The proton collisions in the LHC are recorded by four giant detectors – ATLAS, CMS, ALICE und LHCb – located in large underground halls around the accelerator ring. The two biggest experiments, ATLAS and CMS, are managed by large teams of more than 2000 specialists from around the world, who jointly operate the detector and collect and analyse the data it produces. DESY itself has more than 100 experts working at ATLAS and CMS.
The DESY experts help analyse the huge amount of data that the detectors collect to search for signs of new particles – a task that is like looking for a needle in a haystack. The researchers develop software tools for the data acquisition as well as for the simulation, reconstruction and analysis of the collisions. Another focal point are theoretical studies of the physics at the LHC. DESY specialists regularly travel to Geneva to operate the detectors in shifts or discuss the highly complex data analyses with colleagues from around the globe. The physicists have set up control rooms for both detectors at DESY, which allows them to remotely evaluate the quality of the data the experiments produce. In doing so, the DESY scientists benefit from their experience of operating the HERA accelerator in Hamburg.
DESY also provides large computing and storage systems for the data processing of ATLAS, CMS and LHCb. This so-called Tier-2 centre is one of the largest among the more than 170 centres of the worldwide LHC computer network and is used by research groups around the world. Closely linked to the Tier-2 centre is the National Analysis Facility (NAF), a computer complex at DESY that is available for physics analysis purposes to all German research groups participating in the LHC.
Upgrade for the LHC
DESY's expertise in the construction and operation of detectors is also in great demand at the LHC experiments. Around 2020, CERN is planning an expansion of the accelerator, after which the LHC is expected to produce up to ten times more proton collisions than at present. That change will also require an upgrade of the detectors. DESY contributes to the preparations for this upgrade.
The inside of the CMS detector will be completely replaced and fitted with new sensors made of state-of-the-art materials to make them more robust, lighter and more sensitive. The problem is that the more collisions occur within a particle detector, the more its sensors are subjected to high-energy radiation. Ordinary chips like the ones used in cell phone cameras would fail very soon. That’s why DESY researchers in conjunction with industrial scientists are searching for new, extremely robust sensor materials. Candidate materials are being tested, among other locations, at DESY in Hamburg and Zeuthen.
Radiation resistance is not the only attribute sought in the new sensors – they also need to be finer grained. In the same way that digital cameras are providing more and more megapixels, the researchers aim to substantially increase the resolution of their sensors. In doing so, they are benefiting from the continuing advances in chip manufacturing technology. In collaboration with several universities, DESY is slated to assemble one of the end caps of ATLAS. This will involve more than 3000 individual modules with a total of 25 square metres of silicon.