The program began with theoretical input sessions, providing an introduction to cosmic radiation, particle detection, and the physical principles behind modern detector technologies. These sessions laid the foundation for the subsequent practical work and helped the students place their own measurements into a broader scientific context.
This was followed by guided tours of the Research and Technology Center for Detector Physics, during which the students gained direct insight into current research activities, laboratory environments, and experimental infrastructure. The tours offered a close-up view of how detector development and testing are carried out in a professional research setting.
A central element of the Cosmic Day was the hands-on experiment phase. Working in small groups, the students measured the angular distribution of cosmic radiation using three COSMO detectors. By collecting and analyzing their own data, the participants learned how cosmic-ray measurements are performed, how detector geometry influences results, and how experimental uncertainties arise. The experiment provided an authentic experience of scientific data taking and analysis.
The day concluded with a large international conference session, connecting the Bonn group with institutes and student teams from other international Cosmic Day locations. During this session, the participants presented and discussed their results, compared measurements, and exchanged ideas with peers from different countries. This international exchange highlighted the collaborative nature of modern physics research and gave the students a sense of being part of a global scientific community.
Overall, the Cosmic Day 2025 at the Research and Technology Center for Detector Physics in Bonn was a great success. The combination of theory, hands-on experimentation, and international collaboration made cosmic-ray physics tangible and engaging, and provided the students with valuable insights into both scientific research and the everyday work of physicists.