Scientific research at the Large Hadron Collider at CERN won’t stop with the confirmation of evidence, recently announced, of the existence of the Higgs boson – a tiny but crucial subatomic particle sometimes referred to as the “God particle.” Instead, the Large Hadron Collider will continue to operate in order to study the existence and behaviour of many other subatomic particles, hopefully hinting at answers to some of the most important unanswered questions in particle physics today.
The European Organization for Nuclear Research (CERN) took 10 years to build the Large Hadron Collider (LHC), and it has been in operation since 2008. At 17 miles long, it is the world’s largest particle accelerator: a massive underground looped pipeline that accelerates two tiny beams of protons or atomic nuclei to almost the speed of light and then smashes them together in front of a set of very precisely tuned sensors. The particles detected very briefly after the resulting “collisions” are believed to resemble some of those found in the very early universe, shortly after the Big Bang.
In addition to the circuit of the collider itself, though, the Large Hadron Collider is actually a collection of different sensors, referred to as “experiments,” which can potentially be tuned for use in quite a number of different studies. The search for the Higgs boson is only one of the uses to which these sensors can be put, although so far it has been one of the most important projects.
The Large Hadron Collider exists to answer a set of problems associated with the Standard Model, a set of theories which has been influential in particle physics for decades. The Standard Model predicts the existence of an assortment of different “elementary” particles, with the most massive and most recent ones being baryons like protons and neutrons. These form the nucleus of an atom. Many of these elementary particles, however, no longer exist in large quantities in readily observable form. Instead, according to the model, some were only prevalent in the extremely dense, high-energy conditions shortly after the Big Bang. Projects like the Large Hadron Collider exist to simulate those conditions and, in doing so, to find evidence for the existence or non-existence of some of the most elusive elementary particles predicted by the Standard Model.
One of the most important of these studies was the search for the Higgs boson, and researchers at the Large Hadron Collider announced during the summer of 2012 that they believed they had detected evidence of this particle. However, other research is also ongoing, using the sort of collisions which so far only the Large Hadron Collider can create. The ALICE experiment, a set of detectors and projects which is part of the search for the Higgs boson, produces “temperatures more than 100,000 times hotter than the heart of the Sun.” At that temperature, the protons and neutrons that make up atomic nuclei “melt,” resulting in a mix which CERN calls “quark-gluon plasma,” and which it thinks was probably prevalent in the very early, very hot universe.
Other experiments are searching for other exotic and largely theoretical particles predicted by the Standard Model as well as other alternative theories of physics. The ATLAS detector, for instance, has been installed at CERN to study the possibility of extra dimensions as well as to search for clear evidence of dark matter, a form of matter which is so far invisible but which appears to make up even more of the mass of the universe than normal, observable matter. The compact muon solenoid detector, another sensor installed in the Collider, is part of both the dark matter search and the Higgs boson search.
CERN lists three other important experiments on its public website. One, LHCb, will be studying a “particle called the beauty quark” in order to explore why the universe is currently made up of matter instead of antimatter – a group of particles which have the same mass as those prevalent in our universe, but with their charges reversed, so that antiprotons have negative charges. Another, TOTEM, will be used to measure precisely “the size of the proton.”
The last experiment, LHCf, will use the collider to simulate not the conditions of the early universe, but the conditions of the upper atmosphere, where extremely high-energy electromagnetic radiation, known as cosmic rays, are continually colliding with the nuclei of the atoms that make up Earth’s atmosphere.
Even if the search for the Higgs boson is over – and it won’t be for quite some time yet, as researchers refine their approach and begin to explore the characteristics of this famous particle – the Large Collider at CERN will continue looking for several other particles and studying their characteristics, as well. Excited by the prospects for this sort of resaerch, several countries have even begun exploring the construction of an even longer device tentatively named the International Linear Collider, which would not be more powerful but which might allow more refined measurements of the same sorts of collisions that are now being studied at CERN.