In 2008, the world’s largest machine started operating at the European research centre CERN near Geneva: the Large Hadron Collider LHC, a gigantic particle accelerator ring with a circumference of 26.7 kilometres. In a depth of up to 175 metres below the Geneva outskirts and the French Jura mountains, protons or heavy ions collide with one another head-on – at the highest energies ever attained in such collisions in a particle accelerator.
The world's most powerful accelerator
The LHC acts in effect like a time machine that enables physicists to look back billions of years into the past. Indeed, using the high-energy particle collisions in the LHC, they recreate the conditions that prevailed in the universe tiny fractions of a second after the big bang. The DESY physicists also participate in this exciting journey back to the origin of our cosmos.
Proton-proton storage ring at CERN in Geneva
Can also be operated with heavy ions
Research operation: beginning in 2009
Length: 26 659 m
Proton collision energy: 14 teraelectronvolts (TeV)
Lead ion collision energy: 1150 TeV
Experiments: ALICE, ATLAS, CMS, LHCb, LHCf, TOTEM
From the Higgs particle to extra dimensions
As the flagship of particle physics worldwide for the next 15 to 20 years, the LHC promises to revolutionize our view of the world – from the realm of the smallest particles to the far reaches of the universe. For decades, the Standard Model has rendered excellent services, enabling the physicists to describe the laws of nature with increasing detail. 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 particles acquire their mass? Is there a Higgs boson? What exactly are the unknown dark matter and dark energy, which make up 95 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, as some theories postulate?
To be able to answer these questions and pave the way towards a comprehensive “Theory of Everything”, physicists require new experimental data in the energy range of the Terascale – i.e. at substantially higher energies than what could be achieved at particle accelerators so far. With the LHC, they will venture far into this uncharted territory in the hope of finally being able to answer a whole range of these questions.
A joint project of superlatives
The LHC is the most complicated piece of technology mankind ever built. The accelerator alone, whose 9300 superconducting magnets are cooled down to minus 271 degrees Celsius – i.e. 1,9 degrees above absolute zero – by the world’s largest refrigeration system, is a technological and logistic masterpiece.
The same holds for the LHC detectors, which are used by physicists from all over the world to observe, measure and analyse the particle collisions generated in the LHC. Their complexity and size is simply breathtaking. More than 2000 scientists, technicians and engineers from over 37 countries are participating in each of the LHC experiments ATLAS and CMS. ATLAS is the largest detector ever realized at a particle accelerator: It is 46 metres long, 25 metres wide, 25 metres high and weighs 7000 tonnes – this is half the size of Notre Dame Cathedral in Paris. The CMS detector is more compact, but weighs a staggering 12 500 tonnes.
ATLAS and CMS have been conceived as general-purpose detectors suitable for the widest possible range of physics investigations, while ALICE and LHCb – the two smaller experiments – utilize specialized detectors designed to study very specific issues. They too, are operated by large international teams of up to 1000 scientists from all around the world.
Worldwide computer network
For 15 years, the LHC experiments will produce roughly 15 million gigabytes of data annually. This is enough to fill 100 000 DVDs a year! Thousands of scientists around the world analyse this data – an enormous challenge with respect to data storage and computing capacity. To meet these needs, LHC designers rely upon the concept of grid computing, in which computers distributed around the globe are linked together in such a way that they can be used as a powerful supercomputer by users from all over the world. The data from the experiments is thus not stored and processed in one place any more, but distributed to a series of large computer centres with sufficient storage capacity, from which they are transferred to other facilities, and ultimately to the participating scientists.
CERN (Conseil Européen pour la Recherche Nucléaire), the European Organization for Nuclear Research in Geneva, is the world’s largest centre for fundamental research in the field of physics.
- Founded: 1954
- 20 member states; Germany is a founding member
- Total budget for 2007: approximately 650 million euros, with 20 per cent provided by Germany
- Guest scientists at CERN: more than 8000 from 85 nations
- Largest accelerator: Large Hadron Collider LHC. Nearly 1000 German scientists are conducting research at the LHC.
DESY participation in the LHC
DESY groups from Hamburg and Zeuthen have been participating in the LHC and the ATLAS and CMS experiments, in particular, since 2006. They have made substantial contributions not only to the detectors, but also to the computer infrastructure for the analysis of the data and to the commissioning of the LHC accelerator itself. One example of an important DESY contribution is the establishment of a computing centre for ATLAS, CMS and most recently LHCb as part of the LHC Computing Grid, the global computer network for the evaluation of the LHC data. DESY operates a Tier-2 centre, whose large computing and storage capacity is available to scientists the world over for the analysis of the LHC data. Closely linked to the Tier-2 centre is also the National Analysis Facility at DESY, a computing complex that provides computer resources for physics analysis – in particular of ATLAS, CMS and LHCb data – to all German research groups working on LHC and ILC as part of the Helmholtz Alliance “Physics at the Terascale”.
The DESY researchers are also involved in various aspects of the ATLAS and CMS experiments. Some of them staff important, executive-level management functions in the large international teams operating the detectors. The DESY groups are working on the development, installation and operation of various detector components. In addition to helping with the set-up of the grid computing for the analysis of the LHC data, the DESY researchers are also involved in the development of the software tools for the data acquisition and for the simulation, reconstruction and analysis of the collisions. Another focal point are studies of the physics at the LHC. Several members of the HERA machine group are also supporting the LHC team with the commissioning of the accelerator.
Furthermore, control centres are being built at DESY so that the operation and data taking of ATLAS and CMS can be monitored remotely. First up was the CMS Centre DESY, which went into operation in October 2008. Whereas the LHC experiments are run from local control rooms near the detectors for reasons of safety, the data acquisition can also be checked remotely. The proper functioning of the complex detectors can thus be monitored from CERN, from Fermilab in Chicago and now also from DESY. The researchers in Geneva, Chicago and Hamburg are in constant contact via a special audio and video link. Thanks to these control centres at DESY, the German scientists participating in ATLAS and CMS can take shifts for checking the data taking without having to travel to Geneva.