The International Masterclass workshops on particle physics offer high school students the opportunity to learn about the world of quarks and leptons and to conduct their own measurements using data captured by experiments at CERN and other research centers. Students could meet real researchers and connect with peers from other countries. At the event, researchers presented the basics of particle physics, medical physics, and detectors used in research. During a virtual tour, students explored the interior of the Belle II detector and talked to researchers about their work at CERN and in Japan. In the afternoon workshop, they searched for unknown short-lived particles and selected a radiation plan that would effectively stop tumor growth. The event took place live at the Jožef Stefan Institute.