It is a story of years of research, meticulous attention to detail and a firm belief that even the smallest particles can reveal the greatest secrets of the universe. The CMS experiment (Compact Muon Solenoid) at the Large Hadron Collider (LHC) in the European Laboratory for Particle Physics CERN near Geneva is operated by a collaboration that brings together researchers from all over the world to track down the fundamental building blocks of the universe. KIT researchers from the Institute for Experimental Particle Physics (ETP) have been involved in the CMS experiment for many years, as Professor Ulrich Husemann from the ETP reports: “I myself have been a member of the CMS collaboration since 2011. Together with my team, we develop and build special detection devices for the experiment – more precisely, particle detectors.”

Big experiment for the smallest particles

The experimental set-up at CERN with particle accelerator is 15 meters high, 25 meters long and contains all kinds of high-tech equipment. The aim of the large-scale research facility is to bring elementary particles to collision at the highest energies currently available in the laboratory and to analyze what happens at the smallest scale. Physicist Husemann explains the experiment: “Up to one billion protons are brought into collision with each other every second. What is interesting for us are the collisions that produce new particles, which then decay very quickly into known particles. We have to piece together from this puzzle what might have happened by measuring different properties of these particles with extreme precision, for example their place of origin, momentum and charge as well as their course of movement. Using computer analysis, we can follow the tracks of all the particles and draw conclusions about what kind of physical process could have happened.” For these measurements, the first few meters from the point of collision are equipped with almost 13,000 so-called track detectors, which are manufactured by ten production centers worldwide as part of the collaboration. KIT is one of the largest of these and, with a specially equipped production line, is also one of the most advanced production facilities for the specially developed detectors.

Reading the tracks

Project manager Husemann and his team have devoted a lot of time to the special challenge of developing a next-generation detector module. “Our modules consist of special silicon sensors that are arranged in double layers for the first time. Over the course of ten years of development, we worked our way up to the solution using several prototypes. The double layer enables us to record the trajectory of the particles that shoot through the detector at high speed very accurately. A charged particle flying through leaves electrical signals in the electrodes of the sensor layers. In order to obtain information about the momentum, we have to correlate the puncture points in the different layers,” Husemann continues. This technology can be used to determine whether a particle is traveling on a straight trajectory or whether its path is curved - crucial information for physicists to distinguish between truly significant events and ordinary collisions.

The module in seven days

The production line in the clean room combines state-of-the-art technology with engineering skill: “Setting up the production line was a challenge. We had to develop many of our tools and test systems ourselves because the requirements are so specific,” reports Husemann. Every work step is designed to ensure the highest quality and meet the requirements of particle physics. “We have set up production in such a way that new modules are fed into production every day, which ensures continuous capacity utilization. It takes a total of seven to eight days with several bonding and curing times until a module is fully assembled. Before it leaves the cleanroom, it is extensively tested. Our process ensures that every component can withstand the extreme conditions at CERN,” Husemann explains.

Shifting the boundaries of knowledge

For the researchers at KIT, the work on the detector is more than just a technical project – it is a mission that extends the boundaries of scientific knowledge. From 2030, the detectors produced at KIT will be part of the CMS experiment at CERN, where they will help to decipher the fundamental forces of the universe. Hartmann, who is coordinating the installation in Switzerland, emphasizes the importance of this: “The track detectors are a central building block for the success of the CMS experiment at CERN. They enable us to measure subatomic particles with unprecedented precision. We are constantly faced with challenges, but that is what makes our work so exciting.”

The expertise from Karlsruhe goes beyond particle physics. Husemann mentions projects in which the knowledge gained from detector development is used for medical purposes, for example in radiotherapy: “For example, we have started to develop detectors for the Ion Beam Center in Heidelberg,” he explains. In addition to research, Husemann emphasizes that the project also prepares the employees involved well for later tasks in industry. “What makes our work special is the combination of precision craftsmanship and the ability to find innovative solutions to previously unsolved challenges – a quality of our doctoral students. Our employees don't just learn the basics of physics here. They work on cutting-edge systems that combine technological innovations and complex development processes.”