It’s the world's most powerful accelerator and currently the most exciting endeavour in particle physics: the Large Hadron Collider LHC, a gigantic underground particle accelerator ring with a circumference of 27 kilometres at the CERN research centre in Geneva. The LHC accelerates protons to head-on collisions at record energies. Thus, it has the potential to generate completely new building blocks of matter – as in 2012, when it detected the long-sought Higgs boson. DESY is involved in the LHC experiments.

The current particle theory – the Standard Model of particle physics – renders excellent services when describing processes in the microcosm. The Model contains many gaps, however; it raises questions that a comprehensive theory of the building blocks and forces in the universe should actually answer. How do the elementary particles acquire their mass? What exactly are the unknown dark matter and dark energy, which make up 96 percent of the universe? Why is there more matter than antimatter in the cosmos? What did the universe look like in the first second after the big bang? Are there more than three dimensions of space?

To answer these questions and pave the way towards a comprehensive “Theory of Everything”, physicists require new experimental results at substantially higher energies than what could be achieved at particle accelerators so far. Thanks to the record energies provided by the LHC, they hope to finally be able to answer a whole range of these questions. Using the LHC's high-energy particle collisions, the researchers effectively recreate the conditions that prevailed in the universe tiny fractions of a second after the big bang. The LHC thus acts like a time machine that enables physicists to look back billions of years into the past to the very beginning of our universe.

The discovery of the Higgs particle

Two years after the start of data taking, the LHC experiments reported a spectacular success: in 2012, they announced the discovery of the Higgs particle, which the physicists had sought for nearly 50 years. In the 1960s, the Scottish physicist Peter Higgs and others proposed a theory that explains how elementary particles acquire their mass. According to what became known as the Higgs mechanism, the cosmos is permeated by a special field that operates in a manner similar to honey when a spoon moves through it: it offers the particles due resistance and thereby makes them “heavy”. With the sensational discovery of the associated Higgs particle, the LHC physicists confirmed that the Higgs mechanism is actually true. In the fall of 2013, the Belgian physicist François Englert and Peter Higgs were awarded the Nobel Prize in Physics for their prediction.

The LHC researchers are now striving to precisely determine the properties of the new particle. They aim to find out whether it is exactly the Higgs particle predicted by the Standard Model, or whether it might have other properties that could hint at "new physics" beyond the Standard Model.

From SUSY particles to extra dimensions

The largest scientific machine in the world could also detect entirely different, so far merely speculative phenomena. One fascinating result would be the discovery of supersymmetric, or SUSY, particles. These could play a major role in the universe. By virtue of their gravitational force, they could hold the galaxies together like invisible glue – and thus explain what the dark, invisible matter in our unverse is made of. The LHC might also provide evidence that our world is not just four-dimensional – three spatial dimensions and time. The cosmos could instead have significantly more dimensions. These however would be so well hidden that a super-accelerator like the LHC is required to even detect signs of their existence.

Facts and figures

Proton-proton storage ring at CERN in Geneva
Can also be operated with heavy ions
Circumference: 27 kilometres
Location: 100 metres underground on the Franco-Swiss border
Research operation: since 2009
Maximum energy per proton beam: 7 teraelectronvolts (TeV)
Experiments: ALICE, ATLAS, CMS, LHCb, LHCf, TOTEM