Over the past 25 years, KATRIN has advanced precision beta-decay spectroscopy to unprecedented levels. By studying the endpoint region of tritium beta decay with extreme accuracy, the experiment has established the world’s most stringent limit on the neutrino mass from a direct measurement and has become a flagship experiment in astroparticle physics. Yet behind this success lies far more than technical excellence alone: the 1,000-day milestone represents years of perseverance, innovation, and international collaboration.
Reaching this level of sensitivity required overcoming a formidable learning curve. Operating a 70-meter-long experiment at the limits of technological feasibility demanded continuous developments in detector performance, tritium handling, electric and magnetic field stability, background reduction, and data analysis. Scientists, engineers, technicians, and students across generations steadily transformed challenges into expertise, enabling KATRIN to evolve into the world-leading instrument it is today.
The symposium reflected this collective achievement. Scientific talks traced the origins and history of KATRIN, highlighted its latest physics results, and outlined the future TRISTAN and KATRIN++ phases. The event was hosted by the KATRIN spokespersons, Max Planck director Susanne Mertens and Kathrin Valerius, who now co-lead the experiment through its next phase. Particularly symbolic was the strong participation of early-career researchers, who presented the future scientific program and demonstrated how KATRIN continues to evolve through new ideas and fresh perspectives.
The managing director of the Max-Planck-Institut für Kernphysik Klaus Blaum delivered welcoming remarks for the event and highlighted the Max Planck Society’s broad contributions to KATRIN, spanning technological developments and scientific leadership. These include key hardware components such as the rear wall chamber and major detector developments at the Max Planck Semiconductor Laboratory for the TRISTAN project. In Heidelberg, Mertens' division has established a new research direction focused on KATRIN, its extension with the TRISTAN detector, and the exploration of new ideas for a direct neutrino mass measurement. Moreover, also at the Max-Planck Institut für Kernphysik in Heidelberg, the independent research group OMNIA, led by Thierry Lasserre, contributes to extending KATRIN’s scientific reach toward sterile and relic neutrino searches. Together, these activities reflect the Max Planck Society’s strong and growing engagement in shaping KATRIN's future.
Greetings and contributions followed from collaborators and institutional representatives around the world, including the U.S. Department of Energy (DOE), the Italian National Institute for Nuclear Physics (INFN), the Helmholtz Association, Deutsches Elektronen-Synchrotron (DESY), and partner universities. Video messages from Nobel Laureates Arthur B. McDonald and Takaaki Kajita further underscored KATRIN’s international standing within the global neutrino-physics community. The celebration also brought together colleagues and long-standing friends from many neutrino experiments worldwide, reflecting the strong scientific ties and collaborative spirit that have accompanied KATRIN throughout its journey.
Musical performances by students from a local school provided memorable interludes throughout the day. They created a warm, festive atmosphere before participants gathered at the KATRIN experimental hall for tours, informal discussions, and an evening soirée.
Although the first major measurement phase has concluded, KATRIN’s scientific mission is far from over. The extensive dataset, accumulated over 1,000 days, is still being analysed, with the collaboration aiming for its ultimate neutrino-mass sensitivity. At the same time, preparations for the TRISTAN upgrade are already opening new opportunities in the search for sterile neutrinos and dark matter.
The celebration in Karlsruhe, therefore, marked more than the completion of a measurement campaign. It honoured a global effort that, over many years, combined persistence, creativity, and scientific ambition to bring us closer to answering one of the fundamental questions in physics: how much does the neutrino weigh?
