the nuclear force that binds the building blocks of atoms together by measuring their properties. While the discovery of the new particles is not quite as exciting as the discovery of the Higgs boson, this still constitutes a major find made possible by the extreme sensitivity of the LHC’s particle detectors.
The five particles are called baryons, which are subatomic particles made up of three smaller units called quarks, the basic and fundamental building blocks of matter. The six types of quarks — referred to as “flavours” — are top, bottom, up, down, strange and charm. The newly discovered particles are high-energy versions of the omega-c baryon, a particle made up of two strange quarks and one charm quark.
Quarks combine to form composite particles called hadrons, the most stable of which are protons and neutrons — the components of atomic nuclei. Quarks’ intrinsic properties include mass, spin and electric and colour charge.
The quest for the Higgs boson
In July 2012, Large Hadron Collider Scientists made history be capturing the fabled Higgs boson, also called the “God particle”, a term physicists tend to dislike for its sensationalism. This new particle had a mass between 125 and 127 GeV/c2 (the electronvolt unit of mass with c being the speed of light in vacuum).
Evidence of the existence of the Higgs field has been very difficult to obtain, although it is believed that the field is pervasive throughout the universe and is a fundamental part of the universe that had been missing since its existence was first predicted in the sixties. Finding the Higgs field was a 40-year search that led the construction of CERN’s Large Hadron Collider to create and research particles such as Higgs bosons.
Since its discovery, the particle has been shown to interact, behave and decay in many of the ways predicted by the standard model of particle physics — the theory that concerns the various electromagnetic interactions and classifies all the elementary particles known, and which was developed through the collaborative effort of scientists around the world.
The Higgs boson is named after Peter Higgs, one of the six physicists who in 1964 proposed the Higgs mechanism that suggests the existence of the particle.
Fast facts
When the 27km-long circular tunnel was excavated between Lake Geneva and the Jura mountain range, the two ends met up to within 1cm.
Each of the 6 000 to 9 000 superconducting filaments of niobium–titanium in the cable produced for the LHC is about 0.007mm thick, about 10 times thinner than a normal human hair. If you added all the filaments together they would stretch to the sun and back six times with enough left over for about 150 trips to the moon.
All protons accelerated at CERN are obtained from standard hydrogen. Although proton beams at the LHC are very intense, only two nanograms of hydrogen are accelerated each day. Therefore, it would take the LHC about a million years to accelerate a gram of hydrogen.
The central part of the LHC is the world’s largest fridge. At a temperature colder than deep outer space, it contains iron, steel and the all important superconducting coils.
The pressure in the beam pipes of the LHC is nearly like the atmosphere of the moon. This is an ultrahigh vacuum.
Protons at the design energy in the LHC travel at 0.999999991 times the speed of light. Each proton goes round the 27km ring more than 11 000 times a second.
At full energy, each of the two proton beams in the LHC have a total energy equivalent to a 400 tonne train travelling at 150km/h. This is enough energy to melt 500kg of copper.
The sun never sets on the A Toroidal LHC Apparatus (ATLAS) collaboration. Scientists working on the experiment come from every continent in the world, except Antarctica.
The CMS magnet system contains about 10 000 tonnes of iron, which is more iron than in the Eiffel Tower.
The data recorded by the big experiments at the LHC is enough to fill around 50 000 1TB hard disks every year.
Source: European Council for Nuclear Research (CERN)